The BRIKEN Project: extensive measurements of ß-delayed neutron emitters for the astrophysical r process

An ambitious program to measure decay properties, primarily ß-delayed neutron emission probabilities and half-lives, for a significant number of nuclei near or on the path of the rapid neutron capture process, has been launched at the RIKEN Nishina Center. We give here an overview of the status of the project.Postprint (published version

Conceptual design of the BRIKEN detector: A hybrid neutron-gamma detection system for nuclear physics at the RIB facility of RIKEN

BRIKEN is a complex detection system to be installed at the RIB-facility of the RIKEN Nishina Center. It is aimed at the detection of heavy-ion implants, ß-particles, ¿-rays and ß-delayed neu- trons. The whole detection setup involves the Advanced Implantation Detection Array (AIDA), two HPGe Clover detectors and a large set of 166 counters of 3He embedded in a high-density polyethy- lene matrix. This article reports on a novel methodology developed for the conceptual design and optimisation of the 3He-tubes array, aiming at the best possible performance in terms of neutron detection. The algorithm is based on a geometric representation of two selected parameters of merit, namely, average neutron detection efficiency and efficiency flatness, as a function of a reduced num- ber of geometric variables. The response of the detection system itself, for each configuration, is obtained from a systematic MC-simulation implemented realistically in Geant4. This approach has been found to be particularly useful. On the one hand, due to the different types and large number of 3He-tubes involved and, on the other hand, due to the additional constraints introduced by the ancillary detectors for charged particles and gamma-rays. Empowered by the robustness of the al- gorithm, we have been able to design a versatile detection system, which can be easily re-arranged into a compact mode in order to maximize the neutron detection performance, at the cost of the gamma-ray sensitivity. In summary, we have designed a system which shows, for neutron energies up to 1(5) MeV, a rather flat and high average efficiency of 68.6%(64%) and 75.7%(71%) for the hybrid and compact modes, respectively. The performance of the BRIKEN system has been also quantified realistically by means of MC-simulations made with different neutron energy distributions.Postprint (published version

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

Measuring the ß-decay Properties of Neutron-rich Exotic Pm, Sm, Eu, and Gd Isotopes to Constrain the Nucleosynthesis Yields in the Rare-earth Region

The ß-delayed neutron-emission probabilities of 28 exotic neutron-rich isotopes of Pm, Sm, Eu, and Gd were measured for the first time at RIKEN Nishina Center using the Advanced Implantation Detector Array (AIDA) and the BRIKEN neutron detector array. The existing ß-decay half-life (T1/2) database was significantly increased toward more neutron-rich isotopes, and uncertainties for previously measured values were decreased. The new data not only constrain the theoretical predictions of half-lives and ß-delayed neutron-emission probabilities, but also allow for probing the mechanisms of formation of the high-mass wing of the rare-earth peak located at A ˜ 160 in the r-process abundance distribution through astrophysical reaction network calculations. An uncertainty quantification of the calculated abundance patterns with the new data shows a reduction of the uncertainty in the rare-earth peak region. The newly introduced variance-based sensitivity analysis method offers valuable insight into the influence of important nuclear physics inputs on the calculated abundance patterns. The analysis has identified the half-lives of 168Sm and of several gadolinium isotopes as some of the key variables among the current experimental data to understand the remaining abundance uncertainty at A = 167–172.Peer ReviewedPostprint (published version

Advances and new ideas for neutron-capture astrophysics experiments at CERN n_TOF

The version of record of this article, first published in [The Europen Physics Journal A], is available online at Publisher’s website: http://dx.doi.org/10.1140/epja/s10050-022-00876-7This article presents a few selected developments and future ideas related to the measurement of (n,¿) data of astrophysical interest at CERN n_TOF. The MC-aided analysis methodology for the use of low-efficiency radiation detectors in time-of-flight neutron-capture measurements is discussed, with particular emphasis on the systematic accuracy. Several recent instrumental advances are also presented, such as the development of total-energy detectors with ¿ - ray imaging capability for background suppression, and the development of an array of small-volume organic scintillators aimed at exploiting the high instantaneous neutron-flux of EAR2. Finally, astrophysics prospects related to the intermediate i neutron-capture process of nucleosynthesis are discussed in the context of the new NEAR activation areaPeer ReviewedArticle escrit per 139 auors/autores C. Domingo-Pardo, V. Babiano-Suarez, J. Balibrea-Correa, L. Caballero, I. Ladarescu, J. Lerendegui-Marco, J. L. Tain, A. Tarifeño-Saldivia, O. Aberle, V. Alcayne, S. Altieri, S. Amaducci, J. Andrzejewski, M. Bacak, C. Beltrami, S. Bennett, A. P. Bernardes, E. Berthoumieux, M. Boromiza, D. Bosnar, M. Caamaño, F. Calviño, M. Calviani, D. Cano-Ott, A. Casanovas, F. Cerutti, G. Cescutti, S. Chasapoglou, E. Chiaveri, N. M. Chiera, P. Colombetti, N. Colonna, P. Console Camprini, G. Cortés, M. A. Cortés-Giraldo, L. Cosentino, S. Cristallo, S. Dellmann, M. Di Castro, S. Di Maria, M. Diakaki, M. Dietz, R. Dressler, E. Dupont, I. Durán, Z. Eleme, S. Fargier, B. Fernández, B. Fernández-Domínguez, P. Finocchiaro, S. Fiore, F. García-Infantes, A. Gawlik-Ramięga , G. Gervino, S. Gilardoni, E. González-Romero, C. Guerrero, F. Gunsing, C. Gustavino, J. Heyse, W. Hillman, D. G. Jenkins, E. Jericha, A. Junghans, Y. Kadi, K. Kaperoni, F. Käppeler, G. Kaur, A. Kimura, I. Knapová, U. Köster, M. Kokkoris, M. Krtička, N. Kyritsis, C. Lederer-Woods, G. Lerner, A. Manna, T. Martínez, A. Masi, C. Massimi, P. Mastinu, M. Mastromarco, E. A. Maugeri, A. Mazzone, E. Mendoza, A. Mengoni, P. M. Milazzo, I. Mönch, R. Mucciola, F. Murtas, E. Musacchio-Gonzalez, A. Musumarra, A. Negret, A. Pérez de Rada, P. Pérez-Maroto, N. Patronis, J. A. Pavón-Rodríguez, M. G. Pellegriti, J. Perkowski, C. Petrone, E. Pirovano, J. Plaza, S. Pomp, I. Porras, J. Praena, J. M. Quesada, R. Reifarth, D. Rochman, Y. Romanets, C. Rubbia, A. Sánchez, M. Sabaté-Gilarte, P. Schillebeeckx, D. Schumann, A. Sekhar, A. G. Smith, N. V. Sosnin, M. Stamati, A. Sturniolo, G. Tagliente, D. Tarrío, P. Torres-Sánchez, J. Turko, S. Urlass, E. Vagena, S. Valenta, V. Variale, P. Vaz, G. Vecchio, D. Vescovi, V. Vlachoudis, R. Vlastou, T. Wallner, P. J. Woods, T. Wright, R. Zarrella, P. ŽugecPostprint (published version

miniBELEN: a modular neutron counter for (a, n) reactions

miniBELEN is a modular and transportable neutron moderated counter with a nearly flat neutron detection efficiency up to 10 MeV. Modularity implies that the moderator can be reassembled in different ways in order to obtain different types of response. The detector has been developed in the context of the Measurement of Alpha Neutron Yields (MANY) collaboration, which is a scientific effort aiming to carry out measurements of (a, n) production yields, reaction cross-sections and neutron energy spectra. In this work we present and discuss several configurations of the miniBELEN detector. The experimental validation of the efficiency calculations using 252Cf sources and the measurement of the 27Al(a, n) 30P reaction is also presented.This work has been supported by the Spanish Ministerio de Economía y Competitividad under grants FPA2017-83946- C2-1 & C2-2 and PID2019-104714GB-C21 & C22, the Generalitat Valenciana Grant PROMETEO/2019/007, both cofounded by FEDER (EU), and the SANDA project funded under H2020-EURATOM-1.1 Grant No. 847552. The authors acknowledge the support from Centro de Microanálisis de Materiales (CMAM) - Universidad Autónoma de Madrid, for the beam time proposal (Comissioning of neutron detector systems for (a,݊n) reaction measurements) with code P01156, and its technical staff for their contribution to the operation of the accelerator.Article signat per 41 autors/es: N. Mont-Geli, A. Tarifeño-Saldivia, L.M. Fraile, S. Viñals, A. Perea, M. Pallàs, G. Cortés, E. Nácher, J.L. Tain, V. Alcayne, A. Algora, J. Balibrea-Correa, J. Benito, M.J.G. Borge, J.A. Briz, F. Calviño, D. Cano-Ott, A. De Blas, C. Domingo-Pardo, B. Fernández, R. Garcia, G. García, J. Gómez-Camacho, E.M. González-Romero, C. Guerrero, J. Lerendegui-Marco, M. Llanos, T. Martínez, E. Mendoza, J.R. Murias, S.E.A. Orrigo, A. Pérez de Rada, V. Pesudo, J. Plaza, J.M. Quesada, A. Sánchez, V. Sánchez-Tembleque, R. Santorelli, O. Tengblad, J.M. Udías and D. Villamarín.Postprint (published version

Neutron capture reactions on Fe and Ni isotopes for the astrophysical s-process

Neutron capture cross sections in the keV neutron energy region are the key nuclear physics input to study the astrophysical slow neutron capture process. In the past years, a series of neutron capture cross section measurements has been performed at the neutron time-of-flight facility n TOF at CERN focussing on the Fe/Ni mass region. Recent results and future developments in the neutron time-of-flight technique are discussed.Postprint (published version

Estudi de les propietats de desintegració de nuclis del Ba a Nd (A~160) rellevants per a la formació del pic de terres rares del procés r

Half-lifes (T1/2) of exotic neutron-rich isotopes of Ba, La, Ce, Pr, and Nd were measured at the RIKEN Nishina Center. The experimental setup consisted of the BigRIPS in-flight separator for ion selection identification, the Advance Implantation Detector Array (AIDA) for ions and ß detection, and the BRIKEN detector for neutron counting. Using this setup, 4 new T1/2 have been measured for the first time, and 38 T1/2 have been remeasured with improved precision in several cases. These new experimental data should help to constrain theoretical models for calculations of T1/2. The status of the experimental analysis and preliminary results are provided in this contribution.This work has been supported by the Spanish Ministerio de Economía y Competitividad under Grants. FPA2014- 52823-C2-1-P, FPA2014-52823-C2-2-P, FPA2017-83946- C2-1-P, FPA2017-83946-C2-2-P and grants from Ministerio de Ciencia e Innovacion PID2019-104714GB-C21, PID2019-104714GB-C22. Supported by Generalitat Valenciana regional grant PROMETEO/2019/007. Supported by European Union FEDER funds. It also has been supported by NKFIH (NN128072).Article signat per 61 autors/es: M. Pallàs, A. Tarifeño-Saldivia, G. G. Kiss, J. L. Tain, A. Tolosa-Delgado, A. Vitéz- Sveiczer, F. Calviño, J. Agramunt, P. Aguilera, A. Algora, J. M. Allmond, H. Baba, N. T. Brewer, R. Caballero-Folch, P. J. Coleman-Smith, G. Cortes, T. Davinson, I. Dillmann, C. Domingo-Pardo, A. Estrade, N. Fukuda, S. Go, C. J. Griffin, R. K. Grzywacz, O. Hall, L. J. Harkness-Brennan, T. Isobe, D. Kahl, T. T. King, A. Korgul, S. Kovács, S. Kubono, M. Labiche, J. Liu, M. Madurga, K. Miernik, F. Molina, N. Mont-Geli, A. I. Morales, E. Nácher, A. Navarro, N. Nepal, S. Nishimura, M. Piersa-Silkowska, V. Phong, B. C. Rasco, J. Romero-Barrientos, B. Rubio, K. P. Rykaczewski, Y. Saito, H. Sakurai, Y. Shimizu, M. Singh, T. Sumikama, H. Suzuki, T. N. Szegedi, H. Takeda, K. Wang, M. Woli´nska-Cichocka, P. J. Woods, and R. Yokoyama for the BRIKEN collaboration.Postprint (published version

Estudi de les propietats de desintegració de nuclis del Ba a Nd rellevants per a la formació del pic de les terres rares del procés r (A~160)

At the RIKEN Nishina Center, exotic neutron-rich isotopes of Ba, La, Ce, Pr, and Nd were measured. This work reports their half-lives (T1/2) and ß-delayed neutron-emission probabilities (Pxn). The setup consisted of the BigRIPS in-flight separator for particle identification, the Advanced Implanta- tion Detector Array (AIDA) for ions and ß detection, and the BRIKEN neutron counter for neutron detection. Using this arrangement, 4 new T1/2 and 14 new P1n were measured. Furthermore, 38 T1/2 and 2 P1n values were remeasured, decreasing the uncertainties for some of them. In addition to improving predic- tions of nucleosynthesis models that describe the production of the rare-earth peak at A~160 via the r-process, these additional experimental data should help to constrain theoretical models for calculations of T1/2 and Pxn in this region.This work has been supported by the Spanish Ministerio de Economía y Competitividad un- der Grants nos. FPA2014-52823-C2-1-P, FPA2014-52823-C2-2-P, FPA2017-83946-C2-1-P, FPA2017-83946-C2-2-P and grants from Ministerio de Ciencia e Innovacion nos PID2019- 104714GB-C21, PID2019-104714GB-C22. It was also supported by NKFIH (NN128072) and by the ÚNKP-22-2 and ÚNKP-22-3 New National Excellence Program of the Ministry for Culture and Innovation from the source of the National Research, Development and In- novation Fund (Project numbers: ÚNKP-22-2-I-DE-75; ÚNKP-22-3-II- DE-132).Article signat per 61 autors/es: M. Pallàs, A. Tarifeño-Saldivia, G. G. Kiss, J. L. Tain, A. Tolosa- Delgado, A. Vitéz-Sveiczer, F. Calviño, J. Agramunt, P. Aguilera, A. Algora, J. M. Allmond, H. Baba, N. T. Brewer, R. Caballero-Folch, P. J. Coleman-Smith, G. Cortes, T. Davinson, I. Dillmann, C. Domingo-Pardo, A. Estrade, N. Fukuda, S. Go, C. J. Griffin, R. K. Grzywacz, O. Hall, L. J. Harkness-Brennan, T. Isobe, D. Kahl, T. T. King, A. Korgul, S. Kovács, S. Kubono, M. Labiche, J. Liu, M. Madurga, K. Miernik, F. Molina, N. Mont-Geli, A. I. Morales, E. Nácher, A. Navarro, N. Nepal, S. Nishimura, M. Piersa- Silkowska, V. Phong, B. C. Rasco, J. Romero-Barrientos, B. Rubio, K. P. Rykaczewski, Y. Saito, H. Sakurai, Y. Shimizu, M. Singh, T. Sumikama, H. Suzuki, T. N. Szegedi, H. Takeda, K. Wang, M. Woli´nska-Cichocka, P. J. Woods, and R. Yokoyama for the BRIKEN collaboration.Postprint (published version