K. Ernst Rehm

Design of a New Recoil Separator for Measurements of Radiative Capture Reactions in Astrophysics

The rates of proton‐ and alpha‐capture reactions on unstable proton‐rich nuclei are needed to understand the energy generation and element synthesis occurring in novae, X‐ray bursts, and other explosions. Direct measurements of the cross sections of some of these reactions are now possible with radioactive beams and a recoil separator. A new device for such measurements, the Separator for CApture Reactions [SECAR], is being designed for use at the Facility for Rare Isotope Beams (FRIB). The specifications and preliminary conceptual design will be discussed along with plans for the first set of measurements.

Studies of Light Charged Particle Emission From Fission and ER Reactions in the System 344 Mev 28Si+121Sb-149Tb (E=240 MeV)

Abstract Light charged particles (LCP) have been measured for the reaction 344 MeV 28 Si + 121 Sb in singles and in coincidence with evaporation residues (ER), fusion–fission fragments (FF), and other LCP. A major feature of this experiment was the use of a gas-filled magnetic spectrometer in the forward direction to separate ER from the much more abundant yield of elastically scattered projectiles and projectile-like fragments. The dominant sources of evaporative 1 H and 4 He emission are the ER (approximately 75%), with the remainder being largely associated with fission reactions. For these latter reactions, most of the 1 H and 4 He can be well accounted for by evaporation from the composite system prior to fission and by evaporation from the postfission fragments. LCP emission cross sections were determined for each identified source, and a comparison has been made to previous studies. From this comparison, indications were found for significant entrance channel effects, with the more asymmetric channels exhibiting much larger LCP cross sections. Statistical model predictions for ER emissions are in good agreement with observed LCP energy spectra, angular distributions, and integrated inclusive and exclusive cross sections, with all calculations using the same unique set of model parameters. This result contrasts strongly with recent reports for light mass systems, where model calculations were unable to simultaneously reproduce all observables.