S. Andriamonje

β-delayed proton radioactivity of 44Cr, 47Mn, 48,49Fe and 50Co

Abstract The proton-rich nuclei 44 Cr, 47 Mn, 48,49 Fe and 50 Co have been produced by fragmentation of a 58 Ni beam at 650 MeV/u. The isotopic separation of these nuclei has been achieved with the GSI Projectile-Fragment Separator FRS. The isotopes have been identified in flight by ΔE -ToF- Bϱ measurements. After implantation in a stack of seven silicon detectors, the signals measured for implantation and radioactive decay were unambiguously correlated in time due to low counting rates. On the basis of the two proton peaks observed for 50 Co at (2034±30) keV and (2740±41) keV with a half-life of (44±4) ms, a partial decay scheme is proposed for this nucleus. A single proton peak at (959±33) keV was observed for 48 Fe with a half-life of (44±7) ms. This emission is attributed to the decay of the T = 2 isobaric analog state in 48 Mn. No deviation from the quadratic form of the isobaric multiplet mass equation is observed. Additional information on β-delayed proton branches of 49 Fe, 44 Cr and 47 Mn was also obtained.

Neutron radiative capture cross section of

Abstract The neutron capture cross section of 232Th has been measured relative to σ(n, γ) for 197Au and σ(n,f) for 235U in the energy range from 60 keV to 2 MeV. Neutrons were produced by the 7Li(p,n) and T(p,n) reactions at the 4-MV Van de Graaff Accelerator of CEN Bordeaux-Gradignan. The activation technique was used, and the cross section was measured relative to the 197Au(n,γ) standard cross section up to 1 MeV. The characteristic gamma lines of the product nuclei 233Pa and 198Au were measured with a 40% high-purity germanium detector. Above this energy, the reaction 235U(n,f) was also used as a second standard, and the fission fragments were detected with a photovoltaic cell. The results, after applying the appropriate corrections, indicate that the cross sections are close to the JENDL-3 database values up to 800 keV and over 1.4 MeV. For energies in the intermediate range, our values are slightly lower than those from all the libraries.

^{232}

Abstract In an experiment at the LISE3 facility of GANIL, we produced the proton-rich isotope 22Al by the fragmentation of a 36Ar primary beam at 95 MeV/nucleon. After implantation in a detector telescope, the decay of 22Al via β-delayed proton emission, β-delayed two-proton emission as well as, for the first time, via β-delayed α emission has been studied. An α peak has been observed at (3.27 ± 0.04) MeV with a branching ratio of (0.31 ± 0.09) %. The comparison of the different decay channels to those of the mirror nucleus 22F and to shell-model calculations favor a 3+ state as being the ground state of 22Al. A half life of T1/2 = (59 ± 3) ms has been measured.

Th in the energy range from 0.06 to 2 MeV

Abstract In an experiment at the LISE3 facility of GANIL, we used the projectile fragmentation of a 36 Ar primary beam at 95 MeV/nucleon to produce neutron-deficient isotopes in the Al-Si region. The selected isotopes were implanted in a detector telescope, where their decay particles were observed. We report here on the study of the βp, β2p, and βα decay of the isotopes 22,23,24 Si and 22 Al. Beta-decay half-lives have been measured. The ground-state mass excess of 23 Si has been determined. Partial decay schemes are presented on the basis of the transitions associated with the observed decay peaks.

The spectroscopy of 22Al: a βp, β2p and βα emitter

Abstract Two new isomeric states in the self-conjugate nucleus 66 As have been observed at the final focus of the LISE3 spectrometer at GANIL. The nucleus has been produced in a fragmentation reaction of 78 Kr at 73A MeV. The 66 m 1, m 2 As isomeric levels are placed at excitation energies of E ∗m1 =3023.9 keV and E ∗m2 =1356.7 keV. Half-lives of T 1/2 m 1 =17.5(15) μ s and T 1/2 m 2 =1.9(5) μ s have been measured for the isomers and a decay scheme has been established.

Beta-p,-2p,-alpha spectroscopy of 22,23,24Si and 22Al

Abstract In an experiment at the LISE3 facility of GANIL, we used the projectile fragmentation of a 36 Ar primary beam at 95 MeV/nucleon to produce the isotope 24 Si. The beta decay half-life of 24 Si has been determined to be T 1/2 = (140 ± 8) ms, in agreement with earlier measurements. In addition to the decay of the isobaric analog state, several proton peaks are observed for the first time allowing to identify most of the Gamow-Teller transitions to unbound states and to present a partial decay scheme for 24 Si. These results are compared with shell-model predictions.

Isomeric states in 66As

Abstract In an experiment at the SISSI/LISE facility of GANIL, we produced proton-rich isotopes in the selenium-to-strontium region by projectile fragmentation of a 78 Kr primary beam at 73 MeV/nucleon. The emission of β-delayed protons from 67 Se, 71 Kr, and 75 Sr was observed for the first time and the corresponding branching ratios were determined. The proton energy spectra were compared to predictions of a statistical model. The half-lives of 67 Se, 71 Kr, and 75 Sr were deduced from the time characteristics of the observed proton activity. The half-life of 75 Sr was measured for the first time. For 67 Se and 71 Kr, the obtained half-lives are compared to previous measurements.

Beta-delayed proton spectroscopy of 24Si

Abstract A method for measuring the cross sections for the neutron removal from relativistic secondary projectiles by means of a two-stage magnetic spectrometer is presented. Its application to the 1n- and 2n-removal from 56 Ni and 52 Fe at 470 A ·MeV in an aluminum target is described. The results are compared to the intranuclear-cascade plus evaporation model and to the statistical abrasion-ablation model. The influence of the nuclear surface on the few-nucleon removal reactions is discussed. The neutron-removal cross sections are combined with total charge-changing cross sections to obtain the total interaction cross sections of 56 Ni and 52 Fe.

β-delayed proton emission from the proton-rich isotopes 67Se, 71Kr, and 75Sr

Abstract Two aspects of heavy ion channeling are presented. The first aspect is related to the fact that channeled ions interact only with the most loosely bound target electrons. One can take benefit of this feature to study processes such as radiative electron capture (REC) and resonant transfer and excitation (RTE) in a dense quasi-free electron gas. The experimental work, performed at GANIL, devoted to these two processes is described. A possible extension to Nuclear RTE or NEEC (nuclear excitation by electron capture) studies is also described. The second aspect discussed is related to the periodicity of the potential experienced by channeled ions. We show that in a well chosen case this could lead to a significant and detectable coherent excitation of the projectile nucleus.

One- and two-neutron removal from the radioactive secondary projectiles 56Ni and 52Fe

β-delayed one- and two-proton and α spectroscopic studies of the neutron-deficient nuclei 22,23,24Si and 22Al produced in projectile fragmentation of a 36Ar primary beam at 95 MeV/u have been performed at GANIL. Isotopes of interest were analyzed using the LISE3 spectrometer and were implanted in a telescope made of silicon detectors and a micro-strip gaseous counter where decay particles were detected.