Beta decay studies of neutron rich nuclei for astrophysics and nuclear technology
J. Tain Enriquez 1*, for the DESPEC collaboration
1 Instituto de Fisica Corpuscular
Very neutron rich nuclei are produced abundantly in nuclear reactors in the fission of the fuel elements. They are also produced in the neutron capture processes which lead to the formation of the heavier elements in the Universe.
As the neutron excess increases the emission of neutrons from states in the daughter nucleus above the neutron separation energy competes efficiently with the electromagnetic de-excitation. This beta delayed neutron emission is a crucial ingredient in reactor control while the total decay pattern determines the gamma-ray and beta components of the decay heat and the neutrino spectrum released from the reactor. In the astrophysical context the decay pattern determines the half-life and therefore the primary elemental abundances and the speed of the rapid neutron capture process, while the delayed neutrons emission influences the final elemental abundances.
The distribution of the beta decay intensity and the fraction of which proceeds through neutron emission are fundamental quantities which depend on the structure of the nuclei and are not easy to predict theoretically. A global understanding requires a measurement of the complete decay pattern which must involve for these nuclei the detection of both gamma-rays and neutrons.
A program of combined measurements, using a total absorption gamma-ray spectrometer and both a 4pi neutron counter and a neutron time of flight spectrometer, has been started aiming at the determination of the complete beta-decay intensity distribution of neutron rich nuclei. The relative merit of the different techniques will be discussed. The results of first experiments at JYFL (Jyvaskyla) will be presented and the plans for measurements of more exotic nuclei at GSI (Darmstadt) and future radioactive beam facilities will be outlined.