Nuclei Yield from High Temperature Target
On-Line Delay Time and Yield Measurements of Short Lived Produced from High Temperature Refractory Targets
Tech Area / Field
- PHY-PFA/Particles, Fields and Accelerator Physics/Physics
8 Project completed
Senior Project Manager
Bugaev D V
Nuclear Physics Institute, Russia, Leningrad reg., Gatchina
- Khlopin Radium Institute, Russia, St Petersburg
- Argonne National Laboratory (ANL), USA, IL, Argonne
Project summaryAt the present time nearly all physical information about short lived radioactive nuclei is being obtained by experiments, making use ISOL (Isotope Separator On-Line) facilities installed on the beams of different bombarding particles: protons, neutrons and heavy ions. The use of high energy 500-2000 MeV proton beams at currents 2-200 mA gives the possibility of producing the widest range of proton and neutron rich radioactive nuclei. Protons bombarding thick (some hundred grams) targets provide very high yields of radioactive isotopes by spallation, fission and fragmentation reactions. The production of intensive accelerated radioactive nuclear beams (RNB) is of great importance for astrophysics, when the ideas of the formation of chemical elements in Universe and evolution of stars are being tested experimentally by the interaction of RNB with a hydrogen target, for solid state physics, where radioactive ion implantation is widely used to investigate the properties of materials, particularly, semiconductors, and for modern medicine, as well, providing a fast and harmless way of cancer diagnostic.
One of the main parts of any ISOL installation is its target system where radioactive nuclides are being produced by the interaction of bombarding particles with the target material. The choice and working quality of the target unit determine the number of produced nuclides, the ISOL system efficiency and its speed of response. This is the reason why the investigation and development of universal, highly efficient and fast target unit is of great importance for the future progress of ISOL installations and for their effective use in many fields of science.
Over the past twenty years on the proton beam of the synchrocyclotron of PNPI (Petersburg Nuclear Physics Institute) the only in Russia ISOL installation IRIS (Investigation of Radioactive Isotopes on Synchrocyclotron) built for the production and investigation of short lived nuclei lying far from beta-stability has been working. IRIS  is a very complex and expensive installation that includes the mass-separator working on line on the proton beam, three ion beam lines allowing to carry out three independent experiments simultaneously, the laser installation for the laser ion source [2,3] supply and for laser-nuclear on-line investigation [4,5]. One line is equipped with a large NaJ (Tl) crystal with a cylindrical hole inside to measure isotope yields with the efficiency close to 100%. A very important direction of investigations at IRIS facility is the development and on-line investigation of new target units and ion sources [6,7,8].
At present the scientists using IRIS as the basic installation of on-line short lived nuclei investigations have to reduce their work activity as the financing of Russian Academy of Science is not enough for appropriate scientific equipment modernization and for needed time of the accelerator operation funding. ISTC foundation of the project could help essentially to solve these problems and to provide the effective work of the scientific group of IRIS and the IRIS installation itself.
The aim of the project is the development and investigation of a high temperature target unit to produce intensive mass-separated radioactive ion beams using high current proton accelerators with the proton beam intensity up to 200 mА and with the proton energy 500-1000 MeV. The target unit to be developed will allow producing a wide range of proton and neutron rich radioactive isotopes of more than 40 elements from Li to Lu by spallation, fission and fragmentation reactions.
At the IRIS facility at PNPI in Catchina a working model on a scale 1:5 of the real proposed target unit was built and on-line investigated. The main advantage of the target being developed in comparison with high temperature targets used before consists in using tungsten instead of tantalum as a material for the target container manufacture. Tungsten is considerably more solid and high temperature resistant material, its melting point 414°C higher than of tantalum. Making use a tungsten container for target material heating provides a possibility of (400-600)°C temperature rise that gives the decrease of the delay times of produced isotopes by more than order of magnitude and the considerable rise of short lived isotope yields.
The target being developed can be successfully used for solving the power dissipation problem of high current proton beam facilities. The use of the tungsten target container enables the target to have a working temperature (2800-3000)°C and, hence, the target can work under stable conditions with the beam power dissipation up to 60 kW.
As a result of the proposed project a new high temperature target unit will be built and investigated. The target unit will have a mass of some hundred grams and allow dissipating proton beam power up to 60 kW without the target distraction. It is suggested, as well, to measure on-line the yields and delay times of radioactive isotopes Li, Na, K, Rb, Cs, Ba, Eu, Ho, Tm and Yb at temperatures (2000-3000)°C.
The developed target unit on-line use will give the possibility to rise 20-30 times the release speed of reaction products from the target volume and accordingly to increase 20-30 times produced radioactive nuclide yields. That will allow to reduce considerably the accelerator time needed for produced isotope investigation and to enlarge essentially the region of available nuclides to be investigated.
At the IRIS facility on-line with the PNPI synchrocyclotron some experimental runs have been carried out by the use of working models of a new proposed target. The measurements of the yields and of the delay times of radioactive isotopes Li, Na, Rb and Cs in the temperature range (2500-2900)°C have shown that the target prototype deliveres a fast release and high yields of nuclides .
1. G.D.Alkhazov, A.E.Barzakh et al., NIM B69 (1992) 517.
2. G.D.Alkhazov, L.Kh.Batist et al., NIM A306 (1991) 400-402.
3. A.E. Barzakh, V.D.Denisov et al., NIM B126 (1997) 85-87.
4. G.D.Alkhazov, A.E.Barzakh et al, Int.Conf. on Atomic Masses and Fundamental Constants, BernKastel-Kues, 1992.
5. G.D.Alkhazov, V.S.Letokhov et al., J.Phys.G: Nucl.Part.Phys. 18 (1992) 1177-1192.
6. V.N.Panteleev, A.E.Barzakh et al. On-line investigation of a high temperature refractory target. Proc. of VI International school-seminar on Heavy Ion Physics. September 22-27,1997, Dubna, Russia.
7. G.D.Alkhazov, E.Ye.Berlovich et al., and V.N.Panteleev. NIM A280 (1989) 141.
8. A.E. Barzakh, V.I.Beznosyuck et.al, NIM B126 (1997) 150-153.
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