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Dr. Paul DeYoung, Physics

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The r-process predicts the formation of elements heavier than iron and occurs in neutron star mergers and supernovae. The β decay strength function reveals nuclear structure properties necessary to improve r-process models. Measurements of the 91Rb strength function, a nucleus involved in the r process, were made at the National Superconducting Cyclotron Laboratory (NSCL) this past July (2018). The 91Rb were made with the A1900 fragment recoil separator, then stopped in a long gas cell, and finally implanted in a mylar tape. Spectra and multiplicity of γ rays from the daughter, 91Sr, coincident with β particles from the decay of implanted 91Rb give one the information needed to determine the β decay strength function. Electrons produced by the β decay were measured in a plastic detector constructed at Hope College and γ rays were detected in the Summing NaI (SuN) detector. Coincidences between electrons and γ rays were needed to identify the energy level in the 91Sr daughter nucleus to which the parent 91Rb decayed and to quantify the probability of that decay path. β particles from the decay of 91Rb are difficult to distinguish from background events due to the buildup of long-lived daughter particles that subsequently also β decay. A tape system extending into the beam pipe through SuN is needed to move radioactive daughter particles away from the detector. Thus, a conventional Si surface barrier β detector could not be employed because of minimal space inside the beam pipe. The needed β detector was fabricated to fit inside the small beam pipe and around the tape system. The 20 cm long, barrel-shaped detector was constructed out of scintillating plastic with wave-shifting fiber optic cables on the exterior leading to photomultiplier tubes outside the SuN detector. Preliminary results are shown.


This material is based upon work supported by the National Science Foundation under Grant No. 1613188.

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