Total Absorption Spectroscopy Study of Rb-92 Decay: A Major Contributor to Reactor Antineutrino Spectrum Shape

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. Rb-92 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 Rb-92 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

Total absorption gamma-ray spectroscopy study of the β-decay of 186Hg

7 pags., 9 figs., 1 tab.The Gamow-Teller strength distribution of the decay of Hg into Au has been determined for the first time using the total absorption gamma spectroscopy technique and has been compared with theoretical QRPA calculations using the SLy4 Skyrme force. The measured Gamow-Teller strength distribution and the half-life are described by mixing oblate and prolate configurations independently in the parent and daughter nuclei. In this theoretical framework the best description of the experimental beta strength is obtained with dominantly prolate components for both parent Hg and daughter Au. The approach also allowed us to determine an upper limit of the oblate component in the parent state. The complexity of the analysis required the development of a new approach in the analysis of the X-ray gated total absorption spectrum.This work was supported by Spanish Ministerio de Economía y Competitividad under grants FPA2011-24553, FPA2014-52823-C2-1-P, FPA2017-83946-C2-1-P, FPA2017-87568-P, Ministerio de Ciencia e Innovación grants PID2019-104714GB-C21 and RTI2018-098868-B-100, program Severo Ochoa (SEV-2014-0398), ENSAR (grant 262010) and by the European Union Horizon 2020 research and innovation programme under Grant Agreement No. 654002. S.E.A.O. thanks the support of CPAN Consolider-Ingenio 2010 Programme CSD2007-00042 grant. E.G. acknowledges support from TÜBITAK 2219 Abroad Research Fellowship Programme. R.B.C. acknowledges support by the Max-Planck-Partner group. Support from the technical staff and engineers of ISOLDE-CERN is acknowl- edged. W.G. acknowledges the support of STFC (UK) council grant ST/P005314/1. V.G. acknowledges the support of the National Science Center, Poland, under Contract No. 2019/35/D/ST2/02081. This work was also supported by the National Research, Development and Innovation Fund of Hungary, financed under the K18 funding scheme with Projects No. K 128729 and NN128072. P.S. acknowledges support from MCI/AEI/FEDER, UE (Spain) under grant PGC2018-093636-B-I0

Total Absortion Spectroscopy of Fission Fragments Relevant for Reactor Antineutrino Spectra Determination

8 pags., 3 figs., 1 tab. ; Presented at the XXXIV Mazurian Lakes Conference on Physics, Piaski, Poland, September 6–13, 2015.The contribution of each fission fragment to the reactor antineutrino spectra was determined using the summation method based on the existing information on fission yields and decay data contained in nuclear databases and the reactor evolution code MURE. The beta decay of some of the main contributors has been studied using the Total Absorption Spectroscopy (TAS) technique during two experimental campaigns at the IGISOL facility, in Jyväskylä (Finland). Results on the decay of 92Rb, the most important contributor in the 4–8 MeV energy region are reported. The status of the analysis of the second experiment is presented as well.Peer Reviewe

Characterization of a cylindrical plastic β-detector with Monte Carlo simulations of optical photons

V. Guadilla et al. -- 5 pags., 8 figs., tab.In this work we report on the Monte Carlo study performed to understand and reproduce experimental measurements of a new plastic β-detector with cylindrical geometry. Since energy deposition simulations differ from the experimental measurements for such a geometry, we show how the simulation of production and transport of optical photons does allow one to obtain the shapes of the experimental spectra. Moreover, taking into account the computational effort associated with this kind of simulation, we develop a method to convert the simulations of energy deposited into light collected, depending only on the interaction point in the detector. This method represents a useful solution when extensive simulations have to be done, as in the case of the calculation of the response function of the spectrometer in a total absorption γ-ray spectroscopy analysis.This work has been supported by the Spanish Ministerio de Economía y Competitividad under grants FPA2011-24553, AIC-A-2011-0696, FPA2014-52823-C2-1-P and the program Severo Ochoa (SEV-2014-0398), by the European Commission under the FP7/EURATOM contract 605203, and by the Spanish Ministerio de Educación under the FPU12/01527 grant.Peer Reviewe

Total absorption spectroscopy study of the β decay of Br 86 and Rb 91

S. Rice et al. -- 10 pags., 12 figs., 4 tabs.The beta decays of Br86 and Rb91 have been studied using the total absorption spectroscopy technique. The radioactive nuclei were produced at the Ion Guide Isotope Separator On-Line facility in Jyväskylä and further purified using the JYFLTRAP. Br86 and Rb91 are considered to be major contributors to the decay heat in reactors. In addition, Rb91 was used as a normalization point in direct measurements of mean gamma energies released in the beta decay of fission products by Rudstam et al. assuming that this decay was well known from high-resolution measurements. Our results show that both decays were suffering from the Pandemonium effect and that the results of Rudstam et al. should be renormalized. The relative impact of the studied decays in the prediction of the decay heat and antineutrino spectrum from reactors has been evaluated.This work was supported by Spanish Ministerio de Economía y Competitividad under grants FPA2008-06419, FPA2010-17142, FPA2011-24553, FPA2014-52823-C2-1- P, FIS2014-51971-P, and CPAN CSD-2007-00042 (Ingenio2010), and the program Severo Ochoa (SEV-2014-0398), by EPSRC and STFC (UK), and by the CHANDA European project, the In2p3 institute of the CNRS, and the NEEDS challenge through the NACRE project. Work at ANL was supported by the U.S. Department of Energy under contract DE-AC02-06CH11357.Peer Reviewe

Experimental study of 100Tc β decay with total absorption γ-ray spectroscopy

V. Guadilla et al. -- 10 pags., 10 figs., 2 tabs.The β decay of Tc100 has been studied by using the total absorption γ-ray spectroscopy technique at the Ion Guide Isotope Separator On-Line facility in Jyväskylä. In this work the new Decay Total Absorption γ-ray Spectrometer in coincidence with a cylindrical plastic β detector has been employed. The β intensity to the ground state obtained from the analysis is in good agreement with previous high-resolution measurements. However, differences in the feeding to the first-excited state as well as weak feeding to a new level at high excitation energy have been deduced from this experiment. Theoretical calculations performed in the quasiparticle random-phase approximation framework are also reported. Comparison of these calculations with our measurement serves as a benchmark for calculations of the double β decay of Mo100.This work has been supported by the Spanish Ministerio de Economía y Competitividad under Grants No. FPA2011-24553, No. AIC-A-2011-0696, No. FPA2014-52823-C2-1-P, No. FPA2015-65035-P, and No. FPI/BES-2014-068222, and by the program Severo Ochoa (SEV-2014-0398), by the Spanish Ministerio de Educación, Cultura y Deporte under the FPU12/01527 Grant, by the European Commission under the FP7/EURATOM contract 605203 and the FP7/ENSAR contract 262010, and by the Junta para la Ampliación de Estudios Programme (CSIC JAE-Doc contract) co-financed by FSE. This work has been partially supported by the Academy of Finland under the Finnish Centre of Excellence Programme 2012-2017 (Project No. 213503, Nuclear and Accelerator Based Programme at JYFL). W.G. was supported by the UK Science and Technology Facilities Council (STFC) Grant ST/F012012/1 and by the Atracció de talent VLC-CAMPUS Programme of the University of Valencia.Peer Reviewe

TAGS measurements of 100Nb ground and isomeric states and 140Cs for neutrino physics with the new DTAS detector

V. Guadilla et al. -- 4 pags., 6 figs. -- Open Access funded by Creative Commons Atribution Licence 4.0In this work we report on total absorption ¿-ray spectroscopy measurements of the ß decay of fission products that are important contributors to the antineutrino spectrum. The experiment was performed at IGISOL as a part of a campaign of measurements with the new DTAS spectrometer. Preliminary results of the analysis of the ß decay of 100Nb,100mNb and 140Cs are presented.This work has been supported by the Spanish Ministerio de Economía y Competitividad under the FPA2011-24553, the AIC-A-2011-0696, the FPA2014-52823-C2-1-P and the SEV- 2014-0398 Grants, by the European Commission under the FP7/EURATOM contract 605203, and by the Spanish Ministerio de Educación under the FPU12/01527 Grant.Peer Reviewe

Characterization of the DTAS detector and first measurements

V. Guadilla et al.; EMIS 2015, Grand Rapids, Michigan, in the United States, May 11 through May 15, 2015A new Total Absorption Gamma-Ray Spectrometer for beta-decay studies (DTAS) has been developed within the DESPEC experiment of the NUSTAR collaboration [1]. The instrument has been designed [2] to determine accurately the beta-decay intensity distribution for exotic nuclei produced in high-energy reactions, which will be separated and identified by means of the Super Fragment Separator at the future FAIR facility. DTAS has a modular construction with up to 18 large NaI(Tl) detector modules (module dimension: 25cmx15cmx15cm) which can be assembled in a 4pi geometry with little dead material around the AIDA implantation detector, a stack of double sided Si strip-detectors [2]. We have recently performed the first experiment with this setup at the upgraded IGISOL IV (Jyväskylä, Finland) facility. The low energy radioactive beams have been further purified with the JYFLTRAP Penning trap [3]. The experiment aimed to study fission products of relevance in neutrino physics and reactor decay heat time evolution. The measurements allowed us to perform a careful characterization of the detector and to study the overall performance of the setup. The results of this work will be presented, including the performance of the gain stabilization system, the correction of electronic pulse pileup, the sensitivity to neutrons and the calibration of the response of the spectrometer to decay radiation by means of Geant4 Monte Carlo simulations.Peer Reviewe

Study of the β decay of fission products with the DTAS detector

V. Guadilla et al. -- 5 pags., fig., tab.Total Absorption Spectroscopy measurements of the beta decay of Mo-103 and Tc-103, important contributors to the decay heat summation calculation in reactors, are reported in this work. The analysis of the experiment, performed at IGISOL with the new DTAS detector, show new beta intensity that was not detected in previous measurements with Ge detectors.This work has been supported by the Spanish Ministerio de Economía y Competitividad under the FPA2011-24553, the AIC-A-2011-0696, the FPA 2014-52823-C2-1-P and the SEV-2014-0398 grants, and by the Spanish Ministerio de Educación under the FPU12/01527 grant.Peer Reviewe

First experiment with the NUSTAR/FAIR Decay Total Absorption γ-Ray Spectrometer (DTAS) at the IGISOL IV facility

V. Guadilla et al. ; 4 págs.; 4 figs.; 1 tab.The new Decay Total Absorption Spectrometer (DTAS) has been commissioned with low energy radioactive beams at the upgraded IGISOL IV facility. The DTAS is a segmented detector composed of up to 18 NaI(Tl) crystals and it will be a key instrument in the DESPEC experiment at FAIR. In this document we report on the experimental setup and the first measurements performed with DTAS at IGISOL. The detector was characterized by means of MC simulations, and this allowed us to calculate the response function of the spectrometer and analyse the first cases of interest. 2015 Elsevier B.V. All rights reserved.This work has been supported by the Spanish Ministerio de Economía y Competitividad – Spain under the FPA2011-24553, the AIC-A-2011-0696, the FPA2014-52823-C2-1-P and the SEV-2014-0398 Grants, by the European Commission – Belgium under the FP7/EURATOM contract 605203, and by the Spanish Ministerio de Educación – Spain under the FPU program.Peer Reviewe