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An experiment was performed to extend the knowledge of excited states in neutron-deficient Ca isotopes.
In particular, the first excited state in 36Ca was searched for to obtain information on the isospin dependence of the nucleon-nucleon interaction near the proton drip line from a comparison with its stable mirror nucleus, 36S.
 The 36Ca ions were produced using a two-step fragmentation technique with a 37Ca secondary beam, and in-beam γ-rays were measured.
 First results are the energy of the first 2+state in 36Ca, E(2+)=3036(11) keV, and the cross section for the reaction 37Ca → 36Ca at 61.A MeV.
In addition, the de-excitaion of the first 2+state in 28S has been observed.

Following mass measurements in the region N= 20 and N= 28, we have studied inelastic nuclear scattering for the nuclei 34Si, 33Al and 32Mg. No evidence for a low-lying shape isomeric 0+state was found in 34Si, and an upper limit for the population cross-section could be established, rendering its existence very unlikely. A new transition was found in 33Al, that is a good candidate for a 2p-2h state and therefore a determination of the 2p-2h gap at N= 20. Inelastic nuclear scattering strongly excites 3-states, as seen in 34Si. A strong transition was found in 32Mg that should correspond to the first 3-in this nucleus, lying very low as compared to theory and systematics in this region.

The neutron drip line in a neon–magnesium region has been explored by the projectile fragmentation of a 59.8 A MeV ⁴⁸Ca beam using the new fragment separator LISE 2000 at GANIL. New neutron-rich isotopes, ³⁴Ne and ³⁷Na, have been observed together with some evidence for the particle instability of ³³Ne and ³⁶Na.

A mass measurement experiment by a time of flight method with the SPEG spectrometer at GANIL has been performed to investigate the N=20 and N=28 shell closures far from stability. The masses of 31 neutron-rich nuclei in the range A=29–47 have been measured. The precision of 19 masses has been significantly improved and 12 masses were measured for the first time. The neutron-rich Cl, S and P isotopes are seen to exhibit a change in shell structure around N=28. Comparison with shell model and relativistic mean field calculations demonstrate that the observed effects arise from deformed prolate ground state configurations associated with shape coexistence. The evidence of an isomeric state in the 43S and its interpretation by a shell model calculation confirm the analysis of the masses and constitutes the first evidence of the predicted shape coexistence around N=28.

Six quasi-stationary states of 13Be populated in the 14C(11B,12N) 13Be reaction at Elab= 190 MeV are reported. A Q-value = −39.60(9) MeV and a mass excess, M.E.= 33.95(9) MeV, have been found for the lowest observed spectral line. The ground state is unstable with respect to one-neutron emission by 0.80(9) MeV. Excitation energies of 1.22(10), 2.10(16), 4.14(12), 5.09(14) and 7.0(2) MeV have been obtained for the observed spectral lines.

A multiparameter system designed to measure as many as six parameters of a single fission event on line with an EC 1010 computer is described. The kinematics of emitted fragments and the calibration of light particle and fragment spectra are discussed. Fragment energy spectra from the thermal neutron induced fission of235U have been measured. Results of light particle emission from spontaneous fission of252Cf and from neutron induced fission of235U are presented.

The LRA particles energy spectrum from ternary thermal neutron induced fission of235U has been measured. A nonshielded semiconductor telescope technique has been used. The experimental spectrum has been fitted by the Gaussian distribution with average alpha energy of 15·65 ±0·09 MeV and full width at half maximum of 9·56±0.10 MeV.

The fluctuations of uranium X-rays yield in coincidence with fission of the235U nucleus were observed at several neutron resonances. The results show the dependence ofKα1 yield on fission widthΓf. This dependence is explained by the (n, γf) process which is the result of competition between fission and γ-decay during the deexcitation of the236U compound nucleus. The mean width 〈Γf〉 was determined to be equal to (2·1

The measurement of X-rays emitted before the fission of235U induced by resonance neutrons is described. Preliminary results show the dependence of the X-ray yield on fission widthΓf. It is explained on the bases of the existence of the two-step (n,γf) process. The estimate of the width of the (n,γf) process is of the order of 4 MeV and theγ-transitions taking place before fission of236U compound nucleus are mostly of the M1 type.

The alpha particle spectra from ternary fission of U235 have been investigated in the thermal and the resonance neutron energy regions. The resonance neutrons have been obtained by passing the reactor neutron flux through a boron filter. A silicon surface barrier detector telescope technique for alpha particle detection has been used. In the resonance neutron energy region the ratio af/Gf< has been found to be 1·02 ± 0·2 times the value of ?af/?f in the thermal region. The non-gaussian tail of the LRA energy distribution has been observed.

The cross section of the149Sm(n, a) reaction for several alpha transitions has been measured. Using an arrangement where only the target is situated in the beam while the detector is placed in some distance aside, the influence of a high background has been successfully eliminated. A detailed analysis of the background has been performed. The obtained resolution in the alpha particle energy (FWHM=65 keV) makes it possible to distinguish seven transitions for which average cross sections for the thermal neutron spectrum withT= 400 °K have been evaluated.

Abstract.: An experiment was performed to extend the knowledge of excited states in neutron-deficient Ca isotopes. In particular, the first excited state in 36Ca was searched for to obtain information on the isospin dependence of the nucleon-nucleon interaction near the proton drip line from a comparison with its stable mirror nucleus, 36S. The 36Ca ions were produced using a two-step fragmentation technique with a 37Ca secondary beam, and in-beam γ-rays were measured. First results are the energy of the first 2+ state in 36Ca, E(2+)=3036(11) keV, and the cross section for the reaction 37Ca → 36Ca at 61.A MeV. In addition, the de-excitaion of the first 2+ state in 28S has been observed.