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Nuclear level densities and $\gamma$-ray strength functions of $^{56,57}$Fe have been extracted from proton-$\gamma$ coincidences. A low-energy enhancement in the $\gamma$-ray strength functions up to a factor of 30 over common theoretical E1 models is confirmed. Angular distributions of the low-energy enhancement in $^{57}$Fe indicate its dipole nature, in agreement with findings for $^{56}$Fe. The high statistics and the excellent energy resolution of the large-volume LaBr$_{3}$(Ce) detectors allowed for a thorough analysis of $\gamma$ strength as function of excitation energy. Taking into account the presence of strong Porter-Thomas fluctuations, there is no indication of any significant excitation-energy dependence in the $\gamma$-ray strength function, in support of the generalized Brink-Axel hypothesis., Comment: 24 pages, 17 figures, accepted for publication in J. Phys. G: Nucl. Phys; Special Issue

The CLYC (Cs2LiYC6:Ce) crystal belongs to the elpasolite scintillator family, discovered about 15 years ago. It is a very interesting material because of its good energy resolution and its capability to identify and measure gamma rays and fast/thermal neutrons. In the present work, the fast neutron detection efficiency for two different CLYC cylindrical samples has been measured. These two crystals, both with dimension (thickness x diameter) 1"×1", were respectively enriched with more than 99% of 7Li (CLYC-7) and with ~ 95% of 6Li (CLYC-6). The presence of the 6Li isotope makes the CLYC-6 ideal to detect thermal neutrons. In order to compare the two scintillators, only the detection efficiency for fast neutrons was considered, neglecting the energy region associated to thermal neutrons in both the crystals. The measurement was performed at the L.A.S.A. Laboratory of INFN and University of Milano (Italy), using a 241Am-Be source.

We measured the performance of a 2"×2" tapered cylindrical SrI2:Eu, a 2" × 3" cylindrical CeBr3, a 2" × 0.3" cylindrical GYGAG:Ce. The gamma-ray energy resolution was measured up to 9 MeV. A scan along three axes of each scintillator was performed using a collimated source of 137Cs. The signals of the detectors were also digitized and compared. We tested two 1" × 1" cylindrical CLYC crystals. One was enriched with 6Li at 95% while the other was enriched with 99% of 7Li. The response of the two detectors to gamma rays, thermal and fast neutrons was measured. The PSD performances have been tested with a different types of PMTs.

Scintillation light is often detected by photo-multiplier tube (PMT) technology. PMTs are however intrinsically non linear devices, especially when operated with high light yield scintillators and high input photon flux. Many physical effects (e.g. inter-dynode field variation, photocathode resistivity, etc.) can spoil the ideal PMT behavior in terms of gain, ending up in what are addressed as the under-linearity and over-linearity effects.Established techniques implemented in the PMT base (e.g. increasing bleeding current, active voltage divider, etc.) can mitigate these effects, but given the unavoidable spread in manufacturing and materials, it turns out that, with respect to linearity at the percent level, every PMT sample is a story of its own.The residual non linearity is usually accounted for with polynomial correction of the spectrum energy scale, starting from the position of a few known energy peaks of calibration sources, but uncertainly remains in between of calibration peaks. We propose to retrieve the calibration information from the entire energy spectrum and not only the position of full energy peaks (FEP), by means of an automatic procedure that also takes into account the quality (signal/noise ratio) of the information about the non-linearity extracted from the various regions of the spectrum.

The main aim of this study was a deeper understanding of the nuclear structure properties of the soft dipole modes in 140 Ce, excited via inelastic scattering of weakly bound 17 O projectiles. An important aim was to investigate the ‘splitting’ of the PDR into two parts: a low-energy isoscalar component dominated by neutron-skin oscillations and a higher-energy component lying on the tail of the giant dipole resonance of a rather isovector character. This was already observed for this nucleus, investigated in (α, α′) and (γ, γ′) experiments. The experiment was performed at Laboratori Nazionali di Legnaro, Italy. Inelastic scattering of 17 O ion beam at − 2 0M eV A 1 was

Neutron-rich nuclei beyond N = 126 in the lead region were populated by fragmenting a 238U beam at 1 GeV A on a Be target and then separated by the Fragment Separator (FRS) at GSI. Their isomeric decays were observed, enabling study of the shell structure of neutron-rich nuclei around the Z=82 shell closure. Some preliminary results are reported in this paper.

An experiment aiming at finding evidence for γ-decay of the giant dipole resonance built on superdeformed nuclear states has been made using the EUROBALL γ-detector array coupled to the large BaF2 detectors of the HECTOR system. The reaction 110Pd(37Cl, 4n)143Eu at beam energies of 165 MeV and 170 MeV has been employed. A report of the analysis of a part of the data at Ebeam = 165 MeV is given here. Results based on more inclusive and on very exclusive high-energy γ-ray spectra are presented. In particular, the spectrum of high-energy γ-rays gated by low-energy transitions between states fed by the superdeformed states are found to show some excess of yield in the 9–11 MeV region with respect to the spectrum gated by transitions not fed by the superdeformed states. This is the γ-ray energy region where one expects to find the γ-decay of the giant dipole oscillation along the long axis of a superdeformed axially symmetric nucleus. The measured excess is found to be of the same order as that predicted by schematic statistical model calculations assuming that the excitation of the GDR built on excited states is restricted to a region of the phase space a few MeV above the yrast line at very high spins.