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The ground-state Gamow-Teller transition in the decay of $^{14}\mathrm{O}$ is strongly hindered and the electron spectrum shape deviates markedly from the allowed shape. A reanalysis of the only available data on this spectrum changes the branching ratio assigned to this transition by seven standard deviations: Our new result is $(0.54\ifmmode\pm\else\textpm\fi{}0.02)%$. The Kurie plot data from two earlier publications are also examined, and a revision to their published branching ratios is recommended. The required nuclear matrix elements are calculated with the shell model, and, for the first time, consistency is obtained between the M1 matrix element deduced from the analog \ensuremath{\gamma} transition in $^{14}\mathrm{N}$ and that deduced from the slope in the shape-correction function in the \ensuremath{\beta} transition, a requirement of the conserved-vector current hypothesis. This consistency is obtained, however, only if renormalized rather than free-nucleon operators are used in the shell-model calculations. In the mirror decay of $^{14}\mathrm{C}$, a similar situation occurs. Consistency among the $^{14}\mathrm{C}$ lifetime, the slope of the shape-correction function, and the M1 matrix element from \ensuremath{\gamma} decay can be achieved only with renormalized operators in the shell-model calculation.

The masses of the radioactive nuclei {sup 46}V and its decay daughter {sup 46}Ti have been measured with the Canadian Penning Trap on-line Penning trap mass spectrometer to a precision of 1x10{sup -8}. A Q{sub EC} value of 7052.90(40) keV for the superallowed beta decay of {sup 46}V is obtained from the difference of these two masses. With this precise Q value, the Ft value for this decay is determined with improved precision. An investigation of an earlier Q-value measurement for {sup 46}V uncovers a set of 7 measurements that cannot be reconciled with modern data and affects previous evaluations of V{sub ud} from superallowed Fermi decays. A new evaluation, adding our new data and removing the discredited subset, yields new values for G{sub V} and V{sub ud}. When combined with recent results for V{sub us}, this yields modified constraints for the unitarity of the Cabibbo-Kobayashi-Maskawa matrix and other extensions of the standard model.

We have measured the total intensity of K x rays relative to 129.4-keV \ensuremath{\gamma} rays from decay of the second excited state in $^{191}\mathrm{Ir}$. This ($M1+E2$) transition was observed following the \ensuremath{\beta} decay of 15.4-d $^{191}\mathrm{Os}$. Our measured ratio yields the result ${\ensuremath{\alpha}}_{K}{\ensuremath{\omega}}_{K}=2.044(11)$. When combined with a recent measurement of the same ratio for the 80.2-keV $M4$ transition from $^{193}\mathrm{Ir}{}^{m}$, this result strongly confirms the need for the K-shell hole to be included in calculations of internal-conversion coefficients ${\ensuremath{\alpha}}_{K}$. Since the ${\ensuremath{\alpha}}_{K}$ value calculated for the $^{191}\mathrm{Ir}$ transition is virtually independent of the hole treatment, our result also yields a model-independent value for the iridium fluorescence yield, ${\ensuremath{\omega}}_{K}=0.954(9)$.

A complete and critical survey is presented of all half-life, decay-energy, and branching-ratio measurements related to 20 superallowed ${0}^{+}\ensuremath{\rightarrow}{0}^{+}$ decays; no measurements are ignored, although some are rejected for cause and others updated. A new calculation of the statistical rate function f is described and experimental $ft$ values determined. The associated theoretical corrections needed to convert these results into ``corrected'' $\mathcal{F}t$ values are discussed, and careful attention is paid to the origin and magnitude of their uncertainties. As an exacting confirmation of the conserved vector current hypothesis, the corrected $\mathcal{F}t$ values are seen to be constant to three parts in ${10}^{4}$. These data are also used to set a new limit on any possible scalar interaction (assuming maximum parity violation) of ${C}_{S}/{C}_{V}=\ensuremath{-}(0.00005\ifmmode\pm\else\textpm\fi{}0.00130)$. The average $\mathcal{F}t$ value obtained from the survey, when combined with the muon liftime, yields the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, ${V}_{ud}=0.9738\ifmmode\pm\else\textpm\fi{}0.0004$, and the unitarity test on the top row of the matrix becomes $|{V}_{ud}|{}^{2}+|{V}_{us}|{}^{2}+|{V}_{ub}|{}^{2}=0.9966\ifmmode\pm\else\textpm\fi{}0.0014$ using the Particle Data Group's currently recommended values for ${V}_{us}$ and ${V}_{ub}$. If ${V}_{us}$ comes instead from two recent results on ${K}_{e3}$ decay, the unitarity sum becomes 0.9996(11). Either result can be expressed in terms of the possible existence of right-hand currents. Finally, we discuss the priorities for future theoretical and experimental work with the goal of making the CKM unitarity test more definitive.

High-precision measurements of the half-life and \ensuremath{\beta}-branching ratios for the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of $^{26}\mathrm{Na}$ to $^{26}\mathrm{Mg}$ have been measured in \ensuremath{\beta}-counting and \ensuremath{\gamma}-decay experiments, respectively. A 4\ensuremath{\pi} proportional counter and fast tape transport system were employed for the half-life measurement, whereas the \ensuremath{\gamma} rays emitted by the daughter nucleus $^{26}\mathrm{Mg}$ were detected with the $8\ensuremath{\pi}$ \ensuremath{\gamma}-ray spectrometer, both located at TRIUMF's isotope separator and accelerator radioactive beam facility. The half-life of $^{26}\mathrm{Na}$ was determined to be ${T}_{1/2}=1.07128\ifmmode\pm\else\textpm\fi{}0.00013\ifmmode\pm\else\textpm\fi{}0.00021\phantom{\rule{0.3em}{0ex}}\text{s}$, where the first error is statistical and the second systematic. The logft values derived from these experiments are compared with theoretical values from a full sd-shell model calculation.

A low-noise room temperature 205 GHz heterodyne radiometer has been designed and built for the Upper Atmosphere Research Satellite Microwave Limb Sounder instrument. The radiometer design features a low loss quasi-optical broad-band signal/LO coupler, a solid state local oscillator and a single-ended fundamental mixer.

International audience; The Canadian Penning trap (CPT) mass spectrometer at the Argonne National Laboratory makes precise mass measurements of nuclides with short half-lives. Since the previous ENAM conference, many significant modifications to the apparatus were implemented to improve both the precision and efficiency of measurement, and now more than 60 radioactive isotopes have been measured with half-lives as short as one second and with a precision ( Δm/m) approaching 10-8. The CPT mass measurement program has concentrated so far on nuclides of importance to astrophysics. In particular, measurements have been obtained of isotopes along the rp-process path, in which energy is released from a series of rapid proton-capture reactions. An X-ray burst is one possible site for the rp-process mechanism which involves the accretion of hydrogen and helium from one star onto the surface of its neutron star binary companion. Mass measurements are required as key inputs to network calculations used to describe the rp-process in terms of the abundances of the nuclides produced, the light-curve profile of the X-ray bursts, and the energy produced. This paper will present the precise mass measurements made along the rp-process path with particular emphasis on the "waiting-point" nuclides 68Se and 64Ge.

A new critical survey of all world data on superallowed beta decays provides demanding tests of, and tight constraints on, the weak interaction. In confirmation of the conserved vector current (CVC) hypothesis, the vector coupling coupling constant is demonstrated to be constant to better than 3 parts in 10^4, and any induced scalar current is limited to fs \leq 0.0013 in electron rest-mass units. The possible existence of a fundamental scalar current is similarly limited to |Cs/Cv| \leq 0.0013. The superallowed data also determine the CKM matrix element to be Vud = 0.9738(4). With PDG values for Vus and Vub, the top-row test of CKM unitarity yields Vud^2 + Vus^2 + Vub^2 = 0.9966(14); although, if a recent result on Ke3 decay is used exclusively to obtain Vus, this sum becomes 0.9999(16). Limits on possible right-hand currents are given., 4 pages, one postscript file

The 10.5-day isomer in {sup 193}Ir decays by a single 80.2-keV M4 transition directly to the ground state of that nucleus. We have measured the total intensity of K x rays relative to 80.2-keV {gamma} rays for this transition to be 98.7(6). With the K-shell fluorescent yield for iridium taken to be 0.958(4), this result yields {alpha}{sub K}=103.0(8) for the K-shell internal conversion coefficient (ICC). The calculated {alpha}{sub K} for this transition is particularly sensitive to the treatment of the hole that is created by conversion in the atomic K shell. Recent ICC tables, which ignore the hole, yield {alpha}{sub K}=92.0. We demonstrate that calculations incorporating the hole produce values between 99.6 and 103.3 depending on the approximation used. Our result strongly supports the need to include the hole.

The masses of the radioactive nuclei {sup 22}Mg and {sup 22}Na have been measured with the Canadian Penning trap on-line mass spectrometer to a precision of 3x10{sup -8} and 1x10{sup -8}, respectively. A Q{sub EC} value of 4124.39(73) keV for the superallowed {beta} decay of {sup 22}Mg is obtained from the difference of these two masses. With this precise Q value, the Ft value for this decay is determined with improved precision and is found to be consistent with the existing precision data set of superallowed Fermi emitters. This provides an important test of the isospin symmetry-breaking corrections. If the mass of {sup 22}Mg determined here is used in the calibration of a recent {sup 21}Na(p,{gamma}){sup 22}Mg measurement, part of the discrepancy observed in that measurement is removed.

Previously we used relative and absolute efficiency measurements combined with Monte Carlo calculations to define the efficiency of an HPGe gamma-ray detector with 0.2% accuracy from 50 to 1400 keV. This work has been extended to 4.8 MeV with measurements of relative efficiencies from 24Na, 56Co, and 66Ga sources. The combined results of experiment and calculation yield an efficiency curve up to 3.5 MeV with 0.4% accuracy. Single- and double-escape peak contributions also agree with calculation if positron annihilation-in-flight is incorporated.

The value of the Vud matrix element of the Cabibbo‐Kobayashi‐Maskawa matrix can be derived from nuclear superallowed beta decays, neutron decay and pion beta decay. Today, the most precise value of Vud (0.05% precision) comes from the nuclear decays; and its precision is limited not by experimental error but by the estimated uncertainty in theoretical corrections, which themselves are of order 1%. When combined with the accepted values for Vus and Vub, the result differs at the 98% confidence limit from the unitarity condition for the CKM matrix. The focus of recent work on superallowed beta decay has been to test and refine the small nuclear‐structure‐dependent corrections so that the precision on the value of Vud can be improved and the unitarity test sharpened. A consistent set of calculated corrections has been produced not only for the nine superallowed transitions currently measured to high precision, but for a number of additional superallowed transitions in nuclei not previously accessible to exac...

The half-life, 3.8755(12) s, and superallowed branching ratio, 0.5315(12), for 22Mg beta decay have been measured with high precision. The latter depended on gamma-ray intensities being measured with an HPGe detector calibrated for relative efficiencies to an unprecedented 0.15%. Previous precise measurements of 0+ --> 0+ transitions have been restricted to the nine that populate stable daughter nuclei. No more such cases exist, and any improvement in a critical Cabibbo-Kobayashi-Maskawa unitarity test must depend on precise measurements of more exotic nuclei. With this branching-ratio measurement, we show those to be possible for T(z)=-1 parents. We obtain a corrected Ft value of 3071(9) s, in good agreement with expectations.

We report a study of the $\ensuremath{\beta}$ decay of ${}^{62}\mathrm{Ga},$ whose dominant branch is a superallowed ${0}^{+}\ensuremath{\rightarrow}{0}^{+}$ transition to the ground state of ${}^{62}\mathrm{Zn}.$ We find the total half-life to be $115.84\ifmmode\pm\else\textpm\fi{}0.25\mathrm{ms}.$ This is the first time that the ${}^{62}\mathrm{Ga}$ half-life has been measured with a purified source. We find that $(0.120\ifmmode\pm\else\textpm\fi{}0.021)%$ of the $\ensuremath{\beta}$ decays are followed by $\ensuremath{\gamma}$ cascades that pass through the ${}^{62}\mathrm{Zn}$ ${2}^{+}$ first excited state at 0.954 MeV. The branching ratio to the first-excited ${0}^{+}$ state in ${}^{62}\mathrm{Zn}$ at 2.33 MeV is $l0.043%.$ We conclude that the branching ratio for the superallowed transition is ${99.85}_{\ensuremath{-}0.15}^{+0.05}%.$

We describe a small multi-parametric acquisition system based on KmaxNT software for a Windows NT computer operating-system. The system will be used for very precise measurements and, thus, our main goal was to reduce the system dead-time to a minimum. As presented, the acquisition system introduces essentially no extra dead-time relative to that corresponding to the digital converters. It also includes converters with a wide range of conversion times (e.g. the EG&G Ortec ADC, model AD413A and the LeCroy QDC, model 4300B). The events are buffered in two FERA/CAMAC dual-port memories (LeCroy, model 4302). The system uses a FERA bus for the readout of the converters and a CAMAC bus for the buffered readout of the events.

The Canadian Penning Trap (CPT) mass spectrometer, currently located at the Argonne National Laboratory (ANL), is designed to make precise mass measurements of a wide variety of nuclides with half-lives longer than 30 ms. The radioactive nuclides investigated here are produced through fusion-evaporation reactions using heavy-ion beams from the Argonne Tandem Linac Accelerator System (ATLAS). Once created, the nuclides of interest are separated from the beam using a gas-filled magnetic spectrometer. They are then stopped in a gas catcher filled with 150 Torr of helium, extracted and subsequently guided to a radio-frequency quadrupole ion trap where they are accumulated before being transferred to a high-precision Penning trap. This paper will discuss the mass measurement program underway at ANL using the CPT mass spectrometer with particular emphasis on the latest mass measurements obtained of proton-rich nuclides at A ~ 68 from the reaction of a 225 MeV 58Ni beam upon a 12C target.

Precise measurements of the ft- values for superallowed nuclear β-decay yield results that support conservation of the weak vector current but violate the unitarity of the Cabibbo-Kobayashi-Maskawa matrix by more than two standard deviations. This apparent violation of the Standard Model has led to considerable theoretical and experimental activity largely focussed on reducing uncertainties in the small correction terms that account for charge-dependent nuclear effects. This activity is outlined and the prospects for future sharpening of the unitarity test are assessed.

The measured $ft$-values for superallowed $0^{+} \to 0^{+}$ nuclear $\beta$-decay can be used to obtain the value of the vector coupling constant and thus to test the unitarity of the Cabibbo-Kobayashi-Maskawa matrix. An essential requirement for this test is accurate calculations for the radiative and isospin symmetry-breaking corrections that must be applied to the experimental data. We present a new and consistent set of calculations for the nuclear-structure-dependent components of these corrections. These new results do not alter the current status of the unitarity test -- it still fails by more than two standard deviations -- but they provide calculated corrections for eleven new superallowed transitions that are likely to become accessible to precise measurements in the future. The reliability of all calculated corrections is explored and an experimental method indicated by which the structure-dependent corrections can be tested and, if necessary, improved., Comment: Revtex4, one figure

The most precise value of V(ud), which is obtained from superallowed nuclear beta decay, leads to a violation of Cabibbo-Kobayashi-Maskawa unitarity by 2.2sigma. Experiments are underway on two continents to test and improve this result through decay studies of odd-odd N = Z nuclei with A>or=62. We show, in a series of illustrative shell-model calculations, that numerous weak Gamow-Teller branches are expected to compete with the superallowed branch in each of these nuclei. Though the total Gamow-Teller strength is significant, many of the individual branches will be unobservably weak. Thus, new techniques must be developed if reliable ft values are to be obtained with 0.1% precision for the superallowed branches.

Beta-delayed proton emission was first observed thirty-six years ago. At the time, its unique signature opened a window onto a new world of exotic nuclei: on-line isotope separation was not yet available to isolate newly produced nuclei, but a readily separable decay mode was a fine alternative. In the first two decades after its discovery, beta-delayed proton decay was a rich source of spectroscopic information on nuclei far from stability, yielding everything from analog states and atomic masses to level densities and excited-state lifetimes in the femtosecond region. However, with the advent of more sophisticated methods for the production and isolation of exotic nuclei, the importance of beta-delayed protons as an identifier of new nuclei effectively disappeared. Nevertheless, the potential spectroscopic value of the process remains undiminished. In fact, as the number of known beta-decaying nuclei steadily increases, beta-delayed proton emission is seen to be a widely occurring phenomenon. Its usefulness needs to be rediscovered. This paper presents an overview of beta-delayed proton emission, its occurrence, its usefulness and its potential for the future.

Superallowed $0^+ \to 0^+$ nuclear beta decay provides a direct measure of the weak vector coupling constant, $\GV$. We survey current world data on the nine accurately determined transitions of this type, which range from the decay of $^{10}$C to that of $^{54}$Co, and demonstrate that the results confirm conservation of the weak vector current (CVC) but differ at the 98% confidence level from the unitarity condition for the Cabibbo-Kobayashi-Maskawa (CKM) matrix. We examine the reliability of the small calculated corrections that have been applied to the data, and conclude that there are no evident defects although the Coulomb correction, $\delta_C$, depends sensitively on nuclear structure and thus needs to be constrained independently. The potential importance of a result in disagreement with unitarity, clearly indicates the need for further work to confirm or deny the discrepancy. We examine the options and recommend priorities for new experiments and improved calculations. Some of the required experiments depend upon the availability of intense radioactive beams. Others are possible with existing facilities., Comment: 12 pages, LaTeX with aipproc2.sty (included) and epsf.sty; Invited talk at Nuclear Structure 98, Gatlinburg, Tennessee, Aug. 1998

Superallowed $0^+ \to 0^+$ nuclear beta decay provides a direct measure of the weak vector coupling constant, $\GV$. We survey current world data on the nine accurately determined transitions of this type, which range from the decay of $^{10}$C to that of $^{54}$Co, and demonstrate that the results confirm conservation of the weak vector current (CVC) but differ at the 98% confidence level from the unitarity condition for the Cabibbo-Kobayashi-Maskawa (CKM) matrix. We examine the reliability of the small calculated corrections that have been applied to the data, and assess the likelihood of even higher quality nuclear data becoming available to confirm or deny the discrepancy. Some of the required experiments depend upon the availability of intense radioactive beams. Others are possible today., 6 pages, LaTeX with aipproc.sty and epsf.sty; Talk at Int. Conf. on Exotic Nuclei and Atomic Masses (ENAM98), Michigan, June 1998

Beta-decay and muon-capture experiments in nuclei are reviewed. The conserved vector current hypothesis is confirmed through the observed constancy of the vector coupling constant determined from the superallowed Fermi transitions and from the measurement of the weak-magnetism term in mirror Gamow-Teller transitions. The axial-vector and pseudoscalar coupling constants in the nucleon are determined from neutron decay and muon capture on the proton respectively. In finite nuclei, evidence for these coupling constants being reduced relative to their free-nucleon values is discussed. Meson-exchange currents are shown to be an important correction to the time-like part of the axial current as evident in first-forbidden beta decays. Tests of the Standard Model are discussed, as well as extensions beyond it involving right-hand currents and scalar interactions.

In several radiative proton capture reactions important in novae and XRBs, the resonant parts play the capital role. We use decay spectroscopy techniques to find these resonances and study their properties. We have developed techniques to measure beta- and beta-delayed proton decay of sd-shell, proton-rich nuclei produced and separated with the MARS recoil spectrometer of Texas A&M University. The short-lived radioactive species are produced in-flight, separated, then slowed down (from about 40 MeV/u) and implanted in the middle of very thin Si detectors. This allows us to measure protons with energies as low as 200 keV from nuclei with lifetimes of 100 ms or less. At the same time we measure gamma-rays up to 8 MeV with high resolution HPGe detectors. We have studied the decay of 23Al, 27P, 31Cl, all important for understanding explosive H-burning in novae. The technique has shown a remarkable selectivity to beta-delayed charged-particle emission and works even at radioactive beam rates of a few pps. The states populated are resonances for the radiative proton capture reactions 22Na(p,γ)23Mg (crucial for the depletion of 22Na in novae), 26mAl(p,γ)27Si and 30P(p,γ)31S (bottleneck in novae and XRB burning), respectively. Lastly, results with a new detector that allowed us to measure down to about 80 keV proton energy are announced.

We have studied the β-delayed proton decay of 23Al with a novel detector setup at the focal plane of the MARS separator at the Texas A&M University to resolve existing controversies about the proton branching of the IAS in 23Mg and to determine the absolute proton branchings by combining our results to the latest βγ-decay data. We have made also a high precision mass measurement of the ground state of 23Al to establish more accurate proton separation energy of 23Al. Here the description of the used techniques along with preliminary results of the experiments are given.

Studies of superallowed 0+→0+ β decays furnish the necessary experimental data to test the Conserved Vector Current hypothesis and extract a precise value for the weak vector coupling constant, Gv. The Vud quark-mixing element of the Kobayashi-Maskawa matrix is directly related to this coupling constant and the one extracted from muon decay. Consequently, its value is essential to establishing the unitarity of this matrix and the viability of the three-generation Standard Model as well as probing for the effects of right-handed currents and heavy neutrinos.

Purpose: Developing a method of an HPGe detector precise γ efficiency calibration which is very important for accurate radiation detection during cancerradiotherapy practices. Method and Materials: 24 Al radioactive nucleus produced and separated with Momentum Achromat Recoil Spectrometer (MARS) at the K500 superconducting cyclotron of Texas A&M University has positron decays followed by γ transitions up to 8 MeV from 24 Mg excited states, which is used for a β‐γ coincidence measurement with a 1‐mm‐thick BC404 plastic scintillator, an HPGe detector and a fast tape‐transport system to calibrate the HPGe detector.Results: By carefully considering the effects of summing, positron annihilation, internal conversion, and β detector efficiency when analyzing 24 Al spectrum, we got the efficiency for γ‐ray 7070 keV at 49 mm distance away from the source sample 24 Al , which was 0.192(6)%. The Monte Carlo(MC) simulation with CYLTRAN code gave a value of 0.189%, which was in agreement with our measurements. The precise efficiency calibration curve of the HPGe detector up to 7070 KeV at 49 mm distance away from the source sample was obtained. By using the same procedure, we got the efficiency for the 7070 keV γ‐ray at 151 mm distance away from the source sample 24 Al , which was 0.0385(8)%. MC simulation value was 0.0399%, which differed from measurement by 4(2)%. This discrepancy led us to assign an uncertainty of 4% to our efficiencies at 151 mm up to 7070 KeV. The Monte Carlo calculations also reproduced the intensity of observed single‐and double‐escape peaks, providing that the effects of positron annihilation‐in‐flight were incorporated. Conclusion: A new method was established. The precise calibration curves obtained from this work are useful for accurate radiation detection and improving quality control to quality assurance (QA) for intensity‐modulated radiation therapy (IMRT). Research sponsored by Department of Energy and Robert Welch Foundation.

The UARS Microwave Limb Sounder (MLS) measures ClO (~25-45 km), O3 (~15-80 km), H2O (~15-85 km), and pressure (~30-60 km). ClO is the dominant form of chlorine which destroys ozone in the stratosphere; its measurement on a global scale, which will be done by the MLS, is essential for understanding and monitoring the depletion of stratospheric ozone by chlorine from industrial products. Simultaneous measurements of O3 and H2O provide additional important information on stratospheric ozone chemistry. The H2O and O3 measurements will be to higher altitudes than previously explored on a global basis. The pressure measurements provide the vertical reference for composition measurements. Secondary MLS measurement goals include H2O2, HNO3, temperature, and one component of wind in the mesosphere. Measurements are made by observing millimeter-wavelength spectral line thermal emission as the instrument field-of- view is vertically scanned through the atmospheric limb. All are made simultaneously and continuously, at all times of day and night. Prior development for the UARS MLS included an aircraft [1,2] and balloon [3,4,5] MLS. Development has also started on an MLS experiment for the future Earth observing system (Eos); the Eos MLS is described in a separate paper presented at this meeting.

Measurements of superallowed 0[sup +][r arrow]0[sup +] nuclear [beta] decays, corrected for radiative and charge-dependent effects, yield fundamental properties of the weak interaction. Model predictions of the necessary corrections exist, but they have never been tested directly by experiment. The present work reports, for the first time, observations of (or limits on) nonanalog 0[sup +][r arrow]0[sup +] branches in [sup 38[ital m]]K, [sup 46]V, [sup 50]Mn, and [sup 54]Co, and tests of the model predictions for isospin-mixing corrections. The resulting unitarity test of the top row of the Kobayashi-Mashawa matrix is 0.9983[plus minus]0.0015.

The isotope 74 Br was produced as the daughter of 74 Kr. This production mode leads to a 74 Br isomer whose half-life was measured to be 25.3 ± 0.3 min. A decay scheme based on the 85 observed β-delayed γ-rays suggests the spin assignment (0, 1) − . Previous detailed studies have reported a 41.5 ± 1.5 min, 4 − isomer of 74 Br which is produced directly in nuclear reactions. There is no indication which of the two isomers represents the ground state of 74 Br.

Recent experimental data have significantly improved the overall consistency of ft values for superallowed 0+ → 0+ nuclear β-decays. All relevant data are collated in this paper and theoretical electromagnetic corrections applied. The resulting corrected F t values are constant to within two parts in 3000. This constitutes an exacting experimental confirmation of the CVC hypothesis. Statistical tests applied to the data gave no positive indication of any inadequacies in the theoretical corrections. These tests also set a new limit for the Fierz interference constant, bF ≦ 0.006, which is an order of magnitude smaller than previous determinations. The value of the vector coupling constant of nuclear β-decay, established from these data, is compared with muon and hyperon β-decays as a test of Cabibbo universality. It is shown that universality is achieved under specific conditions on the mass of the neutral vector boson.

The response of a hybrid detector telescope to mono-energetic beams of positrons and electrons has been determined. The particle beams were obtained from the Chalk River iron-free π√2 beta spectrometer, which was equipped with radioactive sources of 66 Ga and 106 Ru. The measured positron response function was described by one constant and six energy dependent parameters, whereas two constant and three energy dependent parameters sufficed for the electron case. We conclude from a comparison of the detector response for the two types of particles that the practice of deriving positron response functions from measured electron response functions is inadequate for experiments where good precision is required.

Isgur has shown that some properties of the weak neutral current can be studied by investigating a nuclear Jπ = 0− ↔ 0+ transition. We have used the (p,n) reaction on targets of 42Ca and 46Ti to populate states in the self-conjugate nuclei 42Sc and 46V in a search for a Jπ = 0− isomer. The possible production of the isomer was probed by searching for long-lived β+-and γ-ray activities. For each nucleus our results indicate that the yield of a 0− isomeric state is −3 of that for the ground state.

The new isotopes $_{72}^{163}\mathrm{Hf}$ [${T}_{\frac{1}{2}}=40.0(6)$ s] and $_{72}^{162}\mathrm{Hf}$ [${T}_{\frac{1}{2}}=37.6(8)$ s] were produced in $_{60}^{142}\mathrm{Nd}$ ($_{12}^{24}\mathrm{Mg}$, $\mathrm{xn}$) reactions and transported to a measuring station by use of the He-jet technique. Decay properties were observed with $\ensuremath{\alpha}$, $\ensuremath{\gamma}$, and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ spectroscopy. The $Z$ assignment of the new isotopes was based on a cross bombardment, $_{12}^{24}\mathrm{Mg}$+$_{59}^{141}\mathrm{Pr}$, and on results of $\ensuremath{\gamma}$-x-ray coincidence measurements. The mass assignment was deduced from measured excitation functions. Beta-delayed $\ensuremath{\gamma}$ rays were identified, 11 for $^{163}\mathrm{Hf}$ and 3 for $^{162}\mathrm{Hf}$, and level schemes for $_{71}^{163}\mathrm{Lu}$ and $_{71}^{162}\mathrm{Lu}$ are proposed based on the results of intensity and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence measurements. A small $\ensuremath{\alpha}$ branch [${I}_{\ensuremath{\alpha}}={0.0087 }_{(\ensuremath{-}37}^{+17)}$%] with a decay energy of ${E}_{\ensuremath{\alpha}}=4308$ (10) keV was found in the decay of $^{162}\mathrm{Hf}$. The reduced $\ensuremath{\alpha}$ width ${W}_{\ensuremath{\alpha}}={2.6}_{(\ensuremath{-}1.2}^{+0.6)}$ for $^{162}\mathrm{Hf}$ is in accordance with those for neighboring nuclei. With the new $^{162}\mathrm{Hf}$ $\ensuremath{\alpha}$-decay energy, mass values were derived for $_{72}^{162}\mathrm{Hf}$, $_{74}^{166}\mathrm{W}$, $_{76}^{170}\mathrm{Os}$, $_{78}^{174}\mathrm{Pt}$, and $_{80}^{178}\mathrm{Hg}$. The new masses as well as values deduced for two-proton binding energies are compared with predictions of current mass formulas.RADIOACTIVITY $^{163,162}\mathrm{Hf}$ from $^{142}\mathrm{Nd}$($^{24}\mathrm{Mg}$,$\mathrm{xn}$); measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, ${E}_{\ensuremath{\alpha}}$, ${I}_{\ensuremath{\alpha}}$, and ${T}_{\frac{1}{2}}$; $^{163,162}\mathrm{Lu}$ deduced level schemes; deduced reduced $\ensuremath{\alpha}$ width for $^{162}\mathrm{Hf}$; deduced mass values for $^{162}\mathrm{Hf}$, $^{166}\mathrm{W}$, $^{170}\mathrm{Os}$, $^{174}\mathrm{Pt}$, and $^{178}\mathrm{Hg}$. He-jet technique; Ge(HP), Ge(Li), and Si surface-barrier detectors.

An on-line isotope separator facility has been built at the Chalk River MP tandem Van de Graaff accelerator. The main design characteristics are high resolution ( M / ΔM > 7000) and a current capability of 20 mA for masses between 1 and 300. The system incorporates an inhomogeneous 135° magnet of high dispersion, D = 2250mm. A novel feature, two pairs of corrective coils acting independently on the linear and quadratic magnetic field terms, has proven to be extremely advantageous for fine tuning of the magnetic dipole. The separator has been tested off-line, and is now frequently used on-line, with overall efficiencies reaching tens of per cent for light elements such as Na, Cl, K, Mn, Zn and Br.

We have developed a helium jet and skimmer system intended as an interface between a target location at the Chalk River tandem accelerator and the ion source of an on-line separator presently under construction. The system consists of a target chamber, a 125 cm long capillary, and a one stage skimmer chamber. The designs of the target and skimmer chambers allow us to vary a large number of independent flow and geometrical parameters with accurate reproducibility. Experiments with the β-delayed proton emitter 25 Si (t 1 2 = 218 ms ) produced in the reaction 24 Mg( 3 He, 2n) 25 Si show that under optimized conditions about 75% of the reaction products leaving the target are transported to the skimmer. Of those, more than 90% pass through the skimmer orifice, which separates off 97.5% of the transport gas, helium. By introducing an additional helium flow across the skimming orifice the amount of helium separated off the transport jet can be increased to beyond 99.85%, leaving the high throughput of recoils unaffected.

The T z =+ 1 2 beta-delayed proton precursors 65Ge, 69Se, 73Kr and 77Sr have been identified and their decay energies, half-lives and proton branching ratios determined. The half-life of the previously unreported 77Sr is 9.0± 1.0 s.

The Chalk River On-line Isotope Separator has been used by itself to determine the masses of unstable nuclei. The addition of a high-resolution mass spectrometer for the further analysis of beams from the separator, currently on-line at the TASCC facility at Chalk River, offers an improvement in the accuracy and sensitivity of the mass measurement system. The characteristics and projected performance of the proposed apparatus are described.

The decay of 74 Kr has been studied. Its half-life was determined to be T 1 2 = 11.50 ± 0.11 min . A decay scheme is proposed, based on γ-γ and β + -γ coincidence measurements, which takes account of 99 % of the strength of 57 observed γ-rays. The total decay energy was measured to be Q EC = 3327 ± 125 keV. The decay feeds the (0, 1) − , T 1 2 = 25.3 min isomer of 74 Br.

Recent advances in nuclear accelerators and experimental techniques have led to an increased ability to synthesize new isotopes. As isotopes are produced with more and more extreme combinations of neutrons and protons in their nuclei, new phenomena are observed, and the versatility of the nucleus is increased as a laboratory for studying fundamental forces. Among the newly discovered decay modes are (i) proton radioactivity, (ii) triton, two-proton, two-neutron, and three-neutron decays that are beta-delayed, as well as (iii)(14)C emission in radioactive decay. Precise tests of the properties of the weak force have also been achieved.

Kinematic shifts of α particles from the β + delayed α decay of 20 Na have been measured as a function of the energy of the coincident β + particles. Beta-neutrino-alpha triple-correlation coefficients were determined for six β + transitions from 20 Na( J π , T = 2 + , 1) to excited 2 + states in 20 Ne; ft values were also deduced. For the superallowed 2 + → 2 + transition to the T = 1 analogue state in 20 Ne the results yielded a measurement of the vector weak coupling constant, G ' V /( c ) 3 = (1.103±0.028) × 10 −5 GeV −2 . For the other five (allowed Gamow-Teller) transitions, limits were established for the vector (Fermi) component and, from them, limits deduced on isospin mixing amplitudes for the daughter states in 20 Ne. Weak, previously unknown, β-transitions were assigned to the decay of 20 Na based on the observation of new α groups and one new γ-transition.

A new technique has been developed to measure the spacing of atomic mass doublets of radioactive isotopes directly with an on-line isotope separator. It relies not on ion detection but on observation of the specific radioactive signature of the isotopes under study. Consequently, line shapes and centroids can be determined, free of interference and with great accuracy, even if the corresponding beams strongly overlap or if they are contaminated by unwanted isobars or isomers. In particular, it is of no consequence if one or both members of the doublet are masked by stable background peaks. Doublets are peak matched as in a conventional mass spectrometer. The technique has been evaluated with beams of radioactive nuclides whose masses are known independently. Based on careful calibrations, two new mass values have been obtained: 72Br, 71 936 340 ± 430 μu and 63Ga, 62 939 570 ± 150 μu.

Neutron-deficient caesium isotopes with mass numbers from 114 to 118 have been studied at the ISOLDE facility. Half-lives have been determined from counting of β-particles, β-delayed protons, and γ-rays. A short-lived isomer ( T 1 2 = 0.7 sec ) in 116Cs has been observed and the new delayed-particle precursors 116Cs (protons and α-particles), 115Cs (protons), and 114Cs (protons and α-particles) have been identified. Coincidences between delayed particles and γ-rays have been measured for 118Cs (pγ and αγ) and 116Cs (pγ). A search for the possible proton-radioactive isotope 113Cs has been performed and an upper limit for its production yield is given.

Neutron-deficient osmium and rhenium isotopes were produced by bombarding an enriched144Sm target with beams of27Al and28Si. Previously reported decay data concerning168,169,170Os were confirmed. Three newα groups, observed in the144Sm+27Al reaction, were assigned to the decay of166,167,168Re based on excitation functions,α-energy systematics and theoretical half-life predictions. Their decay properties are: $$\begin{gathered} {}^{166}\operatorname{Re} , E_\alpha = 5,372 (10) keV, T_{1/2} = 2.8 (3) s; \hfill \\ {}^{167}\operatorname{Re} , E_\alpha = 5,136 (8) keV, T_{1/2} = 6.1 (2) s and \hfill \\ {}^{168}\operatorname{Re} , E_\alpha = 4,894 (10) keV, T_{1/2} = 6.9 (8) s. \hfill \\ \end{gathered}$$