Isobar separation of ⁹³Zr and ⁹³Nb at 24 MeV with a new multi-anode ionization chamber

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• 作者：Martin Martschini^a ; ^{martin.martschini@univie.ac.at" class="auth_mail" title="E-mail the corresponding author} ; Josef Buchriegler^a ; ^c ; Philippe Collon^b ; Walter Kutschera^a ; Johannes Lachner^a ; Wenting Lu^b ; Alfred Priller^a ; Peter Steier^a ; Robin Golser^a
• 关键词：Ionization chamber ; AMS ; 93Zr ; Isobar suppression ; Energy loss characteristics
• 刊名：Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
• 出版年：2015
• 出版时间：15 October 2015
• 年：2015
• 卷：361
• 期：Complete
• 页码：201-206
• 全文大小：1368 K

文摘

⁹³Zr with a half-life of 1.6 Ma is produced with high yield in nuclear fission, and thus should be present as a natural or anthropogenic trace isotope in all compartments of the general environment. Sensitive measurements of this isotope would immediately find numerous applications, however, its detection at sufficiently low levels has not yet been achieved. AMS measurements of ⁹³Zr suffer from the interference of the stable isobar ⁹³Nb. At the Vienna Environmental Research Accelerator VERA a new multi-anode ionization chamber was built. It is optimized for isobar separation in the medium mass range and is based on the experience from AMS experiments of ³⁶Cl at our 3-MV tandem accelerator facility. The design provides high flexibility in anode configuration and detector geometry. After validating the excellent energy resolution of the detector with ³⁶S, it was recently used to study iron–nickel and zirconium–niobium–molybdenum isobar separation. To our surprise, the separation of ⁹⁴Zr (Z = 40) from ⁹⁴Mo (Z = 42) was found to be much better than that of ⁵⁸Fe (Z = 26) from ⁵⁸Ni (Z = 28), despite the significantly larger 螖Z/Z of the latter pair. This clearly contradicts results from SRIM-simulations and suggests that differences in the stopping behavior may unexpectedly favor identification of ⁹³Zr. At 24 MeV particle energy, a ⁹³Nb (Z = 41) suppression factor of 1000 is expected based on a synthetic ⁹³Zr spectrum obtained by interpolation between experimental spectra from the two neighboring stable isotopes ⁹²Zr and ⁹⁴Zr. Assuming realistic numbers for chemical niobium reduction, a detection level of ⁹³Zr/Zr below 10⁻⁹ seems feasible.