Peer-Reviewed

1st Author Publications

Development of a processing route for carbon allotrope-based TiC porous nanocomposites

J.P. Ramos, A.M.R. Senos, T. Stora, C.M. Fernandes, P. Bowen
Journal of the European Ceramic Society, volume 37, issue 13, pages 3899-3908, 2017

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Ti-foils are currently used as a spallation target material to produce radioisotopes for physics research at the ISOLDE facility at CERN. However, radioisotope production rates often decrease over time due to material degradation from high operation temperatures. Due to enhanced release rates, porous nanomaterials are being studied as spallation target materials for isotope production. TiC is a material with a very high melting point making it an interesting material to replace the Ti-foils. However, in its nanometric form it sinters readily at high temperatures. To overcome this, a new processing route was developed where TiC was co-milled with graphite, carbon black or multi-wall carbon nanotubes in order to hinder the sintering of TiC. The obtained nanocomposite particle sizes, density, specific surface area and porosity were characterized and compared using ANOVA. All carbon allotropes mixed with the TiC, were able to successfully stabilize the nanometric TiC, hindering its sintering up to 1500 °C for 10 h.

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Sintering Kinetics of Nanometric Calcium Oxide in Vacuum Atmosphere

J.P. Ramos, C.M. Fernandes, T. Stora, A.M.R. Senos
Ceramics International, volume 41, issue 6, pages 8093-8099, 2015

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A recent application for nanometric CaO powder is its use as a spallation target material for the production of isotope beams at CERN. The stability of the nanostructure at high operation temperatures is a crucial feature to provide stable and improved isotope release rates. Prior to operation, sintering studies under thermal conditions similar to those of the target operation are required to establish the microstructural evolution due to coarsening and densification processes. This knowledge enables the identification of the limiting temperatures for the target operation, ensuring a stable nanostructure for higher and constant isotope release rates.
In this study, nanometric CaO powder with 58 m2 g−1 of specific surface area was obtained from vacuum decomposition of calcium carbonate at 800 °C. The microstructure evolution of porous powder compacts was investigated under vacuum atmosphere, from 1000 to 1250 °C, for holding times from 3 to 600 min. For temperatures higher than 1000 °C, a significant surface area reduction was observed, accompanied by porosity decrease. The morphological analysis of the pore evolution revealed a differential sintering of the porous compacts, mainly occurring inside the aggregates. The kinetic analysis of the surface area reduction pointed to aggregate shrinkage controlled by volume diffusion with surface diffusion as an underlying mechanism for lower temperatures.

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Intense 31-35Ar Beams Produced with a Nanostructured CaO Target at ISOLDE

J.P. Ramos, A.G. Gottberg, T.M. Mendonça, C. Seiffert, A.M.R. Senos, H.O.U Fynbo, O. Tengblad, J.A. Briz, M.V. Lund, G.T. Koldste, M. Carmona-Gallardo, V. Pesudo, T. Stora
Nuclear Instruments and Methods in Physics Research B, volume 320, pages 83-88, 2014

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At the ISOLDE facility at CERN, thick targets are bombarded with highly energetic pulsed protons to produce radioactive ion beams (RIBs). The isotopes produced in the bulk of the material have to diffuse out of the grain and effuse throughout the porosity of the material to a transfer line which is connected to an ionizer, from which the charged isotopes are extracted and delivered for physics experiments. Calcium oxide (CaO) powder targets have been used to produce mainly neutron deficient argon and carbon RIBs over the past decades. Such targets presented unstable yields, either decaying over time or low from the beginning of operation. These problems were suspected to come from the degradation of the target microstructure (sintering due to high temperature and/or high proton intensity). In this work, a CaO microstructural study in terms of sintering was conducted on a nanostructured CaO powder synthesized from the respective carbonate. Taking the results of this study, several changes were made at ISOLDE in terms of the CaO target production, handling and operation in order to produce and maintain the nanostructured CaO. The new target, the first nanostructured target to be operated at ISOLDE, showed improved yields of (exotic) Ar and more importantly a stable yield over the whole operation time, while operating with lower temperatures. This contradicts the ISOL paradigm of using the highest possible temperature regardless of the target’s microstructure degradation.

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Conference Proceedings


Target nanomaterials at CERN-ISOLDE: synthesis and release data

J.P. Ramos, A. Gottberg, R.S. Augusto, T.M. Mendonca, K. Riisager, C. Seiffert, P. Bowen, A.M.R. Senos, T. Stora
Nuclear Instruments and Methods in Physics Research B, volume 376, pages 81-85, 2016
XVIIth International Conference on ElectroMagnetic Isotope Separators and Techniques Related to their Applications, May 11–15, 2015 at Grand Rapids, United States of America

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Five different nanostructured target materials were tested and operated at ISOLDE in the year of 2014, three of them being carbon-based nanocomposites. In most cases such target materials have higher radioisotope intensities than standard targets and with apparently longer release characteristics. Here, an isotope release profile from a standard calcium oxide (CaO) powder target is compared to the nanostructured one. For all target materials, the synthesis is the key process since it determines the material characteristics and maximum operation temperature which, in turn, defines the final isotope yields (especially for exotic isotopes). An unexpected release of Ar isotopes from a nanometric CaO powder target, with its oven set to room temperature is described and a release mechanism is proposed: spallation recoil momentum from the natCa(p,x)35Ar reaction.

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Invited/Special Talks

Target materials for radioisotope production II: advanced materials

J.P. Ramos 
La Foresta European Center, Leuven, Belgium
Invited lecturer, MEDICIS-Promed specialized training on radioisotope production, 7th of September 2017

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Target materials for the production of radioisotopes: the importance of the microstructure

J.P. Ramos
Waikaloa, Big Island (Hawaii), USA
Invited - 12th Pacific Rim Conference on Ceramics and Glass Technology (PACRIM12), 21st - 26th of May 2017
Symposium 25 - Ceramics for Next Generation Nuclear Energy (Session: Development of Production of Critical Isotopes and Targets)

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At ISOLDE facility (ISOL DEvice, where ISOL stands for Isotope Separator OnLine) at CERN - the European Organization for Nuclear Research - more than 1000 isotopes from 74 chemical elements are produced and delivered for physics studies. Radioactive ion beams (RIB) are produced in ISOLDE with nuclear reactions resulting from the bombardment of thick targets with highly energy protons. The thermalized isotopes diffuse to the material grains surface and effuse throughout the material porosity, by keeping the target at high temperatures. After, they effuse through a transfer line to an ion source where they are ionized, creating a RIB. At ISOLDE, the target materials are mainly oxides, carbides or metals in powder, pellet or even liquid form in a total of more than 100 different materials which were tried, where 23 are commonly used. Even though ISOL is 66 years old, it was only 10 years ago, that microstructure engineering towards submicron and nanomaterials was considered to improve the isotope release processes: diffusion and effusion (grain size reduction and high porosity). So far out the existing 23 materials, 6 were investigated in that sense: multi wall carbon nanotubes (MWCNT), SiC, CaO, TiC-Carbon, UC2-MWCNT and LaC2-MWCNT. In this presentation an overview of the target materials for RIB production used at ISOLDE will be done, where the main focus will R&D towards nanomaterials.

 

 

 

Nanostructured materials for particle beams: the example of ISOLDE targets

J.P. Ramos 
CERN, Geneva, Switzerland
PhD Public Defense/CERN Accelerators and Technology Sector Seminar, 26th of January 2017

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More than 1000 different isotope beams from 74 chemical elements are produced at the ISOLDE - Isotope Separator OnLine DEvice - facility at CERN, which are of interest for the nuclear, atomic, solid state, astro and bio-physics communities. The radioisotopes are created through nuclear reactions, by bombarding a target material with the pulsed 1.4 GeV protons from the PSB. After thermalization and during irradiation, the isotopes diffuse out of the material grains, keeping the target material at high temperatures, and effuse throughout the target’s porosity. After leaving the material envelope, the isotopes effuse through a transfer line which connects the target oven to an ion source where they are ionized, extracted, mass separated and ready to be delivered for physics experiments where they can be post-accelerated to high energies with the HIE-ISOLDE LINAC.
The target material ultimately limits the facility beam intensities due to the lengthy nature of the diffusion process when compared to the short isotope half-lives (down to tens of millisecond range) which are increasingly requested for physics. Even though the ISOL technique is almost 70 years old it was only in the last 10 years that the target material microstructure engineering was considered in order to improve the isotope release processes. By reducing the target grain size, creating highly porous nanograined materials, the diffusion distances can be greatly reduced, favouring the isotope release and so increasing the beam intensities. Furthermore, during such studies, the nanometric targets are developed to be stable in such harsh conditions of high temperature and irradiation, bringing stable beam intensities over time, unlike other standard ISOL materials. Being less dense and more efficient these novel target materials also present the advantage of reducing the radioactive waste generated by ISOLDE.
In this seminar an overview of the ISOL target materials and respective properties important for isotope production, will be made. This will be followed by case studies of the ISOLDE target nanomaterials (TiC, CaO, UC2, carbon nanotubes, etc.) from the development, scale-up production process, to test and operation phases.

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Titanium carbide-carbon porous nanocomposite for radioactive ion beam production: processing, sintering and isotope release properties

J.P. Ramos 
CERN, Geneva, Switzerland
Invited - ISOLDE Physics Group Meeting, 9th of November 2016

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Highly porous nanograined materials have been developed throughout the last 10 years at ISOLDE-CERN, to deliver high and stable intensities of radioactive ion beams. The small grains provide short diffusion distances to the produced isotopes, while, after evaporation from the grain surface, the high porosity is beneficial for the isotope to escape the material envelope. Embossed and rolled Ti metal foils of 30 μm thickness, have been used at ISOLDE to deliver beams of Sc, Ca and K. However, even though they provide good beam intensities in the beginning, their intensity rapidly decays over operation time. TiC is a highly refractory material with potential to become an ISOL nanometric material even though it has been discarded in the past in its 1-50 μm particle form. Since nanometric TiC sinters at T>1200 °C, TiC-C nanocomposites were developed to improve its stability, where C is either graphite, carbon black (CB) or multi wall carbon nanotubes (MWCNT). The selected nanocomposites were irradiated using the MEDICIS montrac system and studied for release using the solid state diffusion chamber at ISOLDE. TiC-CB presented the best release properties. This material was then upscaled to produce a full target and tested at ISOLDE as a prototype (#527) with a Re surface ion source. The TiC-CB target release was tested from 1300 to 2000 °C showing improved yields of Na and Li in comparison with the best Ti foils target yields. However, lower yields on K and Ca were obtained, where we suspect that the CB may be hindering the release of these elements. Nonetheless, contrarily to Ti foils, the yields were stable during the full prototype operation period. An apparently longer release time-structure was observed for all isotopes as seen for other nanomaterials operated at ISOLDE. The new TiC target provides improvements on some of the beams available for the physics program from the Ti-based target materials at ISOLDE. Nevertheless, an improved TiC-MWCNT nanocomposite has now been developed and waits prototype testing with the purpose of improving the n-def K and Ca yields, such as 35Ca and 35K.

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Beam Research and Developments at ISOLDE

J.P. Ramos (on behalf of the ISOLDE-CERN Target and Ion Source Development Team)
GANIL, Caen, France
Invited - SPIRAL1 Workshop - Physics Opportunities with the SPIRAL upgrade, 8th of February 2016

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The Target and Ion Source Development Team (TISD) at CERN-ISOLDE develops beams of new elements or of shorter-lived isotopes. To deliver intense, pure and stable beams over time to the physics community is also one of the daily responsibilities of the TISD team, by insuring that the current targets and ion sources operate with optimized settings.
Target nanomaterials prototypes were developed and operated over the last years which in many cases brought high yields or/and new beams. In this contribution, some of these prototypes will be detailed, namely a calcium oxide target operated at room temperature and various carbide-carbon nanocomposites. Subsequently, recent results obtained on the production of 8B beam as a BF2+ molecule, from a carbon nanotubes target will be detailed.
Finally, a short overview of the negative ion beams will be given followed by a glance at other projects such as development of refractory metal beams, molten metal loop target (LIEBE) and ion source developments.

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Radioactive Beams at ISOLDE: Status and Developments

J.P. Ramos (on behalf of the ISOLDE-CERN Target and Ion Source Development Team)
CERN, Geneva, Switzerland
Invited - ISOLDE Workshop and Users Meeting, 3rd of December 2015

Best Young Speaker Award

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The mission of the Target and Ion Source Development Team (TISD) at CERN-ISOLDE is to develop beams of new elements or shorter-lived isotopes. It is also to make sure that the current targets and ion sources operate with optimized settings and deliver high, pure and stable beams over time to the physics community. In this contribution, a report on the isotope yields of the uranium carbide targets produced from a new uranium oxide batch, will be given. In general, good and stable beam intensities that match and even surpass ISOLDE database values were obtained. A special focus will be given to online target nanomaterial prototypes tested over 2015 and 2014, namely a room temperature calcium oxide and various carbide-carbon nanocomposites. Furthermore, a short overview of the negative ion beams tests at ISOLDE will be given and also an update on the on-going beam development projects.

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Radioactive Ion Beam Production at CERN - The importance of Materials research

J.P. Ramos
Department of Materials and Ceramic Engineering, University of Aveiro, Portugal
Invited - Isolated Seminar, 25th of February 2015

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The European Organization for Nuclear Research (CERN), situated close to the Geneva in the Franco-Swiss border, is an organization which aims to determine the fundamental structure of the universe. For that that many types of particles are accelerated and studied in dedicated and physics experimental setups. One type of such particles are radio-isotopes which are produced at the ISOLDE facility (Isotope Separator OnLine DEvice). ISOLDE produces more than a 1000 different isotope beams from 72 chemical elements which production requires a multidisciplinary expertise in different fields such as physics, chemistry and materials science. The facility gathers several hundreds of users which use the beams provided for physics experiments both in fundamental and applied studies, in fields such as nuclear and atomic physics, solid state physics and bio-physics.
The isotope beams are produced from a thick target which is in vacuum, at high temperatures (400 to 2100°C, depending on the material) and is bombarded with high energetic pulsed proton beams. The protons induce nuclear reactions that produce various isotopes (depending on the material production cross-sections). The products have then to diffuse out of the material bulk and effuse through the material open porosity. After the isotopes escape the target material they are ionized and accelerated creating a beam which is mass separated and delivered to physics setups.
Target material research has been proved to be crucial to deliver high intensities of (exotic – short lived) isotope beams. By engineering the microstructure of the target material, one can improve the release rates of the produced radio-isotopes. It has been shown that the release rates can be improved significantly by using target materials which have open porous nanostructures. Assuming that the release is diffusion driven, such structures reduce the diffusion distances (and so the times) and the also effusion times, allowing the isotopes to travel further without colliding with the material walls.
General overviews of CERN and ISOLDE will be done, together with principles of radioactive ion beam production. Special focus is given to the target materials microstructure and other characteristics important for the beam intensities.

Peer-reviewed

Co-author Publications

The 68mCu/68Cu isotope as a new probe for hyperfine studies: The nuclear moments

A. S. Fenta, S. Pallada, J.G. Correia, M. Stachura, K. Johnston, A. Gottberg, A. Mokhles Gerami, J. Röder, H. Grawe, B.A. Brown, U. Köster, T.M. Mendonça, J.P. Ramos, B.A. MArsh, T. Day Goodacre, V.S. Amaral, L.M.C. Pereira, M.J.G. Borge, H. Haas
Europhysics Letters, volume 115, number 6, page 62002, 2016

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Time Differential Perturbed Angular Correlation of γ-rays (TDPAC) experiments were performed for the first time in the decay of 68m Cu (6-, 721 keV, 3.75 min) produced at the ISOLDE facility at CERN. Due to the short half-life of the source isotope, the measurements were carried out online. The intermediate state (2+, 84.1 keV, 7.84 ns) offers the unique opportunity to study the electromagnetic fields acting at a copper probe in condensed matter via hyperfine interactions. The present work allowed determination of the nuclear moments for this state. The electric quadrupole moment |Q(2+, 84.1 keV)|=0.110(3) b was obtained from an experiment performed in Cu2O and the magnetic dipole moment |μ|=2.857(6) μN from measurements in cobalt and nickel foils. The results are discussed in the framework of shell model calculations and the additivity rule for nuclear moments with respect to the robustness of the N = 40 sub-shell.

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Experimental tests of an advanced proton-to-neutron converter at ISOLDE-CERN

A. Gottberg, T.M. Mendonca, R. Luis, J.P Ramos and C. Seiffert, S. Cimmino, S. Marzari, B. Crepieux, V. Manea, V., R.N. Wolf, F. Wienholtz, S. Kreim, V.N. Fedosseev, B.A. Marsh, S. Rothe, P. Vaz, J.G. Marques, T. Stora
Nuclear Instruments and Methods in Physics Research Section B, volume 336, pages 143-148, 2014

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The suppression of isobaric contaminations is of growing importance for many scientific programs using radioactive isotopes produced at isotope separation on-line (ISOL) facilities, such as ISOLDE-CERN. A solid tungsten proton-to-neutron converter has been used for ten years to produce neutron-rich fission fragments from an UCx target while suppressing the production of neutron-deficient isobaric contaminants. The remaining contamination is mainly produced by primary protons that are scattered by the heavy neutron converter and finally impinge on the UCx target itself. Therefore, the knowledge of the energy-dependant cross-sections of proton and neutron induced fission events is crucial in order to evaluate future converter concepts. In this paper, an improved neutron converter prototype design is presented together with the experimentally assessed radioisotope production of Rb, Zn, Cu, Ga and In that validate the converter concept aiming at beams of higher purity neutron-rich isotopes. The experimentally derived release efficiencies for isotopes produced by the 1.4 GeV protons available at ISOLDE are used to evaluate the Monte Carlo code FLUKA and the cross-section codes TALYS and ABRABLA, respectively.

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Production and release of ISOL beams from molten fluoride salt targets

T.M. Mendonca, R. Hodak, V. Ghetta, M. Allibert, D. Heuer, E. Noah, S. Cimmino, M. Delonca, A. Gottberg, M. Kronberger, J.P. Ramos, C. Seiffert, T. Stora
Nuclear Instruments and Methods in Physics Research B, volume 329, pages 1-5, 2014

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In the framework of the Beta Beams project, a molten fluoride target has been proposed for the production of the required 101318Ne/s. The production and extraction of such rates are predicted to be possible on a circulating molten salt with 160 MeV proton beams at close to 1 MW power. As a most important step to validate the concept, a prototype has been designed and investigated at CERN-ISOLDE using a static target unit. The target material consisted of a binary fluoride system, NaF:LiF (39:61 mol.%), with melting point at 649 °C. The production of Ne beams has been monitored as a function of the target temperature and proton beam intensity. The prototype development and the results of the first online tests with 1.4 GeV proton beam are presented in this paper.

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Production of molecular sideband radioisotope beams at CERN-ISOLDE using a Helicon-type plasma ion source

M. Kronberger, A. Gottberg, T.M. Mendonca, J.P. Ramos, C. Seiffert, P. Suominen, T. Stora
Nuclear Instruments and Methods in Physics Research B, volume 317, pages 438-441, 2013

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In order to account for the increasing demand for strong molecular beams for nuclear physics experi- ments at ISOLDE, a new radioactive ion source concept based on an RF discharge in a magnetized plasma was developed at CERN. Experimental studies at the ISOLDE offline separator show that the optimum conditions for CO+ and CO2 ion production are given when the ion source is operated with He plasma, in line with expectations based on their electron impact ionization cross-sections. At optimum tuning, ionization efficiencies of 2.5% and 4% were measured for CO+ and Ar+, respectively. The capability of the Helicon ion source prototype for ISOL operation was evaluated during two online runs at the General Purpose Separator of CERN-ISOLDE, yielding the first observation of 17CO+ with a HfO2 fibre target, and a more than 50-fold enhancement of the 10CO+ and 11CO+ yields with a nanostructured CaO target and an upgraded ion source prototype.

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Conference Proceedings


Blurring the boundaries between ion sources: The application of the RILIS inside a FEBIAD type ion source at ISOLDE

T. Day Goodacre, J. Billowes, R. Catherall, T.E. Cocolios, B. Crepieux, D.V. Fedorov, V.N. Fedosseev, L.P. Gaffney, T. Giles, A. Gottberg, K.M. Lynch, B.A. Marsh, T.M. Mendonça, J.P. Ramos, R.E. Rossel, S. Rothe, S. Sels, C. Sotty, T. Stora, C. Van Beveren, M. Veinhard
Nuclear Instruments and Methods in Physics Research B, volume 376, pages 39-45, 2016
XVIIth International Conference on ElectroMagnetic Isotope Separators and Techniques Related to their Applications, May 11–15, 2015 at Grand Rapids, United States of America

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For the first time, the laser resonance photo-ionization technique has been applied inside a FEBIAD-type ion source at an ISOL facility. This was achieved by combining the ISOLDE RILIS with the ISOLDE variant of the FEBIAD ion source (the VADIS) in a series of off-line and on-line tests at CERN. The immediate applications of these developments include the coupling of the RILIS with molten targets at ISOLDE and the introduction of two new modes of FEBIAD operation: an element selective RILIS mode and a RILIS + VADIS mode for increased efficiency compared to VADIS mode operation alone. This functionality has been demonstrated off-line for gallium and barium and on-line for mercury and cadmium. Following this work, the RILIS mode of operation was successfully applied on-line for the study of nuclear ground state and isomer properties of mercury isotopes by in-source resonance ionization laser spectroscopy. The results from the first studies of the new operational modes, of what has been termed the Versatile Arc Discharge and Laser Ion Source (VADLIS), are presented and possible directions for future developments are outlined.

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Advances in surface ion suppression from RILIS: Towards the Time-of-Flight Laser Ion Source (ToF-LIS)

S. Rothe, R. Catherall, B. Crepieux, T. Day Goodacre, V.N. Fedosseev, T. Giles, B.A. Marsh, J.P. Ramos, R.E. Rossel
Nuclear Instruments and Methods in Physics Research B, volume 376, pages 86-90, 2016
XVIIth International Conference on ElectroMagnetic Isotope Separators and Techniques Related to their Applications, May 11–15, 2015 at Grand Rapids, United States of America

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We present results from the development towards the Time-of-Flight Laser Ion Source (ToF-LIS) aiming for the suppression of isobaric contaminants through fast beam gating. The capability to characterize high resistance ion sources has been successfully demonstrated. A ninefold selectivity gain has been achieved through suppression of surface ionized potassium, while maintaining >90% transmission for laser-ionized gallium using a thin wall graphite ionizer cavity combined with a fast beam gate. Initial results from the investigation of glassy carbon as a potential hot cavity ion source are presented. Power-cycle tests of a newly designed mount for fragile ion source cavities indicates its capability to survive the thermal stress expected during operation in an ISOLDE target unit. Finally, we introduce fast ion beam switching at a rate of 10 kHz using the ISOLDE ion beam switchyard as a new concept for ion beam distribution and conclude by highlighting the potential applications of this ion beam multiplexing technique.

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First application of the Laser Ion Source and Trap (LIST) for on-line experiments at ISOLDE

D.A. Fink, S.D. Richter, B. Bastin, K. Blaum, R. Catherall, T.E. Cocolios, D.V. Fedorov, V.N. Fedosseev, K.T. Flanagan, L. Ghys, A. Gottberg, N. Imai, T. Kron, N. Lecesne, K.M. Lynch, B.A. Marsh, T.M. Mendonca, D. Pauwels, E. Rapisarda, J.P. Ramos, R.E. Rossel, S. Rothe, M.D. Seliverstov, M. Sjödin, T. Stora, C. Van Beveren, K.D.A. Wendt
Nuclear Instruments and Methods in Physics Research B, volume 317, part B, pages 417-421, 2013
XVIth International Conference on ElectroMagnetic Isotope Separators and Techniques Related to their Applications, December 2–7, 2012 at Matsue, Japan

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The Laser Ion Source and Trap (LIST) provides a new mode of operation for the resonance ionization laser ion source (RILIS) at ISOLDE/CERN, reducing the amount of surface-ionized isobaric contaminants by up to four orders of magnitude. After the first successful on-line test at ISOLDE in 2011 the LIST was further improved in terms of efficiency, selectivity, and reliability through several off-line tests at Mainz University and at ISOLDE. In September 2012, the first on-line physics experiments to use the LIST took place at ISOLDE. The measurements of the improved LIST indicate more than a twofold increase in efficiency compared to the LIST of the 2011 run. The suppression of surface-ionized francium contaminants has enabled the first in-source laser spectroscopy of 217Po and 219Po.

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Academic Degree

Thesis

Titanium carbide-carbon porous nanocomposite materials for radioactive ion beam production: processing, sintering and isotope release properties

J.P. Ramos
PhD Thesis - Laboratory of Powder Technology, École Polytechnique Fédérale de Lausanne, Switzerland
Oral Exam on the 27th October 2016 | Public defense - 26th January 2017 - see special/invited talks above
Thesis advisors: Prof. P. Bowen and Dr. T. Stora

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The Isotope Separator OnLine (ISOL) technique is used at the ISOLDE - Isotope Separator OnLine DEvice facility at CERN, to produce radioactive ion beams for physics research. At CERN protons are accelerated to 1.4GeV and made to collide with one of two targets located at ISOLDE facility. When the protons collide with the target material, nuclear reactions produce isotopes which are thermalized in the bulk of the target material grains. During irradiation the target is kept at high temperatures (up to 2300 °C) to promote diffusion and effusion of the produced isotopes into an ion source, to produce a radioactive ion beam.
Ti-foils targets are currently used at ISOLDE to deliver beams of K, Ca and Sc, however they are operated at temperatures close to their melting point which brings target degradation, through sintering and/or melting which reduces the beam intensities over time. For the past 10 years, nanostructured target materials have been developed and have shown improved release rates of the produced isotopes, due to the short diffusion distances and high porosities.
In here a new Ti-based refractory material is developed to replace the currently used Ti-foils. Since nanometric TiC can’t be maintained at high temperatures (T> 1200 °C) due to sintering, a processing route was developed to produce TiC-C nanocomposites where the carbon allotropes used were either graphite, carbon black or multi wall carbon nanotubes (MWCNT). The developed nanocomposites sinterability was tested up to 1800 °C and they were characterized according to dimensional changes, relative density, mass losses, surface area, TiC particle size and microstructure morphology.
All carbon allotropes had a significant effect on the stabilization of the nanometric TiC where the best result was obtained for a 1:1 volume ratio of TiC:carbon black at 1800 °C where TiC crystallite sizes were of 76 nm (from 51 nm) and density of 55 %, followed by TiC:MWCNT with TiC of 138 nm (58 % dense). The processing introduced a ZrO2 contamination from the milling media, forming ZrC that solubilizes in the TiC phase, increasing its lattice parameter.
TiC sintering kinetics were studied through the master sintering curve and the activation energy determined for sintering, 390 kJ/mol, were close to the ones obtained in the literature was obtained. Using the same method, activation energy for TiC-carbon black was 555 kJ/mol resulting from the carbon which reduces the TiC sintering, reducing its coordination number.
The nanocomposites referred (and the TiC) were irradiated and studied in terms of isotope (Be, Na, Mg, K, Sc and Ca) release, where the nanocomposite with the highest isotope released fraction, TiC-carbon black was selected for the final target material. To produce a full target the processing was scaled up and a target prototype was build and tested at ISOLDE. Li, Na and K isotope intensities and release time-structure were measured from the target prototype, where in comparison with Ti-based materials, Na and Li intensities were higher, K were slightly lower and Ca were lower.
The target presents an apparently longer release time structure when comparing with standard materials, as seen in other nanomaterial targets, which is likely related with effusion of the isotopes in the material porosity. Furthermore, contrarily to the Ti-foil targets, the obtained intensities were stable over the full operation time. At the end of this thesis suggestions for a future work which include a second iteration of the TiC-C nanocomposite (already developed) and modeling.

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Effect of Calcium Oxide Microstructure on the Diffusion of Isotopes

J.P. Ramos
Master Thesis - Department of Materials and Ceramics Engineering, Universidade de Aveiro, Portugal
Defended on 14th February 2012
Thesis advisors: Prof. A.M.R. Senos and Dr. T. Stora

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Calcium oxide (CaO) powder targets have been successfully used at CERN-ISOLDE to produce neutron deficient exotic argon and carbon isotopes under proton irradiation at high temperatures (>1000°C). These targets outperform the other related targets for the production of the same beams. However, they presented either slow release rates (yields) from the beginning or a rapid decrease over time. This problem was believed to come from the target microstructure degradation, justifying the material investigation. In order to do so, the synthesis, reactivity in ambient air and sintering kinetics of CaO were studied, through surface area determination by N2 adsorption, X-ray diffraction for crystalline phase identification and crystallite size determination, and scanning and transmission electron microscopy to investigate the microstructure. The synthesis studies revealed that a nanometric material is obtained from the decarbonation of CaCO3 in vacuum at temperatures higher than 550°C, which is very reactive in air. This reactivity was studied, and it was observed that the CaO powder microstructure is changed through the reaction with air (hydration and carbonation of the oxide) and that this change is not completely reversible after thermal decomposition of the reaction products. Therefore, special care was taken in the target handling at CERN-ISOLDE. From the sintering kinetics, studied in the range of 1000-1200°C, it was determined that this material’s microstructure degrades, with the reduction of the specific surface area and decrease of the powder porosity. At 1200°C, the specific surface area reduction is accentuated, reaching values of 50% of surface area reduction in 10h. These results suggest that the use of high temperatures, equal or higher than 1000°C must be avoided, if the microstructural characteristics of the targets are to be preserved. At CERN-ISOLDE, selected conditions for synthesis, handling of the target and target operation temperatures were chosen, based on the previous material research, and the obtained target material was tested under proton irradiation. From the online studies, the newly developed target proved to show better initial and stable over time release rates of almost all isotopes investigated and especially the exotic ones. These results are essentially due to the nanometric characteristics of the produced target and to the use of operation and handling conditions that decreased the degradation of the microstructural characteristics. Diffusion studies of Ar and Ne were also done in CaO through the application of a mathematical model, to the release curves of the respective isotopes at different temperatures, which enables the determination of the respective diffusion coefficients and activation energies.

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Conferences and Workshops

Talks

Nanomaterials for radioisotope production

J.P. Ramos
LTP 10th & Final Extra-Muros “A Powder Technology Workshop – 29 years of badly behaved powders… or not?”, Rigi Kaltbad, Switzerland, 11-13th October 2017.

 

High power molten targets for the production of radioactive ion beams

J.P. Ramos, R. Augusto, P. Bricault, M. Delonca, M. Dierckx, L. Egoriti, A. Gottberg, D. Houngbo, T. Mendonca, L. Popescu, S. Rothe, T. Stora, S. Warren
International Atomic Energy Agency 1st Workshop on “Challenges for Coolants in Fast Neutron Spectrum Systems: Chemistry and Materials”, IAEA, Vienna, Austria, 5th-7th July 2017.

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In the Isotope Mass Separation OnLine (ISOL) approach, Radioactive Ion Beams are produced by interception of an intense primary particle beam with a thick target and by the extraction of the isotopes from the target “online” to produce a secondary beam. ISOLDE at CERN has been operating for fifty years and exploits a wide range of target materials made of refractory solids and molten materials. In some cases, a solid spallation neutron source is used to generate fast neutrons from the primary proton beam and induce fission in a hot uranium carbide target situated at close proximity [1].
Several projects, in the design studies or well under construction, rely on the proper design and operation of high power targets. These new designs must be conceived and prototyped for heat dissipation in the kW to 100’s kW range, while the target can still efficiently extract refractory isotopes [2].
Prototypes have recently been developed, based on static targets of molten salt (NaF:LiF) and molten metals (Pb, PbBi, Sn), and operated under the pulsed 1.4 GeV proton beam of the Proton Synchrotron Booster. These molten targets can be used in a circulating loop, where a first prototype is expected to operate at CERN within the LIEBE project collaboration [2]. Finally, a design of a compact spallation source made of tungsten and passive cooling with molten PbBi is investigated for operation at the ISAC facility in TRIUMF [3].

[1] 6th High Power Targetry Workshop, STFC, Oxford, UK (2016),
https://eventbooking.stfc.ac.uk/uploads/6thhptwbookofabstractswebversion.pdf, accessed May 2017.
[2] De Melo Mendonca, T. M. High Power Molten Targets for Radioactive Ion Beam Production: from Particle Physics to Medical Applications. No. CERN-ACC-2014-0183. 2014.
[3] Gottberg, A., et al. "Experimental tests of an advanced proton-to-neutron converter at ISOLDE-CERN." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 336 (2014): 143-148.

 

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Porous titanium carbide-carbon nanocomposites for radioactive ion beam production at CERN-ISOLDE

J.P. Ramos, A. Gottberg, T. Mendonça, A.M.R. Senos, T. Stora, P. Bowen
14th International Conference European Ceramic Society 2015, Toledo, Spain, 21st-25th June 2015.

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Titanium carbide (TiC) materials are very refractory, extremely hard and have a high chemical stability. They are mainly used in tools, aerospace applications, reinforcement in composites and plastics and as surface coatings.
Here we introduce, for the first time, a TiC-carbon nanocomposite which displays high porosity, high specific surface area and extended stability under high temperatures and intense and highly pulsed proton beam conditions. These characteristics have been found to be beneficial for the constant production of 37K radioactive beams at the CERN-ISOLDE facility.
Beams of radioactive isotopes are produced at the ISOLDE facility at CERN for nuclear, atomic, solid state and bio physics studies. Nuclear reactions in the bulk of a thick target are induced by proton bombardment, producing isotopes of interest. During proton irradiation, these targets are kept at high temperatures in order to promote diffusion of the isotopes out of the material grains to the surface, where they evaporate and effuse through the material porosity. Effusion continues through a transfer line until the isotopes reach an ion source, where they are ionized, creating a beam. By reducing the grain size of the target material (which can be an oxide, carbide or a metal) and increasing its porosity, one can increase the release rates, decreasing the diffusion and effusion times [1, 2]. Such effects have been observed even at lower release temperatures, used to avoid structure degradation by sintering [2].
Commercial nanometric TiC was mixed with three different carbon allotropes (graphite, carbon black and multi walled nanotubes), in different volume ratios, in order to stabilize the TiC nanostructure and maintain porosity at high temperatures (>1500oC). Using attrition milling the degree of agglomeration of the TiC powder was reduced with Dv50 decreasing from 1.7 µm to 370 nm. The milling was carried out in isopropanol and polyvinylpyrrolidone was used to stabilise the suspension [3, 4]. The three different types of TiC and carbon suspensions were mixed, dried, pressed and sintered in high vacuum at 1500, 1650 and 1800oC. The nanostructured composites had porosities varying from about 5% to 60%, depending on the amount of carbon and the sintering temperature.
In order to study the material release properties, release studies were done. Selected structures were irradiated with protons at CERN-ISOLDE, producing the isotopes of interest. These structures were then submitted to a heating cycle to promote the isotope release and gamma spectroscopy was done before and after each heating cycle, to quantify the release.
A final composite was selected and a target prototype was produced by successfully scaling up attrition milling from the used 3 g batches, to two batches of 40 g in order to produce a full target (2 cm diameter and 20 cm of length).
The produced nanostructures, using the different carbon allotropes, before and after the sintering treatments, will be presented together with preliminary results on the release studies on selected materials. Preliminary results on the first successful use of TiC-carbon target (prototype) operated at CERN-ISOLDE will also be presented.

References

[1] S. Fernandes, CERN-THESIS-2010-170/EPFL-4813.
[2] J.P. Ramos et al., Nucl. Instr. Meth. B, 310 (2014), 83.
[3] P. Bowen et al., Ceram. Trans. 51 (1995) 621.
[4] P. Bowen et al., Third Euro-Ceramics, 1 (1993) 549.

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Proton irradiation and high temperature effects on spallation target (nano)materials microstructure at ISOLDE-CERN

J.P. Ramos
10ème Colloque « Matériaux, Mécanique, Microstructure », Matériaux en Conditions Extrêmes, INSTN, Saclay, France, 18th-19th June 2015.

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Radioisotope beams are produced at CERN in the ISOLDE facility for nuclear, atomic, bio and solid state physics research. Irradiating a specific target material with high energy pulsed proton beams produces radioisotopes through nuclear reactions. During the irradiation the target is kept at high temperatures (up to 2100°C), in vacuum, and the produced isotopes have then to diffuse out of the bulk and effuse through the material microstructure and travel to an ion source where they are ionized. Afterwards the ions are extracted forming a beam which is mass separated and conducted to a physics experiment. Such target materials can be made of oxide, carbide, metal or salt materials and they can be in powder, pellet, foils or liquid form depending on the material and the isotope to produce. To produce short lived isotopes (ms half-life), ideally the target material should be refractory, of small grain size (submicron or nano – to reduce diffusion paths), highly porous (to decrease effusion times), should withstand radiation damage and have a low vapour pressure at the operation temperatures (<10-4 mbar).
At ISOLDE, it is common that the isotope release rates (yields) are decaying over time, which is usually linked to the target microstructure degradation (sintering) due to the high temperatures used and/or the proton impact on target. In the last years, special attention has been given to use porous composite nanomaterials as target materials. In the case of such materials special attention must be taken if one wants a stable structure under such extreme conditions.
Examples like irradiation damage on submicron silicon carbide [1], material characteristics vs yields degradation on nanostructured calcium oxide [2,3] and other examples will be given. Ways to avoid such degradation, such as creating composite materials or reducing the grain size and operation temperatures and/or proton intensity will also be detailed [2,3]. Additionally a small part of the contribution will be dedicated to the extraction of diffusion and effusion material characteristics from the release time-structure of the isotope from the target unit [4,5].
References:
[1] S. Fernandes, et al. “Microstructure evolution of nanostructured and submicron porous refractory ceramics induced by a continuous high-energy proton beam”. Journal of Nuclear Materials, Vol. 416, pp 99-110, 2011.
[2] J.P. Ramos, et al. “Intense 31–35Ar beams produced with a nanostructured CaO target at ISOLDE”. Nuclear Instruments and Methods in Physics Research B, Vol. 320, pp 83-88, 2014.
[3] J.P. Ramos, et al. “Sintering kinetics of nanometric calcium oxide in vacuum atmosphere”. Ceramics International, Vol. 41, pp 8093-8099, 2014.
[4] T. Stora, et al. “A high intensity 6He beam for the β-beam neutrino oscillation facility”. EPL (Europhysics Letters) Vol. 98, No. 3 pp 32001, 2012.
[5] J.P. Ramos “Effect of Calcium Oxide Microstructure on the Diffusion of Isotopes”. Master Thesis, University of Aveiro, Aveiro, 2012.

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Calcium Oxide and Titanium Carbide-Carbon Nanomaterials for Spallation Targets at CERN-ISOLDE

J.P. Ramos, P. Bowen, A.M.R. Senos, A. Gottberg, M. Czapski, T. Mendonça, R.S. Augusto, C. Seiffert, T. Stora
E-MRS 2014 Fall Meeting, Warsaw University of Technology, Warsaw, Poland, 16th September 2014.

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At CERN, radioactive isotopes are produced through nuclear reactions, by bombarding thick targets with pulsed proton beams in the ISOLDE facility. During the irradiation, the high temperature applied to the target promotes the diffusion of the produced isotopes out of the material bulk which then effuse through the material porosity to a transfer line which connects to an ionizer, producing a beam which is used for physics experiments. Grain size reduction in oxide and carbide materials, with porosity increase, has been shown to increase the release rates even if target materials have to be operated at lower temperatures (avoid sintering of the microstructure), reducing diffusion and effusion times.
Following this concept, a nanometric calcium oxide powder target was developed and studied in terms of sintering and operated at ISOLDE as the first nanomaterial target. This target revealed higher and stable (exotic) neutron-deficient argon release rates, contrarily to previous conventional target materials.
Taking target material development to the next step, in order to stabilize nanometric titanium carbide at high temperatures, a biphasic material is being developed by mixing the former with carbon in different forms (graphite, carbon black and nanotubes). This development represents the first biphasic nano-composite target material being developed at ISOLDE. Such material should open the way for the production of high intensity exotic beams of neutron-deficient calcium, potassium and magnesium. In order to benchmark such nanostructures, irradiations will be followed by isotope release studies with gamma spectroscopy and finally a target prototype.

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Fast Release of radioisotopes from nanostructured target materials for beam production at CERN-ISOLDE

J.P. Ramos
Nanostructures probed by intense particle beams – Short Course, Faculty of Sciences – KU Leuven, Leuven, Belgium, 17th April 2013.

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The first nanostructured target (calcium oxide powder - CaO) was used successfully, to produce radioactive ion beams, at the ISOLDE facility at CERN. The CaO targets, in the past, outperformed others to produce beams of neutron-deficient carbon and argon but the yields were unstable: either decreasing over the operation time or being low from the beginning. The new nanostructured CaO target was able to deliver stable and superior (exotic) argon yields. The higher yields are due to a faster release of the finite lifetime isotopes, from the target material, due to shorter diffusion paths of the (much smaller) grains in the CaO. This result was obtained due to a detailed microstructural study of the target material, not only in terms of production but also in terms of handling and operation conditions, in order to avoid degradation of the material. A nanostructured material was produced, was kept under controlled atmosphere due to its reactivity and the kinetics of sintering were assed to select an appropriate operation temperature, which was much lower than for the past CaO targets.
Due to the increased stability and yield absolute values obtained in the case of the CaO targets, this concept is to be applied for the production of exotic potassium and calcium beams, by the use of titanium based refractory materials. The aim of this study is to produce a nanostructured titanium carbide/oxide that is stable at high temperatures and able to provide higher release rates of these isotopes. Offline isotope release studies were done and material studies are ongoing in order to in the future build a prototype target.

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Nanostructured target materials for intense secondary beam production at CERN-ISOLDE

J.P. Ramos
Students’coffee – 16th meeting, CERN, Geneva, Switzerland, 11th March 2013.

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The first nanostructured target (calcium oxide powder - CaO) was used successfully, to produce radioactive ion beams, at the ISOLDE facility at CERN. The CaO targets, in the past, outperformed others to produce beams of neutron-deficient carbon and argon but the yields were unstable: either decreasing over the operation time or being low from the beginning. The new nanostructured CaO target was able to deliver stable and superior (exotic) argon yields. The higher yields are due to a faster release of the finite lifetime isotopes, from the target material, due to shorter diffusion paths of the (much smaller) grains in the CaO. This result was obtained due to a detailed microstructural study of the target material, not only in terms of production but also in terms of handling and operation conditions, in order to avoid degradation of the material. A nanostructured material was produced, was kept under controlled atmosphere due to its reactivity and the kinetics of sintering were assed to select an appropriate operation temperature, which was much lower than for the past CaO targets.
Due to the increased stability and yield absolute values obtained in the case of the CaO targets, this concept is to be applied for the production of exotic potassium and calcium beams, by the use of titanium based refractory materials. The aim of this study is to produce a nanostructured titanium carbide/oxide that is stable at high temperatures and able to provide higher release rates of these isotopes. Offline isotope release studies were done and material studies are ongoing in order to in the future build a prototype target.

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Nanostructured Calcium Oxide Targets for the Production of Argon Beams

J.P. Ramos, A.M.R. Senos, T. Stora
ISOLDE Workshop and Users meeting 2011, CERN, Geneva, Switzerland, 7th December 2011.

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Calcium oxide powder targets have been successfully used at ISOLDE-CERN to produced neutron deficient exotic argon isotopes and carbon isotopes, released as CO and CO2 molecules. Such targets outperform other related targets used to produce the same beams, such as MgO sintered powder or TiOx fibers. However, either some CaO target units displayed slow release rates (or low absolute yields) from the beginning or a rapid decrease over time when operated under proton irradiation.[1] We found that the good performance of the ISOLDE historical targets was related to a structure of a nanometric scale.[2,3] Its fast degradation was mainly caused by sintering due to the high operation temperatures and/or high proton intensities being responsible for the fast drop of the yields. Taking this into account, systematic studies of: the synthesis conditions, sintering kinetics and the air reactivity of the nanometric powder were performed; all in order to improve/maintain the target nanostructural properties. A new production and operation methods were proposed and tested at ISOLDE in order to improve the release properties, in terms of diffusion and effusion of isotopes. Improved yields of exotic Ar beams and no sign of degradation were observed during the operation of the CaO #469, target unit of this year.
References:
[1] Ravn, H. L. et al. Bunched Release of Gases from Oxide Targets. Nuclear Instruments and Methods in Physics Research B: Beam Interactions with Materials and Atoms 1997, 126, 176-181.
[2] Stora, T. et al., Nanostructured Target for Isotope Production, WO 2010/034364 A1, 2010.
[3] Fernandes, S. Submicro- and Nanostructured Porous Materials for Productin of High-Intensity Exotic Radioactive Ion Beams; PhD Thesis; École Polytechnique Fédérale de Lausanne: Lausanne, 2011.

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Conferences and Workshops

Posters

Online prototype TiC-carbon nanocomposite target material: constant release properties and material development

J.P. Ramos, A. Gottberg, T.M. Mendonça, R.S. Augusto, B. Blank, K. Johnston, P. Bowen, A.M.R. Senos, J. Lehnert, M. Deicher, H. Wolf, T. Stora
ISOLDE Workshop and Users meeting 2016, CERN, Geneva, Switzerland, 7th-9th December, 2016.

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Highly porous nanograined materials have been developed throughout the last 10 years at ISOLDE-CERN, to deliver high and stable intensities of radioactive ion beams. The small grains provide short diffusion distances to the produced isotopes, while, after evaporation from the grain surface, the high porosity is beneficial for the isotope to escape the material envelope.
Embossed and rolled Ti metal foils of 30 μm thickness, have been used at ISOLDE to deliver beams of Sc, Ca and K. However, even though they provide good beam intensities in the beginning, their intensity rapidly decays over operation time. TiC is a highly refractory material with potential to become an ISOL nanometric material even though it has been discarded in the past in its 1-50 μm particle form.
Since nanometric TiC sinters at T>1500 °C, TiC-C nanocomposites were developed to improve its stability, where C is either graphite, carbon black (CB) or multi wall carbon nanotubes (MWCNT). The selected nanocomposites were irradiated using the MEDICIS montrac system and studied for release using the solid state diffusion chamber at ISOLDE. TiC-CB presented the best release properties. This material was then upscaled to produce a full target and tested at ISOLDE as a prototype (#527) with a Re surface ion source.
The TiC-CB target release was tested from 1300 to 2000 °C showing improved yields of Na and Li in comparison with the best Ti foils target yields. However, lower yields on K and Ca were obtained, where we suspect that the CB may be hindering the release of these elements. Nonetheless, contrarily to Ti foils, the yields were stable during the full prototype operation period. An apparently longer release time-structure was observed for all isotopes as seen for other nanomaterials operated at ISOLDE.
The new TiC target provides improvements on some of the beams available for the physics program from the Ti-based target materials at ISOLDE. Nevertheless, an improved TiC-MWCNT nanocomposite has now been developed and waits prototype testing with the purpose of improving the n-def K and Ca yields, such as 35Ca and 35K.

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Advanced High Power Neutron Converter - Spallation Source - for Radioactive Ion Beam Production

J.P. Ramos, P. Bricault, C. Cimmino, M. Delonca, A. Gottberg, R. Luis, S. Marzari, T.M. Mendonca, L. Popescu, T. Stora
6th High Power Targetry Workshop, Merton College, Oxford, United Kingdom, 11th-15th April 2016.

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The delivery of highly intense and pure beams of radioisotopes of (ultimately) all chemical elements, for physics research, is the mission of the ISOL facilities such as HIE-ISOLDE at CERN, ISAC at TRIUMF and the future ISOL@MYRRHA facility at SCK-CEN. As a result, these facilities are always thriving to upgrade themselves, through research and development of new ways to produce, extract and ionize the radioisotopes. In particular, the neutron converter, a spallation source which is used to induce n-rich fission fragments from uranium carbide targets, avoiding the n-deficient isobaric contaminations (which are produced irradiating directly the target with protons). In the last years new optimized geometries have been proposed for the ISOLDE neutron converter [1,2,3] and an example was tested and validated[3]. Such geometry is optimized in a way so that the protons scattered by the neutron converter don’t hit the target nearby while maximizing the neutron interaction with the target. As an example, one of the proposed geometries is a thick-walled cylindrical tube shaped target centred around a tungsten cylinder shifted downstream from the target relatively to the proton beam. Such geometry presents many engineering challenges which will have to be validated with simulation codes (FLUKA – for isotope production and beam power deposition and ANSYS – for thermal profiles) and additional prototypes will have to be built. Additionally, designs for the very different facility target units and respective driver beam properties (high power – instantaneously or continuous) will have to be done and tested. Facilities around the world, have very different driver beam properties such as ISAC with 50kW, CW 500MeV proton beam, HIE-ISOLDE up to 2GeV pulsed proton beam and 12kW (10GW instantaneous power), ISOL@MYRRHA with 600MeV proton beam and 100 kW beam power and RISP with 160 kW, 160 MeV protons.

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Titanium-based refractory nanomaterials for isotope production and release at ISOLDE-CERN

J.P. Ramos, T. Stora, A.M.R. Senos, A. Gottberg, T. Mendonça, P. Bowen
EDMX Research Day 2015, EPFL, Lausanne, Switzerland, 23rd November 2015.

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Porous oxide and carbide materials are used at ISOLDE-CERN as targets, at very high temperatures to produce radioactive ion beams. Such targets often deliver unstable beam intensities, decreasing over time, which are linked to the target microstructure degradation (mainly through sintering). The isotopes are produced through nuclear reactions, by bombarding thick targets with pulsed 1.4 GeV proton beam. During the irradiation, the isotope diffusion is promoted by keeping the target at high temperatures which after also promotes effusion through the material porosity and then to a connected ion source, producing a beam to be used for physics experiments. It has been shown that particle size reduction (and high porosity) results in an increase of the release rates, due to the reduced diffusion times, especially in the case of exotic, short lived (10s millisecond range) isotopes. Such targets provide very stable beam intensities due to having a stable microstructure at the operation temperatures. A target material has to have small, nanometric particle sizes, high porosity and be able to operate at high temperatures. Sintering can be avoided by reducing the coordination number of the target material particles by for e.g. introducing a second refractory material.
Titanium carbide (TiC) is very refractory material and a good candidate to produce K and Ca beams for ISOLDE. As such, to have stable nanometric TiC at high temperatures, TiC-C composites were produced by mixing commercially available TiC and one carbon allotrope (graphite, carbon black or carbon nanotubes) in 25, 50 and 75 vol.% in attrition mill in isopropanol (with 0.5 wt.% polyvinylpyrrolidone, PVP). The TiC agglomeration degree was reduced from Dv50 1.7 µm to 370 nm. The resulting materials were dried, pressed into compacts and heat treated to remove the PVP. The obtained composites were then thermal treated at different temperatures (1500,1650, 1800, 2000°C for 10 h) in a vacuum oven to test them for microstructure stability.
The composites developed have shown stabilized nanometric TiC at very high temperatures (up to 2000°C), especially the TiC + 50 vol.% carbon black composite. Isotope release studies show a higher release from the nanocomposites comparing to the pure nanometric TiC. The process was scaled up to produce a full ISOLDE target (70 g - 23x from the sample batches) and a target was successfully operated to bring isotope beams of Li, Na, K, Al and Ca.
Preliminary results on modeling of the effect of the different carbon allotropes on the sintering of TiC, which reduce its coordination number, will also be presented, as well as modeling of their isotope release properties.

 

Radioactive ion beam production at CERN-ISOLDE with nanometric, highly porous target materials – a review

J.P. Ramos, A. Gottberg, C. Seiffert, W. Hwang, J. Guillot, T. Mendonça, A.M.R. Senos, P. Bowen, T. Stora
International Conference on Electromagnetic Isotope Separators and Related Topics - EMIS 2015, Grand Rapids, Michigan, United States of America, 11th-15th May 2015.
(see 1st Author Publications section for Conference Proceedings)

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After isotope production in the bulk of the target material, the beam intensities in ISOL facilities are mainly defined by: the release from the target material, ionization, mass separation and transport efficiencies. Although production can be up to 1E10 /s, by far the most limiting step is the release of the isotopes from the target itself, where release efficiencies can go down to 1E-6 or even less, especially in the case of very short lived isotopes. Apart from this, beam intensities are sometimes decreasing over time, which can be due to the target material degradation. For those reasons, the target material research at ISOL facilities is crucial to deliver stable, high intensity and new exotic beams. The stabilization of open porous, nanostructured materials at high temperatures is the key to improve release efficiencies by reducing the isotope diffusion times, assuming this process is limiting the release.
The nanomaterial target family [1] at ISOLDE has been extended, with novel nano materials operated last year. Nano calcium oxide [2,3] has been operated and has delivered significant intensities of 31Ar even at room temperature. A new material was added to the ISOLDE target material collection - titanium carbide and carbon black nanocomposite [4] - which displayed no decrease of yields as opposed to the previously used Ti foils targets. For the first time, a target exclusively made of multiwall carbon nanotubes (MWCNT) was operated and showed indications of the first 8B beams.
With ~70% of the beam time at ISOLDE, the development of uranium carbide with excess carbon (UCx) targets represents the most significant gains for the facility. A composite made of UCx and MWCNT was developed showing high and stable yields on almost all measured isotopes [5]. Using the same recipe, a nanometric lanthanum carbide-MWCNT composite was successfully developed and tested to provide high and stable beams of neutron-deficient Ba and Cs isotopes.
These materials will be reviewed in terms of synthesis, material characteristics, time-structure and release rates of selected isotopes. From the release results the modelling of physical parameters (effusion and diffusion) will be shown [6].

References
[1] T. Stora, NIMB, 317 (2013) 402-410 (EMIS 2012)
[2] J.P. Ramos et al., NIMB, 310 (2014), 83
[3] J.P. Ramos et al., to be submitted
[4] J.P. Ramos et al., E-MRS 2014 Fall Meeting
[5] A. Gottberg et al., to be submitted
[6] T. Stora et al., NIMB, 98 (2012), 32001

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Titanium-based refractory nanomaterials for isotope production and release at ISOLDE-CERN

J.P. Ramos, M. Czapski, T.M. Mendonça, A. Gottberg, C. Seiffert, P. Bowen, T. Stora, A.M.R. Senos
EDMX Research Day 2013, EPFL, Lausanne, Switzerland, 6th September 2013.

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Neutron deficient exotic calcium and potassium intense beams are demanded for physics experiments at ISOLDE. These beams are produced through the ISOL method: bombarding a target material with high energetic protons, inducing nuclear reactions that produce the isotopes. The produced isotopes have then to diffuse out of the target material and effuse through the material porosity. They arrive at a transfer line, where after they are ionized, accelerated up to 60 keV, mass separated and made available for physics experiments. Titanium foils and titanium oxide (TiO2) fibers have been used at ISOLDE to produce several beams and studied in terms of release properties, together with titanium carbide, (TiC).
Nanostructured/sub-micron materials have shown indications of improved yields, especially in the exotic isotopes, due to the smaller diffusion distances [1,2] when compared to other target materials, with larger grain size. The same concept is now applied to Ti-based refractory targets, using as starting materials commercially available TiC and TiO2 nanometric powders (particle size of ~100 nm) were formed by dry pressing, sintered and release studies. While nanometric TiO2 sinters fast at 1000oC, TiC maintains a nanometric/sub-micron structure until ~1450oC. These materials were first irradiated with protons using the RaBIT system at ISOLDE to produce the isotopes for the release studies. The samples were then heated up at different temperatures (chosen in accord with the sintering studies, i.e., to 1000oC in the case of TiO2 and 1200, 1300, 1400 and 1450oC in the case of TiC) for 5 min and gamma spectroscopy was used to check for the fractional activity remaining in the irradiated samples. The samples were reheated for 10 and 20 min and rechecked for release. Release is seen in the case of TiC at 1300oC and 1400oC for K, Mg, Na and Be.
References:
[1] S. Fernandes (2010), Submicro- and Nanostructured Porous Materials for Production of High-Intensity Exotic Radiaoctive Ion Beams, PhD Thesis, EPFL.
[2] J.P. Ramos, Effect of Calcium Oxide Microstructure on the Diffusion of Isotopes (2012), Master Thesis, University of Aveiro.

 

Development of Nanostructured Calcium Oxide Target for Isotope Production at CERN-ISOLDE

J.P. Ramos, C.M. Fernandes, T. Stora, A. Gottberg, T.M. Mendonça, C. Seiffert, B. Crepieux, A.M.R. Senos
Junior EUROMAT 2012, Université de Lausanne, Lausanne, Switzerland, 26th July 2012 (with flash talk of 3 min).

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Calcium oxide (CaO) powder targets have been successfully used at the ISOLDE facility at CERN, to produce neutron deficient argon and carbon isotopes, released as CO and CO2 at high temperatures (>1000oC) under proton irradiation. These targets outperform other related ones to produce the same type of beams, but they either display slow release rates from the beginning or a rapid decrease over time. It was found that the good performance of the CaO targets is related with a nanometric scale structure. However, a fast microstructure degradation due to pre-sintering effects occurs at high operation temperatures which explains the fast drop of the yields. A material investigation was done aiming at increase/maintain the target nanostructural characteristics during the target production and operation. By systematically studying the synthesis conditions, sintering kinetics and the air reactivity of the CaO powder a new target production and operation procedures were proposed and tested online at ISOLDE. Improved yields of exotic Ar beams and no sign of degradation were observed during the operation of the newly developed nanostructured CaO target. Diffusion of argon and neon in CaO was studied by applying a mathematical model to the online release curves.

 

Stable operation of a nanostructured CaO target for production of Ar beams at CERN-ISOLDE

J.P. Ramos, A. Gottberg, T.M. Mendonça, C. Seiffert, B. Crepieux, C.M. Fernandes, A.M.R. Senos, T. Stora
EURORIB 2012 – European Radioactive Ion Beam Conference 2012, Padova, Italy, 20th-25th May, 2012.

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At the ISOLDE facility at CERN calcium oxide powder (CaO) targets have been successfully used to produce neutron deficient argon and carbon isotopes released as CO and CO2, by proton bombardment. These targets outperform other related targets to produce the same beams, but either some CaO targets display slow release rates (or low absolute yields) from the beginning or a rapid decrease over time when operated under proton irradiation. It was found that the good performance of these targets was related with a nanometric scale structure which quickly degraded due to sintering. This was mainly caused by the high operation temperatures and explaines the fast drop of the yields. Taking this into account a material investigation was done, doing systematic studies on the synthesis conditions, sintering kinetics and the air reactivity of the nanometric powder. The goal was to improve/maintain the target nanostructural properties, and improving the release properties in terms of diffusion of isotopes. A new target production and operation methods were proposed and tested at ISOLDE. Improved yields of exotic Ar beams and no sign of degradation were observed during the operation of the newly developed nanostructured CaO target.

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Microstructure control and isotope release in nanometric calcium oxide powder targets

J.P. Ramos, A.M.R. Senos, T. Stora
IX CICECO Meeting, Universidade de Aveiro, Aveiro, Portugal, 2nd-3rd May 2012.

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At ISOLDE-CERN, CaO powder targets have been used to produce argon and carbon isotopes by proton irradiation. Such targets outperform other ones to produce the same beams (MgO powders and TiOx fibers) but the release rates either decayed fast in time or were low from the beginning. This was due to target microstructure degradation during handling, and operation at high temperatures. Nanometric CaO was synthesised and the air reactivity at RT and the microstructure stability at high temperature were investigated. New experimental conditions were applied for the target production and online operation at ISOLDE-CERN. The best ever release results on Argon isotopes were obtained.

 

Microstructural evolution during vacuum sintering of nanometric calcium oxide powder

J.P. Ramos, C.M. Fernandes, T. Stora, A.M.R. Senos
VI International Materials Symposium MATERIAIS 2011, Universidade do Minho, Guimarães, Portugal, 18th April 2011.

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Calcium oxide (CaO) powder targets have been very successful at CERN (ISOLDE) to produce neutron deficient exotic argon isotopes and carbon isotopes, released as CO and CO2. Because of the very low half-lives of the nuclei produced, a high diffusivity is needed and can be obtained by using a nanometric material and high operating temperatures. Nonetheless, nanometric CaO targets, when operated under proton radiation, at 900-1100ºC, in vacuum (10-2Pa), display slow release rates from the beginning or a rapid decrease over time. Those drawbacks are believed to come from a degradation of the initial microstructure of the targets, caused by powder sintering effects. Therefore, the objective of this work is to investigate the microstructure evolution of nanometric CaO powder samples in conditions of temperature and pressure close to that of the isotope release experiments target operation under proton irradiation.
A nanometric CaO powder was produced from a micrometric calcium carbonate (CaCO3), 99.5% pure, by calcination in vacuum (1-100 Pa) at 800ºC, 2h. The obtained CaO powder had a specific surface area, SSA, as determined by BET, of (54m2/g to 64m2/g)and was carefully maintained under vacuum atmosphere to preserve it from hydration. CaO powder samples, slightly packed (porosity, P>59%), were heated in a vacuum furnace (10-2 – 10-3 Pa. A constant heating rate of 10ºC min-1 was used until the maximum temperature, ranging 900-1200ºC, and the holding time was varied from 3-600 min. The cooling rate was imposed to be 15ºC min-1.
X-ray diffraction was applied to determine the structure and the crystallite size, BET for the SSA and internal porosity measurements and scanning electron microscopy (SEM) for the microstructure characterization. The degree of sintering was analyzed taking SSA as the kinetic parameter, complemented by the microstructure observations.

 

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Although I've been educated in materials science and engineering mainly for industrial applications, I've followed the researchers path (a very unique one).

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Now putting my career on the side, I love my life, my wife and my parents and brothers. In my free time I love to travel, go out with friends and play computer games.

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