J. Agramunt

Gamow–Teller strength distribution near 100Sn. The beta decay of 102In

One of the main motivations of today’s β-decay studies is to investigate whether the presence of many bound nucleons affects the value of the Gamow—Teller (GT) axialvector coupling constant. The quest for 100Sn is driven by the hope that its particulary simple decay scheme may help to perform improved tests of the models used to calculate the summed GT strength (B GT). Since 100Sn can not yet be produced in sufficient quantity, the experiments are restricted to nearby nuclei. In this paper we report on a study of the β decay of 102In, performed at the GSI Online Mass Separator. This odd—odd nucleus has a very complicated decay scheme and thus represents indeed a great challenge. The loss of numerous weak transitions in high resolution mesurements is suspected to be one of the main reasons for incomplete B GT measurements. Therefore, the experiment with a cube-like array of 6 Euroball Cluster high-resolution germanium detectors (Euroball Cube), with 7 crystals per Cluster, was complemented by the measurement with a total-absorption gamma spectrometer (TAS) [1].

Enhanced γ-Ray Emission from Neutron Unbound States Populated in β Decay.

Total absorption spectroscopy is used to investigate the β-decay intensity to states above the neutron separation energy followed by γ-ray emission in (87,88)Br and (94)Rb. Accurate results are obtained thanks to a careful control of systematic errors. An unexpectedly large γ intensity is observed in all three cases extending well beyond the excitation energy region where neutron penetration is hindered by low neutron energy. The γ branching as a function of excitation energy is compared to Hauser-Feshbach model calculations. For (87)Br and (88)Br the γ branching reaches 57% and 20%, respectively, and could be explained as a nuclear structure effect. Some of the states populated in the daughter can only decay through the emission of a large orbital angular momentum neutron with a strongly reduced barrier penetrability. In the case of neutron-rich (94)Rb the observed 4.5% branching is much larger than the calculations performed with standard nuclear statistical model parameters, even after proper correction for fluctuation effects on individual transition widths. The difference can be reconciled by introducing an enhancement of 1 order of magnitude in the photon strength to neutron strength ratio. An increase in the photon strength function of such magnitude for very neutron-rich nuclei, if it proves to be correct, leads to a similar increase in the (n,γ) cross section that would have an impact on r process abundance calculations.

First measurements with the BEta deLayEd neutron detector (BELEN-20) at JYFLTRAP

A prototype version of the BEta deLayEd Neutron detector, which is being developed for the FAIR/DESPEC experiment, has been used for the first time in an experiment at JYFL (Finland). This detector is based on 3He counters and its first run was primarily intended to commission the detector and verify the working principles for future experiments. A new triggerless DAQ has been developed for these measurements. This DAQ time-stamps the events and allows complete flexibility to construct correlations offline. An isotopically pure beam was obtained using the JYFLTRAP Penning trap setup at the IGISOL facility and it was implanted on a movable tape placed in the centre of the BELEN-20 detector. The measurements were performed for known delayed neutron emitters of interest for nuclear power generation: 88Br, 94,95Rb, 138I. The characteristics of the BELEN-20 detector and the first experiment at JYFL are presented in this paper.

The GT Resonance revealed in β+-Decay using new experimental techniques

Abstract The GT beta decay of 150 Ho has been studied with a Total Absorption Spectrometer (TAS), with an array of 6 Euroball CLUSTER Ge detectors (the CLUSTER CUBE), and with an alpha detector. The three techniques complement each other. The results provide the first observation of an extremely sharp resonance in GT beta decay.

β Decay of the exotic Tz=-2 nuclei Fe 48, Ni 52, and Zn 56

S. E. A. Orrigo, ∗ B. Rubio, Y. Fujita, 3 W. Gelletly, 4 J. Agramunt, A. Algora, 5 P. Ascher, B. Bilgier, B. Blank, L. Cáceres, R. B. Cakirli, E. Ganioğlu, M. Gerbaux, J. Giovinazzo, S. Grévy, O. Kamalou, H. C. Kozer, L. Kucuk, T. Kurtukian-Nieto, F. Molina, 9 L. Popescu, A. M. Rogers, G. Susoy, C. Stodel, T. Suzuki, A. Tamii, and J. C. Thomas Instituto de F́ısica Corpuscular, CSIC-Universidad de Valencia, E-46071 Valencia, Spain Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan Department of Physics, University of Surrey, Guildford GU2 7XH, Surrey, UK Inst. of Nuclear Research of the Hung. Acad. of Sciences, Debrecen, H-4026, Hungary Centre d’Etudes Nucléaires de Bordeaux Gradignan, CNRS/IN2P3 Université de Bordeaux, 33175 Gradignan Cedex, France Department of Physics, Istanbul University, Istanbul, 34134, Turkey Grand Accélérateur National d’Ions Lourds, CEA/DSM CNRS/IN2P3, BP 55027, F-14076 Caen, Cedex 5, France Comisión Chilena de Enerǵıa Nuclear, Casilla 188-D, Santiago, Chile SCK.CEN, Boeretang 200, 2400 Mol, Belgium Physics Division, Argonne National Laboratory, Argonne, Illinois 60439, USA The results of a study of the beta decays of three proton-rich nuclei with Tz = -2, namely Fe, Ni and Zn, produced in an experiment carried out at GANIL, are reported. In all three cases we have extracted the half-lives and the total β-delayed proton emission branching ratios. We have measured the individual β-delayed protons and β-delayed γ rays and the branching ratios of the corresponding levels. Decay schemes have been determined for the three nuclei, and new energy levels are identified in the daughter nuclei. Competition between β-delayed protons and γ rays is observed in the de-excitation of the T = 2 Isobaric Analogue States in all three cases. Absolute Fermi and Gamow-Teller transition strengths have been determined. The mass excesses of the nuclei under study have been deduced. In addition, we discuss in detail the data analysis taking as a test case Zn, where the exotic β-delayed γ-proton decay has been observed.

A triggerless digital data acquisition system for nuclear decay experiments

In nuclear decay experiments an important goal of the Data Acquisition (DAQ) system is to allow the reconstruction of time correlations between signals registered in different detectors. Classically DAQ systems are based in a trigger that starts the event acquisition, and all data related with the event of that trigger are collected as one compact structure. New technologies and electronics developments offer new possibilities to nuclear experiments with the use of sampling ADC-s. This type of ADC-s is able to provide the pulse shape, height and a time stamp of the signal. This new feature (time stamp) allows new systems to run without an event trigger. Later, the event can be reconstructed using the time stamp information. In this work we present a new DAQ developed for β-delayed neutron emission experiments. Due to the long moderation time of neutrons, we opted for a self-trigger DAQ based on commercial digitizers. With this DAQ a negligible acquisition dead time was achieved while keeping a maximum of event information and flexibility in time correlations.

Shapes of Pb-192,Pb-190 ground states from beta-decay studies using the total-absorption technique

8 pags.; 5 figs.; 2 tabs.; PACS number(s): 23.40.Hc, 27.80.+w, 29.30.Kv; Open Access funded by Creative Commons Atribution Licence 3.0

Characterization and performance of the DTAS detector

Abstract 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.

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

In this work we report on the Monte Carlo study performed to understand and reproduce experimental measurements of a new plastic b{eta}-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 {gamma}-ray spectroscopy analysis.

Measurement of very low (alpha,n) cross sections of astrophysical interest

The reactions C-13(alpha,n)O-16 and Ne-22(alpha,n)Mg-25 are the primary sources of neutrons for the astrophysical s-process. The feasibility of cross section measurements within the respective Gamow windows is discussed in quantitative terms for a 4 pi neutron counter, based on He-3 tubes and a neutron moderator, placed in an underground lab.