High-Precision Branching Ratio Measurement and Spin Assignment Implications for $^{62}$Ga Superallowed $β$ Decay
A. D. MacLean, A. T. Laffoley, C. E. Svensson, G. C. Ball, J. R. Leslie, C. Andreoiu, A. Babu, S. S. Bhattacharjee, H. Bidaman, V. Bildstein, C. Burbadge, M. Bo… 展开作者
A. D. MacLean, A. T. Laffoley, C. E. Svensson, G. C. Ball, J. R. Leslie, C. Andreoiu, A. Babu, S. S. Bhattacharjee, H. Bidaman, V. Bildstein, C. Burbadge, M. Bowry, C. Cheng, D. S. Cross, A. Diaz-Varela, I. Dillmann, M. R. Dunlop, R. Dunlop, L. J. Evitts, P. Finlay, S. Gillespie, A. B. Garnsworthy, P. E. Garrett, E. Gopaul, C. J. Griffin, G. F. Grinyer, G. Hackman, J. Henderson, B. Jigmeddorj, K. G. Leach, E. Kassanda, J. McAfee, M. Moukaddam, C. Natzke, S. Nittala, B. Olaizola, J. Park, C. Paxman, J. L. Pore, C. Porzio, A. J. Radich, P. Ruotsalainen, Y. Saito, S. Sharma, J. Smallcombe, J. K. Smith, R. Sultana, J. Turko, J. Williams, D. Yates, T. Zidar
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A text label in Figure 12 has been corrected compared to the original submission
A high-precision branching ratio measurement for the superallowed Fermi $β^{+}$ 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 $γ$-ray transitions, with intensities down to $\approx$1 part per million (ppm) per $^{62}$Ga $β^{+}$ decay, to be placed in the level scheme of the daughter nucleus $^{62}$Zn, establishing the superallowed $β$ 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, $γ-γ$ 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, $δ_{C1}$, in $^{62}$Ga superallowed Fermi $β$ decay.
The half-life, 3.8755(12) s, and superallowed branching ratio, 0.5315(12), for ^{22}Mg 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^+ to 0^+ transitions have been restricted to the nine that populate stable daughter nuclei. No more such cases exist, and any improvement in a critical CKM unitarity test must depend on precise measurements of more exotic nuclei. With this branching-ratio measurement, we show thos…
We have measured the half-life of the superallowed 0+ -to- 0+ beta+ emitter 26Si to be 2245.3(7) ms. We used pure sources of 26Si and employed a high-efficiency gas counter, which was sensitive to positrons from both this nuclide and its daughter 26mAl. The data were analyzed as a linked parent-daughter decay. To contribute meaningfully to any test of the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, the ft value of a superallowed transition must be determined to a precision of 0.1% or better. With a precision of 0.03% the present result is more than sufficient to be compatable with…
We present a new measurement of the branching ratio for the decay of $^{14}$O to the ground state of $^{14}$N. The experimental result, $λ_0/λ_{\rm total} = (4.934 \pm 0.040\kern 1pt{\rm (stat.)} \pm 0.061\kern 1pt{\rm (syst.)}) \times 10^{-3}$, is significantly smaller than previous determinations of this quantity. The new measurement allows an improved determination of the partial halflife for the superallowed $0^+ \rightarrow 0^+$ Fermi decay to the $^{14}$N first excited state, which impacts the determination of the $V_{ud}$ element of the CKM matrix. With the new measurement in place, the…
\textbf{Background}: Superallowed $0^+ \rightarrow 0^+$ $β$ decays of isospin $T=2$ nuclides can be used to test theoretical isospin symmetry breaking corrections applied to extract the CKM matrix element $V_{ud}$ from $T = 0,1$ decays by measuring precise $ft$ values and also to search for scalar currents using the $β-ν$ angular correlation. Key ingredients include the $Q_{\textrm{EC}}$ value and branching of the superallowed transition and the half life of the parent. \textbf{Purpose}: To determine a precise experimental $Q_{\textrm{EC}}$ value for the superallowed $0^+ \rightarrow 0^+$ $β$ …
Superallowed $β$-decay studies provide some of the best constraints on the possibility of additional quark generations, as well as limits on exotic currents in the weak interaction. The three experimental quantities that are required for performing these tests using $0^+\rightarrow0^+$ nuclear decays (branching ratio, half-life, and $Q$-value) can all be measured to high-precision with rare-isotope beams at the TRIUMF-ISAC facility in Vancouver, Canada. This proceeding presents a brief outline of the general experimental techniques used at TRIUMF over the past 15 years, as well as recent theor…
We report the first branching-ratio measurement of the superallowed 0+-to-0+ beta transition from 38Ca. The result, 0.7728(16), leads to an ft value of 3062.3(68)s with a relative precision of +/-0.2%. This makes possible a high-precision comparison of the ft values for the mirror superallowed transitions, 38Ca-to-38mK and 38mK-to-38Ar, which sensitively tests the isospin symmetry-breaking corrections required to extract Vud, the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, from superallowed beta decay. The result supports the corrections currently used, and poin…
Two experiments, (1) a measurement of the superallowed $0^{+} \rightarrow 0^{+}$ branching ratio in $^{10}$C, and (2) a measurement of (or limit on) non-analogue $0^{+} \rightarrow 0^{+}$ branches in $^{38m}$K, $^{46}$V, $^{50}$Mn and $^{54}$Co, are described. The implications these experiments have on the test of the conservation of the weak vector current (CVC) and the unitarity of the Cabibbo-Kobayashi-Maskawa matrix are surveyed.
We present the full description of a measurement of the branching ratios for the beta-decay of 38Ca. This decay includes five allowed 0+ --> 1+ branches and a superallowed 0+ --> 0+ one. With our new result for the latter, we determine its ft value to be 3062.3(68) s, a result whose precision (0.2%) is comparable to the precision of the thirteen well known 0+ --> 0+ transitions used up till now for the determination of Vud, the up-down quark-mixing element of the CKM matrix. The 38Ca superallowed transition thus becomes the first addition to this set of transitions in nearly a decade and the f…
The positron-neutrino correlation in the 0^+ \to 0^+ βdecay of ^{32}Ar was measured at ISOLDE by analyzing the effect of lepton recoil on the shape of the narrow proton group following the superallowed decay. Our result is consistent with the Standard Model prediction; for vanishing Fierz interference we find a=0.9989 \pm 0.0052 \pm 0.0036. Our result leads to improved constraints on scalar weak interactions. The positron-neutrino correlation in ^{33}Ar decay was measured in the same experiment; for vanishing Fierz interference we find a=0.944 \pm 0.002 \pm 0.003. The ^{32}Ar and ^{33}Ar corre…
We report on a new measurement of the strength of the superallowed 0+->0+ transition in the beta-decay of 10C: 10C(0+,g.s.)->10B(0+,1.74MeV)+e+nu. The experiment was done at the LBNL 88-inch cyclotron using forty seven GAMMASPHERE germanium detectors. Precise knowledge of this branching ratio is necessary to compute the superallowed Fermi ft, which gives the weak vector coupling constant and the u to d element of the Cabibbo-Kobayashi- Maskawa quark mixing matrix.
A complete and critical survey is presented of all half-life, decay-energy and branching-ratio measurements related to 20 superallowed decays; no measurements are ignored, though some are rejected for cause and others updated. A new calculation of the statistical rate function is described and experimental ft values determined. The associated theoretical corrections needed to convert these results into Ft 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 Ft values a…
We used the 8$π$ $γ$-ray spectrometer at the TRIUMF-ISAC radiocative ion beam facility to obtain high-precision branching ratios for $^{19}$Ne $β^+$ decay to excited states in $^{19}$F. Together with other previous work, our measurements determine the superallowed $1/2^+ \to 1/2^+$ beta branch to the ground state in $^{19}$F to be 99.9878(7)\%, which is three times more precise than known previously. The implications of these measurements for testing a variety of weak interaction symmetries are discussed briefly.
A new critical survey is presented of all half-life, decay-energy and branching-ratio measurements related to 20 superallowed 0+ --> 0+ beta decays. Included are 222 individual measurements of comparable precision obtained from 177 published references. Compared with our last review in 2008, we have added results from 24 new publications and eliminated 9 references, the results from which having been superseded by much more precise modern data. We obtain world-average ft-values for each of the eighteen transitions that have a complete set of data, then apply radiative and isospin-symmetry-brea…
A new critical survey is presented of all half-life, decay-energy and branching-ratio measurements related to 20 0+ to 0+ beta decays. Compared with our last review, there are numerous improvements: First, we have added 27 recently published measurements and eliminated 9 references; of particular importance, the new data include a number of high-precision Penning-trap measurements of decay energies. Second, we have used the recently improved isospin symmetry-breaking corrections. Third, our calculation of the statistical rate function now accounts for possible excitation in the daughter atom. …
A complete survey is presented of all half-life and branching-ratio measurements related to the isospin T = 1/2 mirror beta transitions ranging from 3He to 83Mo. No measurements are ignored, although some are rejected for cause. Using the decay energies obtained in the 2003 Mass Evaluation experimental ft values are then determined for the transitions up to 45V. For the first time also all associated theoretical corrections needed to convert these results into "corrected" Ft values, similar to the superallowed 0+ -> 0+ pure Fermi beta transitions, were calculated. Precisions of the resulting v…
The half-life of \tsups{37}K has been measured to be $1.23651(94)~\mathrm{s}$, a value nearly an order of magnitude more precise than the best previously reported. The $β^+$ decay of \tsups{37}K occurs mainly via a superallowed branch to the ground-state of its $T=1/2$ mirror, \tsups{37}Ar. This transition has been used recently, together with similar transitions from four other nuclei, as an alternative test of CVC and method for determining $V_{ud}$, but the precision of its $ft$ value was limited by the relatively large half-life uncertainty. Our result corrects that situation. Another moti…
We have measured proton and alpha-particle branching ratios of excited states in 19Ne formed using the 19F(3He,t) reaction at a beam energy of 25 MeV. These ratios have a large impact on the astrophysical reaction rates of 15O(alpha,gamma), 18F(p,gamma) and 18F(p,alpha), which are of interest in understanding energy generation in x-ray bursts and in interpreting anticipated gamma-ray observations of novae. We detect decay protons and alpha-particles using a silicon detector array in coincidence with tritons measured in the focal plane detector of our Enge split-pole spectrograph. The silicon a…
The $β$-decay of neutron-rich $^{129}$In into $^{129}$Sn was studied using the GRIFFIN spectrometer at the ISAC facility at TRIUMF. The study observed the half-lives of the ground state and each of the $β$-decaying isomers. The level scheme of $^{129}$Sn has been expanded with thirty-one new $γ$-ray transitions and nine new excited levels, leading to a re-evaluation of the $β$-branching ratios and level spin assignments. The observation of the $β$-decay of the (29/2$^{+}$) 1911-keV isomeric state in $^{129}$In is reported for the first time, with a branching ratio of 2.0(5)$\%$.
A precise measurement of the hypertriton lifetime is presented. In this letter, the mesonic decay modes $\mathrm{{^3_Λ}H \rightarrow ^3He + π^-}$ and $\mathrm{{^3_Λ}H \rightarrow d + p + π^-}$ are used to reconstruct the hypertriton from Au+Au collision data collected by the STAR collaboration at RHIC. A minimum $χ^2$ estimation is used to determine the lifetime of $τ= 142^{+24}_{-21}\,{\rm (stat.)} {\pm} 31\,{\rm (syst.)}$ ps. This lifetime is about 50\% shorter than the lifetime $τ= 263\pm2$ ps of a free $Λ$, indicating strong hyperon-nucleon interaction in the hypernucleus system. The branc…
Excited states in $^{14}$O have been investigated both experimentally and theoretically. Experimentally, these states were produced via neutron-knockout reactions with a fast $^{15}$O beam and the invariant-mass technique was employed to isolate the 1$p$ and 2$p$ decay channels and determine their branching ratios. The spectrum of excited states was also calculated with the Shell Model Embedded in the Continuum that treats bound and scattering states in a unified model. By comparing energies, widths and decay branching patterns, spin and parity assignments for all experimentally observed level…
The structure of $^{34}$Si was studied through $γ$ spectroscopy separately in the $β^-$ decays of $^{34}$Mg and $^{34}$Al at the ISOLDE facility of CERN. Different configurations in $^{34}$Si were populated independently from the two recently identified $β$-decaying states in $^{34}$Al having spin-parity assignments $J^π= 4^-$ dominated by the normal configuration $π(d_{5/2})^{-1} \otimes ν(f_{7/2})$ and $J^π= 1^+$ by the intruder configuration $π(d_{5/2})^{-1} \otimes ν(d_{3/2})^{-1}(f_{7/2})^{2}$. The paper reports on spectroscopic properties of $^{34}$Si such as an extended level scheme, sp…
The $β^-$ decay of $^{47}$K to $^{47}$Ca is an appropriate mechanism for benchmarking interactions spanning the $sd$ and $pf$ shells, but current knowledge of the $β^-$-decay scheme is limited. We have performed a high-resolution, high-efficiency study of the $β^-$-decay of $^{47}$K with the GRIFFIN spectrometer at TRIUMF-ISAC. The study revealed 48 new transitions, a more precise value for the $^{47}$K half-life (17.38(3)~s), and new spin and parity assignments for eight excited states. Levels placed for the first time here raise the highest state observed in $β^-$ decay to within 568(3) keV …
We present recent results on the structure of the one-valence-particle $^{41}$Ca and $^{49}$Ca, and one-valence-hole $^{47}$Ca, nuclei. The isotopes of interest were populated via the cold-neutron capture reactions $^{40}$Ca(n,$γ$), $^{48}$Ca(n,$γ$) and $^{46}$Ca(n,$γ$), respectively. The experiments were performed at the Institut Laue-Langevin, within the EXILL campaign, which employed a large array of HPGe detectors. The $γ$ decay and level schemes of these nuclei were investigated by $γ$-ray coincidence relationships, leading to the identification of 41, 10, and 6 new transitions in $^{41}$…
