Speaker
Description
The Total Absorption Spectrometers (TAS) are designed to determine a true $\beta$ decay pattern and energy of the decay of fission products like neutron-rich nuclei produced in this process. In certain nuclei many $\beta$ decays, associated with low probabilities, contribute to numerous final, high-energy states in the region of high density. De-exciting $\gamma$ rays from such a levels are sometimes out of the capabilities of $\beta$-$\gamma$ spectroscopy using germanium detectors in terms of energy detection limits including its efficiency. TAS spectroscopy perfectly complements the germanium spectroscopy. TAS measurements provide information about the energy of populated states in daughter nuclei as well as their $\beta$-transitions probability.
A significant advancement in this type of spectroscopy is provided by the Modular Total Absorption Spectrometer (MTAS) detector, developed by Oak Ridge National Laboratory (ORNL) in cooperation with the Faculty of Physics at the University of Warsaw. Due to its size, which makes it the largest TAS detector in the world, the total efficiency for detection of $\gamma$ photons is remarkably high for a very wide range of $\gamma$-ray energies. Moreover, the modular construction allows both individual analysis of events in separate modules or module rings and simultaneously using all modules.
During its first experimental campaign in 2012 at ORNL, the various neutron-rich isotopes, created in the fission process of ${}^{238}\text{U}$, were studied by the MTAS detector. Among them were isotopes with mass $A=143$, like ${}^{143}\text{Cs}$, ${}^{143}\text{Ba}$, and ${}^{143}\text{La}$, which were produced in both ways: by the proton-induced fission of ${}^{238}\text{U}$ and in the following decay chain: ${}^{143}\text{Cs} \rightarrow {}^{143}\text{Ba} \rightarrow {}^{143}\text{La}$.
Investigation of those fission fragments finds an application in the studies of decay heat (DH) in a nuclear reactor. There is a real demand to acquire knowledge of the amount of heat generated in this way and to classify it in order to achieve better efficiency of reactor operation and storage of spent nuclear fuel.
The poster will present preliminary results from analysis of ${}^{143}\text{La}$ by the MTAS detector. Results of recent GEANT4 simulations including newly introduced quasi-energy levels will be presented and compared with the experimentally obtained spectrum in order to identify rare $\beta$-transitions in ${}^{143}\text{La}$.