Agramunt, J. et al, Algora, A., Domingo-Pardo, C., Jordan, D., Rubio, B., Tain, J. L., et al. (2014). New Beta-delayed Neutron Measurements in the Light-mass Fission Group. Nucl. Data Sheets, 120, 74–77.
Abstract: 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 4 pi 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 Br-91, As-86, As-85, and Ge-85 nuclei.
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Agramunt, J. et al, Tain, J. L., Albiol, F., Algora, A., Domingo-Pardo, C., Jordan, M. D., et al. (2016). Characterization of a neutron-beta counting system with beta-delayed neutron emitters. Nucl. Instrum. Methods Phys. Res. A, 807, 69–78.
Abstract: A new detection system for the measurement of beta-delayed neutron emission probabilities has been characterized using fission products with well known beta-delayed neutron emission properties. The setup consists of BELEN-20, a 4 pi-neutron counter with twenty He-3 proportional tubes arranged inside a large polyethylene neutron moderator, a thin Si detector for beta counting and a self-triggering digital data acquisition system. The use of delayed-neutron precursors with different neutron emission windows allowed the study of the effect of energy dependency on neutron, beta and beta-neutron rates. The observed effect is well reproduced by Monte Carlo simulations. The impact of this dependency on the accuracy of neutron emission probabilities is discussed. A new accurate value of the neutron emission probability for the important delayed-neutron precursor I-137 was obtained, P-n = 7.76(14)%.
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Aguilera, P. et al, Rubio, B., Orrigo, S. E. A., Gelletly, W., Agramunt, J., Algora, A., et al. (2025). β decay of the Tz =-2 nucleus 64Se and its descendants: The T=2 isobaric multiplet. Phys. Rev. C, 112(5), 054319–20pp.
Abstract: In this paper we present our results on the decay of 64Se. It is the heaviest Tz = -2 nucleus that both 9 decays and has a stable mirror partner (Tz = +2), thus allowing comparison with charge exchange reaction studies. The 9 decays of 64Se and its descendants were studied at the RIKEN Nishina Center (Japan) following their production in the fragmentation of 78Kr on a beryllium target. 9-Delayed gamma-ray and particle radiation was identified for each of the nuclei in the decay chain allowing us to obtain decay schemes for 64Se, 64As, and 63Ge. Thus new excited states could be found for the descendant nuclei, including the interesting case of the N = Z nucleus 64Ge. Furthermore, we observed for the first time the 9-delayed proton emission of 64Se and 64As. Based on these results we obtained proton branching ratios of 48.0(9)% in 64Se decay and 4.4(1)% in 64As decay. We obtained a half-life value of 22.5(6) ms for 64Se decay and half-lives slightly more precise than those in the literature for each nucleus involved in the decay chain. Using our results on the excited levels of 64As and the mass excess in the literature for 63Ge we obtained-39588(50) keV for the mass excess of 64As. Then based on the isobaric mass multiplet equation we obtained the mass excess of-27429(88) keV for 64Se by extrapolation. The mirror process of 64Se 3 decay, the charge exchange reaction 64Zn(3He, t)64Ga, has already been measured allowing us to study the mirror symmetry through the comparison of the weak force (3a decay) and strong force (charge exchange reaction). An interpretation of the decay schemes based on the idea of the antisnalogue tate is proposed.
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Algora, A. et al, Agramunt, J., Tain, J. L., Garcia Cabrera, H., & Victoria, J. A. (2025). Study of the Beta Spectrum Shape of 92Rb and 142Cs Decays for the Prediction of Reactor Antineutrino Spectra. Phys. Rev. Lett., 135(14), 142502–10pp.
Abstract: The shapes of the beta spectra of 92Rb and 142Cs, two of the beta decays most relevant for the prediction of the antineutrino spectrum in reactors, have been measured. A new setup composed of two Delta E-E telescopes has been used. High-purity radioactive beams of the isotopes of interest were provided by the IGISOL facility using the JYFLTRAP double Penning trap. The resulting beta spectra have been compared with model predictions using beta decay feedings from total absorption gamma spectroscopy measurements and shape corrections employed in the calculation of the antineutrino spectrum, corroborating both further. The procedure can be extended to other relevant nuclei in the future, providing solid ground for the prediction of the antineutrino spectrum in reactors.
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Algora, A. et al, Jordan, D., Tain, J. L., Rubio, B., Agramunt, J., Perez-Cerdan, A. B., et al. (2011). Improvements on Decay Heat Summation Calculations by Means of Total Absorption Gamma-ray Spectroscopy Measurements. J. Korean Phys. Soc., 59(2), 1479–1482.
Abstract: 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 Jyvaskyla, 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.
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Algora, A. et al, Jordan, D., Tain, J. L., Rubio, B., Agramunt, J., Perez-Cerdan, A. B., et al. (2010). Reactor Decay Heat in Pu-239: Solving the gamma Discrepancy in the 4-3000-s Cooling Period. Phys. Rev. Lett., 105(20), 202501–4pp.
Abstract: The beta feeding probability of Tc-102,Tc- 104,Tc- 105,Tc- 106,Tc- 107, Mo-105, and Nb-101 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 Pu-239 in the 4-3000 s range.
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Algora, A. et al, Rubio, B., Agramunt, J., Guadilla, V., Montaner-Piza, A., Morales, A. I., et al. (2025). Isospin Symmetry Breaking in the 71Kr and 71Br Mirror System. Phys. Rev. Lett., 134(16), 162502–9pp.
Abstract: Isospin symmetry is a fundamental concept in nuclear physics. Even though isospin symmetry is partially broken, it holds approximately for most nuclear systems, which makes exceptions very interesting from the nuclear structure perspective. In this framework, it is expected that the spins and parities of the ground states of mirror nuclei should be the same, in particular for the simplest systems where a proton is exchanged with a neutron or vice versa. In this Letter, we present evidence that this assumption is broken in the mirror pair 71Br and 71Kr system. Our conclusions are based on a high-statistics /3 decay study of 71Kr and on state-of-the-art shell model calculations. In our work, we also found evidence of a new state in 70Se, populated in the /3-delayed proton emission process which can be interpreted as the long sought coexisting 0 & thorn; state.
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Algora, A. et al, Valencia, E., Tain, J. L., Jordan, M. D., Agramunt, J., Rubio, B., et al. (2014). Total Absorption Study of Beta Decays Relevant for Nuclear Applications and Nuclear Structure. Nucl. Data Sheets, 120, 12–15.
Abstract: 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 Br-87,Br-88 using a new segmented total absorption spectrometer are presented. The measurements were performed at the IGISOL facility using trap-assisted total absorption spectroscopy.
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Algora, A., Ganioglu, E., Sarriguren, P., Guadilla, V., Fraile, L. M., Nacher, E., et al. (2021). Total absorption gamma-ray spectroscopy study of the beta-decay of Hg-186. Phys. Lett. B, 819, 136438–7pp.
Abstract: The Gamow-Teller strength distribution of the decay of Hg-186 into Au-186 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-186 and daughter Au-186. 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.
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Appleton, C. J. et al, Algora, A., Victoria, J. A., Rubio, B., Agramunt, J., Nacher, E., et al. (2025). Measurements of β-delayed proton emitters in the region of 100Sn. Phys. Rev. C, 112(3), 034310–18pp.
Abstract: An experiment on neutron-deficient nuclei in the region of doubly magic 100Sn was carried out at the Radioactive Ion Beam Factory (RIBF) at the RIKEN Nishina Center in Japan. N Z 50 nuclei were produced following fragmentation of an intense primary 124Xe beam and implanted in the Advanced Implantation Detector Array silicon setup for the first study of proton-rich nuclei with this system at RIKEN. Measurements of the f-delayed proton emitter decay half-lives, branching ratios and proton energy spectra of nuclei in the region of 100Sn were performed, with improved precision in many cases. New results for the energy spectrum of 101Sn are presented, where a 2.03(5)-MeV peak was observed. These results are compared to shell-model calculations, using the recent precise measurement of the 101In proton separation energy are presented.
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