21-29 July 2022
US/Pacific timezone

Cross Section Measurements of (n,x) Reactions at 17.9 and 18.9 MeV Using Highly Enriched Ge Isotopes

27 Jul 2022, 11:00
Folsom ()



Sotirios Chasapoglou


The study of neutron induced reactions on Ge isotopes is of major importance, both for practical applications and fundamental research in Nuclear Physics. Practical applications include dosimetry, nuclear medicine, astrophysical projects, reactor and detector technology. As far as the fundamental research is concerned, some of the residual nuclei following (n,2n) and (n,a) reactions are produced in high spin isomeric states, the decay of which is governed by the spin distribution of the continuum phase space and the spins of the discrete levels involved. Through the accurate experimental determination of isomeric cross sections, the formation and the de-excitation of the compound nucleus can be studied. Finally, the optimization of input parameters in statistical model calculations can also be achieved, via the simultaneous reproduction of a plethora of reaction channels in Ge isotopes.
Usually a $^{nat}Ge$ target is used, containing 5 natural isotopes ($^{70}Ge$, $^{72}Ge$, $^{73}Ge$, $^{74}Ge$ and $^{76}Ge$). However, the residual nucleus produced in some reaction channels can also be produced by interfering reaction channels from neighbouring isotopes, acting as a contamination to the measured reaction. This contribution can be compensated for, via theoretical corrections based on Hauser-Feshbach calculations, that will insert extra uncertainties in the final cross section results. The use of highly enriched targets on the other hand, yields more accurate experimental results, since no interfering reactions from neighbouring isotopes take place, and no theoretical corrections are needed. In this scope, five highly enriched Ge samples of ~2g each have been used in this work. These samples have become available from the CERN n_TOF collaboration, with enrichment levels reaching up to ~97.71%. The irradiations of the samples were carried out at the neutron beam facility of the NCSR “Demokritos” at the 5.5 MV Tandem Van de Graaff accelerator. The quasi mono energetic neutron beam was produced via the $^{3}H(d,n)^{4}He$ reaction at neutron energies of 17.9 and 18.9 MeV and the Ge targets were irradiated together with high purity Al reference foils. The accurate cross section results for the $^{70}Ge(n,2n)^{69}Ge$, $^{72}Ge(n,p)^{72}Ga$, $^{72}Ge(n,α)^{69m}Zn$, $^{73}Ge(n,p)^{73}Ga$, $^{73}Ge(n,n+p)^{72}Ga$, $^{73}Ge(n,n+a)^{69m}Zn$, $^{74}Ge(n,α)^{71m}Zn$, $^{74}Ge(n,n+p)^{73}Ga$ and $^{76}Ge(n,2n)^{75}Ge$ studied in the present work, that are produced via the use of highly enriched targets, could improve the existing theoretical models and evaluation curves.

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