Search

The half-life of the superallowed Fermi β+ emitter 18Ne has been determined via two high-precision β counting experiments at TRIUMF's Isotope Separator and Accelerator facility. Using two different 4π continuous-flow gas-proportional counters, two independent measurements were made, yielding a weighted average of T1/2=1.66400+0.00057-0.00048 s, which is consistent with but approximately 2 times more precise than a previous high-precision measurement based on γ-ray counting. The present work achieves ±0.034% precision for the 18Ne half-life and will enable the inclusion of 18Ne among the set of precisely measured superallowed Fermi β-decay ft values once improved measurements are made for its Q value and superallowed branching ratio. As a test of systematic uncertainties, the half-life of 23Ne was measured and the world average has been improved, by a factor of 1.7, to 37.148±0.032 s. [ABSTRACT FROM AUTHOR]

The half-life of the superallowed Fermi β+ emitter l4O has been determined via simultaneous direct β and γ counting experiments at TRIUMF's Isotope Separator and Accelerator (ISAC) facility. A γ-ray counting measurement was performed by detecting the 2312.6-keV γ rays emitted from an excited state of the daughter l4N following the implantation of samples at the center of the 8π γ-ray spectrometer, a spherical array of 20 high-purity germanium (HPGe) detectors. A simultaneous β counting experiment was performed using a fast plastic scintillator positioned behind the implantation site with a solid angle coverage of ~20%. The results, T1/2(β) = 70.610 ± 0.030 s and T1/2(γ) = 70.632 ± 0.094 s, form a consistent set and, together with eight previous measurements, establish anew average for the l40 half-life of T1/2 = 70.619 ± 0.011 s with a reduced X² of 0.99. [ABSTRACT FROM AUTHOR]

Precision measurements of superallowed Fermi β-decay transitions, particularly for the lightest superallowed emitters 10C and 14O, set stringent limits on possible scalar current contributions to the weak interaction. In the present work, a discrepancy between recent measurements of the 10C half-life is addressed through two high-precision half-life measurements, via γ-ray photopeak and β counting, that yield consistent results for the 10C half-life of T1/2 = 19.2969 ± 0.0074 s and T1/2 = 19.3009 ± 0.0017 s, respectively. The latter is the most precise superallowed β-decay half-life measurement reported to date and the first to achieve a relative precision below 10-4. A fit to the world superallowed β-decay data including the 10C half-life measurements reported here yields bF = -0.0018 ± 0.0021 (68% C.L.) for the Fierz interference term and CS/CV = +0.0009 ± 0.0011 for the ratio of the weak scalar to vector couplings assuming left-handed neutrinos. [ABSTRACT FROM AUTHOR]

A search for excited 0+ states in 62Zn was conducted via the 64Zn(p, t)62Zn reaction. Four such states in 62Zn were observed up to an excitation energy of 5.4 MeV. The measured angular distribution for the previously assigned 0j state at 2342 keV is consistent with a 2+ assignment, and thus the first excited 0+ state is now assigned at 3043 keV. Due to the energy scaling in the currently adopted formalism for isospin-mixing corrections in superallowed Fermi β decay, δc1 for 62Ga is reduced by nearly a factor of two. This result shifts the theoretical value closer to previous experimental determinations of the same quantity through 62Ga superallowed β-decay branching-ratio measurements. [ABSTRACT FROM AUTHOR]

Shape coexistence between the strongly deformed ground state and the weakly deformed 02+ state in 98Sr has been a major topic of interest due to the energy difference of 215 keV, which is the smallest in all even-even nuclei. The electric monopole transition strength ρ²(E0) is an important quantity that can relate the deformation difference and the shape mixing between the two 0+ states, which are admixtures of the vibrational (S) and the rotational (D) states in a simple mixing model. In a β-decay spectroscopy experiment, the experimental ρ²(E0) was measured. A value of 0.053(5) is consistent with the previous measurement and was combined with known electric quadrupole transition strengths B(E2) in calculations of a two-state mixing model. Based on a systematic study on neighboring Kr, Zr, and Mo isotopes, the mixing of the 0+ and 2+ states in 98Sr was determined to be 8.6% and 1.3%, respectively, corresponding to deformation parameters βD = 0.38(1) and βS = -0.23(2). These parameters reproduce experimental transition strengths well except for the 41+ → 21+ transition, which suggests a smaller D-band deformation for J ⩾ 4. [ABSTRACT FROM AUTHOR]

States in 112Cd have been studied with the 111Cd(d,p) 12Cd reaction using 22 MeV polarized deuterons. The protons from the reaction were momentum analyzed with a Q3D magnetic spectrograph, and spectra have been recorded with a position-sensitive detector located on the focal plane. Angular distributions of cross sections and analyzing powers have been constructed for the low-lying negative-parity states observed, including the 3-,4-, and 5- members of the previously assigned quadrupole-octupole quintuplet. The 5- member at 2373-keV possess the second largest spectroscopic strength observed, and is reassigned as having the s1/2 ⊗ h11/2 two-quasineutron configuration as the dominate component of its wave function. [ABSTRACT FROM AUTHOR]

A high-precision branching-ratio measurement for the superallowed β+ decay of 74Rb was performed at the TRIUMF Isotope Separator and Accelerator (ISAC) radioactive ion-beam facility. The scintillating electron-positron tagging array (SCEPTAR), composed of 10 thin plastic scintillators, was used to detect the emitted β particles; the 8Π spectrometer, an array of 20 Compton-suppressed HPGe detectors, was used for detecting γ rays that were emitted following Gamow-Teller and nonanalog Fermi β+ decays of 74Rb; and the Pentagonal Array of Conversion Electron Spectrometers (PACES), an array of 5 Si(Li) detectors, was employed for measuring β-delayed conversion electrons. Twenty-three excited states were identified in 74Kr following 8.241(4)×108 detected 74Rb β decays. A total of 58 γ-ray and electron transitions were placed in the decay scheme, allowing the superallowed branching ratio to be determined as B0=99.545(31)%. Combined with previous half-life and Q-value measurements, the superallowed branching ratio measured in this work leads to a superallowed ft value of 3082.8(65) s. Comparisons between this superallowed ft value and the world-average-corrected Ft value, as well as the nonanalog Fermi branching ratios determined in this work, provide guidance for theoretical models of the isospin-symmetry-breaking corrections in this mass region. [ABSTRACT FROM AUTHOR]

With the recent inclusion of core orbitals to the radial-overlap component of the isospin-symmetry-breaking (ISB) corrections for superallowed Fermi ß decay, experimental data are needed to test the validity of the theoretical model. This work reports measurements of single-neutron pickup reaction spectroscopic factors into 63Zn, one neutron away from 62Zn, the superallowed daughter of 62Ga. The experiment was performed using a 22-MeV polarized deuteron beam, a Q3D magnetic spectrograph, and a cathode-strip focal-plane detector to analyze outgoing tritons at nine angles between 10° and 60°. Angular distributions and vector analyzing powers were obtained for all 162 observed states in 63Zn, including 125 newly observed levels, up to an excitation energy of 4.8 MeV. Spectroscopic factors are extracted and compared to several shell-model predictions, and implications for the ISB calculations are discussed [ABSTRACT FROM AUTHOR]

The half-life of the superallowed Fermi β+ emitter 18Ne has been determined to ±0.07% precision by counting 1042 keV delayed γ rays that follow approximately 8% of all β decays. The deduced half-life, T1/2 = 1.6648 (11)s, includes a 0.7% correction that accounts for systematic losses associated with rate-dependent detector pulse pileup that was determined using a recently developed γ-ray photopeak-counting technique. This result is a factor of two times more precise than, and in excellent agreement with, a previous lower-statistics mea-surement that employed the same experimental setup. High-resolution β-delayed γ-ray spectroscopy results for the relative γ-ray intensities and β-decay branching ratios to excited states in the daughter 18F are also presented. [ABSTRACT FROM AUTHOR]

Over a period of several years we have performed three separate experiments at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron in which 235U (thick target) was Coulomb-excited. The program involved standalone experiments with Gammmasphere and with the 8pi Spectrometer using 136Xe beams at 720 MeV, and a CHICO-Gammasphere experiment with a 40Ca beam at 184 MeV. In addition to extending the known negative-parity bands to high spin, we have assigned levels in some seven positive-parity bands which are in some cases (e.g., [631]l/2, [624]7/2, and [622]5/2) strongly populated by E3 excitation. The CHICO data have been analyzed to extract E2 and E3 matrix elements from the observed yields. Additionally, many M1 matrix elements could be extracted from the γ-ray branching ratios. A number of new features have emerged, including the unexpected attenuation of magnetic transitions between states of the same Nilsson multiplet, the breakdown of Coriolis staggering at high spin, and the effect of E3 collectivity on Coriolis interactions. [ABSTRACT FROM AUTHOR]

An experimental study of the 62Zn nucleus has been performed by combining the data sets from four fusion-evaporation reaction experiments. Apart from the previously published data, the present results include ten new rotational band structures and two more superdeformed bands. The Gammasphere Ge-detector array in conjunction with the 4? charged-particle detector array Microball allowed for the detection of γ rays in coincidence with evaporated light particles. The deduced level scheme includes some 260 excited states, which are connected with more than 450 λ-ray transitions. Spins and parities of the excited states have been determined via directional correlations of λ rays emitted from oriented states. The experimental characteristics of the rotational bands are analyzed and compared with results from cranked Nilsson-Strutinsky calculations. The present analysis, combined with available experimental results in the A ~ 60 mass region, can be used to improve the current set of Nilsson parameters in the N = 3 and N = 4 oscillator shells. [ABSTRACT FROM AUTHOR]

We report a precise determination of the 19Ne half-life to be T1/2 = 17.262 ± 0.007 s. This result disagrees with the most recent precision measurements and is important for placing bounds on predicted right-handed interactions that are absent in the current standard model. We are able to identify and disentangle two competing systematic effects that influence the accuracy of such measurements. Our findings prompt a reassessment of results from previous high-precision lifetime measurements that used similar equipment and methods. [ABSTRACT FROM AUTHOR]

A high-precision branching-ratio measurement for the superallowed ß+ emitter 26Alm was performed at the TRIUMF-ISAC radioactive ion beam facility. An upper limit of <12 ppm at 90% confidence level was found for the second forbidden yS+ decay of 26Alm to the 2 state at 1809 keV in 26Mg. An inclusive upper limit of 15 ppm at 90% confidence level was found when considering all possible nonanalog jö+/EC decay branches of 26 Alm, resulting in a superallowed branching ratio of 100.0000+0-0.0015 %. [ABSTRACT FROM AUTHOR]

Lifetimes of 21+ and 41+ states as well as some negative-parity and nonyrast states in 188-200Hg were measured using γ-γ electronic fast timing techniques with the LaBr3(Ce) detector array of the GRIFFIN spectrometer. The excited states were populated in the ε/β+ decay of Jπ = 7+/2- 188-200Tl produced at the TRIUMF-ISAC facility. The deduced B(E2) values are compared to different interacting boson model predictions. The precision achieved in this paper over previous ones allows for a meaningful comparison with the different theoretical models of these transitional Hg isotopes, which confirms the onset of state mixing in 190Hg. [ABSTRACT FROM AUTHOR]

Detailed spectroscopic measurements of excited states in 50Cr and 62Zn were performed using 24-MeV (p,t) transfer reactions on 52Cr and 64Zn, respectively. In total, 45 states in 50Cr and 67 states in 62Zn were observed up to excitation energies of 5.5 MeV, including several previously unobserved states. These experimental results are compared to ab-initio shell-model calculations using chiral effective field theory with the valence-space in-medium similarity renormalization group method. This comparison demonstrates good agreement in the level orderings with these new theoretical methods, albeit with a slight overbinding in the calculations. This work is part of a continued push to benchmark ab-initio theoretical techniques to nuclear-structure data in 0+→0+ superallowed Fermi β-decay systems. [ABSTRACT FROM AUTHOR]

Gamma-ray spectroscopy and lifetime measurements using the Doppler shift attenuation method (DSAM) were performed on the nucleus 28Mg near the N=20 "island of inversion," which was populated using a 12C(18O,2p)28Mg fusion-evaporation reaction to investigate the impact of shell evolution on its high-lying structure. Three new levels were identified at 7203(3), 7747(2), and 7929.3(12) keV along with several new gamma rays. A newly extracted B(E2;4+1→2+1) of 42(7) e²fm4 indicates reduced collectivity in the yrast band at high spin, consistent with ab initio symmetry adapted no-core shell model (SA-NCSM) calculations. At high excitation energy, evidence for the population of intruder orbitals was obtained through identification of negative parity levels [Iπ=(0,4)-, (4,5)-]. Calculations using the SDPF-MU interaction indicate that these levels arise from single neutron excitation to the pf shell and provides evidence for the lowering of these intruder orbitals approaching the island of inversion. [ABSTRACT FROM AUTHOR]

The energy levels and γ-ray decay scheme of the positive-parity states in the Tz=1/2 nucleus 67As have been studied by using the 40Ca(36Ar,2αp)67As reaction at a beam energy of 145 MeV. Two new band structures have been identified which can be connected to the previously known levels. The results for these bands are compared with configuration-dependent cranked Nilsson-Strutinsky calculations. The good level of agreement between theory and experiment suggests that these structures can be interpreted in terms of configurations that involve three g9/2 particles and that both possess noncollective terminating states. [ABSTRACT FROM AUTHOR]

Background: The evolution of nuclear magic numbers at extremes of isospin is a topic at the forefront of contemporary nuclear physics. N=50 is a prime example, with increasing experimental data coming to light on potentially doubly magic 100Sn and 78Ni at the proton-rich and proton-deficient extremes, respectively; however, experimental discrepancies exist in the data for less exotic systems. Purpose: In 86Kr the B(E2;2+1→0+1) value--a key indicator of shell evolution--has been experimentally determined by two different methodologies, with the results deviating by 3σ. Here, we report on a new high-precision measurement of this value, as well as the first measured lifetimes and hence transition strengths for the 2+2 and 3-(2) states in the nucleus. Methods: The Doppler-shift attenuation method was implemented using the TRIUMF-ISAC γ-ray escape-suppressed spectrometer (TIGRESS) γ-ray spectrometer and the TIGRESS integrated plunger device. High-statistics Monte Carlo simulations were utilized to extract lifetimes in accordance with state-of-the-art methodologies. Results: Lifetimes of τ(2+1)=336±4(stat.)±20(sys.) fs, τ(2+2)=263±9(stat.)±19(sys.) fs, and τ(3-(2))=73±6(stat.)±32(sys.) fs were extracted. This yields a transition strength for the first-excited state of B(E2;2+1→0+1)=259±3(stat.)±16(sys.) e² fm4. Conclusions: The measured lifetime disagrees with the previous Doppler-shift attenuation method measurement by more than 3σ, while agreeing well with a previous value extracted from Coulomb excitation. The newly extracted B(E2;2+1→0+1) value indicates a more significant reduction in the N=50 isotones approaching Z=40. [ABSTRACT FROM AUTHOR]

The GRIFFIN spectrometer at TRIUMF-ISAC has been used to study excited states and transitions in 50Sc following the β decay of 50Ca. Branching ratios were determined from the measured γ-ray intensities, and angular correlations of γ rays have been used to firmly assign the spins of excited states. The presence of an isomeric state that decays by an M3 transition with a B(M3) strength of 13.6(7) W.u. has been confirmed. We compare the first ab initio calculations of B(M3) strengths in light- and medium-mass nuclei from the valence-space in-medium similarity renormalization group approach, using consistently derived effective Hamiltonians and effective M3 operator. The experimental data are well reproduced for isoscalar M3 transitions when using bare g factors, but the strength of isovector M3 transitions are found to be underestimated by an order of magnitude. [ABSTRACT FROM AUTHOR]

A high-precision half-life measurement for the superallowed β+ transition between the isospin T=1/2 mirror nuclei 21Na and 21Ne has been performed at the TRIUMF-ISAC radioactive ion beam facility yielding T1/2=22.4506(33) s, a result that is a factor of 4 more precise than the previous world-average half-life for 21Na and represents the single most precisely determined half-life for a transition between mirror nuclei to date. The contribution to the uncertainty in the 21Na Ftmirror value due to the half-life is now reduced to the level of the nuclear-structure-dependent theoretical corrections, leaving the branching ratio as the dominant experimental uncertainty. [ABSTRACT FROM AUTHOR]

A high precision lifetime measurement of the 21+ state in 94Sr was performed at TRIUMF's ISAC-II facility by coupling the recoil distance method implemented via the TIGRESS integrated plunger with unsafe Coulomb excitation in inverse kinematics. Due to limited statistics imposed by the use of a radioactive 94Sr beam, a likelihood ratio χ² method was derived and used to compare experimental data to Geant4 simulations. The B(E2; 21+ → 01+) value extracted from the lifetime measurement of 7.80-0.4+00.50 (stat.) ± 0.07 (sys.) ps is approximately 25% larger than previously reported while the relative error has been reduced by a factor of approximately 8. A baseline deformation has been established for Sr isotopes with N ≤ 58 which is a necessary condition for the quantum phase transition interpretation of the onset of deformation in this region. A comparison to existing theoretical models is presented. [ABSTRACT FROM AUTHOR]

Background: A previous measurement of the β-γ directional coefficient in 22Naβ decay was used to extract recoil-order form factors. The data indicate the requirement of a significant induced-tensor matrix element for the decay. This conclusion largely relies on a standard-model-allowed weak magnetism form factor which was determined using an unpublished value of the analog 2+1→3+1 γ branch in 22Na, with the further assumption that the transition is dominated by its isovector M1 component. Purpose: Our aim is to determine the 2+1→3+1 width in 22Na in order to obtain an independent measurement of the weak magnetism form factor for the β decay. Methods: A 21Ne(p,γ) resonance reaction on an implanted target was used to produce the first 2+ state in 22Na at Ex=1952 keV. Deexcitation γ rays were registered with two 100% relative efficiency high purity germanium detectors. Results: We obtain for the first time an unambiguous determination of the 2+1→3+1 branch in 22Na to be 0.45(8)%. Conclusions: Using the conserved vector current (CVC) hypothesis, our branch determines the weak magnetism form factor for 22Naβ decay to be |b/Ac1|=8.9(1.2). Together with the β-γ angular correlation coefficient, we obtain a large induced-tensor form factor for the decay that continues to disagree with theoretical predictions. Two plausible explanations are suggested. [ABSTRACT FROM AUTHOR]

A 52Cr(p,t)50Cr two-neutron pickup reaction was performed using the Q3D magnetic spectrograph at the Maier-Leibnitz-Laboratorium in Garching, Germany. Excited states in 50Cr were observed up to an excitation energy of 5.3 MeV. Despite significantly increased sensitivity and resolution over previous work, no evidence of the previously assigned first excited 0+ state was found. As a result, the 0+2 state is reassigned at an excitation energy of Ex=3895.0(5) keV in 50Cr. This reassignment directly impacts direct searches for a nonanalog Fermi &#946+ decay branch in 50Mn. These results also show better systematic agreement with the theoretical predictions for the 0+ state spectrum in 50Cr using the same formalism as the isospin-symmetry-breaking correction calculations for superallowed nuclei. The experimental data are also compared to ab-initio shell-model predictions using the IM-SRG formalism based on NN and 3N forces from chiral-EFT in the pf-shell for the first time. [ABSTRACT FROM AUTHOR]

The β-decay half-lives of 128-130Cd have been measured with the newly commissioned GRIFFIN γ-ray spectrometer at the TRIUMF-ISAC facility. The time structures of the most intense γ rays emitted following the β decay were used to determine the half-lives of 128Cd and 130Cd to be T1/2=246.2(21) ms and T1/2=126(4) ms, respectively. The half-lives of the 3/2+ and 11/2− states of Cd129 were measured to be T1/2(3/2+)=157(8) ms and T1/2(11/2-)=147(3) ms. The half-lives of the Cd isotopes around the N=82 shell closure are an important ingredient in astrophysical simulations to derive the magnitude of the second r-process abundance peak in the A∼130 region. Our new results are compared with recent literature values and theoretical calculations. [ABSTRACT FROM AUTHOR]

The excited states of N=44 ^{74}Zn were investigated via γ-ray spectroscopy following ^{74}Cu β decay. By exploiting γ-γ angular correlation analysis, the 2&#95;{2}^{+}, 3&#95;{1}^{+}, 0&#95;{2}^{+}, and 2&#95;{3}^{+} states in ^{74}Zn were firmly established. The γ-ray branching and E2/M1 mixing ratios for transitions deexciting the 2&#95;{2}^{+}, 3&#95;{1}^{+}, and 2&#95;{3}^{+} states were measured, allowing for the extraction of relative B(E2) values. In particular, the 2&#95;{3}^{+}→0&#95;{2}^{+} and 2&#95;{3}^{+}→4&#95;{1}^{+} transitions were observed for the first time. The results show excellent agreement with new microscopic large-scale shell-model calculations, and are discussed in terms of underlying shapes, as well as the role of neutron excitations across the N=40 gap. Enhanced axial shape asymmetry (triaxiality) is suggested to characterize ^{74}Zn in its ground state. Furthermore, an excited K=0 band with a significantly larger softness in its shape is identified. A shore of the N=40 "island of inversion" appears to manifest above Z=26, previously thought as its northern limit in the chart of the nuclides.

We have performed the first direct measurement of the ^{83}Rb(p,γ) radiative capture reaction cross section in inverse kinematics using a radioactive beam of ^{83}Rb at incident energies of 2.4 and 2.7A  MeV. The measured cross section at an effective relative kinetic energy of E&#95;{cm}=2.393  MeV, which lies within the relevant energy window for core collapse supernovae, is smaller than the prediction of statistical model calculations. This leads to the abundance of ^{84}Sr produced in the astrophysical p process being higher than previously calculated. Moreover, the discrepancy of the present data with theoretical predictions indicates that further experimental investigation of p-process reactions involving unstable projectiles is clearly warranted.

The ^{80}Ge structure was investigated in a high-statistics β-decay experiment of ^{80}Ga using the GRIFFIN spectrometer at TRIUMF-ISAC through γ, β-e, e-γ, and γ-γ spectroscopy. No evidence was found for the recently reported 0&#95;{2}^{+} 639-keV level suggested as evidence for low-energy shape coexistence in ^{80}Ge. Large-scale shell model calculations performed in ^{78,80,82}Ge place the 0&#95;{2}^{+} level in ^{80}Ge at 2 MeV. The new experimental evidence combined with shell model predictions indicate that low-energy shape coexistence is not present in ^{80}Ge.

From detailed spectroscopy of ^{110}Cd and ^{112}Cd following the β^{+}/electron-capture decay of ^{110,112}In and the β^{-} decay of ^{112}Ag, very weak decay branches from nonyrast states are observed. The transition rates determined from the measured branching ratios and level lifetimes obtained with the Doppler-shift attenuation method following inelastic neutron scattering reveal collective enhancements that are suggestive of a series of rotational bands. In ^{110}Cd, a γ band built on the shape-coexisting intruder configuration is suggested. For ^{112}Cd, the 2^{+} and 3^{+} intruder γ-band members are suggested, the 0&#95;{3}^{+} band is extended to spin 4^{+}, and the 0&#95;{4}^{+} band is identified. The results are interpreted using beyond-mean-field calculations employing the symmetry conserving configuration mixing method with the Gogny D1S energy density functional and with the suggestion that the Cd isotopes exhibit multiple shape coexistence.

The elusive β^{-}p^{+} decay was observed in ^{11}Be by directly measuring the emitted protons and their energy distribution for the first time with the prototype Active Target Time Projection Chamber in an experiment performed at ISAC-TRIUMF. The measured β^{-}p^{+} branching ratio is orders of magnitude larger than any previous theoretical model predicted. This can be explained by the presence of a narrow resonance in ^{11}B above the proton separation energy.

Angular distributions of the elastic, inelastic, and breakup cross sections of the halo nucleus ^{11}Be on ^{197}Au were measured at energies below (E&#95;{lab}=31.9  MeV) and around (39.6 MeV) the Coulomb barrier. These three channels were unambiguously separated for the first time for reactions of ^{11}Be on a high-Z target at low energies. The experiment was performed at TRIUMF (Vancouver, Canada). The differential cross sections were compared with three different calculations: semiclassical, inert-core continuum-coupled-channels and continuum-coupled-channels ones with including core deformation. These results show conclusively that the elastic and inelastic differential cross sections can only be accounted for if core-excited admixtures are taken into account. The cross sections for these channels strongly depend on the B(E1) distribution in ^{11}Be, and the reaction mechanism is sensitive to the entanglement of core and halo degrees of freedom in ^{11}Be.

Precision measurements of superallowed Fermi β-decay transitions, particularly for the lightest superallowed emitters ^{10}C and ^{14}O, set stringent limits on possible scalar current contributions to the weak interaction. In the present work, a discrepancy between recent measurements of the ^{10}C half-life is addressed through two high-precision half-life measurements, via γ-ray photopeak and β counting, that yield consistent results for the ^{10}C half-life of T&#95;{1/2}=19.2969±0.0074  s and T&#95;{1/2}=19.3009±0.0017  s, respectively. The latter is the most precise superallowed β-decay half-life measurement reported to date and the first to achieve a relative precision below 10^{-4}. A fit to the world superallowed β-decay data including the ^{10}C half-life measurements reported here yields b&#95;{F}=-0.0018±0.0021 (68% C.L.) for the Fierz interference term and C&#95;{S}/C&#95;{V}=+0.0009±0.0011 for the ratio of the weak scalar to vector couplings assuming left-handed neutrinos.

We report a precise determination of the (19)Ne half-life to be T(1/2)=17.262±0.007 s. This result disagrees with the most recent precision measurements and is important for placing bounds on predicted right-handed interactions that are absent in the current standard model. We are able to identify and disentangle two competing systematic effects that influence the accuracy of such measurements. Our findings prompt a reassessment of results from previous high-precision lifetime measurements that used similar equipment and methods.

A high-precision half-life measurement for the superallowed β+ emitter 26Al(m) was performed at the TRIUMF-ISAC radioactive ion beam facility yielding T 1/2 6346.54 ± 0.46(stat) ± 0.60 (syst) ms, consistent with, but 2.5 times more precise than, the previous world average. The 26Al(m) half-life and ft value, 3037.53(61) s, are now the most precisely determined for any superallowed β decay. Combined with recent theoretical corrections for isospin-symmetry-breaking and radiative effects, the corrected Ft value for (26)Al(m), 3073.0(12) s, sets a new benchmark for the high-precision superallowed Fermi β-decay studies used to test the conserved vector current hypothesis and determine the V(ud) element of the Cabibbo-Kobayashi-Maskawa quark mixing matrix.

The branching ratio for the superallowed beta(+) decay of (38)K(m) was measured at TRIUMF's ISAC radioactive ion beam facility. The M3 internal transition between the isomer and the ground state of (38)K(m) was observed with a branching ratio of 330(43) ppm. A search for the nonanalogue beta-decay branch to the first excited 0(+) state in (38)Ar was also performed and yielded an upper limit of < or =12 ppm at 90% C.L. These measurements lead to a revised superallowed branching ratio for (38)K(m) of 99.967(4)%, and increase the (38)K(m) ft value by its entire quoted uncertainty to ft=3052.1(10) s. Implications for tests of the nuclear-structure dependent corrections in superallowed beta decays and the extraction of the Cabibbo-Kobayashi-Maskawa matrix element V(ud) are discussed.

A high-precision branching ratio measurement for the superallowed beta+ decay of 62Ga was performed at the Isotope Separator and Accelerator radioactive ion beam facility. Nineteen gamma rays emitted following beta+ decay of 62Ga were identified, establishing the dominant superallowed branching ratio to be (99.861+/-0.011)%. Combined with recent half-life and Q-value measurements, this branching ratio yields a superallowed ft value of 3075.6+/-1.4 s for 62Ga decay. These results demonstrate the feasibility of high-precision superallowed branching ratio measurements in the A>or=62 mass region and provide the first stringent tests of the large isospin-symmetry-breaking effects predicted for these decays.

Three rotational bands in 74Kr were studied up to (in one case one transition short of) the maximum spin I(max) of their respective single-particle configurations. Their lifetimes have been determined using the Doppler-shift attenuation method. The deduced transition quadrupole moments reveal a modest decrease, but far from a complete loss of collectivity at the maximum spin I(max). This feature, together with the results of mean field calculations, indicates that the observed bands do not terminate at I = I(max).

The decay-out process of the yrast superdeformed band in 59Cu has been investigated. The firm determination of spin, parity, excitation energy, and configuration of the states involved in this process constitutes a unique situation for a detailed understanding of the decay-out mechanism. A theoretical model is introduced that includes a residual interaction and tunneling matrix element between bands, calculated in the configuration-dependent cranked Nilsson-Strutinsky model. This interaction causes the decay to occur via a small number of observed doorway states.

Lifetimes of states in the lowest lying positive parity band in 106Cd have been measured using the Doppler shift attenuation method. The deduced B(E2) transition rates show a marked decrease with increasing spin. Cranking and semiclassical model calculations suggest that the structure has the character of a shears-type band resulting from the coupling of g(9/2) proton holes to aligned pairs of h(11/2) and g(7/2) neutron particles. This is the first clear evidence for the phenomenon of "antimagnetic" rotation in nuclei.

High-angular-momentum states in 108Cd were populated via the (64)Ni((48)Ca,4n) reaction at a beam energy of 207 MeV. Gamma rays were detected using the Gammasphere array. A rotational band has been observed with a dynamic moment of inertia and deduced lower limit of the quadrupole moment suggesting a major-to-minor axis ratio larger than 1.8:1, placing it among the most deformed structures identified in any nucleus, to date.