r Process (n, \(\gamma \)) Rate Constraints from the \(\gamma \) Emission of Neutron Unbound States in \(\beta \)-Decay

Abstract

Total absorption gamma-ray spectroscopy is used to measure accurately the intensity of γ emission from neutron-unbound states populated in the β-decay of delayed-neutron emitters. From the comparison of this intensity with the intensity of neutron emission a constraint on the (n,γ) cross section for highly unstable neutron-rich nuclei can be deduced. A surprisingly large γ branching was observed for a number of isotopes which might indicate the need to increase by a large factor the Hauser-Feshbach (n,γ) cross-section estimates that impact on r process abundance calculations.

Total absorption γ -ray spectroscopy of the β -delayed neutron emitters I137 and Guadilla1, Taín2, Algora3 et al. 2019Phys. Rev. CSelf Cite144110View full textAdd to dashboardCite

“…The impact of replacing the average γ and β energies available at ENDF/B-VII.1 by the present TAGS values has been studied. The effect in the electromagnetic component (γ rays, x rays) of 235 U and 239 Pu is an increase of < 1% and < 0.5%, respectively, for times shorter than 1 s. The light particle component (β particles, conversion electrons, Auger electrons) is reduced by less than 0.5% in both cases below 1 s. Such a modest impact can be understood on the one hand due to the similarity between the TAGS average energies and the values available at ENDF/B-VII.1 for 137 I and on the other hand because of the low cumulative fission yield of 95 Rb [0.0077(3) and 0.0043 (7) in ENDF/B-VII.1 [42] for 235 U and 239 Pu, respectively, while the corresponding cumulative fission yields of 137 I are 0.0307 (9) and 0.0243 (10), respectively].…”

“…These calculations rely on parameters obtained close to the valley of β stability for nuclear level densities (NLD), photon strength functions (PSF), and neutron transmission coefficients (NTC) [6]. In recent years the connection between the β-delayed neutron emission process and (n, γ ) reactions as a possible source of experimental information has been highlighted [7][8][9][10]. In both processes resonant states that decay either by γ or neutron emission are populated, though they usually have different spin-parity values.…”

The Soreq Applied Research Accelerator Facility (SARAF): Overview, research programs and future plans

“…The neutron energy spectrum fits well a Maxwellian also with the broad energy spread of the SARAF-I proton beam ( ~ 20 keV) [61]. This high yield was used in SARAF-I in recent years for Maxwellian-Averaged Cross Section (MACS) measurements of 94,96 Zr [33], 36,38 Ar, 78,80,84,86 Kr, 136,138,140,142 Ce, 147 Pm, 171 Tm [62], 63 Cu, 208 Pb [63] and 209 Bi [64]. The full program of MACS measurements at LiLiT is given in [62].…”

“…These rates may make SARAF the facility of choice for precision measurements of nuclear properties such as masses, half-lives, Q-values, -excitation levels, delayed neutron emission branching ratios, neutron spectra, spin, dipole and quadrupole moments and meansquare charge radii of the abovementioned isotopes. Moreover, -delayed  and/or neutron spectra could impose substantial constraints on the neutron capture cross sections of the decaying isotopes [140], which cannot be measured directly due to their short half-life.…”