0000000000115216
AUTHOR
F. Pougheon
Search for forbidden?-decays of the drip line nucleus12Be
Beta-coincidentγ-rays have been measured from implanted pure samples of12Be separated at the LISE3 spectrometer at GANIL. An intensity of 0.040(26) % can be estimated for the branching ratio of the isospin forbidden pure-Fermi transition to the 0+ excited state of12B and of 0.008(6)% of the transition to the 1−1 excited state. Both are taken to represent upper limits. The half-life has been re-measured to be 26.1(2.4) ms.
Radioactivity of neutron-rich oxygen fluorine and neon isotopes
The $\ensuremath{\gamma}$ radiation and neutrons emitted following the $\ensuremath{\beta}$ decays of ${}^{24}\mathrm{O},$ ${}^{25--27}\mathrm{F},$ and ${}^{28\ensuremath{-}30}\mathrm{Ne}$ have been measured. The nuclides were produced in the quasifragmentation of a 2.8 GeV ${}^{36}\mathrm{S}$ beam, separated in-flight and identified through time-of-flight and energy-loss measurements. The ions were stopped in a silicon detector telescope, which was used to detect the $\ensuremath{\beta}$ particles emitted in their subsequent radioactive decay. The coincident $\ensuremath{\gamma}$ rays were measured using four large volume germanium detectors mounted close to the implantation point and the …
Erratum to “Beta decay half-lives of neutron rich Ti–Co isotopes around N=40” [Nucl. Phys. A 660 (1999) 3–19]
Abstract The neutron-rich 57−59 Ti, 59−62 V, 61−64 Cr, 63−66 Mn, 65−68 Fe, 67−70 Co have been produced at GANIL via interactions of a 60.4 MeV/u 86 Kr 34+ with a 58 Ni target. They have been separated by the doubly achromatic spectrometer LISE3. Beta-decay half-lives have been determined for all produced nuclei, and subsequent γ -rays have been observed for the most efficiently produced nuclei. The measured half-lives of vanadium and chromium isotopes are compared to QRPA calculations using ground states deformations from the FRDM or ETFSI models. In an astrophysical context, the short half-lives of 58 Ti and 64 Cr indicate that these nuclei are potential r-process progenitors, after β -dec…
Neutron-rich isotopesTi54−57
The neutron-rich isotopes $^{54\mathrm{\ensuremath{-}}57}\mathrm{Ti}$ and $^{58\mathrm{\ensuremath{-}}60}\mathrm{Cr}$ are produced by fragmentation of a 64.5 MeV/nucleon $^{65}\mathrm{Cu}^{26+}$ beam in a 90 mg/${\mathrm{cm}}^{2}$ $^{9}\mathrm{Be}$ target. Following particle identification by energy loss and time of flight, the radioactive decay was observed by \ensuremath{\beta} singles and \ensuremath{\beta}\ensuremath{\gamma}-coincidence measurements. The results obtained for $^{58\mathrm{\ensuremath{-}}60}\mathrm{Cr}$ are compared to previous results, whereas the decay of the $^{54\mathrm{\ensuremath{-}}57}\mathrm{Ti}$ isotopes is studied here. \ensuremath{\gamma}-ray intensities and en…
Emission of neutrons and the neutron halo of $^{11}$Li
The matter distribution of the neutron drip-line nuclei has been a subject of intense interest since pioneering radioactive-beam experiments at Berkeley1). Unusually large interaction cross-sections measured at relativistic energies for 11Li,14Be and 17B nuclei were translated into effective matter radii. It was found that these were significantly larger than for other p-shell nuclei. In particular, the root-mean-square (rms) mass radius of 11Li was found to be 3.2fm, which was considerably larger than the 2.4fm radius of 9Li. At the same time, no signatures for significant deformation of 11Li were found in measurements of electric quadrupole moment by means of laser spectroscopy2).
New region of deformation in the neutron-rich 60 24Cr36 and 62 24Cr38
The neutron-rich nuclei 23 60-63V have been produced at GANIL via interactions of a 61.8A·MeV 76Ge beam with a 58Ni target. Beta-decay to 24 60-63Cr has been investigated using combined β- and γ-ray spectroscopy. Half-lives of the 60-63V nuclei have been determined, and the existence of a beta-decay isomer in the 60V nucleus is strongly supported. The observation of low-energy 2+ states in 60Cr (646keV) and 62Cr (446keV) suggests that these isotopes are strongly deformed with β2 ∼ 0.3. This is confirmed by shell model calculations which show the dominant influence of the intruder g and d orbitals to obtain low 2+ energies in the neutron-rich Cr isotopes.
Two-neutron removal reactions for very neutron-rich nuclei
Abstract The two-neutron removal reactions of beams of 11 Li, 14 Be and 8 He upon Be, Ni and Au targets were studied at 30 MeV/u. The cross sections and the neutron forward angular distributions were measured; they correlate strongly with the two-neutron separation energy of the projectile. Even though the coverage of the neutron detectors was limited, a rough neutron-neutron distribution could be extracted. A simplified interpretation of the data is presented.
First beta-decay studies of the neutron-rich isotopes 53-55Sc and 56-59V
The neutron-rich isotopes Sc53-55 and V56-59 have been produced at GANIL in interactions of a 64.5 MeV/u Cu-65 beam with a Be-9 target. They were separated by the doubly achromatic spectrometer LISE3. Beta-decay half-lives and subsequent low-energy gamma-rays were observed for the first time. The present results are compared to QRPA model predictions. The quick drop of the half-life observed at N = 33 for Ca-53(20)33 is water V-56(23)33 and absent for Sc-54(21)33, indicating a vanishing of the N = 32 subshell north to Ca-52(32). In an astrophysical context, these neutron-rich isotopes represent r-process progenitors which, after beta-decay, would produce the correlated isotopic over-abundan…
Beta-decay of light nuclei close to the proton drip-line: 40Ti and 35Ca
The s-decay of40Ti and35Ca have been studied at the LISE3 spectrometer at GANIL. The decay schemes were deduced from the observed s-delayed proton and γ emission of40Ti and35Ca into the ground and first excited states of39Ca and34Ar, respectively. The Gamow-Teller strength functionB(GT) of the40Ti s-decay extracted from the s-decay branching ratios and the precisely measured40Ti half-life, provides for the first time an experimental calibration of the neutrino detection efficiency for the ICARUS solar neutrino detector.
Beta decay studies of neutron-rich $_{21}$Sc-$_{27}$Co nuclei at GANIL
Abstract The neutron-rich nuclei 2157,58Sc, 2258–60Ti, 2258–60Ti, 2360–62V, 2464–66Cr, 2564–68Mn, 2667–70Fe and 2769–71Co have been produced at Ganil via interactions of a 61.8 A.MeV 76Ge beam with a 58Ni target. Beta-decay studies have been achieved, bringing new half-lives and a better nuclear structure knowledge in this region. These results could help for understanding the overabundances of the neutron-rich stable 58Fe, 64Ni in certain inclusions of meteorites.
Beta decay half-lives of neutron rich Ti–Co isotopes around
Abstract The neutron-rich 57 – 59 Ti, 59 – 62 V, 61 – 64 Cr, 63 – 66 Mn, 65 – 68 Fe, 67 – 70 Co have been produced at GANIL via interactions of a 60.4 MeV/u 86 Kr 34+ with a 58 Ni target. They have been separated by the doubly achromatic spectrometer LISE3. Beta-decay half-lives have been determined for all produced nuclei, and subsequent γ -rays have been observed for the most efficiently produced nuclei. The measured half-lives of vanadium and chromium isotopes are compared to QRPA calculations using ground states deformations from the FRDM or ETFSI models. In an astrophysical context, the short half-lives of 58 Ti and 64 Cr indicate that these nuclei are potential r-process progenitors, …
Decay properties of exoticN≃28 S and Cl nuclei and theCa48/46Ca abundance ratio
Beta-decay half-lives and \ensuremath{\beta}-delayed neutron-emission probabilities of the very neutron-rich nuclei $^{44}\mathrm{S}$ and $^{45--47}\mathrm{Cl}$ have been measured. These isotopes, which lie at or close to the N=28 magic shell, were produced in interactions of a 60 MeV/u $^{48}\mathrm{Ca}$ beam from GANIL (Grand Acc\'el\'erateur National d'Ions Lourds) with a $^{64}\mathrm{Ni}$ target, and were separated by the doubly achromatic spectrometer LISE (Ligne d'Ions Super Epluch\'es). Their decay was studied by a \ensuremath{\beta}-n time correlation measurement. The results are compared to recent model predictions and indicate a rapid weakening of the N=28 shell effect below $_{2…
Projectile coulomb excitation with fast radioactive beams
We report a search for gamma rays emanating from Coulomb excitation of fast (30-46 MeV/u) radioactive projectiles He-8, Be-11,Be-12,Be-14 interacting with a lead target. These are clearly identified by their Doppler shift. The 320 keV 1/2(-) --> 1/2(+)gamma transition from Be-11 was observed with a cross-section of 191 +/- 26 mb which is noticeably less than expected from the known lifetime and in the perturbation limit of pure Coulomb excitation. In the other nuclei rather stringent upper limits of 0.01 to 0.2 Weisskopf units, are placed on the hypothetical transition to 1(-) states.
Beta-decay studies of far from stability nuclei near N = 28
Abstract Beta-decay half-lives and β-delayed neutron-emission probabilities of the very neutron-rich nuclei 43 P, 42,44,45 S and 44–46 Cl, 47 Ar, which lie at or close to the N=28 magic shell, have been recently measured through β or β-n time correlation measurement. The results are compared to recent model predictions and indicate a rapid weakening of the N=28 shell effect below 48 Ca. The nuclear structure effects reflected in the decay properties of the exotic S and Cl isotopes may be the clue for the astrophysical understanding of the unusual 48 Ca 46 Ca abundance ratio measured in the solar system.