Scissors resonance in the quasicontinuum of Th, Pa, and U isotopes

Abstract

The γ -ray strength function in the quasicontinuum has been measured for [231][232][233] 232,233 Pa, and 237-239 U using the Oslo method. All eight nuclei show a pronounced increase in γ strength at ω SR ≈ 2.4 MeV, which is interpreted as the low-energy M1 scissors resonance (SR). The total strength is found to be B SR = 9-11 μ 2 N when integrated over the 1-4 MeV γ -energy region. The SR displays a double-hump structure that is theoretically not understood. Our results are compared with data from (γ , γ ) experiments and theoretical sum-rule estimates for a nuclear rigid-body moment of inertia.

Constraining the calculation of U234,236,238(n,γ) cross sections with measurements of the Ullmann1, Kawano2, Baramsai3 et al. 2017Phys. Rev. C

“…Analyses of data on actinides using several methods, including the Oslo method [9], analysis of multi-step cascade spectra [2] and nuclear resonance fluorescence experiments (for example [10]) strongly indicate the presence of a resonance structure in the PSF near 2 MeV. This resonance structure is usually identified with the M1 scissors-mode resonance since it is consistent with the energy systematics of the scissors mode [11].…”

“…The Oslo group has used an approach combining reaction kinematics of charged-particle induced reactions with measured γ-ray spectra to simultaneously determine the PSF's and NLD in several actinide nuclei, including the compound nuclei 237,238,239 U [9,13,14]. A strong double-humped scissors mode was reported.…”

“…It's parameters were deduced by subtracting a smooth background from the total measured photon strength functions. This background was described by the extrapolated tail of the GDR, described by the Generalized Lorentzian Model (GLO) [15] with parameters taken from fits to the photoneutron yield data of Caldwell et al [9,16] with fixed temperature T=0.2 MeV, plus a "pygmy" E1 resonance and the M1 spin-flip resonance, each described by a standard Lorentzian (SLO). Note that the GLO is identical to the Enhanced Generalized Lorentzian (EGLO) [17] with k=1 used in ref.…”

Energy dependence of the promptγ-ray emission from the(d,p)-induced fission ofU*Rose1, Zeiser2, Wilson3 et al. 2017Phys. Rev. CSelf Cite121110View full textAdd to dashboardCite

“…The maximum value for J rms of 12 was obtained from J rms = √ 2T I / , where the nuclear temperature was chosen to be T ≈ 0.45 MeV in line with other actinide nuclei [40,41]. The rigid body of moment of inertia I is given by…”

Nuclear level density: Shell-model approach

“…It is assumed that the level density, at least up to 10 MeV excitation energy, and maybe even higher [56][57][58], can be described by the constant temperature T . This temperature is the single parameter defined, in the simplest version, according to the thermodynamics as…”