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The energy associated with the decay of fission products plays an important role in the estimation of the amount of heat released by nuclear fuel in reactors. In this article we present results of the study of the beta decay of some refractory isotopes that were considered important contributors to the decay heat in reactors. The measurements were performed at the IGISOL facility of the University of Jyvaskyla, Finland. In these studies we have combined for the first time a Penning trap (JYFLTRAP), which was used as a high resolution isobaric separator, with a total absorption spectrometer. The results of the measurements as well as their consequences for decay heat summation calculations are discussed.

The decay heat of fission products plays an important role in predictions of the heat released by nuclear fuel in reactors. In this contribution we present results of the analysis of the measurement of the beta decay of some refractory isotopes that were considered possible important contributors to the decay heat in reactors. The measurements presented here were performed at the IGISOL facility of the University of Jyvaeskylae, Finland. In our measurements we have combined for the first time a Penning trap (JYFLTRAP), which was used as a high resolution isobaric separator, with a total absorption spectrometer. The results of the measurements as well as their consequences for decay heat summation calculations are discussed.

The antineutrino spectra measured in recent experiments at reactors are inconsistent with calculations based on the conversion of integral beta spectra recorded at the ILL reactor. (92)Rb makes the dominant contribution to the reactor antineutrino spectrum in the 5-8 MeV range but its decay properties are in question. We have studied (92)Rb decay with total absorption spectroscopy. Previously unobserved beta feeding was seen in the 4.5-5.5 region and the GS to GS feeding was found to be 87.5(25)%. The impact on the reactor antineutrino spectra calculated with the summation method is shown and discussed.

A study of the Gamow-Teller strength distributions $B$(GT) in the beta decay of ${}^{78}$Sr and ${}^{76,78}$Rb has been made using a total absorption spectrometer (TAS). Following the success in deducing the sign of the deformation for ${}^{76}$Sr, a similar approach is adopted for ${}^{78}$Sr based on a comparison of the measured $B$(GT) with quasiparticle random-phase approximation calculations. This work confirms its previously expected prolate deformation in the ground state. Conclusions about the structure of the odd-odd ${}^{76,78}$Rb isotopes have been drawn based on their measured $B$(GT) distributions.

The $\ensuremath{\beta}$-feeding probabilities for three important contributors to the decay heat in nuclear reactors, namely ${}^{102,104,105}$Tc, have been measured using the total absorption spectroscopy technique. For the measurements, sources of very high isobaric purity have been obtained using a Penning trap (JYFLTRAP). A detailed description of the data analysis is given and the results are compared with high-resolution measurements and theoretical calculations.

Volume: 111 Host publication title: WONDER-2015 Host publication sub-title: 4TH INTERNATIONAL WORKSHOP ON NUCLEAR DATA EVALUATION FOR REACTOR APPLICATIONS Isbn(print): 978-2-7598-1970-6 Beta decay of fission products is at the origin of decay heat and antineutrino emission in nuclear reactors. Decay heat represents about 7% of the reactor power during operation and strongly impacts reactor safety. Reactor antineutrino detection is used in several fundamental neutrino physics experiments and it can also be used for reactor monitoring and non-proliferation purposes. Rb-92,Rb-93 are two fission products of importance in reactor antineutrino spectra and decay heat, but their beta-decay properties are not well known. New measurements of Rb-92,Rb-93 beta-decay properties have been performed at the IGISOL facility (Jyvaskyla, Finland) using Total Absorption Spectroscopy (TAS). TAS is complementary to techniques based on Germanium detectors. It implies the use of a calorimeter to measure the total gamma intensity de-exciting each level in the daughter nucleus providing a direct measurement of the beta feeding. In these proceedings we present preliminary results for Rb-93, our measured beta feedings for Rb-92 and we show the impact of these results on reactor antineutrino spectra and decay heat calculations.

In this contribution we will present recent total absorption measurements of the beta decay of neutron‐rich nuclei performed at the IGISOL facility of the Univ. of Jyvaskyla. In the measurements the JYFL Penning Trap was used as a high resolution isobaric separator. The total absorption technique will be described and the impact of recent results in the fields of reactor physics (decay heat calculations) and nuclear structure will be discussed.

The {beta} feeding probability of {sup 102,104,105,106,107}Tc, {sup 105}Mo, and {sup 101}Nb nuclei, which are important contributors to the decay heat in nuclear reactors, has been measured using the total absorption technique. We have coupled for the first time a total absorption spectrometer to a Penning trap in order to obtain sources of very high isobaric purity. Our results solve a significant part of a long-standing discrepancy in the {gamma} component of the decay heat for {sup 239}Pu in the 4-3000 s range.

The β feeding probability of (102,104,105,106,107)Tc, 105Mo, and 101Nb nuclei, which are important contributors to the decay heat in nuclear reactors, has been measured using the total absorption technique. We have coupled for the first time a total absorption spectrometer to a Penning trap in order to obtain sources of very high isobaric purity. Our results solve a significant part of a long-standing discrepancy in the γ component of the decay heat for 239Pu in the 4-3000 s range.

13 pages, 15 figures.-- Printed version published Jul 1, 2009., Measurements of inelastic proton scattering with high energy resolution at forward scattering angles including 0 degrees are described. High-resolution halo-free beams were accelerated by the cyclotron complex at the Research Center for Nuclear Physics. Instrumental background events were minimized using the high-quality beam. The remaining instrumental background events were eliminated by applying a background subtraction method. As a result, clean spectra were obtained even for a heavy target nucleus such as Pb-208. A high energy resolution of 20 keV (FWHM) and a scattering angle resolution of +/- 0.6 degrees were achieved at an incident proton energy of 295 MeV. (C) 2009 Elsevier B.V. All rights reserved., This work has been partly supported by the Grants-in Aid for Scientific Research no. 14740154 and 18540270 of the Ministry of Education, Culture, Sports, Science and Technology of Japan.

The decay heat of the fission products plays an important role in predicting the heat‐up of nuclear fuel after reactor shutdown. This form of energy release is calculated as the sum of the energy‐weighted activities of all fission products P(t) = ΣEiλiNi(t), where Ei is the decay energy of nuclide i (gamma and beta component), λi is the decay constant of nuclide i and Ni(t) is the number of nuclide i at cooling time t. Even though the reproduction of the measured decay heat has improved in recent years, there is still a long standing discrepancy at t∼1000 s cooling time for some fuels. A possible explanation for this disagreement can been found in the work of Yoshida et al. [1], who demonstrated that an incomplete knowledge of the β‐decay of some Tc isotopes could be the source of the systematic discrepancy. Motivated by [1], we have recently measured the β‐decay process of some Tc isotopes using a total absorption spectrometer at the IGISOL facility in Jyvaskyla. The results of the measurements are discussed, along with their impact on summation calculations.

Gamow–Teller (GT) transitions starting from unstable pf-shell nuclei are of interest not only in nuclear physics, but also in astrophysics, e.g. in violent neutrino induced reactions at the core-collapse stage of type II supernovae. In the β-decay study of these pf-shell nuclei, half-lives can be measured rather accurately. On the other hand, in high-resolution (3He, t) charge-exchange reactions at 0°, individual GT transitions up to high excitations can be studied. Assuming the isospin symmetry for the strengths of Tz = ±1 → 0 analogous GT transitions, we present a unique 'merged analysis' for the determination of absolute B(GT) values.