Isomeric cross section of theAu197(n,2n) reaction

Abstract

In the present work, the 197 Au(n,2n) reaction cross section is experimentally determined relative to the 27 Al(n,α) 24 Na reaction at incident neutron energies of 9.0-10.5 MeV by means of the activation technique. The quasimonoenergetic fast neutron beam was produced via the 2 H(d, n) 3 He reaction at the 5.5-MV Tandem Van de Graaff accelerator at the National Centre of Scientific Research (NCSR) "Demokritos" and was studied to determine the contribution of background "parasitic" neutrons using the multiple foil activation technique and the SULSA unfolding code. The cross sections for the population of the second isomeric state (12 − ) of 196 Au and the sum of the ground (2 − ) and first isomeric state (5 − ) population cross sections were independently determined. Auxiliary Monte Carlo simulations were performed with the MCNP code. Theoretical calculations of the above cross sections in the 8-25 MeV region were carried out with the use of the STAPRE-F, EMPIRE, and TALYS codes, which were also compared in their implementation of the generalized superfluid model. The theoretical results are compared with previous work in the same mass region, and the strong dependence on the level scheme of the nuclei involved was revealed.

On neutron-induced reaction mechanisms at medium energies

“…A particular interest has recently been connected with this issue for nuclei in the transitional region from well deformed to spherical nuclei near the Z=82 shell closure (e.g., Refs. [1][2][3]). Former trials (e.g., [4]) concerned the analysis of the isomeric cross section ratio in order to check the adoption of a variable moment of inertia between the half and 75% of the rigid-body value I r , for the excitation energies from g.s.…”

“…Unfortunately it resulted that even the largest related change is still of the same magnitude with the uncertainties associated with the decay schemes and spread of the experimental data, so that a definitive conclusion on this point was precluded. However the new quite accurate data obtained for the isomeric cross section of the 197 Au(n, 2n) reaction [2] provides a new opportunity which makes the object of the present work.…”

Cross section of the 197Au(n,2n)196Au reaction

“…Quasi-monoenergetic neutrons were produced by means of the 3 H(d,n) 4 He reaction, implementing a new Ti-tritiated target consisting of a 2.3 mg/cm 2 Ti-T layer on a 1 mm thick Cu backing for good heat conduction. The flange with the tritium target assembly was air-cooled during the irradiations and the Au foil was stacked between two Al foils and placed at a distance of ∼2 cm from the tritium target (Fig.…”

“…Neutron induced reactions on Au, especially (n,2n), are proposed as a standard for high energy neutron dosimetry [3] and are also very important as referencemonitor reactions. Moreover, the presence of a high-spin (12 − ) isomeric state (m2) in the residual nucleus of the 197 Au(n,2n) reaction, makes it a sensitive test-case for several nuclear reaction model codes [4,5].…”

“…The cross section for the population of the second isomeric (m2) state of 196 Au was independently determined. The neutron beam was produced at the 5.5 MV tandem T11/25 Accelerator of NCSR "Demokritos" by means of the 3 H(d,n) 4 He reaction, implementing a new Ti-tritiated target of ∼400 GBq activity. Furthermore, theoretical statistical model calculations were performed and compared to all available experimental data in literature.…”