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Classical novae are thermonuclear explosions in stellar binary systems, and important sources of $^{26}$Al and $^{22}$Na. While gamma rays from the decay of the former radioisotope have been observed throughout the Galaxy, $^{22}$Na remains untraceable. The half-life of $^{22}$Na (2.6 yr) would allow the observation of its 1.275 MeV gamma-ray line from a cosmic source. However, the prediction of such an observation requires good knowledge of the nuclear reactions involved in the production and destruction of this nucleus. The $^{22}$Na($p,\gamma$)$^{23}$Mg reaction remains the only source of large uncertainty about the amount of $^{22}$Na ejected. Its rate is dominated by a single resonance on the short-lived state at 7785.0(7) keV in $^{23}$Mg. In the present work, a combined analysis of particle-particle correlations and velocity-difference profiles is proposed to measure femtosecond nuclear lifetimes. The application of this novel method to the study of the $^{23}$Mg states, combining magnetic and highly-segmented tracking gamma-ray spectrometers, places strong limits on the amount of $^{22}$Na produced in novae, explains its non-observation to date in gamma rays (flux < 2.5x$10^{-4}$ ph/(cm$^2$s)), and constrains its detectability with future space-borne observatories., Comment: 18 pages, 3 figures, 1 table

International audience; In this work, we will present the characterization, in terms of gamma response and internal activity of newly developed crystals that contains Lanthanum in their chemical formula. In particular we tested two LaBr 3 :Ce,Sr, one CLLBC and two CLLB crystals with different volumes. These crystals just overcome the prototype stage and, even if the production in still not standardized at least for large optics, they have been very recently commercialized in sizes interesting for high-energy gamma-ray spectroscopy, as for application in nuclear physics experiments. In particular, we will report on the study of the decay time, light yield and energy resolution with gamma rays, on the response as a function of the gamma interaction point and on the internal activity due to the presence of Lanthanum.

In this paper, we present a silicon photomultiplier (SiPM)-based photodetector module designed to readout large cerium-doped lanthanum bromide (LaBr3:Ce) scintillators (cylindrical 1” $\times$ 1” and 2” $\times$ 2”) for nuclear physics experiments. The detector prototype has a modular structure and implements a real-time stabilization of the SiPM gain to compensate for the gain drift with temperature. The SiPM module consists of an array of 5 by 6 near-ultraviolet high-density SiPMs (Fondazione Bruno Kessler, Italy), each one having an active area of 6 mm $\times$ 6 mm and 30- $\mu \text{m}$ microcells. The single array is used for the 1” crystal readout, and it is assembled in a $2{\times} 2$ format to read the 2” scintillator. Spectroscopic measurements were performed with both crystals. The 2” crystal was irradiated with different radioactive sources in an energy range between 122 keV and 1.3 MeV, and an energy resolution of 3.19 ± 0.01% full-width at half-maximum (FWHM) has been achieved at 662 keV. The result is very close to the 3.07 ± 0.03% FWHM measured with Super Bialkali photomultiplier tube (PMT) (Hamamatsu R6233-100) at the same energy with the same 2” crystal. In the framework of the comparison between SiPM and PMT for LaBr3:Ce readout, we provide an analysis of the energy resolution contributions based on the measurements performed with the developed gamma-ray detection system.

The fast neutrons produced by a calibrated 241Am-Be source were detected by two different Cs2LiYCl6:Ce (CLYC) scintillator detectors. The two cylindrical crystals (1''× 1'' in size) were enriched with more than 99% of 7Li (C7LYC) and with about 95% of 6Li (C6LYC), respectively. Both crystals can detect fast neutrons whereas only C6LYC can also detect thermal neutrons, due to the presence of 6Li. The measurement was performed at the L.A.S.A . Laboratory of INFN and University of Milano (Italy). To identify the neutron events, the Pulse-Shape-Discrimination technique was used. The values of 1.41 ± 0.16 for C6LYC and 1.16 ± 0.21 for C7LYC for the detection efficiency of the 241Am-Be emitted neutrons, with energy up to 10 MeV, were deduced.

We present a SiPM-based gamma-ray detection module, which allows to read large LaBr 3 :Ce cylindrical crystals (diameter > 1”), typically adopted in nuclear physics experiments, with spectroscopic performances similar to those achievable with PMTs. High-Density SiPM technology for Near UltraViolet and blue light detection (NUV-HD, Fondazione Bruno Kessler, Italy) were used. These SiPMs show high Photo Detection Efficiency (PDE = 45% at 380 nm) and low Dark Count Rate (DCR 3 :Ce irradiated with 57C, 133Ba, 137Cs and 60Co calibration sources. An energy resolution of 3.19 ± 0.01% was achieved at 662 keV with 2” LaBr 3 :Ce. The same crystal was tested with a Super Bialkali PMT (Hamamatsu R6233-100) showing a similar energy resolution of 3.07 ± 0.03% at 662 keV. Therefore, these results support the equivalence between SiPM and PMT for high-resolution spectroscopy.

K. Hadyńska-Kl¸ek et al. ; 7 pags., 3 figs., 2 tabs., Shape parameters of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in Ca42 were determined from E2 matrix elements measured in the first low-energy Coulomb excitation experiment performed with AGATA. The picture of two coexisting structures is well reproduced by new state-of-the-art large-scale shell model and beyond-mean-field calculations. Experimental evidence for superdeformation of the band built on 02+ has been obtained and the role of triaxiality in the A∼40 mass region is discussed. Furthermore, the potential of Coulomb excitation as a tool to study superdeformation has been demonstrated for the first time. © 2016 American Physical Society, Special gratitude goes to the INFN LNL and HIL Warsaw technical staff for their support and help, in particular, the accelerator crews for providing intense and good-quality 42Ca and 32S beams. K. H.-K. acknowledges support from the Research Council of Norway under the project Grant No. 213442. T. R. R. acknowledges computing time at GSI-Darmstadt and support from Spanish MINECO under Programa Ramon y Cajal 11420 and FIS-2014-53434-P, H. N. acknowledges support from Helmholtz Association through the Nuclear Astrophysics Virtual Institute NAVI (No. VH-VI-417). We also acknowledge the support by Generalitat Valenciana, Spain, under the grant PROMETEOII/2014/019 and by the FEDER funds of the European Commission (A. Gadea), Spanish Ministerio de Economía y Competitividad under Contract No. FPA2014-57196-C5 (A. J., A. Gadea), German Bundesministerium für Bildung und Forschung (BMBF) under Contract No. 05P12PKFNE TP4 (B. Birkenbach), the Polish National Science Centre under Projects No. DEC-2013/10/M/ST2/00427, No. DPN/N190/ AGATA/2009, No. 2011/03/B/ST2/01894, No. UMO- 2014/14/M/ST2/00738 (COPIN-INFN Collaboration), and No. 2015/17/B/ST2/01534.

The crystal Cs2LiYCl6:Ce (CLYC) is a very interesting scintillator material because of its excellent energy resolution and its capability to identify gamma rays and fast/thermal neutrons. In this work, the response to gamma, thermal and fast neutrons of two CLYC 1x1 crystals was measured: the first one, enriched with 6Li at 95% is ideal for thermal neutron measurements while the second one, enriched with 7Li at 99% is suitable for fast neutron measurements. The crystals were coupled to quartz window R6231-1000MOD HAMAMATSU PMTs. The thermal neutrons were measured in both detectors using an AmBe source in the gamma spectroscopy laboratory of the University of Milano, Italy. The measurements of fast neutrons were performed at Frascati (Italy) Neutron Generator facility providing neutrons of 14.1 MeV and 2.5 MeV. © 2014 IEEE.

The Pulse Shape Analysis algorithm “Recursive Subtraction” has been applied to data acquired during the in-beam tests of two different highly segmented HPGe detectors. This algorithm processes the net charge signal, determining the number of interactions per segment and their radial coordinates. The RS algorithm performances are evaluated by comparing the results obtained following its application to experimental pulse shapes with those obtained with specific GEANT simulations. Excellent agreement is found between the experimental distribution of the number of interactions per segment and the simulated one. Deviations between experimental radial distribution and the calculated ones are discussed.

The first excited 2+2+ state of 36Ca has been identified by its γ -decay, exploiting the two-step fragmentation technique at the FRS-RISING setup at GSI. This is the heaviest Tz=−2Tz=−2 nucleus in the Segré chart in which a γ-decay of an excited state has been observed. A stable beam of 40Ca at View the MathML source420AMeV impinged on a primary 9Be target. Out of the secondary beam of fragmentation products, 37Ca was separated by the FRS and struck on a second 9Be target at the final focus of the FRS. The energy for the View the MathML source21+ decay of 36Ca was determined to be 3015(16) keV, which is 276 keV lower than in its T=2T=2 mirror 36S. This mirror energy difference (MED) is discussed in the framework of shell model calculations using a 16O core, the sd shell isospin symmetric interaction USD and experimental single-particle energies from 17O and 17F. The results show that the MED within the sd shell provide a sensitive test for the evolution of the N , Z=14,16Z=14,16 subshell gaps towards the driplines. Especially the N , Z=16Z=16 gap is determined by Thomas–Ehrman shift in the A=17A=17, T=1/2T=1/2 isospin doublet, while Coulomb effects are found to have marginal influence. ispartof: Physics Letters B vol:647 issue:4 pages:237-242 status: published

A. Wendt et al. ; 1 pag. ; PACS number(s): 21.10.Hw, 23.20.Js, 25.70.De, 27.30.+t, 99.10.Fg

The LaBr3:Ce scintillator offers the unique opportunity to study the β− radioactive decay of 138La, that is a 2nd order unique forbidden transition. The 138La isotope is one of the rarest isotopes on earth (it is present as 0.09% in natural Lanthanum) and because of its extremely long lifetime, of the order of 1011 years, large amounts of 138La are needed for the measurement of the β− decay spectrum. In literature, only one experimental measurement is present and the results are not reproduced by the standard nuclear theory. A second measurement of the β− continuum is presented in this work. For this measurement, two LaBr3:Ce scintillators (3″ × 3″) and two different experimental techniques were used. The shape of the β− continuum spectrum, measured down to the energy of 2–3 keV, is found to be identical to the one previously measured and published. On the other side, it is different from the theoretical published spectrum in particular below 75 keV.

A fast gateless pulse stretcher has been developed for an easy acquisition of pulse-shape information of BaF/sub 2/ scintillator signals. Commonly, this information is obtained by the use of two QDCs with different integration windows. This technique becomes complex and rather inconvenient when signals need to be delayed. The developed circuit uses a fast-stretcher technique to generate pulse-shape information, which requires no delay lines or gate signals. The outputs consist of two Gaussian signals whose amplitudes are proportional to the height of the BaF/sub 2/ fast component and to the total energy deposited into the scintillator. These outputs are easily acquired with a standard peak ADC with no gate-timing problems. An excellent Fast-Slow separation has been obtained even with small input signals of only few millivolts. This technology is general purpose and can be used with any other scintillator whose light emission is characterized by two components with different lifetimes.

Matière Nucléaire; International audience; The gamma decay of the nuclei 124,125Ba has been investigated with the EUROBALL array, using the reaction 64Ni+64 Ni at E_{beam} = 255 and 261 MeV. Six new E1 transitions have been found in the nucleus 125Ba, suggesting a significant role of octupole correlations in the origin of its parity doublets. The pi = 3-level of the nucleus 124Ba has been identified for the first time. Its excitation energy is in very good agreement with a prediction based on a microscopic model including octupole interactions.

The first excited 2 + states in 54,56,58Cr were populated by Coulomb excitation at relativistic energies and γ rays were measured using the RISING setup at GSI. For 56Cr and 58Cr the B ( E2 , 2 1 + → 0 + ) values relative to the previously known B ( E 2 ) value for 54Cr are determined as 8.7(3.0) and 14.8(4.2) W.u., respectively. The results are consistent with a subshell closure at neutron number N = 32 which was already indicated by the higher energy of the 2 1 + state in 56Cr. Recent large-scale shell model calculations using effective interactions reproduce the trend in the excitation energies, but fail to account for the minimum in the B ( E 2 ) values at N = 32 .

The Rare ISotopes INvestigation at GSI project combines the former EUROBALL Ge-Cluster detectors, the MINIBALL Ge detectors, BaF2--HECTOR detectors, and the fragment separator at GSI for high-resolution in-beam gamma-ray spectroscopy measurements with radioactive beams. These secondary beams produced at relativistic energies are used for Coulomb excitation or secondary fragmentation experiments in order to explore the nuclear structure of the projectiles or projectile like nuclei by measuring de-excitation photons. The newly designed detector array is described and the performance characteristics are given. Moreover, particularities of the experimental technique are discussed.

The nuclear system at the limit of excitation energy and angular momentum is here studied in the case of the superdeformed nucleus 143 Eu using $\gamma$ -spectroscopy techniques. The data are based on a EUROBALL experiment using the reaction 37 Cl + 110 Pd $\to^{143}$ Eu + 4n. The influence of thermal energy on superdeformed configurations is investigated through the analysis of the quasi-continuum spectra formed by E2 transitions among states of excited rotational bands with energy extending up to 4-5 MeV above the yrast line. In particular, the effective lifetimes of the discrete rotational bands forming ridge structures in $\gamma$ - $\gamma$ coincidence matrices is measured by a Doppler Shift Attenuation Method. The deduced quadrupole deformation of $Q_t \approx$ 10 eb indicates that the nucleus maintains its collectivity with increasing excitation energy, supporting the superdeformed character of the excited nuclear rotation. The obtained number of superdeformed discrete bands forming the ridge structures is found in good agreement with microscopic cranked shell model calculations including the decay-out process into the lower deformation minimum. In addition, the nuclear properties at higher excitation energies are investigated through the E1 $\gamma$ -decay of the giant dipole resonance (GDR). It is found that the intensity of the superdeformed yrast and excited bands increases by a factor of approximately 1.6 when a coincidence with a high-energy $\gamma$ -ray is required, showing the importance of the E1 cooling in the feeding mechanism of the superdeformed states.

Spectra of the yrast and excited superdeformed bands, forming the E2 quasi-continuum, are measured with the EUROBALL array for the nucleus 143 Eu, in coincidence with high-energy γ-rays (Eγ>3 MeV). It is found that the intensity population of the superdeformed states is enhanced by a factor of ≈1.6 when a coincidence with a γ-ray with energy >6 MeV is required, in reasonable agreement with the increase of the line shape of the Giant Dipole Resonance built on a superdeformed configuration. This result shows that when an high energy E1 γ-ray is involved in the decay it is more likely connected with a SD rather than a ND nucleus. In addition, the analysis of the rotational quasi-continuum suggests the presence of a superdeformed component. The data are also compared and found consistent with simulation calculations of the relative intensities of the SD states, including the E1 decay of superdeformed nature.

A study of the performance of a cylindrical HPGe detector segmented in 25 segments is presented. It is based on simulations made with the computer code GEANT and focuses on the reconstruction of a γ-ray path. The effects of the segmentation are initially discussed in terms of Doppler correction. The role of the pulse shape analysis and its effects on tracking algorithms are discussed as a function of the capability to reconstruct a γ-ray path when multiple signals (direct and induced) are present in a single segment. It is found that it is critical to identify correctly at least two signals in a segment in order to have a reasonable efficiency and Compton suppression in the spectra and to make a good use of this type of detectors.

Reduced transition strengths of the deexciting transitions from the first two excited states in 33Ar were measured in a relativistic Coulomb excitation experiment at the GSI Helmholtz center. The radioactive ion beam was produced by fragmentation of a primary 36Ar beam on a 9Be target followed by the selection of the reaction product of interest via the GSI Fragment Separator. The 33Ar beam hit a secondary 197Au target with an energy of approximately 145 MeV/nucleon. An array of high-purity germanium cluster detectors and large-volume BaF2 scintillator detectors were employed for γ -ray spectroscopy at the secondary target position. The Lund-York-Cologne Calorimeter was used to track the outgoing ions and to identify the nuclear reaction channels. For the two lowest energy excited states of 33Ar the reduced transition strengths have been determined. With these first results the Tz = −3/2 nucleus 33Ar is now, together with 21Na (Tz = −1/2), the only neutron-deficient odd-A sd shell nucleus in which experimental transition strengths are available. The experimental values are compared to results of shell-model calculations which describe simultaneously mirror-energy differences and transition-strength values of mirror pairs in the sd shell in a consistent way

An unexpected enhancement in the low-energy part of the γ-strength function for light and medium-mass nuclei has been discovered at the Oslo Cyclotron Laboratory. This enhancement could lead to an increase in the neutron-capture rates up to two orders of magnitude for very exotic, neutron-rich nuclei. However, it is still an open question whether this structure persists when approaching the neutron drip line. © Owned by the authors, published by EDP Sciences, 2014., SCOPUS: cp.p, info:eu-repo/semantics/published

The high-energy γ-rays from the GDR decay of 147Eu*, produced in the reaction 37Cl+110Pd at bombarding energy of 160 and 170 MeV, were measured in coincidence with discrete transitions in residual nuclei and analyzed with statistical model using a Monte Carlo approach. It is found that the present analysis gives information on the moment of inertia at very high spins in different residual nuclei.

High-spin properties of the nucleus 169Hf have been studied through the fusion evaporation reaction 96Zr(76Ge,3n)169Hf at a beam energy of 310 MeV. The known rotational bands have been extended considerably and 6 new bands have been established, four of which form coupled bands with pronounced M1 connections. Quasiparticle assignments are suggested for the new band structures, and it appears that coupling to vibrational degrees of freedom plays a role. Both coupled bands involve the excitation of quasiprotons. In the region of highest spin, a large alignment gain is interpreted in terms of a mixed crossing where an h 9/2 and an h 11/2 quasiproton provide the two signatures of the aligning configuration.

The problems with reconstructing the trajectory of /spl gamma/-rays and identifying their interaction points in segmented coaxial HPGe detectors are discussed here in view of their importance in the design of the next generation of detector arrays for /spl gamma/-ray spectroscopy studies. In fact, the tracking quality of the /spl gamma/-ray interactions in the medium controls the overall detection efficiency. This paper focuses on two main points. One is the study of how the tracking reconstruction efficiency is affected by the ability of disentangling multiple interactions per segment. The other is the study of the consequences that different types of segmentation have on the overall efficiency. Two geometries have been chosen: that of a single cylindrical detector and that of a spherical shell.

Three superdeformed (SD) bands have been found in 168Hf. Lifetime measurements revealed a large quadrupole moment, Q t ∼11.4 e b , for the strongest band (TSD1). Theoretical calculations using the Ultimate Cranker code predict high-spin SD minima (ϵ2∼0.43) with stable triaxial deformations of γ∼+20° and γ∼−15°. The measured Qt value suggests that band TSD1 corresponds, most likely, to a deformation with a positive γ value. This constitutes the first evidence for triaxial superdeformation in an even proton system.

Results from the measurement of the GDR built on excited states of the 147Eu compound nucleus are presented. Data corresponding to restricted regions of angular momenta and more selected data, associated with different residual nuclei are discussed. The behaviour of the GDR width, measured as a function of nuclear spin and temperature, is well described by the predictions of the thermal shape fluctuation model.

A measurement of the response to 15.1 MeV c-rays has been made for the Ge cluster detectors in the EUROBALL array. Each cluster detector consists of seven germanium capsules surrounded by a single anticompton shield of BGO. The reaction D(11B,c)12C# na tE "%!. "19.1 MeV has been employed. The ‘adding-backa of signals simultaneously present in the capsules composing each cluster detector has been made on an event by event basis. The intensity in full-energy peak increases by a factor of three as compared to that of the spectrum obtained by summing the individual spectra of the 7 capsules. The pulse height to energy conversion is found to be very linear from few hundreds keV to 15 MeV. The e$ciency is discussed relative to that of large volume BaF 2 scintillators. ( 2000 Elsevier Science B.V. All rights reserved.

Unresolved γ transitions of 114 Te and of 112 Sn sorted into one-dimensional and two-dimensional spectra have been studied. The reaction 64 Ni + 54 Cr at bombarding energies 230, 240, 250, 260, 270 MeV was used and the γ -rays were detected with the EUROBALL array. In the case of the nucleus 114 Te the values of the multiplicity as a function of bombarding energy and of the moment of inertia were obtained. The effective moment of inertia was found to be almost constant in the interval I=20 – 40 ℏ , in contrast to the decreasing behaviour of the dynamic moment of inertia for the terminating yrast band. The ridge valley structures in E γ 1 ×E γ 2 spectra of 114 Te and of 112 Sn were analysed with the fluctuation analysis technique. The analysis of the two nuclei are compared to simulations based on microscopic cranking calculations with residual interactions included. A rather good agreement is found between data and predictions.

Unresolved $\ensuremath{\gamma}$ rays of ${}^{114}\mathrm{Te}$ sorted into one- and two-dimensional spectra were studied. The reaction ${}^{64}\mathrm{Ni}({E}_{\mathrm{beam}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}230--270\mathrm{MeV}){+}^{54}\mathrm{Cr}$ was used and the $\ensuremath{\gamma}$ rays were detected with the EUROBALL array. The effective moment of inertia for the quasicontinuum was found to be almost constant for $I\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(20--40)\ensuremath{\Elzxh}$, in contrast with the decreasing behavior of the terminating yrast band. A comparative analysis with the nucleus ${}^{164}\mathrm{Yb}$ is presented and the results from a fluctuation analysis were compared with cranked shell model calculations. The comparison shows consistency in the scaling of the rotational damping width with mass number.

The lifetime of the unresolved transitions forming the rotational quasi-continuum spectra has been measured in 164 Yb using the Doppler shift attenuation method. The valley structure in E γ 1 × E γ 2 spectra was analysed using a new technique, based on fluctuation patterns, which provided for the first time experimental lifetimes for rotational damped transitions. The present results show, as predicted by the rotational damping model, that the collectivity persists for highly excited bands. In particular, agreement is found between the experimental results, for discrete and damped transitions, and the predictions corresponding to Q t = 5.5 eb, for the entire interval of γ-ray energies studied.

The γ-decay of the GDR in hot Hg and Eu isotopes has been measured in coincidence with selected low-energy γ-transitions of the evaporation residues. In the Hg case, the GDR width at finite temperature and at different spins was studied by analyzing simultaneously with the statistical model the high-energy γ-ray spectra associated with different residual nuclei and the fractions of residue cross-sections. The measured GDR width was found in good agreement with the predictions of the thermal fluctuations model. In the case of Eu, we have measured the high-energy γ-rays in coincidence with low-energy γ-transitions from different nuclear configurations of 143 Eu in order to search for the GDR decay built on a superdeformed state. The analysis of the data shows a possible evidence of this state. The measured intensity indicates that the superdeformation survives only few MeV above the yrast line.

The lifetime of the unresolved transitions forming the rotational quasi-continuum spectra has been measured in 163 Tm using the Doppler shift attenuation technique. Spectra associated to different values of the coincidence folds, angular anisotropies and the dynamical moment of inertia were also obtained from the present experiment. The Doppler shift has been measured for discrete transitions, for the ridge structures in E γ 1 × E γ 2 spectra and for the rotational E2 bump in one dimensional spectra. The data were compared to the theory using a simulation model which makes use of microscopically calculated levels and transition probabilities. Above 1300 keV the results indicate collectivity with lifetime faster than 10 −14 s, while at lower E γ the results are well described by predictions with B (E2) = 400 WU.

Using the (18O,5n) 163Er reaction a multitude of rotational bands have been established with firm spin and parity assignments in 163Er. In 17 out of 24 band crossings E2 cross-band transitions have been observed. The interaction strength varies between ∼ 1 and ∼ 50 keV with many of the values in the range 10–15 keV. These interactions sample a variety of the lowest (multi) -quasiparticle configurations. For some bands, in particular those with high K-values, the configurations can be established rather well. Quite complicated changes in the wavefunctions must occur at these crossings, and to explain the observed interaction strengths coupling to various vibrational degrees of freedom, in addition to possible residual neutron-proton interactions, may be needed.

Here, the γ-ray strength function of 56Fe has been measured from proton-γ coincidences for excitation energies up to ≈11 MeV. The low-energy enhancement in the γ-ray strength function, which was first discovered in the (3He,αγ)56Fe reaction, is confirmed with the (p,p'γ)56Fe experiment reported here. Angular distributions of the γ rays give for the first time evidence that the enhancement is dominated by dipole transitions.

The damping mechanisms of the giant dipole resonance at finite temperature T and rotational frequency ω are investigated by studying the GDR lineshape of 167 Er associated with a very narrow interval of excitation energy (of the order of 6 MeV) at T = 1.3 MeV. The strength function data can be reproduced either assuming collisional damping width equal to T = 0 and adiabatic thermal fluctuations or assuming a larger collisional damping without thermal fluctuations. The measurement of the angular distribution of the high energy gamma rays rules out the second possibility.

The study of damping of rotational motion applying te rotational plane mapping (RPM) method is presented and discussed. The aim of this technique is to extract the distribution of the rotational transition strength from an analysis of the shape of the “central valley” of two- and three-dimensional γ-ray spectra. The method is applied to a triple γ-coincidence data set of 162,163Tm nuclei formed in 37Cl+130Te reactions. The rotational transition strength is obtained as a function of rotational frequency for selected regions of entry states, and the width is found to be rather constant and approximately equal to 80 keV. This value is significantly smaller than the value predicted theoretically for the rotational damping width Γrot. Also the ratio between the observed depth and width of both the 2D and 3D valleys does not agree with the simple model adopted in the RPM method. These discrepancies point to the presence of both a wide and a narrow component in the distribution of rotational strength as extracted by the RPM method. The analysis of simulated spectra obtained on the basis of realistic band-mixing calculations, including residual interactions, confirms this behaviour.

Experimental investigations of the giant dipole resonance at finite temperature provide new insight into different properties of hot rotating nuclei. Here we discuss the studies aiming at the understanding of the role of thermal and quantal fluctuations in the measured GDR width. We also present the first studies of the properties of super-heavy nuclei through the γ-decay of the GDR in the hot compound prior to fission.

A flexible general purpose data acquisition system based on VME standard modules has been designed for laboratory setup and for small and medium size nuclear physics experiment. The system is composed of a VME crate (housing different kind of front-end modules, TDC, ADC, CFD, Scaler..) and a personal computer physically connected to the hardware with a gigabit PCI to VME interface optical fiber. VME transactions are handled by a DSP server sequencer that collects data from front-end modules and organizes them in formatted buffers that are read by a complete application based on a Kmax environment. Data saving, on line sorting as well as slow control are possible through an efficient graphical user interface. Diagnostic functions and error report messages are also available to detect hardware failures or incorrect setting for the used modules. Integration in a more complex data acquisition system has been already performed in several experiment performed in different laboratories (i.e. LNL, GSI).

New materials with very high light yield and short scintillation decay time have been developed in the past few years: e.g. Cerium doped Lanthanum Bromide (LaBr 3 :Ce), Europium doped Strontium Iodide (SrI 2 : Eu).

Neutron-rich Co isotopes from N = 34 to 40 were studied through multinucleon transfer by bombarding a 238U target with a 460 MeV 70Zn beam at LNL. Gamma-recoil coincidences were recorded identifying the ions by a high-acceptance magnetic spectrometer (PRISMA) and detecting the gamma radiation by an array of HPGe clover detectors (CLARA). The results are discussed in comparison with the predictions of large-scale shell-model calculations.

Measurements of the angular distribution of high energy γ rays emitted in the decay of compound nuclei 165–167 Er, 175,176 Hf, 110 Sn at E ∗ = 50–90 MeV and I ≤ 40 are presented. In all cases the measured anisotropies as a function of the gamma transition energy are small. The compound nuclei were formed with heavy ion fusion reactions and the high energy y rays were detected by the HECTOR array. A comparison between the data and model predictions shows that both shape and orientation fluctuations are very important and must be taken into account to reproduce the experimental results. The dominant role played by orientation fluctuations on the GDR lineshape and the effective induced nuclear deformations are discussed.

Angular distributions of photons associated with the damping of excited-state giant dipole resonances (GDR) in hot and rotating 161,162 Yb nuclei have been measured in exclusive experiments using the HECTOR array. In reactions with heavy ions ( 48 T) angular distributions are determined as a function of the angular momentum of the compound nuclei. In reactions with lighter ions ( 17,18 O) a difference method is applied to isolate GDR decays originating from specific excitation regions. The systematics of the measured angular distributions as a function of excitation energy and angular momentum are compared to theories taking into account fluctuations of the shape and orientation of the excited nuclei.

A study of the strength function and of the angular distribution of the gamma rays from the giant dipole resonance in hot rotating Sn nuclei is presented. The two GDR observables (spectrum and angular distribution) were measured at the nuclear temperature T ∼ 2 MeV for several different angular momentum intervals of the compound nucleus. The data were obtained with the HECTOR detector array that includes a 38 element multiplicity filter. Data are compared to model predictions of adiabatic thermal fluctuations of shape and orientation angles. A satisfactory agreement is found with the exception of the angular anisotropy at the higher rotational frequencies. The systematics of angular momentum dependence of the GDR width and of the a 2 ( E γ ) suggests a constant spreading width at this temperature.

The huge amount of optical photons emitted in burst by Cerium doped Lanthanum bromide scintillators poses a severe constraint on the specifications of photomultipliers, namely they must operate at very large instantaneous current values with minimum saturation of output pulse signals. Acquisition in shape and processing of photomultipliers output pulses by means of high-speed free-running analog to digital converters and processing devices allows specific correction for pulse saturation and distortion effects, due to high-gain tubes operated at relatively high power supply voltage. We analyze the effects of output signal saturation in photomultiplier tubes as a function of the high voltage level and the amount of energy released in the scintillator crystal, proposing a simple model to characterize this complex phenomenon. According to the proposed model, a preliminary first-order correction is calculated and applied to the energy estimations obtained by a traditional analog spectroscopy system, for energies up to 9 MeV, reducing the maximum estimation error by almost an order of magnitude.

The angular distribution of the high energy gamma rays emitted in the decay of the giant dipole resonance from hot rotating atomic nuclei of 109,110Sn has been determined as a function of the angular momentum of the compound nucleus. A strong increase in the amplitude of the angular distribution coefficient as a function of the angular momentum is observed, which is at variance with the predictions of an adiabatic model at finite temperature and frequency.

The angular distribution of the high energy gamma rays emitted in the decay of the giant dipole resonance built on excited states, in mainly 162Yb, has been measured using a differential technique to enhance decays originating from the highest region of nuclear temperatures. A simple formalism to analyze such data is presented. Such experiments provide information on the shapes and orientation distribution of atomic nuclei at finite temperature.

Developments in the study of the gamma decay of Giant Dipole Resonances (GDR) in hot nuclei are discussed. The main emphasis here is on experiments and theoretical efforts aimed at understanding the average shapes and fluctuations of the shapes of excited nuclei from studies of the angular distribution of the high energy gamma rays emitted when Giant Dipole Resonances in nuclei with large thermal energy decay.

The strongly shape driving πh9/2[541]l/2− configuration with α=+1/2 exhibits some anomalous, and so far unexplained, features concerning the crossing frequency, ħωc, the aligned angular momentum, ix, and interaction strength, at the alignment of the first pair of i13/2 quasineutrons in several odd-Z rare earth-nuclei. The h9/2[541]1/2− and h11/2[523]7/2− bands have been studied in the stably deformed rare-earth nucleus163Tm to investigate these features. A difference in band crossing frequency of ∼ 80 keV between the two bands is found. Rotational bands built on these two configurations have been found to cross in the spin range I=25/2–29/2 ħ. Theγ-decay pattern between the two bands is established in the crossing region and analysed in terms of a moderate shape difference between them. A theoretical estimate of the size of the interaction strength between the two bands is presented and compared to the experimental value. The observed band structure in163Tm is very similar to that of167Lu which has 2 protons and 2 neutrons in addition. This observation is discussed in relation to the similarity of the yrast bands of the two even-even “core” nuclei162Er and166Yb, for which theγ-transition energies are identical within ∼0.2 keV below the vi13/2 crossing.

Two new rotational bands of distinct character have been identified in 164 Hf. They are suggested to correspond to the long-anticipated triaxial strongly deformed (TSD) bands predicted by theoretical studies. The bands have been linked to known states, and the level spins and energies could be determined. The bands are also substantially stronger in intensity and are located at lower spins than the previously observed TSD bands in 168 Hf, hereby making 164 Hf the best even-even system so far for the study of TSD structures in the A ∼ 160 mass region. Cranking calculations based on the modified-oscillator model suggest that the bands are associated with four-quasiparticle configurations that involve high-j intruder (i13/2) 2 proton orbitals.

The feasibility of the entire process of γ -ray tracking is demonstrated experimentally for the first time. The accuracy of the results is verified by the capability to carry out a Doppler correction of γ -rays emitted in flight. The resolution of the 846.8 keV transition detected with the MARS detector after Coulomb excitation of a 56 Fe beam could be improved from approximately 16 up to 4.6 keV (FWHM). This result corresponds to an obtained position resolution of about 6 mm (FWHM).