Beta-decay studies for applied and basic nuclear physics

In this review we will present the results of recent $$\beta $$ β -decay studies using the total absorption technique that cover topics of interest for applications, nuclear structure and astrophysics. The decays studied were selected primarily because they have a large impact on the prediction of (a) the decay heat in reactors, important for the safety of present and future reactors and (b) the reactor electron anti-neutrino spectrum, of interest for particle/nuclear physics and reactor monitoring. For these studies the total absorption technique was chosen, since it is the only method that allows one to obtain $$\beta $$ β -decay probabilities free from a systematic error called the Pandemonium effect. The total absorption technique is based on the detection of the $$\gamma $$ γ cascades that follow the initial $$\beta $$ β decay. For this reason the technique requires the use of calorimeters with very high $$\gamma $$ γ detection efficiency. The measurements presented and discussed here were performed mainly at the IGISOL facility of the University of Jyväskylä (Finland) using isotopically pure beams provided by the JYFLTRAP Penning trap. Examples are presented to show that the results of our measurements on selected nuclei have had a large impact on predictions of both the decay heat and the anti-neutrino spectrum from reactors. Some of the cases involve $$\beta $$ β -delayed neutron emission thus one can study the competition between $$\gamma $$ γ - and neutron-emission from states above the neutron separation energy. The $$\gamma $$ γ -to-neutron emission ratios can be used to constrain neutron capture (n,$$\gamma $$ γ ) cross sections for unstable nuclei of interest in astrophysics. The information obtained from the measurements can also be used to test nuclear model predictions of half-lives and Pn values for decays of interest in astrophysical network calculations. These comparisons also provide insights into aspects of nuclear structure in particular regions of the nuclear chart.

EeV astrophysical neutrinos from flat spectrum radio quasars

Context. Flat-spectrum radio quasars (FSRQs) are the most powerful blazars in the γ-ray band. Although they are supposed to be good candidates in producing high-energy neutrinos, no secure detection of FSRQs has been obtained to date, except for a possible case of PKS B1424-418. Aims. In this work, our aim was to compute the expected flux of high-energy neutrinos from FSRQs using standard assumptions for the properties of the radiation fields filling the regions surrounding the central supermassive black hole. Methods. Starting from the FSRQ spectral sequence, we computed the neutrino spectrum assuming interaction of relativistic protons with internal and external radiation fields. We studied the neutrino spectra resulting from different values of free parameters Results. The result we obtained is that high-energy neutrinos are naturally expected from FSRQs in the sub-EeV–EeV energy range and not at PeV energies. This justifies the non-observation of neutrinos from FSRQs with the present technology, since only neutrinos below 10 PeV have been observed. We found that for a non-negligible range of the parameters, the cumulative flux from FSRQs is comparable to or even exceeds the expected cosmogenic neutrino flux. This result is intriguing and highlights the importance of disentangling these point-source emissions from the diffuse cosmogenic background.

Review of uncertainties in the cosmic supernova relic neutrino background

We review the computation of and associated uncertainties in the current understanding of the relic neutrino background due to core-collapse supernovae, black hole formation and neutron star merger events. We consider the current status of uncertainties due to the nuclear equation of state (EoS), the progenitor masses, the source supernova neutrino spectrum, the cosmological star formation rate, the stellar initial mass function, neutrino oscillations, and neutrino self-interactions. We summarize the current viability of future neutrino detectors to distinguish the nuclear EoS and the temperature of supernova neutrinos via the detected relic supernova neutrino spectrum.