Correlations between energy and $\gamma$-ray emission in ${}^{239}\mathrm{Pu}(n,\mathrm{f})$

Abstract

We study $\gamma$-ray emission following ${}^{239}\mathrm{Pu}(n,\mathrm{f})$ over an incident neutron energy range of $2<E_i<40$ MeV. We present the first experimental evidence for positive correlations between the total angular momentum generated in fission and the excitation energy of the compound nucleus prior to fission. The $\gamma$-ray multiplicity increases linearly with incident energy below the 2\textsuperscript{nd}-chance fission threshold with a slope of $0.085\pm 0.010$ MeV${}^{-1}$. This linear trend appears to hold for the average excitation energy of the compound nucleus between $9<⟨E_x⟩<19$ MeV. Most of the multiplicity increase comes from an enhancement around a $\gamma$-ray energy of 0.7 MeV, which we interpret as stretched quadrupole $\gamma$ rays that indicate an increase in total fission-fragment angular momentum with excitation energy.

9 pages, 5 figures

References in corpus (7)

• Calculation of fission observables through event-by-event simulation
• Neutron-gamma competition for $\beta$-delayed neutron emission
• Fission fragments intrinsic spins and their correlations
• Study of angular momentum effects in fission
• Improved modeling of photon observables with FREYA
• Directional-dependence of the event-by-event neutron-$\gamma$ multiplicity correlations in ${}^{252}$Cf(sf)
• Energy dependence of the prompt $\gamma$-ray emission from the $(d,p)$-induced fission of ${}^{234}{\mathrm{U}}^{\ast }$ and ${}^{240}{\mathrm{Pu}}^{\ast }$

Cited by in corpus (2)

• Meaurement of spin vs. TKE of ${}^{144}$Ba produced in spontaneous fission of ${}^{252}$Cf
• Disentangling the influence of excitation energy and compound nucleus angular momentum on fission fragment angular momentum