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8–12 Jul 2024
Vienna International Centre
Europe/Vienna timezone

Study of the $^{169}$Tm$(n,\gamma)$ reaction using DANCE facility at LANSCE

9 Jul 2024, 17:52
1m
M Building, Boardroom A (Vienna International Centre)

M Building, Boardroom A

Vienna International Centre

Wagramerstrasse 5 Vienna A-1400, Austria
Poster Level Densities and Photon Strength Functions Poster Session

Speaker

Kamila Špringlová (Charles University, Prague)

Description

The reason for studying the neutron capture reaction on the mono-isotopic element thulium is twofold. Its only stable isotope, $^{169}$Tm, is often used as a neutron-flux activation monitor. The neutron capture cross-section in the relevant energy range has been measured several times [1-4] in the past and more recently at CSNS [5]. While these data show rough agreement, there are significant differences. Moreover, the uncertainties are often not quoted. These two motivate a state-of-the-art measurement and analysis of the neutron capture cross-section in the keV energy range.

The neutron capture cross-section can also be calculated via the Hauser-Feshbach approach [6], for which the key ingredients are the photon-strength-functions (PSFs) and nuclear level density (NLD). These quantities can be inferred from the $\gamma$-ray spectra of s-wave resonances by comparing them to the simulated spectra.

The neutron-capture reactions on the $^{169}$Tm nuclei have been measured with the DANCE calorimeter [7,8] at LANSCE [9]. The background-corrected sum-energy and multi-step-cascade spectra were extracted for a number of strong isolated s-wave resonances. These experimental coincident $\gamma$-ray spectra are compared with their simulated counterparts using Monte-Carlo code DICEBOX [10] to obtain information about PSFs and NLD. In particular, we investigate the scissors-mode (SM) role in the M1 PSF. Previously, SM parameters of well-deformed rare-earth nuclei were obtained by several experimental techniques, see e.g. Refs. [11-13] and review [14]. They show significant differences, especially in the strength of the mode. The shape of the low-energy tail of the giant electric-dipole resonance is uncertain too. Because of these inconsistencies, additional information on PSFs in this region is of great interest.

The neutron capture cross-section is deduced from the experimental data in the usual fashion, i.e. by subtracting backgrounds, determining the neutron flux using several flux monitors, and normalizing to the standard cross-section. The analysis steps, internal consistency of our data, preliminary results on PSFs, and neutron capture cross-sections will be presented.

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Primary authors

Aaron J. Couture (Los Alamos National Laboratory) C. J. Prokop (Los Alamos National Laboratory) Frank Gunsing (CEA Irfu, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France) G. Rusev (Los Alamos National Laboratory) Ingrid Knapova (Los Alamos National Laboratory) J. M. O'Donnell (Los Alamos National Laboratory) John L. Ullmann (Los Alamos National Laboratory) K. J. Kelly (Los Alamos National Laboratory) Kamila Špringlová (Charles University, Prague) Mr Milan Krtička (Charles University, Prague) R. Reifarth (Los Alamos National Laboratory) Dr Stanislav Valenta (Charles University, Prague)

Presentation materials