US EPA

4839262 

Journal Article 

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

Martschini, M; Buchriegler, J; Collon, P; Kutschera, W; Lachner, J; Lu, W; Priller, A; Steier, P; Golser, R 

2015 

1 

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
ISSN: 0168-583X 

361 

201-206 

10.1016/j.nimb.2015.03.061 

WOS:000363345900039 

Zr-93 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 Zr-93 suffer from the interference of the stable isobar Nb-93. 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 (CI)-C-36 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 S-36, it was recently used to study iron-nickel and zirconium-niobium-molybdenum isobar separation. To our surprise, the separation of Zr-94 (Z = 40) from Mo-94 (Z = 42) was found to be much better than that of Fe-58 (Z = 26) from Ni-58 (Z = 28), despite the significantly larger Delta 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 Zr-93. At 24 MeV particle energy, a Nb-93 (Z = 41) suppression factor of 1000 is expected based on a synthetic Zr-93 spectrum obtained by interpolation between experimental spectra from the two neighboring stable isotopes Zr-92 and Zr-94. Assuming realistic numbers for chemical niobium reduction, a detection level of Zr-93/Zr below 10(-9) seems feasible. (C) 2015 Elsevier B.V. All rights reserved. 

Ionization chamber; AMS; Zr-93; Isobar suppression; Energy loss characteristics