Beta-decay Half-lives Research Articles

Beta-decay half-lives and level ordering of 102m,gRh

Beta-decay half-lives of the ground state and an isomer of 102Rh have been determined 207.3(17) d and 3.742(10) y, respectively, by γ-ray decay curves following each β-decay. It has been found that a state (2 −) which has a shorter half-life (207.3 d) is the ground state from the result that the half-life of the 41.9 keV isomeric γ-transition was equal to 3.742 y. It has also been confirmed that the 41.9 keV transition is certainly an isomeric transition with X– γ coincidence measurement.

First beta-decay studies of the neutron-rich isotopes 53–55Sc and 56–59V

The neutron-rich isotopes 53–55Sc and 56–59V have been produced at GANIL in interactions of a 64.5 MeV/u 65Cu beam with a 9Be target. They were separated by the doubly achromatic spectrometer LISE3. Beta-decay half-lives and subsequent low-energy γ-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 20 53Ca 33 is weaker for 23 56V 33 and absent for 21 54Sc 33, indicating a vanishing of the N = 32 subshell north to 52Ca 32. In an astrophysical context, these neutron-rich isotopes represent r-process progenitors which, after β-decay, would produce the correlated isotopic over-abundances of 54Cr, 58Fe, 64Ni in certain refractory inclusions of meteorites.

Shell-model calculations for the properties of nuclei with A = 86–100 near the proton drip line

Extensive shell-model calculations in the mass range A = 86–100 on the neutron-deficient side of the nuclear chart are performed. The complete spectra of all isotopes are computed and compared to experimental excitation energies where available. Beta decay half lives are evaluated with both free and effective Gamow-Teller operators. The binding energies are obtained using a five parameter fit in addition to the shell-model energies. From the binding energies we deduce the proton drip line.

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

In an experiment at the LISE3 facility of GANIL, we used the projectile fragmentation of a 36Ar 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 22,23,24Si and 22Al. Beta-decay half-lives have been measured. The ground-state mass excess of 23Si has been determined. Partial decay schemes are presented on the basis of the transitions associated with the observed decay peaks.

Beta-Decay Half-Lives and Neutron-Emission Probabilities of Very Neutron-Rich Y to Tc Isotopes.

Neutron-rich ${}_{39}$Y to ${}_{43}$Tc isotopes have been produced by fission of uranium with a 50 MeV ${\mathrm{H}}_{2}^{+}$ beam. Beta-decay half-lives, delayed neutron-emission probabilities, and production yields have been measured and compared with theory. Beta decay of 4 new isotopes is reported, and the $\ensuremath{\beta}$-delayed neutron-emission mode has been discovered for 12 isotopes of the elements niobium and technetium. The results compared to quasiparticle random phase approximation predictions indicate the increasing importance of fast $\ensuremath{\beta}$ transitions to high-lying states of nuclei with large neutron excess.

Production and decay of heavy proton drip-line nuclei

Recent work at the NSCL using unusual isotopic beams to study nuclei along the proton drip-line up to A≈95 is presented. The most recent results were obtained by the fragmentation of a 106Cd beam. Following identification, measurements of the decay properties of such exotic nuclei in specialized measurements of beta-decay half-lives of the stopped ions were undertaken. The results of the studies that focused on the waiting point nuclei 65As and 69Br in the astrophysical rp-process are also presented. Very recent measurements of the masses of some of these exotic nuclei with a direct time of flight technique are briefly described.

Beta-decay studies of far from stability nuclei near N = 28

Beta-decay half-lives and β-delayed neutron-emission probabilities of the very neutron-rich nuclei 43P, 42,44,45S and 44–46Cl, 47Ar, 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 48Ca. 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.

Estimation of bounds for left-right mixing from nuclear double beta decay processes

Nuclear matrix elements, extracted from a systematic calculation of neutrinoless double beta decay rates for 0 + g.s→o + g.s transitions in 76Ge, 82Se, 128Te, 130Te and 136Xe, have been used to compute bounds on the left-right mixing angle ζ of the weak currents. The parameters of the nuclear model have been fixed by calculating the corresponding two-neutrino double beta decay half lives. The present analysis favours a mixing of the order of |tanξ| < 10 −3 which is to be compared with those obtained in muon decay (|tan ξ| ⩽ 0.035) and in supernova (|tan ξ| ⩽ 10 −5) analysis. It shows that nuclear structure calculations yield estimates on ξ which complement the existing data.

Decay properties of exotic N

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 $_{20}^{48}\mathrm{Ca}_{28}$. 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}\mathrm{Ca}$${/}^{46}$Ca abundance ratio measured in the solar system as well as the Ca-Ti-Cr anomalies observed in E. King inclusions of the Allende meteorite.

Operation of the r-process and cosmochronology

The rapid neutron capture process produced about half of the heavy elements in nature beyond the Fe-peak. In the past quite a number of astrophysical sites have been suggested, but none of them has yet been uniquely identified. Without assuming a particular site or model, we deduce the conditions responsible for the production of r-process nuclei by making use of the following information: (1) the solar r-process abundances and (2) nuclear masses and beta decay half lives for nuclei far from stability - in particular experimental information near magic neutron numbers, which determines the shape of the r-process peaks. In addition, we review briefly galactic age determinations based on the long-lived r-process chronometer nuclei 232Th, 235U and 238U.

Microscopic Predictions of β +/EC-Decay Half-Lives

Beta-decay half-lives for β +/EC (electron capture) decay for neutron-deficient nuclei with atomic numbers Z = 10-108 have been calculated up to the proton drip line. For this purpose a proton-neutron quasiparticle random-phase approximation model (pn-QRPA) has been used. Both particle-hole and particle-particle residual interactions are taken into account. The calculated half-lives are in good agreement with experimental data, indicating the applicability of the model to the prediction of half-lives of unknown isotopes. The results of the present calculation are also compared to earlier theoretical work. It is shown that the pn-QRPA leads to considerable improvement over gross theory calculations.

Calculation of beta-decay half-lives of proton-rich nuclei of intermediate mass.

We present the results of a calculation of the beta-decay half-lives of several proton-rich even-even nuclei of intermediate mass: 74Sr, 76Sr, 78Zr, 80Zr, 84Mo, 86Mo, 88Ru, 90Ru, 92Pd, and 96Cd. The calculation is based upon the random phase approximation with the quasiparticle formalism and takes into account the residual particle-particle interaction.

Neutron-rich isotopes around the r-process ?waiting-point? nuclei 29 79 Cu50 and 30 80 Zn50

Beta-decay half-lives (T1/2) and delayed-neutron emission probabilities (Pn) of very neutron-rich Cu to As nuclei have been measured, among them the new isotopes77Cu48,79Cu50,81Zn51 and84Ga53. With the T1/2 and Pn-values of now four N ∼-50 ”waiting-point” nuclei known, our hypothesis that the r-process has attained a local β-flow equilibrium araound A∼-80 is further strengthened.

Half-lives and delayed neutron emission probabilities of neutron-rich Li-Al nuclides.

Beta-decay half-lives and delayed neutron emission probabilities of very neutron-rich nuclides from Li to Al have been measured by a delayed coincidence technique. Neutron-rich nuclides were produced by reaction of 800-MeV protons on a $^{232}\mathrm{Th}$ target and were individually identified by use of the time-of-flight isochronous spectrometer. For 16 previously measured nucides, the half-lives determined here agree with literature values within the uncertainties. The previously unmeasured half-lives for $^{25}\mathrm{F}$ (59\ifmmode\pm\else\textpm\fi{}40 ms) and $^{28}\mathrm{Ne}$ (14\ifmmode\pm\else\textpm\fi{}10 ms) have been determined. Delayed neutron emission has been measured for $^{12}\mathrm{Be}$, $^{14}\mathrm{B}$, $^{17}\mathrm{C}$, $^{18}\mathrm{N}$, $^{25}\mathrm{F}$, and $^{28}\mathrm{Ne}$. Emission probabilities are reported for 19 precursors and upper limits are reported for 12 other nuclides. These data are compared with predictions of several beta-decay models.

Description of the ground-state pionic double charge exchange reaction on 128,130Te

The pionic double change exchange reactions 128,130Te( π +, π −) 128,130Xe are investigated within the proton-neutron random-phase approximation. The approach is fpund to give a satisfactory agreement of the calculated differential cross sections and angular distributions with recent data. A strong dependence of the calculated quantities on the strength g pp of the particle-particle force is observed. This behaviour is similar to that reported for the β + decay in neutron-dificient nuclei and the double beta decay. The role of the DCX for the interpretation of the ratio of the double beta decay half-lives of the tellurium isotopes is discussed.

Beta-decay half-lives of neutron rich Cu and Ni isotopes produced by thermal fission of235U and239Pu

The half-lives of very neutron rich isotopes of Ni and Cu have been measured. The isotopes are produced in very asymmetric thermal fission of235U and239Pu at the I.L.L. high flux reactor. They are separated by means of the Lohengrin spectrometer. They are identified with aΔE-E ionization chamber and implanted in one of the 8 Si planar detectors where theβ-particles are also detected. The time correlations between the implantation and the detection ofβ-particles provide the half-life. The values obtained are compared to current theoretical predictions.

Measurement of the beta decay half-life of 17B.

The beta decay half-lives of seven neutron-rich isotopes, $^{9}\mathrm{Li}$, $^{12}\mathrm{B}$, $^{13}\mathrm{B}$, $^{15}\mathrm{B}$, $^{17}\mathrm{B}$, $^{17}\mathrm{C}$, and $^{19}\mathrm{N}$, have been measured. The isotopes were produced by bombarding a tantalum target with a $^{22}\mathrm{Ne}$ beam with 35 MeV/nucleon. The isotopes were separated and identified using a reaction product mass separator. The half-life measurement of $^{17}\mathrm{B}$, 5.3(6) ms, is the first for this isotope.

Elemental technetium and promethium as cosmic-ray clocks

The possibility of using elemental Tc (Z = 43) and Pm (Z = 61) as clocks to measure the mean cosmic-ray confinement time in the Galaxy, tau(epsilon) is considered. For this purpose it is necessary to estimate the unknown beta(+) decay half-lives of several Tc and Pm isotopes; these estimates are obtained using beta-decay systematics. In the case of Tc it is possible to estimate the half-lives sufficiently well and show that this element can indeed be used as a cosmic-ray clock; in the case of Pm the half-lives are too uncertain to permit any conclusion. In order to make meaningful measurement of tau(epsilon) using elemental Tc, a comsic-ray detector must have a charge resolution less than about 0.25e in the region around Tc, and enough collecting power to detect a few hundred Tc nuclei.

Beta-decay half-lives of new neutron-rich chromium-to-nickel isotopes and their consequences for the astrophysical r-process

Beta-decay studies of the new neutron-rich isotopes 58,59Cr, 63Mn, 66,67Co and 69Ni, yielding distinctly shorter half-lives than the corresponding theoretical predictions, are presented. The influence of the short half-lives on the r-process calculations of nuclear abundances is discussed. It is concluded that a significantly higher neutron density than the one obtained from explosive helium burning in supernovae is need to reproduce the observe abundances around A=80.

The properties and effects on stellar burning of fractionally charged nuclei

view Abstract Citations (6) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The properties and effects on stellar burning of fractionally charged nuclei Boyd, R. N. ; Turner, R. E. ; Rybarcyk, L. ; Joseph, C. Abstract The consequences of unconfined quarks which may have been left over from the big bang, especially as to how they might participate in nucleosynthesis, are examined. Possible properties of the fractionally charged nuclei (Q-nuclei) thus produced, including beta-decay half-lives, binding energies, energy level densities, and thermonuclear reaction rates, are studied. Stellar burning cycles are suggested by these considerations in which the Q-nuclei could contribute significantly to stellar nucleosynthesis, even at an extremely low abundance level, provided that they satisfy some constraints. A model is suggested which accommodates all the constraints thus imposed. Possible implications of the existence of Q-nuclei for stellar evolution are considered, and the results of a calculation are presented which confirm that no obvious conflicts with the known parameters of the sun are encountered. The significance of the possible existence of Q-nuclei for future searches for free fractionally charged entities is discussed. Finally, it is noted that any particle which, when added to a nucleus, increases the nucleon binding energy somewhat could perform stellar burning cycles similar to those described in this paper. Publication: The Astrophysical Journal Pub Date: February 1985 DOI: 10.1086/162874 Bibcode: 1985ApJ...289..155B Keywords: Nuclear Fusion; Nuclear Interactions; Nuclei (Nuclear Physics); Quarks; Stellar Cores; Stellar Evolution; Alpha Particles; Half Life; Particle Production; Reaction Kinetics; Solar Neutrinos; Sun; Thermonuclear Reactions; Astrophysics full text sources ADS |