Photoresponse of76Se below 9 MeV

Abstract

The dipole strength distribution of 76 Se has been investigated via photon scattering in the energy region below 9 MeV utilizing bremsstrahlung produced at the S-DALINAC facility at the TU Darmstadt. About 0.20(1)% of the classical E1 sum rule is exhausted by observed J = 1 states of justifiably assumed negative parity. An extrapolation of the GDR below 9 MeV suggests that considerable strength may remain unobserved due to background, finite detector resolution, and fragmentation. The observed strength thus represents a lower limit. Candidates for the 2 + 1,ms state and a fragment of the 1 + sc mixed-symmetry states are presented.

Dipole response of76Se above 4 MeV

“…The vast majority of transitions directly observed in this work and in Ref. [35] are decays to the ground state. If a branching in the decay of a resonantly excited J π = 1 − state is unobserved, the corresponding calculated B(E1) ↑ strength will be underestimated.…”

“…This is also indicated by the rather large asymmetry of the 2 + 1 to ground state transition at 6 MeV, suggesting only one intermediate transition, whereas the negative value at 7. 35 By considering the decays of the 2 + states, the total scattering cross section for all decays from the initially excited J π = 1 − states to excited states at each beam energy can be deduced. The W (θ) for the 2 + to ground state transitions were chosen to correspond to the cascade that described best the observed asymmetry.…”

“…The matrix elements which describe 0ν2β decay [27,34] can only be extracted from theoretical models, therefore tests for whether they can correctly describe the structure of involved nuclei over broad energy ranges are crucial. In this paper, results from a ( γ, γ ) photon scattering experiment performed at the High Intensity γ-Ray Source (HIγS) facility at Triangle Universities Nuclear Laboratory are presented, complementing our previous work [35], to obtain a more complete picture of the nature of the dipole response in 76 Se. In addition to the parity determination of the dipole excited states, the high photon fluxes allow observation of many new states, the majority of them at energies exceeding 7 MeV.…”

“…In our previous work performed at the Darmstadt High Intensity Photon Setup (DHIPS) facility [36] at TU Darmstadt, excitation energies up to 9 MeV were investigated [35]. There was, however, no means available to distinguish the parities of the observed states.…”