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The β decays of more than twenty fission fragments were measured in the first experiments with radioactive-ion beams employing the Decay Total Absorption γ-ray Spectrometer. In this work, we summarize the main results obtained so far from this experimental campaign carried out at the Ion Guide Isotope Separator On-Line facility. The advances introduced for these studies represent the state-of-the-art of our analysis methodology for segmented spectrometers. peerReviewed

17 pags., 13 figs., 4 tabs., The spins and parities of low-lying states in Br72 populated in the β decay of Kr72 have been studied via conversion electron spectroscopy. The measurements were carried out at ISOLDE using a miniorange spectrometer with Si(Li) and HPGe detectors for electrons and γ ray detection. Results of the conversion coefficients corresponding to transitions deexciting 12 levels in Br72 are reported. The multipolarities of the transitions are deduced and the spins and parities of the levels involved are discussed. From the multipolarities of the most intense transitions to the ground state, the spin and parity of the Br72 ground state have been definitely established as 1+. The spin of the 101.2-keV isomeric state is determined to be 3-. The level scheme is compared with mean-field and shell-model calculations and oblate deformation for the Br72 ground state is deduced. No E0 transitions have been found in Br72. E0 transitions in the neighboring isobaric nuclei, Se72 and Ge72, have also been studied., The authors of the IS370 collaboration want to acknowledge the support of the ISOLDE Collaboration and technical teams at CERN. J.A.B. acknowledges the predoctoral Grant No. BES-2008-009412 associated to the research Project No. FPA2007-62170 funded by Ministerio de Ciencia e Innovación (Spain). This work has been partly supported by the Spanish Funding Agency for Research (AEI) through Projects No. FPA2017-87568-P, No. RTI2018-098868-B-I00, No. PGC2018-093636-B-I00, No. PID2019-104390GB-I00, and No. PID2019-104714GB-C21 and by STFC (UK) through Grant No. T/P005314/1.

Nucleosynthesis in Type I X-ray bursts (XRB) proceeds eventually through the rp-process near the proton drip-line. Several N=Z nuclei act as waiting points in the reaction network chain. Astrophysical calculations of XRB light curves depend upon the theoretical modelling of the beta decays of interest, with the N=Z waiting points 64Ge, 68Se, 72Kr, 76Sr, and their second-neighbours N=Z+2 being key nuclei in this context. We have carried out different experimental campaigns at ISOLDE (CERN) to determine the B(GT) distributions, in the decay of several N=Z, N=Z+2 and their daughters, of particular relevance in rp-process calculations. To this aim the Total Absorption Spectroscopy technique is applied. Here we present results on the beta decay of 64Ga and the status of the analysis of 64Ge. Our results provide benchmarks for testing and constraining models under terrestrial conditions that can be used later for predictions in stellar environments.

The accurate determination of reactor antineutrino spectra remains a very hot research topic, where new questions have emerged in recent years. Indeed, after the “reactor anomaly” – a deficit of measured antineutrinos at short baseline reactor experiments with respect to spectral predictions – the three international reactor neutrino experiments Double Chooz, Daya Bay and Reno have evidenced spectral distortions in their measurements with respect to the same spectral predictions. This puzzle is called the “shape anomaly”. Recently summation calculations of reactor antineutrino spectra based on the use of nuclear data have obtained the best agreement to date with the reactor neutrino flux measurements at the level of 2% thanks to a decade of Total Absorption Gamma-ray Spectroscopy (TAGS) measurements at the radioactive beam facility of the University of Jyväskylä in two experimental campaigns. A selection of the results obtained so far is presented.

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-I00

We report here the results of a study of the $\beta$ decay of the proton-rich Ge isotopes, $^{60}$Ge and $^{62}$Ge, produced in an experiment at the RIKEN Nishina Center. We have improved our knowledge of the half-lives of $^{62}$Ge (73.5(1) ms), $^{60}$Ge (25.0(3) ms) and its daughter nucleus, $^{60}$Ga (69.4(2) ms). We measured individual $\beta$-delayed proton and $\gamma$ emissions and their related branching ratios. Decay schemes and absolute Fermi and Gamow-Teller transition strengths have been determined. The mass excesses of the nuclei under study have been deduced. A total $\beta$-delayed proton-emission branching ratio of 67(3)% has been obtained for $^{60}$Ge. New information has been obtained on the energy levels populated in $^{60}$Ga and on the 1/2$^-$ excited state in the $\beta p$ daughter $^{59}$Zn. We extracted a ground state to ground state feeding of 85.3(3)% for the decay of $^{62}$Ge. Eight new $\gamma$ lines have been added to the de-excitation of levels populated in the $^{62}$Ga daughter.

James Philip Elliott made important contributions to improve our understanding of the structure of atomic nuclei in the second half of the twentieth century. In 1958 he proposed the SU(3) model, explaining rotational behaviour of nuclei in the context of the shell model. His idea, based on elegant and seminal group-theoretical concepts, reconciled the independent-particle with the liquid-drop model, which until then existed as disconnected views of the nucleus. In the 1960s and 1970s he developed methods to extract properties of the nuclear interaction from the phase shifts of nucleon–nucleon scattering. From 1980 until his death he contributed to the development of the interacting boson model of Arima and Iachello, and its microscopic understanding in terms of symmetries of the shell model. For his outstanding achievements in theoretical physics, in 2002 he and Francesco Iachello were awarded the Lise Meitner prize of the European Physical Society for ‘their innovative applications of group-theoretical methods to the understanding of atomic nuclei’. His achievements were also recognized by the award of the Rutherford Medal and Prize of the Institute of Physics in 1994.

The β decay of ^{208}Hg into the one-proton hole, one neutron-particle _{81}^{208}Tl_{127} nucleus was investigated at CERN-ISOLDE. Shell-model calculations describe well the level scheme deduced, validating the proton-neutron interactions used, with implications for the whole of the N>126, Z

The β decay of 207Hg into the single-proton-hole nucleus 207Tl has been studied through γ-ray spectroscopy at the ISOLDE Decay Station (IDS) with the aim of identifying states resulting from coupling of the πs−11/2, πd−13/2, and πh−111/2 shell model orbitals to the collective octupole vibration. Twenty-two states were observed lying between 2.6 and 4.0 MeV, eleven of which were observed for the first time, and 78 new transitions were placed. Two octupole states (s1/2-coupled) are identified and three more states (d3/2-coupled) are tentatively assigned using spin-parity inferences, while further h11/2-coupled states may also have been observed for the first time. Comparisons are made with state-of-the-art large-scale shell model calculations and previous observations made in this region, and systematic underestimation of the energy of the octupole vibrational states is noted. We suggest that in order to resolve the difference in predicted energies for collective and noncollective t=1 states (t is the number of nucleons breaking the 208Pb core), the effect of t=2 mixing may be reduced for octupole-coupled states. The inclusion of mixing with t=0,2,3 excitations is necessary to replicate all t=1 state energies accurately.

Acta physica Polonica / B 51(3), 587 (2020). doi:10.5506/APhysPolB.51.587, Published by Inst. of Physics, Jagellonian Univ., Cracow

6 pags., 3 figs., 1 tab. -- 27th International Nuclear Physics Conference (INPC2019) 29 July - 2 August 2019, Glasgow, UK, In this contribution we summarize the recent study of the β decay of neutron-rich nuclei with isomeric states close in energy to the ground states. The disentanglement of each pair of β-decaying states was achieved by applying different strategies and using the purification capabilities of the JYFLTRAP double Penning trap system at the Ion Guide Isotope Separator On-Line facility in Jyväskylä. The Total Absorption γ-ray Spectroscopy technique was employed to determine the β intensity probabilities populating the excited states in the daughter nuclei. Previously undetected β intensity was found and we have already evaluated the impact of part of these results on reactor summation calculations. The possibility to populate states associated with the Pygmy Dipole Resonance in the β decay of 96gsY has also been investigated thanks to the sensitivity of our technique to high-lying strength in the daughter nuclei., This work has been supported by the CNRS challenge NEEDS and the associated NACRE project, as well as by the Spanish Ministerio de Econom´ıa y Competitividad under Grants No. FPA2011-24553, No. AIC-A-2011-0696, No. FPA2014-52823-C2-1-P, No. FPA2015-65035-P, No. FPI/BES-2014-068222, No. FPA2017-83946-C2-1-P and the program Severo Ochoa (SEV-2014-0398), by the Spanish Ministerio de Educacion 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 Ampliacion de Estudios ´ Programme (CSIC JAE-Doc contract) co-financed by ESF.

12 pags., 6 figs., 3 tabs., In β-decay studies the determination of the decay probability to the ground state (g.s.) of the daughter nucleus often suffers from large systematic errors. The difficulty of the measurement is related to the absence of associated delayed γ -ray emission. In this work we revisit the 4π γ − β method proposed by Greenwood and collaborators in the 1990s, which has the potential to overcome some of the experimental difficulties. Our interest is driven by the need to determine accurately the β-intensity distributions of fission products that contribute significantly to the reactor decay heat and to the antineutrinos emitted by reactors. A number of such decays have large g.s. branches. The method is relevant for nuclear structure studies as well. Pertinent formulas are revised and extended to the special case of β-delayed neutron emitters, and the robustness of the method is demonstrated with synthetic data. We apply it to a number of measured decays that serve as test cases and discuss the features of the method. Finally, we obtain g.s. feeding intensities with reduced uncertainty for four relevant decays that will allow future improvements in antineutrino spectrum and decay heat calculations using the summation method., 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, No. FPI/BES-2014-068222, No. FPA2017-83946-C2-1-P, and No. RTI2018-098868-BI00 and the program Severo Ochoa (SEV-2014-0398); by the Spanish Ministerio de Educación under Grant No. FPU12/01527; by the Spanish Ministerio de Ciencia e Innovación under Grant No. PID2019-104714GB-C21; by the European Commission under CHANDA project funded under FP7-EURATOM-FISSION Grant No. 605203; the FP7/ENSAR Contract No. 262010; the SANDA project funded under H2020-EURATOM-1.1 Grant No. 847552; the Horizon 2020 research and innovation programme under Grant No. 771036 (ERC CoG MAIDEN); by the Generalitat Valenciana regional funds PROMETEO/2019/007/; and by the Junta para la Ampliacion de Estudios ´ Programme (CSIC JAE-Doc contract) co-financed by ESF. We acknowledge the support of the UK Science and Technology Facilities Council (STFC) Grant No. ST/P005314/1; of the Polish National Agency for Academic Exchange (NAWA) under Grant No. PPN/ULM/2019/1/00220; and of the National Science Center, Poland, under Contract No. 2019/35/D/ST2/02081. This work was also supported by the Academy of Finland under the Finnish Centre of Excellence Programme (Project No. 213503, Nuclear and Accelerator-Based Physics Research at JYFL). A.K. and T.E. acknowledge support from the Academy of Finland under Projects No. 275389 and No. 295207, respectively. This work has also been supported by the CNRS challenge NEEDS and the associated NACRE project, the CNRS/in2p3 PICS TAGS between Subatech and IFIC, and the CNRS/in2p3 Master projects Jyvaskyla and OPALE.

The decays of the β-delayed neutron emitters I137 and Rb95 have been studied with the total absorption γ-ray spectroscopy technique. The purity of the beams provided by the JYFLTRAP Penning trap at the ion guide isotope separator on-line facility in Jyvaskyla allowed us to carry out a campaign of isotopically pure measurements with the decay total absorption γ-ray spectrometer, a segmented detector composed of 18 NaI(Tl) modules. The contamination coming from the interaction of neutrons with the spectrometer has been carefully studied, and we have tested the use of time differences between prompt γ rays and delayed neutron interactions to eliminate this source of contamination. Due to the sensitivity of our spectrometer, we have found a significant amount of β intensity to states above the neutron separation energy that deexcite by γ rays, comparable to the neutron emission probability. The competition between γ deexcitation and neutron emission has been compared with Hauser-Feshbach calculations, and it can be understood as a nuclear structure effect. In addition, we have studied the impact of the β-intensity distributions determined in this work on reactor decay heat and reactor antineutrino spectrum summation calculations. The robustness of our results is demonstrated by a thorough study of uncertainties and with the reproduction of the spectra of the individual modules and the module-multiplicity gated spectra. This work represents the state-of-the-art of our analysis methodology for segmented total absorption spectrometers.

The accurate determination of reactor antineutrino spectra is still a challenge. In 2017 the Daya Bay experiment has measured the evolution of the antineutrino flux with the fuel content of the reactor core. The observed deficit of the detected flux compared with the predictions of the conversion model was almost totally explained by the data arising from the fissions of 235U while the part dominated by the fission of 239Pu was in good agreement with the conversion model. The TAGS collaboration has carried out two experimental campaigns during the last decade at the JYFLTRAP of Jyväskylä (Finland) measuring a large set of data in order to improve the quality of the predictions of our summation method. These measurements allow the correction of the nuclear data for the Pandemonium effect, thus making an important contribution to calculating the antineutrino spectra. The impact of these ten years of measurement from our collaboration on the predicted antineutrino energy spectrum and flux are shown using our summation calculations. The results are compared with the Daya Bay measurements showing the best agreement in shape (in the antineutrino energy range 2 to 5 MeV) and in flux obtained so far with a model. The flux deficit observed by Daya Bay with respect to the summation method is now reduced to 1.9% leaving little room for the reactor anomaly. The shape anomaly between 5 and 7 MeV in antineutrino energy is still observed and remains unexplained.

Even mass neutron-rich niobium isotopes are among the principal contributors to the reactor antineutrino energy spectrum. They are also among the most challenging to measure due to the refractory nature of niobium, and because they exhibit isomeric states lying very close in energy. The beta-intensity distributions of Nb-100gs,Nb-100m and Nb-102gs,Nb-02m beta decays have been determined using the total absorption.-ray spectroscopy technique. The measurements were performed at the upgraded Ion Guide Isotope Separator On-Line facility at the University of Jyvaskyla. Here, the double Penning trap system JYFLTRAP was employed to disentangle the beta decay of the isomeric states. The new data obtained in this challenging measurement have a large impact in antineutrino summation calculations. For the first time the discrepancy between the summation model and the reactor antineutrino measurements in the region of the shape distortion has been reduced.

15 pags. 17 figs., 5 tabs., The β-intensity distributions of the decays of Nb100gs,100m and Nb102gs,102m have been determined using the total absorption γ-ray spectroscopy technique. The JYFLTRAP double Penning trap system was employed in a campaign of challenging measurements performed with the decay total absorption γ-ray spectrometer at the Ion Guide Isotope Separator On-Line facility in Jyväskylä. Different strategies were applied to disentangle the isomeric states involved, lying very close in energy. The low-spin component of each niobium case was populated through the decay of the zirconium parent, which was treated as a contaminant. We have applied a method to extract this contamination, and additionally we have obtained β-intensity distributions for these zirconium decays. The β-strength distributions evaluated with these results were compared with calculations in a quasiparticle random-phase approximation, suggesting a prolate configuration for the ground states of Zr100,102. The footprint of the Pandemonium effect was found when comparing our results for the analyses of the niobium isotopes with previous decay data. The β-intensities of the decay of Nb102m, for which there were no previous data, were obtained. A careful evaluation of the uncertainties was carried out, and the consistency of our results was validated taking advantage of the segmentation of our spectrometer. The final results were used as input in reactor summation calculations. A large impact on antineutrino spectrum calculations was already reported, and here we detail the significant impact on decay heat calculations., 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, No. FPI/BES-2014-068222, No. FPA2017-83946-C2-1-P, and the program Severo Ochoa (SEV-2014-0398), by the Spanish Ministerio de Educación under the FPU12/01527 Grant, by the European Commission under the FP7/EURATOM Contract No. 605203 and the FP7/ENSAR Contract No. 262010, and by the Junta para la Ampliación de Estudios Programme (CSIC JAE-Doc contract) co-financed by ESF. We acknowledge the support of the UK Science and Technology Facilities Council (STFC) Grant No. ST/P005314/1. This work was also supported by the Academy of Finland under the Finnish Centre of Excellence Programme (Project No. 213503, Nuclear and AcceleratorBased Physics Research at JYFL). The authors thank the IAEA for supporting and encouraging the work in this field.

International audience; The beta decay of the Tz=-2 nucleus 64Se has been studied in a fragmentation reaction at RIKEN-Nishina Center. 64Se is the heavies Tz=-2 nucleus that decays to bound states in the daughter nucleus and the heaviest case where the mirror reaction 64Zn(3He,t)64Ga on the Tz=+2 64Zn stable target exists and can be compared. Beta-delayed gamma and proton radiation is reported for the 64Se and 64As cases. New levels have been observed in 64As, 64Ge (N=Z), 63Ge and 63Ga. The associated T1/2 values have been obtained.

Even mass neutron-rich niobium isotopes are among the principal contributors to the reactor antineutrino energy spectrum. They are also among the most challenging to measure due to the refractory nature of niobium, and because they exhibit isomeric states lying very close in energy. The β-intensity distributions of ^{100gs,100m}Nb and ^{102gs,102m}Nb β decays have been determined using the total absorption γ-ray spectroscopy technique. The measurements were performed at the upgraded Ion Guide Isotope Separator On-Line facility at the University of Jyväskylä. Here, the double Penning trap system JYFLTRAP was employed to disentangle the β decay of the isomeric states. The new data obtained in this challenging measurement have a large impact in antineutrino summation calculations. For the first time the discrepancy between the summation model and the reactor antineutrino measurements in the region of the shape distortion has been reduced.

9 pags., 3 figs. -- Open Access funded by Creative Commons Atribution Licence 4.0, Three observables of interest for present and future reactors depend on the β decay properties of the fission products: antineutrinos from reactors, the reactor decay heat and delayed neutron emission. In these proceedings, we present new results from summation calculations of the first two quantities quoted above, performed with evolved independent yields coupled with fission product decay data, from various nuclear data bases or models. New TAGS results from the latest experiment of the TAGS collaboration at the JYFL facility of Jyväskylä will be displayed as well as their impact on the antineutrino spectra and the decay heat associated to fission pulses of the main actinides.

Background: $\beta$-delayed multiple neutron emission has been observed for some nuclei with A$\leq$100, with $^{100}$Rb being the heaviest $\beta$2n emitter measured to date. So far, only 25 P$_{2n}$ values have been determined for the $\sim$300 nuclei that may decay in this way. Accordingly, it is of interest to measure P$_{2n}$ values for the other possible multiple neutron emitters throughout the chart of the nuclides. It is of particular interest to make such measurement for nuclei with A$>$100 to test the predictions of theoretical models and simulation tools for the decays of heavy nuclei in the region of very neutron-rich nuclei. In addition, the decay properties of these nuclei are fundamental for the understanding of astrophysical nucleosynthesis processes such as the $r$-process, and safety inputs for nuclear reactors. Purpose: To determine for the first time the two neutron branching ratio, P$_{2n}$ value, for $^{136}$Sb through a direct neutron measurement, and to provide precise P$_{1n}$ values for $^{136}$Sb and $^{136}$Te. Method: Pure beams were provided by the JYFLTRAP at the IGISOL facility of the University of Jyv\"askyl\"a, Finland. The purified ions were implanted into a moving tape at the end of the beam line. The detection setup consisted of a plastic scintillator placed right behind the implantation point, and the BELEN detector, based on neutron counters embedded in a polyethylene matrix. The analysis was based on the study of the $\beta$- and neutron- growth-and-decay curves and the $\beta$-one-neutron and $\beta$-two-neutron time correlations. Results: The P$_{2n}$ value of $^{136}$Sb was found to be 0.31(5)\% and the measured P$_{1n}$ values for $^{136}$Sb and $^{136}$Te were found to be 31.9(15)\% and 1.47(6)\%, respectively. The measured P$_{2n}$ value is a factor 20 smaller than predicted by the FRDM+QRPA model used for $r$-process calculations.

11 pags., 16 figs., 3 tabs., DTAS is a segmented total absorption γ-ray spectrometer developed for the DESPEC experiment at FAIR. It is composed of up to eighteen NaI(Tl) crystals. In this work we study the performance of this detector with laboratory sources and also under real experimental conditions. We present a procedure to reconstruct offline the sum of the energy deposited in all the crystals of the spectrometer, which is complicated by the effect of NaI(Tl) light-yield non-proportionality. The use of a system to correct for time variations of the gain in individual detector modules, based on a light pulse generator, is demonstrated. We describe also an event-based method to evaluate the summing-pileup electronic distortion in segmented spectrometers. All of this allows a careful characterization of the detector with Monte Carlo simulations that is needed to calculate the response function for the analysis of total absorption γ-ray spectroscopy data. Special attention was paid to the interaction of neutrons with the spectrometer, since they are a source of contamination in studies of β-delayed neutron emitting nuclei., This work has been supported by the Spanish Ministerio de Economia 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 Educacion Cultura y Deporte under the FPU12/01527 grant. The work was also supported by the UK Science and Technology Facilities Council (STFC) grant 14 ST/P005314/1. E. Ganioglu was supported by the Istanbul University Scientic Research Project Unit under FYO-2017-24144 project.

International audience; The two-proton radioactivity is a unique tool to study the nuclear structure beyond the proton drip-line. Since its discovery in 2002, the known emitters have been 19Mg, 45Fe, 48Ni, 54Zn and 67Kr. 67Kr was observed for the first time at the RIKEN Nishina Center in 2015. Its decay energy was measured at 1690(17) keV with a branching ratio of 37(14)%. The half-life, 7.4(30) ms, was found in contradiction with theoretical calculations, pointing out effects of decay dynamics and nuclear deformation.

This paper presents the design of a total absorption γ-ray spectrometer for the determination of β-decay intensity distributions of exotic nuclear species at the focal plane of the FAIR-NUSTAR Super Fragment Separator. The spectrometer is a key instrument in the DESPEC experiment and the proposed implementation follows extensive design studies and prototype tests. Two options were contemplated, based on NaI(Tl) and LaBr3:Ce inorganic scintillation crystals respectively. Monte Carlo simulations and technical considerations determined the optimal configurations consisting of sixteen 15 × 15 × 25 cm 3 crystals for the NaI(Tl) option and one hundred and twenty-eight 5.5 × 5.5 × 11 cm 3 crystals for the LaBr3:Ce option. Minimization of dead material was crucial for maximizing the spectrometer full-energy peak efficiency. Module prototypes were build to verify constructional details and characterize their performance. The measured energy and timing resolution was found to agree rather well with estimates based on simulations of scintillation light transport and collection. The neutron sensitivity of the spectrometer, important when measuring β-delayed neutron emitters, was investigated by means of Monte Carlo simulations.

International audience; The β decays of the proton-rich, T z = −2 nuclei 48Fe, 52Ni and 56Zn were investigated by decay spectroscopy at GANIL. The decay schemes were determined, together with absolute Fermi and Gamow-Teller transition strengths. New interesting results were obtained, including the first observation of a new decay mode in the f p-shell, the exotic β- delayed γ-proton decay seen in 56Zn, and the first observation of the 2+ isomer in 52Co. These studies were complemented by Charge Exchange reactions on the stable mirror targets.

The excited states of the proton emitter Lu151 were reinvestigated in a recoil-decay tagging experiment at the Accelerator Laboratory of the University of Jyvaskyla (JYFL). The level scheme built on the ground state of Lu151 was updated with five new γ-ray transitions. Large-scale shell model calculations were carried out in the model space consisting of the neutron and proton orbitals 0g7/2, 1d5/2, 1d3/2, 2s1/2, and 0h11/2 with the optimized monopole interaction in order to interpret the experimental level scheme of Lu151. It is found that the excitation energies of states above the 27/2- and 23/2+ isomeric levels in Lu151 can be sensitive to excitations from g7/2 and d5/2 to single-particle orbitals above N=Z=64.

Author(s): Vogt, A; Siciliano, M; Birkenbach, B; Reiter, P; Hadynska-Klȩk, K; Wheldon, C; Valiente-Dobon, JJ; Teruya, E; Yoshinaga, N; Arnswald, K; Bazzacco, D; Blazhev, A; Bracco, A; Bruyneel, B; Chakrawarthy, RS; Chapman, R; Cline, D; Corradi, L; Crespi, FCL; Cromaz, M; De Angelis, G; Eberth, J; Fallon, P; Farnea, E; Fioretto, E; Fransen, C; Freeman, SJ; Fu, B; Gadea, A; Gelletly, W; Giaz, A; Gorgen, A; Gottardo, A; Hayes, AB; Hess, H; Hetzenegger, R; Hirsch, R; Hua, H; John, PR; Jolie, J; Jungclaus, A; Karayonchev, V; Kaya, L; Korten, W; Lee, IY; Leoni, S; Liang, X; Lunardi, S; MacChiavelli, AO; Menegazzo, R; Mengoni, D; Michelagnoli, C; Mijatovic, T; Montagnoli, G; Montanari, D; Muller-Gatermann, C; Napoli, D; Pearson, CJ; Podolyak, Z; Pollarolo, G; Pullia, A; Queiser, M; Recchia, F; Regan, PH; Regis, JM; Saed-Samii, N; Sahin, E; Scarlassara, F; Seidlitz, M; Siebeck, B; Sletten, G; Smith, JF; Soderstrom, PA; Stefanini, AM; Stezowski, O; Szilner, S; Szpak, B; Teng, R; Ur, C; Warner, DD; Wolf, K; Wu, CY; Zell, KO | Abstract: The transitional nuclei Xe132 and Xe133 are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in Xe136+Pb208 MNT reactions employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (ii) in the Xe136+Pt198 MNT reaction employing the GAMMASPHERE spectrometer in combination with the gas-detector array CHICO, and (iii) as an evaporation residue after a Te130(α,xn)Xe134-xn fusion-evaporation reaction employing the HORUS γ-ray array at the University of Cologne. The high-spin level schemes are considerably extended above the Jπ=(7-) and (10+) isomers in Xe132 and above the 11/2- isomer in Xe133. The results are compared to the high-spin systematics of the Z=54 as well as the N=78 and N=79 chains. Furthermore, evidence is found for a long-lived (T1/2â‰1μs) isomer in Xe133 which closes a gap along the N=79 isotones. Shell-model calculations employing the SN100PN and PQM130 effective interactions reproduce the experimental findings and provide guidance to the interpretation of the observed high-spin features.

The beta decay of Tc-100 has been studied by using the total absorption gamma-ray spectroscopy technique at the Ion Guide Isotope Separator On-Line facility in Jyvaskyla. In this work the new Decay Total Absorption gamma-ray Spectrometer in coincidence with a cylindrical plastic beta detector has been employed. The beta 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 beta decay of Mo-100.

The beta decays of 86Br and 91Rb have been studied using the total absorption spectroscopy technique. The radioactive nuclei were produced at the IGISOL facility in Jyvaskyla and further purified using the JYFLTRAP. 86Br and 91Rb are considered high priority contributors to the decay heat in reactors. In addition 91Rb 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 shows that both decays were suffering from the Pandemonium effect and that the results of Rudstam et al. should be renormalized.

The $\beta$ decay of the odd-odd nucleus $^{70}$Br has been investigated with the BigRIPS and EURICA setups at the Radioactive Ion Beam Factory (RIBF) of the RIKEN Nishina Center. The $T=0$ ($J^{\pi}=9^+$) and $T=1$ ($J^{\pi}=0^+$) isomers have both been produced in in-flight fragmentation of $^{78}$Kr with ratios of 41.6(8)\% and 58.4(8)\%, respectively. A half-life of $t_{1/2}=2157^{+53}_{-49}$ ms has been measured for the $J^{\pi}=9^+$ isomer from $\gamma$-ray time decay analysis. Based on this result, we provide a new value of the half-life for the $J^{\pi}=0^+$ ground state of $^{70}$Br, $t_{1/2}=78.42\pm0.51$ ms, which is slightly more precise, and in excellent agreement, with the best measurement reported hitherto in the literature. For this decay, we provide the first estimate of the total branching fraction decaying through the $2^+_1$ state in the daughter nucleus $^{70}$Se, $R(2^+_1)=1.3\pm1.1\%$. We also report four new low-intensity $\gamma$-ray transitions at 661, 1103, 1561, and 1749 keV following the $\beta$ decay of the $J^{\pi}=9^+$ isomer. Based on their coincidence relationships, we tentatively propose two new excited states at 3945 and 4752 keV in $^{70}$Se with most probable spins and parities of $J^{\pi}=(6^+)$ and $(8^+)$, respectively. The observed structure is interpreted with the help of shell-model calculations, which predict a complex interplay between oblate and prolate configurations at low excitation energies.

Background: Previous measurements of Beta-delayed neutron emitters comprise around 230 nuclei, spanning from the 8He up to 150La. Apart from 210Tl, with a minuscule branching ratio of 0.07%, no other neutron emitter is measured yet beyond A = 150. Therefore new data are needed, particularly in the heavy mass region around N=126, in order to guide theoretical models and to understand the formation of the third r-process peak at A 195. Purpose: To measure both, Beta-decay half-lives and neutron branching ratios of several neutron-rich Au, Hg, Tl, Pb and Bi isotopes beyond N = 126. Method: Ions of interest are produced by fragmentation of a 238U beam, selected and identifed via the GSI-FRS fragment separator. A stack of segmented silicon detectors (SIMBA) is used to measure ion-implants and -decays. An array of 30 3He tubes embedded in a polyethylene matrix (BELEN) is used to detect neutrons with high efficiency and selectivity. A self-triggered digital system is employed to acquire data and to enable time-correlations. The latter are analyzed with an analytical model and results for the half-lives and neutron-branching ratios are derived using the binned Maximum-Likelihood method. Results: Twenty new Beta-decay half-lives are reported for 204

We have measured the $ \beta$ -decay half-lives of 16 neutron-deficient nuclei with $ T_{z} = -1/2$ and -1 , ranging from chromium to germanium. They were produced in an experiment carried out at GANIL and optimized for the production of$^{58}$Zn , for which in addition we present the decay scheme and absolute Fermi and Gamow-Teller transition strengths. Since all of these nuclei lie on the rp -process pathway, the $ T_{1/2}$ values are important ingredients for the rp -process reaction flow calculations and for models of X-ray bursters.

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.

International audience; We report on the observation of 67Kr that has been produced in an experiment performed at the RIKEN/BigRIPS facility. The two-proton decay of 67Kr has been evidenced and this nucleus is thus the fourth observed long lived ground-state two-proton emitter, after 45Fe, 48Ni and 54Zn. In addition, the decay of several isotopes in the mass region has been investigated. While for previous cases of two-proton radioactivity, the theoretical models could reproduce the measured data, this is not the case anymore for 67Kr. Two interpretations have been proposed to explain this discrepancy: a transition between real two-proton and sequential decay or the influence of deformation. These hypotheses will be tested in future experiments by measuring the angular and energy correlations of the emitted protons.

This paper concerns the experimental study of the β decay properties of few proton-rich fp -shell nuclei. The nuclei were produced at GANIL in fragmentation reactions, separated with the LISE spectrometer and stopped in an implantation detector surrounded by Ge detectors. The β -delayed gammas, β -delayed protons and the exotic β -delayed gamma-proton emission have been studied. Preliminary results are presented. The decay of the T z = − 2 nucleus 56 Zn has been studied in detail. Information from the β -delayed protons and β -delayed gammas has been used to deduce the decay scheme. The exotic beta-delayed gamma-proton decay has been observed for the first time in the fp -shell. The interpretation of the data was made possible thanks to the detailed knowledge of the mirror Charge Exchange (CE) process and the gamma de-excitation of the states in 56 Co, the mirror nucleus of 56 Cu.

An overview is given of our activities related to the study of the beta decay of neutron rich nuclei relevant for nuclear applications. Recent results of the study of the beta decay of 87,88 Br using a new segmented total absorption spectrometer are presented. The measurements were performed at the IGISOL facility using trap-assisted total absorption spectroscopy.

A new accurate determination of beta-delayed neutron emission probabilities from nuclei in the low mass region of the light fission group has been performed. The measurements were carried out using the BELEN 4π neutron counter at the IGISOL-JYFL mass separator in combination with a Penning trap. The new results significantly improve the uncertainties of neutron emission probabilities for {sup 91}Br, {sup 86}As, {sup 85}As, and {sup 85}Ge nuclei.

International audience; Total absorption gamma-ray spectroscopy is used to measure accurately the intensity of γ emission from neutron-unbound states populated in the β-decay of delayed-neutron emitters. From the comparison of this intensity with the intensity of neutron emission a constraint on the (n, γ) cross section for highly unstable neutron-rich nuclei can be deduced. A surprisingly large γ branching was observed for a number of isotopes which might indicate the need to increase by a large factor the Hauser-Feshbach (n, γ) cross-section estimates that impact on r process abundance calculations.

We investigate the decay of 87,88Br and 94Rb using total absorption γ -ray spectroscopy. These important fission products are β-delayed neutron emitters. Our data show considerable βγ intensity, so far unobserved in high-resolution γ -ray spectroscopy, from states at high excitation energy. We also find significant differences with the β intensity that can be deduced from existing measurements of the β spectrum. We evaluate the impact of the present data on reactor decay heat using summation calculations. Although the effect is relatively small it helps to reduce the discrepancy between calculations and integral measurements of the photon component for 235U fission at cooling times in the range 1–100 s. We also use summation calculations to evaluate the impact of present data on reactor antineutrino spectra. We find a significant effect at antineutrino energies in the range of 5 to 9 MeV. In addition, we observe an unexpected strong probability for γ emission from neutron unbound states populated in the daughter nucleus. The γ branching is compared to Hauser-Feshbach calculations, which allow one to explain the large value for bromine isotopes as due to nuclear structure. However the branching for 94Rb, although much smaller, hints of the need to increase the radiative width γ by one order of magnitude. This increase in γ would lead to a similar increase in the calculated (n,γ ) cross section for this very neutron-rich nucleus with a potential impact on r process abundance calculations.

The high-spin structures of the N = 81 isotones 135Xe and 137Ba are investigated after multinucleontransfer (MNT) and fusion-evaporation reactions. Both nuclei are populated in (i) 136Xe+238U and (ii) 136Xe+208Pb MNT reactions employing the high-resolution Advanced Gamma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (iii), in the 136Xe+198Pt MNT reaction employing the -ray array GAMMASPHERE in combination with the gas detector array Chico, and (iv) via a 11B+130Te fusion-evaporation reaction. The high-spin level schemes of 135Xe and 137Ba are considerably extended to higher energies. The 2058-keV (19=2 ) state in 135Xe is identified as an isomer, completing the systematics for the N = 81 isotones. Its half-life is measured to be 8.6(10) ns, corresponding to a transition probability of B(E2; 19=2 ! 15=2 ) = 0:539(69) W.u. Latest shell model calculations considering 132Sn as a closed core reproduce the experimental findings and provide guidance to the interpretation of the new levels. The experimentally deduced reduced quadrupole transition probabilities of the isomeric states are compared to shell-model predictions.

J. L. Taín et al. -- 6 pags., 7 figs., 1 tab. -- Open Access funded by Creative Commons Atribution Licence 4.0, Total absorption gamma-ray spectroscopy is used to measure accurately the intensity of ¿ emission from neutron-unbound states populated in the ß-decay of delayed-neutron emitters. From the comparison of this intensity with the intensity of neutron emission one can deduce information on the (n,¿) cross section for unstable neutron-rich nuclei of interest in r process abundance calculations. A surprisingly large ¿ branching was observed for a number of isotopes. The results are compared with Hauser-Feshbach calculations and discussed., This work was supported by Spanish Ministerio de Economía y Competitividad under grants FPA2008-06419, FPA2010- 17142, FPA2011-24553, FPA2014-52823-C2-1-P, CPAN CSD- 2007-00042 (Ingenio2010) and the program Severo Ochoa (SEV-2014-0398). WG would like to thank the University of Valencia for support. This work was supported by the Academy of Finland under the Finnish Centre of Excellence Programme 2012-2017 (Project No. 21350). Work supported by EPSRC(UK) and STFC(UK) and the UK National Measurement Office. Work supported by the European Commission under the FP7/EURATOM contract 605203. FGK acknowledges support from the U.S. Department of Energy, under contract number DEAC02- 06CH11357.

Preliminary results from beta decay studies of nuclei that are important for reactor applications are presented. The beta decays have been studied using the total absorption technique (TAS) and the pure beams provided by the JYFLTRAP system at the IGISOL facility of the University of Jyväskylä. peerReviewed

26 pags., 21 figs., tab. -- Open Access funded by Creative Commons Atribution Licence 3.0, Here we present the experimental activities carried out at ISOLDE with the total absorption spectrometer Lucrecia, a large 4π scintillator detector designed to absorb a full gamma cascade following beta decay. This spectrometer is designed to measure β-feeding to excited states without the systematic error called Pandemonium. The set up allows the measurement of decays of very short half life. Experimental results from several campaigns, that focus on the determination of the shapes of β-decaying nuclei by measuring their β decay strength distributions as a function of excitation energy in the daughter nucleus, are presented., This work has been supported by the Spanish Ministerio de Economia y Competitividad under the FPA 2014-52823-C2-1-P, the AIC-A-2011-0696 and the SEV-2014-0398 grants, by the European Commission under the FP7/EURATOM contract 602503 and by the Spanish Ministerio de Educacion under the FPU12/01527 grant. IFIC is a centre of excellence Severo Ochoa. It was also supported by the Science and Technology facilities Council UK under grant No. ST/FO12012/1. WG acknowledges the support of the University of Valencia. The initial setting up of Lucrecia and the design and building of the shielding was carried out in a collaboration between IFIC-Valencia, University of Surrey, IRES-Strasbourg and IEM-Madrid.

gamma rays following the EC/beta(+) and alpha decay of the N = 126, Fr-213 nucleus have been observed at the CERN isotope separator on-line (ISOLDE) facility with the help of gamma-ray and conversion-electron spectroscopy. These gamma rays establish several hitherto unknown excited states in Rn-213. Also, five new a-decay branches from the Fr-213 ground state have been discovered. Shell model calculations have been performed to understand the newly observed states in Rn-213.