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Abstract: An experimental study was carried out on the neutron response functions of two neutron detector arrays consisting of 39 3He proportional counters with a polyethylene moderator for monoenergetic neutrons within the 0.39–1.54MeV neutron energy range. Experimental data on the sensitivity of neutron counting to a change in neutron energy and the influence of the thickness of polyethylene moderator were obtained. The experimental efficiency curves were compared with the calculated response functions generated by a neutron transport code. [Copyright &y& Elsevier]

A survey of experimental results obtained at GANIL (Caen, France) on the study of the properties of very neutron-rich nuclei (Z=6 – 20, A=20 – 60) near the neutron drip line and resulting in an appearance of further evidence for the new magic number N=16 is presented. Very recent data on mass measurements of neutron-rich nuclei at GANIL and some characteristics of binding energies in this region are discussed. Nuclear binding energies are very sensitive to the existence of nuclear shells, and together with the measurements of instability of doubly magic nuclei [sup 10]He and [sup 28]O, they provide information on changes in neutron shell closures of very neutron-rich isotopes. The behavior of the two-neutron separation energies S[sub 2n] derived from mass measurements gives very clear evidence for the existence of the new shell closure N=16 for Z=9 and 10 appearing between the 2s[sub 1/2] and 1d[sub 3/2] orbitals. This fact, strongly supported by the instability of C, N, and O isotopes with N>16, confirms the magic character of N=16 for the region from carbon up to neon, while the shell closure at N=20 tends to disappear for Z≤13. Decay studies of these hardly accessible short-lived neutron-rich nuclei from oxygen to silicon using in-beam γ-ray spectroscopy are also reported.© 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The paper presents a review of experimental results obtained at GANIL and FLNR Dubna on the study of the particle stability of neutron-rich nuclei near the neutron drip line. Very recent data on mass measurements of neutron-rich nuclei in the range A=29–47 at GANIL and some characteristics of binding energies in this region are presented. Nuclear binding energies are very sensitive to the existence of shells and provide clear signatures of shell closures. Experiments have been mostly performed in cooperation GANIL–Orsay–Dubna–Rˇezˇ–Bucharest–Liverpool. [Copyright &y& Elsevier]

We present a review of experimental studies on the properties of extremely neutronrich nuclei ( Z=6–20, A=20–60) near the neutron drip line. Recent data on mass measurements of neutron-rich nuclei at GANIL (Caen, France) and some characteristics of binding energies in this region are discussed. Being sensitive to the existence of nuclear shells separation energies S2 n together with the evidence of particle instability of doubly magic nuclei 10He and 28O could provide information on changes in shell closures. Particularly opening of an N=16 shell and vanishing of the N=20 shell for very neutron-rich isotopes is under discussion. Decay studies of these hardly accessible short-lived neutronrich nuclei from oxygen to silicon using the in-beam γ-ray spectroscopy are also reported. [ABSTRACT FROM AUTHOR]

A new level scheme of 80Ga has been determined. This nucleus was populated following the β- decay of 80Zn at ISOLDE, CERN. The proposed level scheme is significantly different compared to the previously reported one and contains 26 levels up to 3.4 MeV in excitation energy. The present study establishes that the previously identified 1.9-s β- -decaying 6- isomer is the ground state of 80Ga and the 1.3-s ¿8 "-decaying 3" isomer lies at an excitation energy of 22.4 keV. A new isomeric level was identified at 707.8 keV and its half-life was measured to be 18.3(5) ns, allowing the 685.4-keV transition de-exciting this state to be assigned an Ml multipolarity. The newly measured spectroscopic observables are compared with shell-model calculations using the jj44bpn and JUN45 interactions. [ABSTRACT FROM AUTHOR]

The cross section for the knock-out of a deeply bound valence neutron from 37Ca at an incident beam energy of 60A MeV has been measured along with momentum distributions of the residual nuclei and y rays from the de-excitation of the first excited state in 36Ca. As for other cases of deeply bound nucléons studied using knock-out reactions, the reduction of the measured cross section compared to theoretical predictions is stronger than those observed for near-magic stable nuclei. Both the momentum distributions and the excitation energy of the first excited state in 36Ca indicate a sizable N = 16 gap. [ABSTRACT FROM AUTHOR]

Abstract: Mass measurements of very neutron-rich nuclei near the and 28 shell closures are presented. Seven masses have been determined for the first time and the precision of 36 masses has been significantly improved. These results are used to investigate the evolution of the odd–even staggering of binding energies with neutron number. Special attention is paid to the evolution of the shell closure as the neutron dripline is approached. Changes in shell structure are observed around for the P and S isotopes but not for Si. This may be interpreted as a persistence of the shell closure at or as the result of a very sudden onset in deformation at 42Si. [Copyright &y& Elsevier]

An experiment was performed to study excited states in neutron-deficient nuclei around Ca. After a first fragmentation of the primary beam, the one-neutron knockout reaction was used to produce 36Ca ions from the 37Ca secondary beam and in-beam γ rays were measured. The energy of the first excited 2+ state in 36Ca and the cross section for the 1-neutron knock-out reaction from 37Ca at ≈ 45A MeV were obtained. The 2+ energy in 36Ca is compared to the mirror nucleus 36S to deduce information on the isospin dependence of the nuclear force near the proton drip line. Furthermore, for two other Tz = -2 nuclei, 28S and 32Ar, the deexcitation of the first 2+ states has been observed. [ABSTRACT FROM AUTHOR]

In-beam γ-spectroscopy using fragmentation reactions of radioactive beams have been performed in order to study the structure of excited states in neutron rich oxygen and carbon isotopes. For the produced fragments, γ-ray energies, intensities and γ-γ coincidences have been measured. The experiment was performed at GANIL. New γ-lines have been identified and placed in level schemes for 17-20C. The non observation of any γ-ray in 23,24O suggests that their first excited states lie above the neutron threshold. These results are discussed in the framework of shell model calculations. [Copyright &y& Elsevier]

The neutron drip line in the neon–magnesium region has been explored by the projectile fragmentation of a [sup 48]Ca (59.8 A MeV) beam using the new fragment separator LISE-2000 at GANIL. New neutron-rich isotopes, [sup 34]Ne and [sup 37]Na, have been observed together with some evidence for the particle instability of [sup 33]Ne and [sup 36]Na.© 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

A setup for studying reactions induced by secondary radioactive beams has been constructed. It allows simultaneous measurement of α-particle and fission fragment energy spectra. By measuring the α particles, identification of evaporation residues is achieved. A set of three targets can be used so as to ensure sufficient statistics. Two silicon detectors, located at 90° to the secondary beam direction, face each target, thus covering 30% of the solid angle. This experimental setup is to be used to obtain excitation functions of fusion–fission reactions and of reactions leading to evaporation residue production.© 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

We have studied the structure of light neutron-rich nuclei around N = 16 by employing the in-beam γ-ray spectroscopy technique using the fragmentation of secondary beams of 25,26Ne, 27,28Na and 29,30Mg isotopes. This secondary-beam "cocktail" was obtained by the fragmentation of a 36S beam at 77.5 MeV A by the SISSI/GANIL facility. By a second-step fragmentation, we have measured &gama;-ray- residue coincidences in 17-20C and 23,24 and described the obtained levels in the framework of the shell model. [ABSTRACT FROM AUTHOR]