Search

Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei, GRIFFIN, is a new high-efficiency γ -ray spectrometer designed for use in decay spectroscopy experiments with low-energy radioactive ion beams provided by TRIUMF’s Isotope Separator and Accelerator (ISAC-I) facility. GRIFFIN is composed of sixteen Compton-suppressed large-volume clover-type high-purity germanium (HPGe) γ -ray detectors combined with a suite of ancillary detection systems and coupled to a custom digital data acquisition system. The infrastructure and detectors of the spectrometer as well as the performance characteristics and the analysis techniques applied to the experimental data are described.

A high-precision branching ratio measurement for the superallowed Fermi $\beta^{+}$ emitter $^{62}$Ga was performed with the Gamma-Ray Infrastructure for Fundamental Investigations of Nuclei (GRIFFIN) spectrometer at the Isotope Separator and Accelerator (ISAC) radioactive ion beam facility at TRIUMF. The high efficiency of the GRIFFIN spectrometer allowed 63 $\gamma$-ray transitions, with intensities down to $\approx$1 part per million (ppm) per $^{62}$Ga $\beta^{+}$ decay, to be placed in the level scheme of the daughter nucleus $^{62}$Zn, establishing the superallowed $\beta$ branching ratio for $^{62}$Ga decay to be 99.8577$^{+0.0023}_{-0.0029}\%$, a factor of 4 more precise than the previous world average. For several cascades, $\gamma-\gamma$ angular correlation measurements were performed to assign spins and/or determine the mixing ratios of transitions. In particular, the spin of the 2.342 MeV excited state in the daughter nucleus $^{62}$Zn was definitively assigned as $J = 0$. This assignment resolves a discrepancy between previous measurements and has important implications for the isospin symmetry breaking correction, $\delta_{C1}$, in $^{62}$Ga superallowed Fermi $\beta$ decay.

A search has been performed for neutrinos from two sources, the $hep$ reaction in the solar $pp$ fusion chain and the $��_e$ component of the diffuse supernova neutrino background (DSNB), using the full dataset of the Sudbury Neutrino Observatory with a total exposure of 2.47 kton-years after fiducialization. The $hep$ search is performed using both a single-bin counting analysis and a likelihood fit. We find a best-fit flux that is compatible with solar model predictions while remaining consistent with zero flux, and set a one-sided upper limit of $��_{hep} < 30\times10^{3}~\mathrm{cm}^{-2}~\mathrm{s}^{-1}$ [90% credible interval (CI)]. No events are observed in the DSNB search region, and we set an improved upper bound on the $��_e$ component of the DSNB flux of $��^\mathrm{DSNB}_{��_e} < 19~\textrm{cm}^{-2}~\textrm{s}^{-1}$ (90% CI) in the energy range $22.9 < E_��< 36.9$~MeV., 11 pages, 6 figures

A high-precision half-life measurement for the superallowed Fermi ${\ensuremath{\beta}}^{+}$ emitter $^{22}\mathrm{Mg}$ was performed at the TRIUMF-ISAC facility using a $4\ensuremath{\pi}$ proportional gas counter. The result of ${T}_{1/2}=3.87400\ifmmode\pm\else\textpm\fi{}0.00079$ s is a factor of 3 more precise than the previously adopted world average and resolves a discrepancy between the two previously published $^{22}\mathrm{Mg}$ half-life measurements.

A high-precision half-life measurement for the superallowed ${\ensuremath{\beta}}^{+}$ transition between the isospin $T=1/2$ mirror nuclei $^{21}\mathrm{Na}$ and $^{21}\mathrm{Ne}$ has been performed at the TRIUMF-ISAC radioactive ion beam facility yielding ${T}_{1/2}=22.4506(33)$ s, a result that is a factor of 4 more precise than the previous world-average half-life for $^{21}\mathrm{Na}$ and represents the single most precisely determined half-life for a transition between mirror nuclei to date. The contribution to the uncertainty in the $^{21}\mathrm{Na} \mathcal{F}{t}^{\mathrm{mirror}}$ 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.

High precision measurements of the $ft$ values for superallowed Fermi $\beta$ transitions between $J^\pi~=~0^+$ isobaric analogue states allow for stringent tests of the electroweak interaction described by the Standard Model. These transitions provide an experimental probe of the Conserved-Vector-Current hypothesis, enable the most precise determination of the up-down ($V_{ud}$) element of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix, and allow one to set stringent limits on the existence of scalar currents in the weak interaction. An extensive program of superallowed branching-ratio and half-life measurements at TRIUMF's Isotope Separator and Accelerator (ISAC) facility has covered the full range of superallowed emitters, from the lightest case, $^{10}$C, to the heaviest case for which precision data are currently available, $^{74}$Rb. These experiments have been performed using a 4$\pi$ continuous-flow gas proportional $\beta$ counter, the 8$\pi$ $\gamma$-ray spectrometer, and, most recently, the new high-efficiency GRIFFIN $\gamma$-ray spectrometer. In this paper, recent highlights from the superallowed Fermi $\beta$ decay program at TRIUMF will be summarized, including high-precision half-life measurements for all three of the lightest superallowed emitters, $^{10}$C, $^{14}$O, and $^{18}$Ne, with the greatest sensitivity to a potential weak scalar current contribution, as well as high-precision branching-ratio measurements for the heavy superallowed emitters $^{62}$Ga and $^{74}$Rb.

The Sudbury Neutrino Observatory is a 1000 T D 2 O Cerenkov detector that is sensitive to 8 B solar neutrinos. The energy, radius, and direction with respect to the sun is measured for each neutrino event; these distributions are used to separately determine the rates of the charged current, neutral current and electron scattering reactions of neutrinos on deuterium. Assuming an undistorted 8 B spectrum, the ν e component of the 8 B solar flux is φ e = 1.76 +0.05 −0.05 (stat.) +0.09 −0.09 (syst.) × 10 6 cm −2 s −1 based on events with a measured kinetic enegy above 5 MeV. The non- ν e component is φ μτ = 3.41 +0.45 −0.45 (stat.) +0.48 −0.45 (syst.) × 10 6 cm −2 s −1 , 5.3 σ greater than zero, providing strong evidence for solar ν e flavor transformation. The total flux measured with the NC reaction is φ NC = 5.09 +0.044 −0.43 (stat.) +0.46 −0.43 (syst.) × 10 6 cm −2 s −1 , consistent with solar models. The night minus day rate is 14.0% ± 6.3% +1.5 −1.4 % of the average rate. If the total flux of active neutrinos is additionally constrained to have no asymmetry, the ν e asymmetry is found to be 7.0% ± 4.9% +1.3 −1.2 %. A global solar neutrino analysis is terms of matter-enhanced oscillations of two active flavors strongly favors the Large Mixing Angle (LMA) solution.

Data from the Sudbury Neutrino Observatory have been used to constrain the lifetime for nucleon decay to ``invisible'' modes, such as n -> 3 nu. The analysis was based on a search for gamma-rays from the de-excitation of the residual nucleus that would result from the disappearance of either a proton or neutron from O16. A limit of tau_inv > 2 x 10^{29} years is obtained at 90% confidence for either neutron or proton decay modes. This is about an order of magnitude more stringent than previous constraints on invisible proton decay modes and 400 times more stringent than similar neutron modes., Update includes missing efficiency factor (limits change by factor of 2) Submitted to Physical Review Letters

We have performed three searches for high-frequency signals in the solar neutrino flux measured by the Sudbury Neutrino Observatory (SNO), motivated by the possibility that solar $g$-mode oscillations could affect the production or propagation of solar $^8$B neutrinos. The first search looked for any significant peak in the frequency range 1/day to 144/day, with a sensitivity to sinusoidal signals with amplitudes of 12% or greater. The second search focused on regions in which $g$-mode signals have been claimed by experiments aboard the SoHO satellite, and was sensitive to signals with amplitudes of 10% or greater. The third search looked for extra power across the entire frequency band. No statistically significant signal was detected in any of the three searches., 37 pages, 17 figures, submitted to ApJ

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_{1/2}=19.2969±0.0074 s and T_{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_{F}=-0.0018±0.0021 (68% C.L.) for the Fierz interference term and C_{S}/C_{V}=+0.0009±0.0011 for the ratio of the weak scalar to vector couplings assuming left-handed neutrinos.

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_{1/2}=19.2969±0.0074 s and T_{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_{F}=-0.0018±0.0021 (68% C.L.) for the Fierz interference term and C_{S}/C_{V}=+0.0009±0.0011 for the ratio of the weak scalar to vector couplings assuming left-handed neutrinos.

A general technique that corrects γ -ray gated β decay-curve data for detector pulse pile-up is presented. The method includes corrections for non-zero time-resolution and energy-threshold effects in addition to a special treatment of saturating events due to cosmic rays. This technique is verified through a Monte Carlo simulation and experimental data using radioactive beams of Na 26 implanted at the center of the 8 π γ -ray spectrometer at the ISAC facility at TRIUMF in Vancouver, Canada. The β -decay half-life of Na 26 obtained from counting 1809-keV γ -ray photopeaks emitted by the daughter Mg 26 was determined to be T 1 / 2 = 1.07167 ± 0.00055 s following a 27 σ correction for detector pulse pile-up. This result is in excellent agreement with the result of a previous measurement that employed direct β counting and demonstrates the feasibility of high-precision β -decay half-life measurements through the use of high-purity germanium γ -ray detectors. The technique presented here, while motivated by superallowed-Fermi β decay studies, is general and can be used for all half-life determinations (e.g. α -, β -, X-ray, fission) in which a γ -ray photopeak is used to select the decays of a particular isotope.

The isotope separator and accelerator (ISAC) facility located at the TRIUMF laboratory in Vancouver, Canada, is one of the world’s most advanced isotope separator on-line-type radioactive ion beam facilities. An extensive γ-ray spectroscopy programme at ISAC is centred around two major research facilities: (i) the 8π γ-ray spectrometer for β-delayed γ-ray spectroscopy experiments with the low-energy beams from ISAC-I, and (ii) the next generation TRIUMF-ISAC gamma-ray escape suppressed spectrometer (TIGRESS) for in-beam experiments with the accelerated radioactive-ion beams. An overview of these facilities and recent results from the diverse programme of nuclear structure and fundamental interaction studies they support is presented.

A measurement of the half-life of 62Ga was made as part of a programme of high-precision superallowed Fermi β decay studies at the ISAC radioactive beam facility. The experiment was conducted by counting β+ particles from the decay of 62Ga in a 4π gas proportional counter. The half-life was measured to be 116.01 ± 0.19 ms. Several parameters were varied during the experiment to test for systematic effects, but no significant effects were found.

High-resolution γ-ray spectroscopy is essential to fully exploit the unique, high-quality beams available at the next generation of radioactive ion beam facilities such as the TRIUMF isotope separator and accelerator (ISAC). The 8π spectrometer, which consists of 20 Compton-suppressed HPGe detectors, has recently been reconfigured for a vigorous research programme in weak interaction and nuclear structure physics. With the addition of a variety of ancillary detectors it has become the world's most powerful device dedicated to β-decay studies. This paper provides a brief overview of the apparatus and highlights from recent experiments.

The TRIUMF-ISAC Gamma-Ray Escape-Suppressed Spectrometer (TIGRESS) will consist of twelve units of four high-purity germanium (HPGe) crystals in a common cryostat. The outer contacts of each crystal will be divided into four quadrants and two lateral segments for a total of eight outer contacts. The performance of a prototype HPGe four-crystal unit has been investigated. Integrated noise spectra for all contacts were measured. Energy resolutions, relative efficiencies for both individual crystals and for the entire unit, and peak-to-total ratios were measured with point-like sources. Position-dependent performance was measured by moving a collimated source across the face of the detector.

The properties of high-K isomers have been investigated by measuring γ rays from a source of the 31-year 178Hfm2 isomer and from the decay of implanted 178,179Lu beams. Low-intensity transitions have been identified in the decay of 178Hfm2, demonstrating a consistent extension of K-hindrance systematics to higher multipolarities, and elucidating the spin-dependence of the mixing between the two Kπ = 8- bands. A search is underway for new isomers in 178,179Lu and the preliminary results of the analysis are reported. © 2004 Elsevier B.V. All rights reserved.

Precise measurements of the intensities of superallowed Fermi 0+ → 0+β-decays have provided a powerful test of the CVC hypothesis at the level of 3×10-4 and also led to a result in disagreement with unitarity for the CKM matrix at the 98% confidence level. It is essential to address possible trivial explanations for the apparent non-unitarity such as uncertainties in the isospin symmetry-breaking corrections. We have carefully studied the 74Rb →74Kr β-decay in order to measure the non-analog β-decay branching to the 0+ state at 508 keV in 74Kr. We have determined that this branching is < 3×10-4, far smaller than any published theoretical estimate. We also show that high-precision, complete spectroscopy, measuring the major β-branches to excited 0+ and 1+ states, must be performed if one is to obtain a meaningful branching ratio to the excited 0+ state and concomitantly deal, in a substantial way, with the possibility of β feeding to an array of 1+ states.

At low stellar temperatures the energy release due to the CN cycle is regulated by its slowest reaction ${}^{14}\mathrm{N}(p,\ensuremath{\gamma}){}^{15}\mathrm{O}$, the rate of which strongly depends on the subthreshold resonance at ${E}_{\mathrm{c}}.\mathrm{m}.=\ensuremath{-}504\phantom{\rule{0.28em}{0ex}}\mathrm{keV}$, which corresponds to the 6.79 MeV state in ${}^{15}\mathrm{O}$. By using the Doppler-shift attenuation method and the ${}^{3}\mathrm{He}({}^{16}\mathrm{O},\ensuremath{\alpha}){}^{15}\mathrm{O}$ reaction to populate the state, we obtained an upper limit on the lifetime of this state of $\ensuremath{\tau}l1.8\phantom{\rule{0.28em}{0ex}}\mathrm{fs}$ [68.3% confidence level (C.L.)]. In addition we measured the lifetimes of the 6.18 and 6.86 MeV states to be $\ensuremath{\tau}l2.5$ and $\ensuremath{\tau}=13.{3}_{\ensuremath{-}1.2}^{+0.9}\phantom{\rule{0.28em}{0ex}}\mathrm{fs}$, respectively (68.3% C.L.), in good agreement with the literature.

International audience

Presently, the world data for superallowed {beta} decay leads to a result in disagreement (at the 98% confidence level) with the predictions of the minimal standard model for the unitarity of the Cabibbo-Kobayashi-Maskawa matrix. Precise data for the superallowed 0{sup +}{yields}0{sup +} {beta} decay of {sup 74}Rb would provide a critical test of the nucleus-dependent isospin symmetry-breaking corrections that must be calculated for these superallowed Fermi {beta} decays. The present work reports the first precise measurement of the half-life for {sup 74}Rb (t{sub 1/2}=64.761{+-}0.031 ms ). The data were obtained at the radioactive beam facility (ISAC) at TRIUMF using a beam of {approx}4000 {sup 74}Rb ionss{sup -1} .

The {beta} decay of {sup 37}K is studied in detail. Several new {beta} decay branches and {gamma}-ray transitions are assigned to this nucleus. The l-forbidden 0d{sub 3/2}{r_arrow}1s{sub 1/2} Gamow-Teller branch to the first excited state in {sup 37}Ar is observed for the first time and its branching ratio measured to be (42.2{plus_minus}7.5){times}10{sup {minus}6}. Such l-forbidden branches are very sensitive to extranucleonic effects such as meson-exchange currents and {Delta}-isobar excitations. A calculation of these as well as core-polarization and relativistic effects, predict branching ratios of 8{times}10{sup {minus}6} with universal s-d wave functions and 52{times}10{sup {minus}6} with Chung-Wildenthal wave functions. {copyright} {ital 1997} {ital The American Physical Society}

Precision measurements of superallowed Fermi β-decay allow for stringent tests of the magnitude of isospin-symmetry-breaking effects in nuclei, the validity of the conserved vector current hypothesis, and the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix. A high-precision measurement of the branching ratio for the superallowed β+ decay of 74Rb has been performed at the Isotope Separator and ACcelerator (ISAC) facility at TRIUMF. The 8π spectrometer, an array of 20 HPGe detectors, was used to detect γ-rays emitted following the Gamow-Teller and non-analogue Fermi β-decays of 74Rb. PACES, an array of 5 Si(Li) detectors, was used to detect emitted conversion electrons, while half of SCEPTAR, a close-packed array of 10 plastic scintillators, was used to detect emitted β particles. In this experiment, 23 excited states were identified in 74Kr which were populated following the β-decay of 74Rb. A total of 58 γ-rays were identified following the 8.241(4)x108 detected β-particles. An observed non-superallowed branching ratio of 0.396(7)% was determined from the intensity of the identified γ-rays, while the unobserved non-superallowed intensity was calculated to be 0.05(5)%, leading to a superallowed branching ratio of 99.55(5)%. The superallowed branching ratio is now the most precise experimental quantity in the determination of the superallowed ft-value of 74Rb. Combining the half-life and Q-value with the superallowed branching ratio measured in this work leads to a superallowed ft-value of 3082.6(66) s. Finally, comparisons between the superallowed ft-value, the world average Ft-value, and the non-analogue Fermi branching ratio are made to provide future guidance in the refinement of the theoretical models required to describe the crucial isospin-symmetry-breaking term in superallowed β-decay.

We report results from a combined analysis of solar neutrino data from all phases of the Sudbury Neutrino Observatory. By exploiting particle identification information obtained from the proportional counters installed during the third phase, this analysis improved background rejection in that phase of the experiment. The combined analysis resulted in a total flux of active neutrino flavors from 8B decays in the Sun of (5.25 \pm 0.16(stat.)+0.11-0.13(syst.))\times10^6 cm^{-2}s^{-1}. A two-flavor neutrino oscillation analysis yielded \Deltam^2_{21} = (5.6^{+1.9}_{-1.4})\times10^{-5} eV^2 and tan^2{\theta}_{12}= 0.427^{+0.033}_{-0.029}. A three-flavor neutrino oscillation analysis combining this result with results of all other solar neutrino experiments and the KamLAND experiment yielded \Deltam^2_{21} = (7.41^{+0.21}_{-0.19})\times10^{-5} eV^2, tan^2{\theta}_{12} = 0.446^{+0.030}_{-0.029}, and sin^2{\theta}_{13} = (2.5^{+1.8}_{-1.5})\times10^{-2}. This implied an upper bound of sin^2{\theta}_{13} < 0.053 at the 95% confidence level (C.L.).

The half-life of the superallowed Fermi ${\ensuremath{\beta}}^{+}$ emitter $^{18}\mathrm{Ne}$ has been determined via two high-precision $\ensuremath{\beta}$ counting experiments at TRIUMF's Isotope Separator and Accelerator facility. Using two different $4\ensuremath{\pi}$ continuous-flow gas-proportional counters, two independent measurements were made, yielding a weighted average of ${T}_{1/2}=1.{66400}_{\ensuremath{-}0.00048}^{+0.00057}$ s, which is consistent with but approximately 2 times more precise than a previous high-precision measurement based on $\ensuremath{\gamma}$-ray counting. The present work achieves $\ifmmode\pm\else\textpm\fi{}0.034%$ precision for the $^{18}\mathrm{Ne}$ half-life and will enable the inclusion of $^{18}\mathrm{Ne}$ among the set of precisely measured superallowed Fermi $\ensuremath{\beta}$-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 $^{23}\mathrm{Ne}$ was measured and the world average has been improved, by a factor of 1.7, to $37.148\ifmmode\pm\else\textpm\fi{}0.032$ s.

The half-life of 14 O, a superallowed Fermi β + emitter, has been determined via simultaneous γ and β counting experiments at TRIUMF’s Isotope Separator and Accelerator facility. Following the implantation of 14 O samples at the center of the 8 π spectrometer, a γ counting measurement was performed by detecting the 2313 keV γ -rays emitted from the first excited state of the daughter 14 N using 20 high-purity germanium (HPGe) detectors. A simultaneous β counting experiment was performed using a fast plastic scintillator positioned directly behind the implantation site. The results, T ½ ( γ ) = 70:632 ± 0:094 s and T ½ ( β ) = 70:610 ± 0:030 s, are consistent with one another and, together with eight previous measurements, establish a new average for the 14 O half-life of T ½ = 70:619 ± 0:011 s with a reduced χ 2 of 0.99.

International audience; A program of high-precision half-life and branching-ratio measurements for superallowed Fermi emitters is being carried out at TRIUMF's Isotope Separator and Accelerator (ISAC) radioactive ion beam facility. Recent half-life measurements for the superallowed decays of 14O, 18Ne, and 26Alm, as well as branching-ratio measurements for 26Alm and 74Rb are reported. These results provide demanding tests of the Standard Model and the theoretical isospin symmetry breaking (ISB) corrections in superallowed Fermi decays.

This paper details the solar neutrino analysis of the 385.17-day phase-III data set acquired by the Sudbury Neutrino Observatory (SNO). An array of He-3 proportional counters was installed in the heavy-water target to measure precisely the rate of neutrino-deuteron neutral-current interactions. This technique to determine the total active B-8 solar neutrino flux was largely independent of the methods employed in previous phases. The total flux of active neutrinos was measured to be 5.54(-0.31)(+0.33)(stat.)(-0.34)(+0.36)(syst.) x 10(6) cm(-2) s(-1), consistent with previous measurements and standard solar models. A global analysis of solar and reactor neutrino mixing parameters yielded the best-fit values of Delta m(2) = 7.59(-0.21)(+0.19) x 10(-5) eV(2) and theta = 34.4(-1.2)(+1.3) degrees. DOI: 10.1103/PhysRevC.87.015502

The Sudbury Neutrino Observatory (SNO) has confirmed the standard solar model and neutrino oscillations through the observation of neutrinos from the solar core. In this paper we present a search for neutrinos associated with sources other than the solar core, such as gamma-ray bursts and solar flares. We present a new method for looking for temporal coincidences between neutrino events and astrophysical bursts of widely varying intensity. No correlations were found between neutrinos detected in SNO and such astrophysical sources., United States. Dept. of Energy, National Energy Research Scientific Computing Center (U.S.), Alfred P. Sloan Foundation

A program of high-precision superallowed Fermi β decay studies is being carried out at the Isotope Separator and Accelerator (ISAC) radioactive ion beam facility at TRIUMF. Recent high-precision branching ratio measurements for the superallowed decays of 74Rb and 26Alm, as well as a half-life measurement for 26Alm that is the most precise half-life measurement for any superallowed emitter to date, are reported. These results provide demanding tests of the theoretical isospin symmetry breaking corrections in superallowed Fermi β decays.

The excitation function of the $^{12}\mathrm{C}$(\ensuremath{\alpha},\ensuremath{\gamma}${)}^{16}$O reaction and the angular distribution of its \ensuremath{\gamma} rays were measured at nine center-of-mass energies ranging from E=1.37 to 2.98 MeV. These measurements allowed the separation of the E1 and E2 contributions and their extrapolation to the region of astrophysical interest. The analysis of all the available E1 cross sections with the K-matrix method and with a three-level R-matrix method yields a consistent prediction of 79\ifmmode\pm\else\textpm\fi{}16 keV b for the E1 S factor at 300 keV. The E2 contribution at the same energy is 36\ifmmode\pm\else\textpm\fi{}6 keV b from a cluster model analysis of the present data. The best estimate of the total S factor at 300 keV is 120 keV b, and it is unlikely that it will fall outside the range of 80--160 keV b. \textcopyright{} 1996 The American Physical Society.

We have measured deuterium uptake by thin foils of Zr and Zr-2.5wt%Nb which had been etched with a 0.1% NH 4 HF 2 in D 2 O solution, as a function of applied stress. Qualitatively, the deuterium uptake increased as the stress applied to the foil increased although there were large fluctuations in deuterium uptake for a given value of applied stress.

A search for Gamow-Teller decay branches of 39Ca to excited states in 39K was conducted with a large HPGe detector which observed the decays of 39Ca samples delivered by a helium-jet transport system. A pair of plastic scintillators in front of the HPGe detector were used to reject events due to bremsstrahlung from the 39Ca positrons. With this setup, weak γ-rays could be observed with a degree of sensitivity not previously achieved. The l- forbidden 1 d 3 2 → 2 s 1 2 transition to the first excited state in 39K, was observed with a branching ratio of (2.50 ± 0.27) × 10−5. This result agrees with but is more accurate than the only previous measurement. Thus, the ratio of the l-forbidden Gamow-Teller and isovector M1 matrix elements in mass-39 nuclei continues to disagree with theoretical values obtained by Towner and Khanna from calculations involving core-polarization and meson-exchange currents. This leaves very few possibilities to explain the discrepancy between theory and experiment.

Results are reported from a search for low-multiplicity neutrino bursts in the Sudbury Neutrino Observatory (SNO). Such bursts could indicate detection of a nearby core-collapse supernova explosion. The data were taken from Phase I (November 1999 - May 2001), when the detector was filled with heavy water, and Phase II (July 2001 - August 2003), when NaCl was added to the target. The search was a blind analysis in which the potential backgrounds were estimated and analysis cuts were developed to eliminate such backgrounds with 90% confidence before the data were examined. The search maintained a greater than 50% detection probability for standard supernovae occurring at a distance of up to 60 kpc for Phase I and up to 70 kpc for Phase II. No low-multiplicity bursts were observed during the data-taking period., 11 pages, 4 figures, submitted to ApJ

A high-precision half-life measurement for the superallowed ${\ensuremath{\beta}}^{+}$ emitter $^{26}\mathrm{Al}^{m}$ was performed at the TRIUMF-ISAC radioactive ion beam facility yielding ${T}_{1/2}=6346.54\ifmmode\pm\else\textpm\fi{}{0.46}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{0.60}_{\mathrm{syst}}\text{ }\text{ }\mathrm{ms}$, consistent with, but 2.5 times more precise than, the previous world average. The $^{26}\mathrm{Al}^{m}$ half-life and $ft$ value, 3037.53(61) s, are now the most precisely determined for any superallowed $\ensuremath{\beta}$ decay. Combined with recent theoretical corrections for isospin-symmetry-breaking and radiative effects, the corrected $\mathcal{F}t$ value for $^{26}\mathrm{Al}^{m}$, 3073.0(12) s, sets a new benchmark for the high-precision superallowed Fermi $\ensuremath{\beta}$-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 absolute cross section of the $^{3}\mathrm{He}$(n,\ensuremath{\gamma}${)}^{4}$He reaction was measured at five energies between ${\mathit{E}}_{\mathit{n}}$=0.14--2.0 MeV to an accuracy of \ensuremath{\sim}\ifmmode\pm\else\textpm\fi{}10%. The \ensuremath{\sim}21 MeV gamma rays produced in a $^{3}\mathrm{He}$ gas target were detected at 90\ifmmode^\circ\else\textdegree\fi{} with respect to the beam direction. The results are discussed in light of previous measurements of the two-body photodisintegration of $^{4}\mathrm{He}$.

The half-life of $^{38}\mathrm{K}$${}^{m}$ has been measured to be 924.46(14) ms, a result that is a factor of two more precise than any of the five previous measurements of this quantity. The previous results are not consistent with one another, but our result agrees well with the two most recent ones. The derived $\mathit{ft}$ value for $^{38}\mathrm{K}$${}^{m}$ is now one of the three most precisely known superallowed $\mathit{ft}$ values.

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.

Results are reported from a joint analysis of Phase I and Phase II data from the Sudbury Neutrino Observatory. The effective electron kinetic energy threshold used is T_eff=3.5 MeV, the lowest analysis threshold yet achieved with water Cherenkov detector data. In units of 10^6 cm^{-2} s^{-1}, the total flux of active-flavor neutrinos from 8B decay in the Sun measured using the neutral current (NC) reaction of neutrinos on deuterons, with no constraint on the 8B neutrino energy spectrum, is found to be Phi_NC = 5.140 ^{+0.160}_{-0.158} (stat) ^{+0.132}_{-0.117} (syst). These uncertainties are more than a factor of two smaller than previously published results. Also presented are the spectra of recoil electrons from the charged current reaction of neutrinos on deuterons and the elastic scattering of electrons. A fit to the SNO data in which the free parameters directly describe the total 8B neutrino flux and the energy-dependent nu_e survival probability provides a measure of the total 8B neutrino flux Phi_8B = 5.046 ^{+0.159}_{-0.152} (stat) ^{+0.107}_{-0.123} (syst). Combining these new results with results of all other solar experiments and the KamLAND reactor experiment yields best-fit values of the mixing parameters of theta_{12}=34.06 ^{+1.16}_{-0.84} degrees and Delta m^2_{21}=7.59 ^{+0.20}_{-0.21} x 10^{-5} eV^2. The global value of Phi_8B is extracted to a precision of ^{+2.38}_{-2.95} %. In a three-flavor analysis the best fit value of sin^2\theta_{13} is 2.00 ^{+2.09}_{-1.63} x 10^{-2}. Interpreting this as a limit implies an upper bound of sin^2\theta_{13} < 0.057 (95% C. L.)., Comment: 53 pages, 40 figures, submitted to Phys. Rev. C

Let X i i = 1, 2, 3,… be a sequence of independent and identically distributed random variables with EX i = o and varX i = l. Write F(x) for the distribution function and f(t) for the characteristic function of X i and put \(S_n = \sum\limits_{i = 1}^n {X_i } \). Then, $$F_n(x) = P(S_n \leqq x\sqrt{n})\rightarrow \Phi(x) = \frac{1}{\sqrt{2\pi}} \int\limits^x_{-\infty}e^{-\frac{1}{2}u^2}du$$ as n → ∞. We shall herein be concerned with the influence of moments of X i on the rate of convergence to zero of $$A_{kn} = \sup_x |F_n(x) \-- G_{kn}(x)|$$ where $$G_{kn}(x) = \Phi(x) + \frac{1}{\sqrt{2\pi}}e^{-\frac{1}{2}}x^2 \sum\limits_{s=1}^k Q_s(x)n^{-\frac{1}{2}s}$$ is a given portion of the Chebyshev series corresponding to the X i (see for example Gnedenko and Kolmogorov [2], Section 38), the Q j (x) being polynomials of degree 3j - 1 whose coefficients depend on the first (j + 2) moments of X i . Now, Cramer (see [2], Section 45) has shown that for distributions satisfying the condition (C) (that is, \(\lim\sup_{t\rightarrow \infty}|f(t)

This study allocates farm financial stress into an income problem and a debt problem (leverage and interest rate) for a selected sample of Natal farms. This is done by comparing leverage and interest rates for farms experiencing financial stress (negative rate of return to equity) with a target leverage ratio and interest rate for those farms which are financially successful (positive rate of return to equity). The results show that some 65.4% of financial stress, for sample farms, is due to an income problem, 25.6% to leverage and 9.0% to an interest rate problem. Policies which alleviate the income problem will therefore be the most effective for these farms.