Experimental set-up for the simultaneous measurement of fission and γ-emission probabilities induced by transfer or inelastic-scattering reactions

Abstract

Fission and γ-emission probabilities induced by transfer or inelastic scattering reactions with light projectile nuclei are very valuable quantities for constraining the models that describe the de-excitation of heavy nuclei. We have developed an experimental set-up that allows us to simultaneously measure fission and γ-emission probabilities. The measurement of the γ-emission probability at excitation energies where the fission channel is open is challenging due to the intense background of γ rays emitted by the fission fragments. We discuss the procedure to subtract such a background and the constraints that this subtraction and other experimental conditions put on the set up. We show that our set-up complies with these constraints.

Simultaneous Determination of Neutron-Induced Fission and Radiative Capture Cross Sections from Decay Probabilities Obtained with a Surrogate Reaction

“…The details of our experiment, and the data and uncertainty analysis can be found in [27]; here we only describe the main features. A 30 MeV beam of 4 He delivered by the Tandem accelerator of the ALTO facility in Orsay (France) impinged on a 100 μg=cm 2 PuO 2 target deposited on a carbon support of the same areal density.…”

“…However, measuring γ-emission probabilities of fissionable nuclei is very challenging as it requires removing the intense background of γ rays emitted by the fission fragments. The full details of our experiment and of the data and uncertainty analysis can be found in [27], here we only describe the main features. A 30 MeV beam of 4 He delivered by the Tandem accelerator of the ALTO facility in Orsay (France) impinged on a 100 μg/cm 2 PuO 2 target deposited on a carbon support of the same areal density.…”

“…The number of γ cascades emitted by the fission fragments was determined by calculating the ratio between the number of triple coincidences 4 He'/fission-fragment/γray-cascade and the fission efficiency. To determine the number of γ cascades coming from the fission fragments with sufficient precision, it was necessary to maximize all the detection efficiencies and at the same time determine the fission and the γ-cascade detection efficiencies with a relative uncertainty below 10 and 20 %, respectively, which is a difficult task, see [27]. The decay probabilities were measured at seven 4 He' scattering angles θ 4He' , ranging from 120.7 to 156.0° in steps of about 6°, and no significant differences were observed.…”

Heavy-ion storage rings and their use in precision experiments with highly charged ions

“…In addition, γ rays may be detected with standard high efficiency detectors placed outside of the ring vacuum system. An interesting development pursued within this project is to employ conventional solar cells as position sensitive, ultra-high vacuum compatible, radiation hard particle detectors [298]. If successful, this will be a cost-efficient alternative to silicon detectors.…”