Pulse distributions and tracking in segmented detectors

Abstract 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

Angular distribution of photons from the delay of the GDR in hot and rotating light Yb nuclei from exclusive experiments

Abstract 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

The GDR width in the excited 147 Eu compound nucleus at high angular momentum

Abstract High-energy γ -rays emitted in the decay of the hot compound nucleus 147 Eu have been measured in coincidence with low-energy γ -rays. The γ transitions from the different residual nuclei were detected by a multiplicity filter and by Ge detectors. The employed reaction was 37 Cl + 110 Pd at bombarding energies of 160, 165 and 170 MeV. The measured high-energy γ -ray spectra were analysed within the framework of the statistical model using the Cascade code. The GDR width in the angular momentum interval between 35 and 50 ℏ was found to increase weakly and to be rather well predicted by the thermal shape fluctuation model. Also the deformation parameter β as a function of the average angular momentum extracted from the data was found to be in general agreement with the model

Measurement of 15 MeV γ-rays with the Ge cluster detectors of EUROBALL

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

The rotational γ-continuum in the mass region A≈110

Abstract 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

Effect of E1 decay in the population of superdeformed structures

Abstract 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

Search for 22^{22}Na in novae supported by a novel method for measuring femtosecond nuclear lifetimes

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 tabl

Production de pions sous le seuil dans les reactions induites par des photons de 180 et 201 MeV et des &quot;3He de 283 MeV

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Detection properties and internal activity of newly developed La-containing scintillator crystals

International audienceIn 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