arXiv subjects
Publications and source records attributed to J. Giovinazzo.
A study of the $β$ decay of the proton-rich $T_{z}$ = -2 nucleus $^{56}$Zn has been reported in a recent publication. A rare and exotic decay mode, $β$-delayed $γ$-proton decay, has been observed there for the first time in the $fp$ shell. Here we expand on some of the details of the data analysis, focussing on the charged particle spectrum.
We report the observation of a very exotic decay mode at the proton drip-line, the $β$-delayed $γ$-proton decay, clearly seen in the $β$ decay of the $T_z$ = -2 nucleus $^{56}$Zn. Three $γ$-proton sequences have been observed after the $β$ decay. Here this decay mode, already observed in the $sd$-shell, is seen for the first time in the $fp$-shell. Both $γ$ and proton decays have been taken into account in the estimation of the Fermi (F) and Gamow Teller (GT) strengths. Evidence for fragmentation of the Fermi strength due to strong isospin mixing is found.
We present for the first time precise spectroscopic information on the recently discovered decay mode beta-delayed 3p-emission. The detection of the 3p events gives an increased sensitivity to the high energy part of the Gamow-Teller strength distribution from the decay of 31Ar revealing that as much as 30% of the strength resides in the beta-3p decay mode. A simplified description of how the main decay modes evolve as the excitation energy increases in 31Cl is provided.
A high-purity co-axial germanium detector has been calibrated in efficiency to a precision of about 0.15% over a wide energy range. High-precision scans of the detector crystal and gamma-ray source measurements have been compared to Monte-Carlo simulations to adjust the dimensions of a detector model. For this purpose, standard calibration sources and short-lived on-line sources have been used. The resulting efficiency calibration reaches the precision needed e.g. for branching ratio measurements of super-allowed beta decays for tests of the weak-interaction standard model.
A multi-hit capacity setup was used to study the decay of the dripline nucleus 31Ar, produced at the ISOLDE facility at CERN. A spectroscopic analysis of the beta-delayed three-proton decay of 31Ar is presented for the first time together with a quantitative analysis of the beta-delayed two-proton-gamma-decay. A new method for determination of the spin of low-lying levels in the beta-proton-daughter 30S using proton-proton angular correlations is presented and used for the level at 5.2 MeV, which is found to be either a 3+ or 4+ level, with the data pointing towards the 3+. The half-life of 31Ar is found to be 15.1(3) ms. An improved analysis of the Fermi beta-strength gives a total measured branching for the beta-3p-decay of 3.60(44) %, which is lower than the theoretical value found to be 4.24(43) %. Finally the strongest gamma-transitions in the decay of 33Ar are shown including a line at 4734(3) keV associated to the decay of the IAS, which has not previously been identified.
Resonances just above the proton threshold in 30S affect the 29P(p,gamma)30S reaction under astrophysical conditions. The (p,gamma)-reaction rate is currently determined indirectly and depends on the properties of the relevant resonances. We present here a method for finding the ratio between the proton and gamma partial widths of resonances in 30S. The widths are determined from the beta-2p and beta-p-gamma decay of 31Ar, which is produced at the ISOLDE facility at the European research organization CERN. Experimental limits on the ratio between the proton and gamma partial widths for astrophysical relevant levels in 30S have been found for the first time. A level at 4688(5) keV is identified in the gamma spectrum, and an upper limit on the proton to gamma width of 0.26 (95 % C.L.) is found. In the two-proton spectrum two levels at 5227(3) keV and 5847(4) keV are identified. These levels are previously seen to gamma decay and upper limits on the gamma to proton width of 0.5 and 9, respectively, (95 % C.L.) are found, where the latter differs from previous calculations.
The half-lives of the Tz = -2, 56Zn and Tz = -1, 58Zn isotopes and other nuclei were measured in a β-decay experiment at GANIL. The energy levels populated by the 56Zn β decay were determined. The 56Zn results are compared with the results of the mirror process, the charge exchange reaction 56Fe(3He,t)56Co.
The existence of nuclei with exotic combinations of protons and neutrons provides fundamental information on the forces acting between nucleons. The maximum number of neutrons a given number of protons can bind, neutron drip line1, is only known for the lightest chemical elements, up to oxygen. For heavier elements, the larger its atomic number, the farther from this limit is the most neutron-rich known isotope. The properties of heavy neutron-rich nuclei also have a direct impact on understanding the observed abundances of chemical elements heavier than iron in our Universe. Above half of the abundances of these elements are thought to be produced in rapid-neutron capture reactions, r-process, taking place in violent stellar scenarios2 where heavy neutron-rich nuclei, far beyond the ones known up today, are produced. Here we present a major step forward in the production of heavy neutron-rich nuclei: the discovery of 73 new neutron-rich isotopes of chemical elements between tantalum (Z=72) and actinium (Z=89). This result proves that cold-fragmentation reactions3 at relativistic energies are governed by large fluctuations in isospin and energy dissipation making possible the massive production of heavy neutron-rich nuclei, paving then the way for the full understanding of the origin of the heavier elements in our Universe. It is expected that further studies providing ground and structural properties of the nuclei presented here will reveal further details on the nuclear shell evolution along Z=82 and N=126, but also on the understanding of the stellar nucleosyntheis r-process around the waiting point at A~190 defining the speed of the matter flow towards heavier fissioning nuclei.
A new and independent determination of the Gamow-Teller branching ratio in the beta-decay of 21Na is reported. The value obtained of 5.13 +- 0.43 % is in agreement with the currently adopted value and the most recent measurement. In contrast to previous experiments, the present method was based on the counting of the parent 21Na ions and the resulting 351 keV gamma-rays without coincident beta-particle detection.
The proton-rich nucleus 33Ar has been studied by detailed proton and gamma-ray spectroscopy at the low-energy facility of SPIRAL at GANIL. Proton and gamma-ray singles and coincidence measurements allowed to establish a quasi complete decay scheme of this nucleus. By comparing the proton intensity to different daughter states, tentative spin assignments have been made for some of the states of 33Cl. The Gamow-Teller strength distribution is deduced and compared to shell-model calculations and a quenching factor is determined. States close to the isobaric analogue state are searched for with respect to isospin mixing.
The beta-decay half-life of 26Si was measured with a relative precision of 1.4*10e3. The measurement yields a value of 2.2283(27) s which is in good agreement with previous measurements but has a precision that is better by a factor of 4. In the same experiment, we have also measured the non-analogue branching ratios and could determine the super-allowed one with a precision similar to the previously reported measurements. The experiment was done at the Accelerator Laboratory of the University of Jyvaskyla where we used the IGISOL technique with the JYFLTRAP facility to separate pure samples of 26Si.
Beta-decay branching ratios of 62Ga have been measured at the IGISOL facility of the Accelerator Laboratory of the University of Jyvaskyla. 62Ga is one of the heavier Tz = 0, 0+ -> 0+ beta-emitting nuclides used to determine the vector coupling constant of the weak interaction and the Vud quark-mixing matrix element. For part of the experimental studies presented here, the JYFLTRAP facility has been employed to prepare isotopically pure beams of 62Ga. The branching ratio obtained, BR= 99.893(24)%, for the super-allowed branch is in agreement with previous measurements and allows to determine the ft value and the universal Ft value for the super-allowed beta decay of 62Ga.
Heavy neutron-rich nuclei close to N=126 were produced by fragmentation of a 1 A GeV 208Pb beam at the FRS at GSI. The beta-decay half-lives of 8 nuclides have been determined. The comparison of the data with model calculations including an approach based on the self-consistent ground-state description and continuum QRPA considering the Gamow-Teller and first-forbidden decays provide a first indication on the importance of first-forbidden transitions around A=195. The measured data indicate that the matter flow in the r-process to heavier fissioning nuclei is faster than previously expected.
The decay of the ground-state two-proton emitter 45Fe was studied with a time-projection chamber and the emission of two protons was unambiguously identified. The total decay energy and the half-life measured in this work agree with the results from previous experiments. The present result constitutes the first direct observation of the individual protons in the two-proton decay of a long-lived ground-state emitter. In parallel, we identified for the first time directly two-proton emission from 43Cr, a known beta-delayed two-proton emitter. The technique developped in the present work opens the way to a detailed study of the mechanism of ground-state as well as beta-delayed two-proton radioactivity.
In an experiment performed at the LISE3 facility of GANIL, we studied the decay of 22Al produced by the fragmentation of a 36Ar primary beam. A beta-decay half-life of 91.1 +- 0.5 ms was measured. The beta-delayed one- and two-proton emission as well as beta-alpha and beta-delayed gamma decays were measured and allowed us to establish a partial decay scheme for this nucleus. New levels were determined in the daughter nucleus 22Mg. The comparison with model calculations strongly favours a spin-parity of 4+ for the ground state of 22Al.
Masses of the radioactive isotopes 62Ga, 62Zn and 62Cu have been measured at the JYFLTRAP facility with a relative precision of better than 18 ppb. A Q_EC value of (9181.07 +- 0.54) keV for the superallowed decay of 62Ga is obtained from the measured cyclotron frequency ratios of 62Ga-62Zn, 62Ga-62Ni and 62Zn-62Ni ions. The resulting Ft-value supports the validity of the conserved vector current hypothesis (CVC). The mass excess values measured were (-51986.5 +-1.0) keV for 62Ga, (-61167.9 +- 0.9) keV for 62Zn and (-62787.2 +- 0.9) keV for 62Cu.
The nucleus 54Zn has been observed for the first time in an experiment at the SISSI/LISE3 facility of GANIL in the quasi-fragmentation of a 58Ni beam at 74.5 MeV/nucleon in a natNi target. The fragments were analysed by means of the ALPHA-LISE3 separator and implanted in a silicon-strip detector where correlations in space and time between implantation and subsequent decay events allowed us to generate almost background free decay spectra for about 25 different nuclei at the same time. Eight 54Zn implantation events were observed. From the correlated decay events, the half-life of 54Zn is determined to be 3.2 +1.8/-0.8 ms. Seven of the eight implantations are followed by two-proton emission with a decay energy of 1.48(2) MeV. The decay energy and the partial half-life are compared to model predictions and allow for a test of these two-proton decay models.
In an experiment performed at the Accelerator Laboratory of the University of Jyvaskyla, the beta-decay half-life of 62Ga has been studied with high precision using the IGISOL technique. A half-life of T1/2 = 116.09(17)ms was measured. Using beta-gamma coincidences, the gamma intensity of the 954keV transition and an upper limit of the beta-decay feeding of the 0+_2 state have been extracted. The present experimental results are compared to previous measurements and their impact on our understanding of the weak interaction is discussed.