Analysis of Nuclear Lifetimes Using the Gamma-ray Induced Doppler Shift Attenuation Method

Lifetime measurements allow extraction of fundamental information on the nature of the excited states of a nuclear system. Since nuclear lifetimes cover many orders of magnitude, a number of experimental techniques and detection setups have been developed depending on the range of the lifetime of interest. The Gamma-ray Induced Doppler Shift Attenuation (GRIDSA) Method presented here is applied to the measurement of very short lifetimes, in the femtosecond range. It allows determining the nuclear lifetime by measuring the Doppler shift of a gamma ray emitted from the state of interest, in different directions with respect to a coincident preceding gamma ray, populating the same state and inducing a recoil of the nucleus in the target material with velocities of the order of 104-105 m/s. We realized an experiment in order to test the GRIDSA technique for the measurement of fs lifetimes after (n,\u3b3) reactions. The measurement was performed at the Institut Laue-Langevin (ILL) with the 8 Ge-clover detectors of the FIPPS array. Preliminary results are discussed

Study of the pygmy dipole resonance in 124Sn with AGATA

The \u3b3 decay of the pygmy dipole resonance of 124Sn was measured with the AGATA demonstrator coupled to an array of 9 large volume LaBr3:Ce scintillators. This resonance was populated by the inelastic scattering reaction 17O+124Sn at 20 MeV/u. With AGATA, the \u3b3 decay up to the neutron separation energy was measured with high resolution. The angular distribution was measured both for the \u3b3 rays and the scattered 17O ions. The present results are presented in comparison with the previous findings for (\u3b3, \u3b3') and (\u3b1,\u3b1'\u3b3)

Isospin mixing in Zr 80: from finite to zero temperature

S. Ceruti et al.; 5 págs.; 4 figs.; PACS numbers: 24.30.Cz, 24.60.Dr, 24.80.+y, 25.70.GhThe isospin mixing was deduced in the compound nucleus Zr80 at an excitation energy of E∗=54 MeV from the γ decay of the giant dipole resonance. The reaction Ca40+Ca40 at Ebeam=136 MeV was used to form the compound nucleus in the isospin I=0 channel, while the reaction Cl37+Ca44 at Ebeam=95 MeV was used as the reference reaction. The γ rays were detected with the AGATA demonstrator array coupled with LaBr3:Ce detectors. The temperature dependence of the isospin mixing was obtained and the zero-temperature value deduced. The isospin-symmetry-breaking correction δC used for the Fermi superallowed transitions was extracted and found to be consistent with β-decay data.This work was supported by PRIN No. 2001024324_01302, the Polish National Center for Science Grants No. 2013/08/ M/ST2/00591 and No. 2011/03/B/ST2/01894, and the Spanish Grant No. FPA2011-29854-C04-01. German Bundesministerium für Bildung und Forschung (BMBF) under Contract No. 05P12PKFNE TP4.Peer Reviewe

Position sensitivity in 3 × 3 LaBr3:Ce scintillators

The position sensitivity in a 33 LaBr 3:Ce crystal has been simulated using collimated beams of medium and high energy -rays. The simulations have been done using the GEANT4 libraries which allow to follow both the gamma ray interaction in the detector and the scintillation light up to the photocathode. In the simulations the crystal has been coupled to an ideal PSPMT and/or a shielded PMT. The results indicate that in the 3 3 crystal with darkened surfaces it should be possible to localize the first interaction point of a 662 keV gamma ray within 1 cm, in the case of diffusive surfaces the position sensitivity deteriorates but it is not destroyed. As expected, the position sensitivity improves as the -ray energy increases. The measurements generally confirm the results given by simulations. \ua9 2010 IEEE

Pygmy dipole resonance in Ce 140 via inelastic scattering of O 17

M. Krzysiek et al. ; 8 págs.; 7 figs. ; 2 tabs.The γ decay from the high-lying states of Ce140 excited via inelastic scattering of O17 at a bombarding energy of 340 MeV was measured using the high-resolution AGATA-demonstrator array in coincidence with scattered ions detected in two segmented ΔE-E silicon detectors. Angular distributions of scattered ions and emitted γ rays were measured, as well as their differential cross sections. The excitation of 1- states below the neutron separation energy is similar to the one obtained in reactions with the α isoscalar probe. The comparison between the experimental differential cross sections and the corresponding predictions using the distorted-wave Born approximation allowed us to extract the isoscalar component of identified 1- pygmy states. For this analysis the form factor obtained by folding microscopically calculated transition densities and optical potentials was used. ©2016 American Physical SocietyThis work has been partly supported by the stipend from Marian Smoluchowski Krakow Research Consortium ’Matter-Energy-Future’ as a Leading National Research Center (KNOW) and also by several grants: the Polish National Science Centre under Contracts No. 2015/17/B/ST2/01534, No. 2013/09/N/ST2/04093, No. 2013/08/M/ST2/00591, and No. 2011/03/B/ST2/01894; US-NSF Grants No. PHY-1204486 and No. PHY-1404343; Croatian Science Foundation under Project No. IP-2014-09-9159; the Spanish Ministerio de Economía y Competitividad under Contract No. FPA2014-57196-C5-4-P. Also, A. Gadea has been supported by MINECO, Spain, under Grant No. FPA2014-57196-C5; Generalitat Valenciana, Spain, under Grant No. PROMETEOII/2014/019; and the EU under the FEDER program. The research leading to these results has also received funding from the European Union Seventh Framework Programme FP7/2007-2013 under Grant Agreement No. 262010 - ENSAR.Peer Reviewe

Contrasting properties of particle-particle and hole-hole excitations in 206Tl and 210Bi nuclei

A complete-spectroscopy investigation of low-lying, low-spin states in the one-proton-hole and one-neutron-hole nucleus 206Tl has been performed by using thermal neutron capture and \u3b3-coincidence technique with the FIPPS Ge array at ILL Grenoble. The new experimental results, together with data for the one-proton-particle and one-neutron-particle nucleus 210Bi (taken from a previous study done at ILL in the EXILL campaign), allowed for an extensive comparison with predictions of shell-model calculations performed with realistic interactions. No phenomenological adjustments were introduced in the calculations. In 210Bi, state energies, transition multipolarities and decay branchings agree well with theory for the three well separated multiplets of states which dominate the low-lying excitations. On the contrary, in 206Tl significant discrepancies are observed: in the same energy region, six multiplets were identified, with a significant mixing among them being predicted, as a consequence of the smaller energy separation between the active orbitals. The discrepancies in 206Tl are attributed to the larger uncertainties in the determination of the off-diagonal matrix elements of the realistic shell-model interaction with respect to the calculated diagonal matrix elements, the only ones playing a major role in the case of 210Bi. The work points to the need of more advanced approaches in the construction of the realistic interactions

(n,γ) reactions on rare Ca isotopes: Valence-hole - Coreexcitation couplings in47Ca

Recent results on the structure of 47Ca will be presented. The nucleus of interest was populated via the cold-neutron capture 46Ca(n,\u3b3) reaction, on a rare 46Ca target, during the EXILL experimental campaign at the nuclear reactor of Institut Laue- Langevin in Grenoble. High-resolution \u3b3-ray spectroscopy, performed with a composite array of HPGe detectors, enabled the identification of new transitions deexciting states between the neutron-capture level and the ground state. Experimental data will be compared with a novel microscopic theoretical model, currently under development, specifically designed to describe the low-lying structure of odd-mass nuclei with one valence particle/hole outside a spherical doubly-magic core, using the Skyrme effective interaction self-consistently

Characterization of Large Volume 3.5″ x 8″ LaBr3:Ce Detectors for the HECTOR+ array

A selection of the properties of large volume, cylindrical 3.5" x 8" LaBr 3 :Ce scintillation detectors coupled to a 3.5" PMT (model R10233-1000SEL from HAMAMATSU) and a special designed Voltage Divider (LABRVD) will be discussed. A number of 10 of such detectors constitute the HECTOR + array which, in fall 2012, measured at GSI coupled to the AGATA DEMOSTRATOR at the PRESPEC experimental setup. These crystals are among the largest ever produced and needed to be characterized. We have performed several tests and here we discuss, in particular, the energy resolution measured using monochromatic γ −ray sources and in-beam reactions producing γ −rays up to 22.6 MeV. As already measured in two previous works a saturation in the energy resolution was observed in case of high energy gamma rays. Crystal non-homogeneities and PMT gain drifts can affect the resolution of measurements especially in case of high energy γ −rays

Characterization of segmented HPGe detectors using Pulse Shape Comparison methods

In this work we present the first results of a detector characterization technique named Pulse Shape Comparison Scan (PSCS), applied to a large volume segmented HPGe detector of the AGATA array. The experimental data were collected with the Liverpool University scanning system. Processing two sets of singles scan data acquired with a 137Cs (662 keV) gamma collimated source (with the collimation lines perpendicular one in respect to the other), it has been possible to extract the position response of 4 detector segments. \ua9 2010 IEEE

g-factor measurements of isomeric states in 174W

This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.ISBN: 978-88-7438-101-2; International audience; The experimental setup GAMIPE used for gyromagnetic factormeasurements at Laboratori Nazionali di Legnaro and a recent experimentalwork regarding K-isomers in 174W are described. Aim ofthe experiment is to study the detailed structure of the isomeric stateswave functions, by the measurement of the magnetic dipole moments.This piece of information can provide interesting hints for theoreticalmodels. Preliminary results concerning the population of the isomersof interest and half-lives are presented