Speaker
Description
The study of beta decay of neutron rich nuclei is particularly important for many fields in fundamental and applied physics[1]. In nuclear reactors, fission products, through their decays, produce an additional power called decay heat[5]. The assesment of this energy is essential for nuclear safety since it represents around 7% of the power in an operating reactor and these decays continue after reactor shutdown. Beta decay leads to antineutrino emmission and is thus a good tool for fundamental neutrino research[6] but it can also be used for non-proliferation purposes since the antineutrino flux reflects the reactor power and the fuel content. In nuclear astrophysics, the r-process is a nucleo-synthesis process[3] at the origin of half of the nuclei heavier than iron. It takes place in hot (T~10⁹K) and highly neutron-dense environments. This process is based on the competition between neutron capture (n,γ), photo-dissociation (γ,n) reactions and beta decays. A precise knowledge of the beta properties can constrain the theoretical models used to understand this nucleo-synthesis process. Some of the nuclei involved in these fields of nuclear physics are affected by the pandemonium effect[4]: due to the low efficiency of high-resolution detectors, such as germanium (HPGe), at high gamma energies, some gamma-rays and the corresponding high energy levels can be missed in the decay data leading to a distortion of the beta decay feeding.
New measurements of relevant nuclei for the above mentioned topics have been performed at the IGISOL facility (Jyväskylä, Finland) in September 2022, using Total Absorption Gamma Spectroscopy (TAGS) technique[2]. TAGS is complementary to high resolution gamma-ray spectroscopy and employs a calorimeter to measure the total gamma intensity de-exciting each level of the daughter nucleus providing a direct measurement of the beta feeding. The setup is based on the Rocinante detector, a multi-segmented detector made of 12 barium fluorine (BaF2) crystals, a beta detector acting as a trigger, and a cerium bromine (CeBr3) crystal for identification of contaminants.
The topic of the presentation will be the introduction of Pandemonium effect and the solution our groups choosed to circumvent this effect. Preliminary results of the analysis of the I241 experiment will be presented.
References
[1] A.Algora et al. "Beta-Decay Studies for Applied and Basics Nuclear Physics". In: The European Physical Journal A (2021).
[2] A.Algora et al. "Total absorption spectroscopy measurements for the prediction of the reactor antineutrino spectra" . Ed. by Proposal to the PAC of J¸vask¸la.
[3] E.M.Burbidge et al. "Synthesis Of The Elements In Stars". In: Review Of Modern Physics, Volume 29, Number 4 (1957).
[4] J.C.Hardy et al. "The Essential Decay Of Pandemonium: A Demonstration Of Errors In Complex Beta-Decay Schemes". In: Physics Letters Volume 71B, number 2 (1977).
[5] J.C.Nimal. "Physique Nucléaire Et Sûreté Des Réacteurs" . Ed. by CLEFS CEA N° 45. 2001.
[6] M.Estienne et al. " Updated Summation Model: An Improved Agreement with the Daya Bay Antineutrino Fluxes". In: (2019).
