Search

The predominant branch in the $\ensuremath{\beta}$ decay of $^{34}\mathrm{Ar}$ is the superallowed ${0}^{+}\ensuremath{\rightarrow}\phantom{\rule{0.16em}{0ex}}{0}^{+}$ transition to the ground state of $^{34}\mathrm{Cl}$. To determine its important branching ratio one must first establish the ratios for the competing Gamow-Teller branches based on the measured intensities of $\ensuremath{\gamma}$ rays subsequently emitted from the excited states they populate in $^{34}\mathrm{Cl}$. The strongest of these branches populates the ${1}^{+}$ state at 666 keV in $^{34}\mathrm{Cl}$, which has three possible $\ensuremath{\gamma}$-decay paths. We report here a measurement of the decay of this state, which we populated via resonant proton capture in the reaction $^{33}\mathrm{S}$($p,\ensuremath{\gamma}$)$^{34}\mathrm{Cl}$. We find that the intensity of the 519-keV $\ensuremath{\gamma}$-ray path is 1.46(19)% relative to that of the 666-keV path. This result is critical to new precise measurements of the superallowed decay of $^{34}\mathrm{Ar}$.

Superallowed $\ensuremath{\beta}$-decay between nuclear analog states with isospin 1 and spin-parity ${0}^{+}$ offers access to fundamental tests of the properties of the electroweak interaction. With 15 such transitions precisely measured, the data collectively probe the conservation of the weak vector current, set tight limits on the presence of beyond-standard-model scalar currents, and yield the most precise value for the ${V}_{u\phantom{\rule{0}{0ex}}d}$ element of the CKM quark-mixing matrix. ${V}_{u\phantom{\rule{0}{0ex}}d}$ is a critical ingredient required to test the unitarity of that matrix. This work provides an in-depth review of the relevant nuclear physics input and connects these data to the fundamental couplings.

We have measured the branching ratio for the superallowed ${0}^{+}\ensuremath{\rightarrow}$ ${0}^{+}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$ transition from $^{34}\mathrm{Ar}$ to be 0.9448(8), and determined its $ft$ value to be 3058.1(28) s, a result with $\ifmmode\pm\else\textpm\fi{}0.09$% precision, which is a factor of 3 improvement over the previous result based on current world data. The $ft$-value ratio for the mirror pair of superallowed transitions $^{34}\mathrm{Ar}$ $\ensuremath{\rightarrow}^{34}\mathrm{Cl}$ and $^{34}\mathrm{Cl}$ $\ensuremath{\rightarrow}^{34}\mathrm{S}$ becomes the most precise yet measured and, in a sensitive test of the method used to calculate the isospin-symmetry-breaking correction, ${\ensuremath{\delta}}_{C}$, it agrees well with the ratio as calculated with Woods-Saxon radial wave functions. This confirms the method used in the most recent survey of superallowed decays to extract ${V}_{\text{ud}}$, the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa matrix. In addition, our branching-ratio results for the four observed Gamow-Teller branches to ${1}^{+}$ states in $^{34}\mathrm{Cl}$ are shown to agree well with shell-model calculations based on the same effective interactions that were used in the determination of ${\ensuremath{\delta}}_{C}$.

Superallowed $\ensuremath{\beta}$ decay is an important tool in characterizing the vector component of the weak interaction. Precise $\ensuremath{\beta}$-decay results presently give the best measurement of the up-down quark weak-mixing element, ${V}_{u\phantom{\rule{0}{0ex}}d}$. This new result completes the measurement of a second set of superallowed mirror transitions (${}^{26}$Si-${}^{26m}$Al and ${}^{26m}$Al-${}^{26}$Mg in this case) and has the precision to constrain the theoretical isospin-symmetry-breaking corrections needed in the extraction of ${V}_{u\phantom{\rule{0}{0ex}}d}$.

At present, the best value for Vud, 0.97420(21), comes from superallowed 0+-to-0+ nuclear beta transitions, of which fourteen have now been measured with high precision. The current status of world data is presented and shown to be robust. The derived Vud value is consistent with the considerably less precise results obtained from beta decays of the neutron, the pion and T = 1/2 mirror nuclei. Nuclear isospin symmetry-breaking corrections appear to be well under control, having been tested by on-going experiments.

Because of angular-momentum conservation, superallowed β decay between 0+ analog states involves only the vector part of the weak interaction, so its measured ft value can be used to determine the vector coupling constant, GV. If many such transitions are measured, then the constancy of GV can be established and several important tests made on fundamentals of the electroweak Standard Model. We have developed apparatus that allows us to measure half-lives to ±0.03% and branching ratios to ±0.1% or better, for cyclotron-produced activities with half-lives as short as 100 ms. We present an overview of the equipment and a summary of more than 10 years of results.

The Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix is a central pillar of the Electroweak Standard Model. The elements of the matrix must be determined from experiment, but the Model requires the matrix itself to be unitary. Any deviation from unitarity would signal the presence of “new physics” beyond the Standard Model, so tests of CKM unitarity have attracted considerable attention. Currently the most precise test is of the normalization of the top row, which has now reached a precision of 0.06% based on measurements of superallowed 0+ nuclear β decay and of kaon semileptonic and leptonic decays. This work overviews the status of the normalization tests and speculates on likely future improvements.

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.

A $^{52}\mathrm{Cr}(p,t)^{50}\mathrm{Cr}$ two-neutron pickup reaction was performed using the Q3D magnetic spectrograph at the Maier-Leibnitz-Laboratorium in Garching, Germany. Excited states in $^{50}\mathrm{Cr}$ 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 ${E}_{x}=3895.0(5)$ keV in $^{50}\mathrm{Cr}$. This reassignment directly impacts direct searches for a nonanalog Fermi ${\ensuremath{\beta}}^{+}$ decay branch in $^{50}\mathrm{Mn}$. These results also show better systematic agreement with the theoretical predictions for the ${0}^{+}$ state spectrum in $^{50}\mathrm{Cr}$ 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.

Currently, the most restrictive test of the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix is anchored by nuclear beta decay. Precise measurements of the ft -values for superallowed beta transitions between analog 0 + states are used to determine G V , the vector coupling constant; this, in turn, yields V u d , the up-down element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. When the value for V u d obtained from the latest survey of world data is combined with V u s and V u b , the other top-row elements, it leads to the most demanding test available of the unitarity of that matrix. Important ingredients required in the extraction of V u d from experiment are calculated radiative corrections as well as corrections to account for the isospin symmetry breaking that occurs between the analog parent and daughter states of each superallowed transition. The latter are well supported by comparison with experiment. The current value for the unitarity sum is 0.99995(61), a result that is in remarkable agreement with Standard Model expectations.

Direct reaction studies provide crucial information on nuclear structure for nuclei that are used in weak interaction and fundamental symmetry tests. Motivated by the superallowed Fermi beta-decay studies, we have investigated the structure of Cr-50 and Zn-62, the daughters of the superallowed beta(+)/EC emitters Mn-50 and Ga-62, with (p,t) reactions. For both nuclei, we reassigned the location of the first excited 0(+) state. The data for these reassignments are reviewed and limits on the possible L = 0 transfer to the previously assigned 0(2)(+) states are determined. For Cr-50, we find no evidence for the presence of a 0(+) state at 3695 keV. For Zn-62, the data allow for a possible contribution of L = 0 and L = 2, indicating a possible 0(+)/2(+) doublet of states at 2342 keV. However, this relies on an enhanced cross section at only one data point, and thus the existence of a 0(+) state at this energy is not clear. A preliminary result from a gamma-gamma angular correlation measurement following the beta(+)/EC decay of Ga-62 weakly favours the existence of a 0(+) state, but requires further study with increased statistics.

Prompted by recent measurements, we surveyed world data and calculated radiative and isospin-symmetry-breaking corrections for the superallowed ${0}^{+}\ensuremath{\rightarrow}{0}^{+}$ Fermi transitions from $^{42}\mathrm{Ti},^{46}\mathrm{Cr},^{50}\mathrm{Fe}$, and $^{54}\mathrm{Ni}$. This increases the number of such transition with a complete set of calculated corrections from 20 to 23. The results are compared with their equivalents for the mirror superallowed transitions from $^{42}\mathrm{Sc},^{46}\mathrm{V},^{50}\mathrm{Mn}$, and $^{54}\mathrm{Co}$. The predicted $ft$-value asymmetries of these mirror pairs are sensitive to the correction terms and provide motivation for improving measurement precision so as to be able to test the corrections. To aid in that endeavor, we present a parametrization for calculating the $f$ values for the new transitions to $\ifmmode\pm\else\textpm\fi{}0.01%$.

We present the full description of a measurement of the branching ratios for the $\ensuremath{\beta}$ decay of $^{38}\mathrm{Ca}$. This decay includes five allowed ${0}^{+}\ensuremath{\rightarrow}{1}^{+}$ branches and a superallowed ${0}^{+}\ensuremath{\rightarrow}{0}^{+}$ one. With our new result for the latter, we determine its $ft$ value to be $3062.3\ifmmode\pm\else\textpm\fi{}6.8$ s, a result whose precision (0.2%) is comparable to the precision of the 13 well-known ${0}^{+}\ensuremath{\rightarrow}{0}^{+}$ transitions used up until now for the determination of ${V}_{\text{ud}}$, the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa matrix. The $^{38}\mathrm{Ca}$ superallowed transition thus becomes the first addition to this set of transitions in nearly a decade and the first for which a precise mirror comparison is possible, thus enabling an improved test of the isospin-symmetry-breaking corrections required for the extraction of ${V}_{\text{ud}}$.

Precise measurements of the $\ensuremath{\beta}$ decay between nuclear states of spin-parity ${0}^{+}$ and isospin 1 provide fundamental tests of the properties of the electroweak interaction. Collectively, these transitions sensitively probe the conservation of the vector weak current, set tight limits on the presence of scalar currents, and provide the most precise value for ${V}_{u\phantom{\rule{0}{0ex}}d}$. The latter result has become a linchpin in the most demanding test of the unitarity of the CKM matrix.

We present a parameterization of the statistical rate function, f, for 20 superallowed 0+-to-0+ nuclear beta transitions between T=1 analog states, and for 18 superallowed "mirror" transitions between analog T=1/2 states. All these transitions are of interest in the determination of V_{ud}. Although most of the transition Q_{EC} values have been measured, their precision will undoubtedly be improved in future. Our parameterization allows a user to easily calculate the corresponding new f value to high precision (+/-0.01%) without complicated computing., Comment: 5 pages

Currently, the most restrictive test of the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) ma- trix is anchored by nuclear beta decay. Precise measurements of the ft -values for superallowed beta transitions between analog 0 + states are used to determine GV, the vector coupling constant; this, in turn, yields Vud ,t he up-down quark-mixing element of the CKM matrix. The determination of a transition's ft -value requires the measurement of three quantities: its Q value, branching ratio and parent half-life. To achieve 0.1% precision on the final result, each of these quantities must be measured to substantially better precision, for which spe- cial techniques have had to be developed. A new survey and analysis of world data reveals that there are now fourteen such transitions with ft -values known to ∼ 0.1% precision or better, and that they span a wide range of nuclear masses, from 10 C, the lightest parent, to 74 Rb, the heaviest. Of particular interest is the recent com- pletion of the first mirror pair of 0 + → 0 + transitions, 38 Ca → 38m Ka nd 38m K → 38 Ar, which provides a valuable constraint on the calculated isospin-symmetry-breaking corrections needed to derive GV from the experimental data. As anticipated by the Conserved Vector Current hypothesis, CVC, all fourteen transitions yield consistent values for GV .T he value ofVud derived from their average makes it by far the most precisely known element of the CKM matrix, which, when combined with the other top-row elements, Vus and Vub, leads to the most demanding test available of the unitarity of that matrix. Since CKM unitarity is a key pillar of the Electroweak Standard Model, this test is of fundamental significance.

Central to the Electroweak Standard Model is the Cabibbo-Kobayashi-Maskawa (CKM) matrix, a unitary 3 × 3 matrix that relates the weak- to the mass-eigenstates of the three generations of quarks. The Standard Model itself does not prescribe the values of the individual matrix elements—they must each be determined experimentally—but it does insist that the full matrix must satisfy all conditions of unitarity. Thus, any conclusive experimental demonstration that the unitarity conditions are not met would prove the need for “new physics” extending beyond the current Standard Model. Conversely, if the experiment were instead to confirm unitarity, this result would circumscribe the scope of any possible new physics to an extent limited only by the quoted experimental uncertainties on the unitarity sum. Either way, there is compelling motivation here for precision measurements of the CKM matrix elements aimed at the most demanding tests possible of the matrix's unitarity.

The ft values for superallowed 0+ → 0+ nuclear β transitions are nearly independent of nuclear-structure ambiguities and depend uniquely on the vector part of the weak interaction. They thus provide access to clean tests of some of the fundamental precepts of weak-interaction theory and can even probe physics beyond the standard model. We have just completed a new survey and overview of world data on such transitions, including not just the nine cases considered in the past, but also eleven more from T = 1 parents: even-even Tz = - 1 nuclei from 18Ne to 42Ti; and odd-odd nuclei from 62Ga to 74Rb. These new cases all involve more exotic nuclei and, to yield comparable precision, present real experimental challenges. Nevertheless, three of these new cases are already known well enough to contribute - together with the nine well known transitions - to the setting of limits on fundamental weak-interaction parameters. The remaining eight cases show promise for making important contributions in future.

Precision measurements of weak nuclear decays can probe physics beyond the standard model. Here the parity-violating asymmetry in the $\ensuremath{\beta}$ decay of polarized ${}^{67}$Cu, while consistent with the electro-weak standard model, provides important new constraints on possible tensor-type interactions.

We report the first branching-ratio measurement of the superallowed ${0}^{+}\ensuremath{\rightarrow}{0}^{+}\ensuremath{\beta}$ transition from $^{38}\mathrm{Ca}$. The result, 0.7728(16), leads to an $ft$ value of 3062.3(68) s with a relative precision of $\ifmmode\pm\else\textpm\fi{}0.2%$. This makes possible a high-precision comparison of the $ft$ values for the mirror superallowed transitions, $^{38}\mathrm{Ca}{\ensuremath{\rightarrow}}^{38m}\mathrm{K}$ and $^{38m}\mathrm{K}\ensuremath{\rightarrow}^{38}\mathrm{Ar}$, which sensitively tests the isospin symmetry-breaking corrections required to extract ${V}_{ud}$, the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, from superallowed $\ensuremath{\beta}$ decay. The result supports the corrections currently used and points the way to even tighter constraints on CKM unitarity.

We report the first branching-ratio measurement of the superallowed 0+→0+β transition from Ca38. 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, Ca38→38mK and K38m→Ar38, 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 β decay. The result supports the corrections currently used and points the way to even tighter constraints on CKM unitarity.

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} .

Superallowed β-decay provides a sensitive means for probing the limitations of the Electroweak Standard Model. To date, the strengths (ft-values) of superallowed 0+ → 0+ β-decay transitions have been determined with high precision from nine different short-lived nuclei, ranging from 10C to 54Co. Each result leads to an independent measure for the vector coupling constant Gy and collectively the nine values can be used to test the conservation of the weak vector current (CVC). Within current uncertainties, the results support CVC to better than a few parts in 10,000 — a clear success for the Standard Model! However, when the average value of Gy, as determined in this way, is combined with data from decays of the muon and kaon to test another prediction of the Standard Model, the result is much more provocative. A test of the unitarity of the Cabibbo-Kobayashi-Maskawa matrix fails by more than two standard deviations. This result can be made more definitive by experiments that require extremely precise mass measurements, in some cases on very short-lived (≤100 ms) nuclei. This talk presents the current status and future prospects for these Standard-Model tests, emphasizing the role of precise mass, or mass-difference measurements. There remains a real challenge to mass-measurement technique with the opportunity for significant new results.

Measurements of the decay strength of superallowed 0+ to 0+ nuclear beta transitions shed light on the fundamental properties of weak interactions. Because of their impact, such measurements were first reported 60 years ago in the early 1950s and have continued unabated ever since, always taking advantage of improvements in experimental techniques to achieve ever higher precision. The results helped first to shape the Electroweak Standard Model but more recently have evolved into sensitively testing that model's predictions. Today they provide the most demanding test of vector-current conservation and of the unitarity of the Cabibbo-Kobayashi-Maskawa matrix. Here, we review the experimental and theoretical methods that have been, and are being, used to characterize superallowed 0+ to 0+ beta transitions and to extract fundamentally important parameters from their analysis., 32 pages, 9 figures

The first fully on-line use of the angular distribution of beta emission in detection of NMR of nuclei oriented at low temperatures is reported. The magnetic moments of the single valence particle, intermediate mass, isotopes 67Ni(nup(-1)(1/2);1/2(-)) and 69Cu(pip(1)(3/2);3/2(-)) are measured to be +0.601(5) m(N) and +2.84(1) m(N), respectively, revealing only a small deviation from the neutron p(1/2) single-particle value in the former and a large deviation from the proton p(3/2) single-particle value in the latter. Quantitative interpretation is given in terms of core polarization and meson-exchange currents.

Recent on-line nuclear orientation measurements of nuclear magnetic dipole moments by the method of NMR on oriented nuclei (NMR/ON) have yielded significant new odd-A moments. These include those closest to double magic 132Sn, namely, 133Sb [132Sn plus one g7/2+ proton] and 133Tem [132Sn with a pair of g7/2+ protons and one hole in the h11/2- neutron sub-shell]. These close-to-double-magic results allow stringent tests of nuclear moment theory including, as main contributions to deviations from the simple free nucleon (Schmidt limit) values, configuration mixing in the nuclear wavefunction and mesonic exchange current modification to the dipole moment operator. Comparison with theoretical prediction, using established approaches to both these corrections, is discussed showing success in medium mass nuclei comparable to results previously established in light [to 40Ca] and heavy [near 208Pb] nuclei.

Recent on-line nuclear orientation measurements of odd-A nuclear magnetic dipole moments of odd-A Sb, Te and I isotopes by the method of NMR on oriented nuclei mean that we now have complete series ...

On-line low temperature nuclear orientation (OLNO) experiments have been performed on the isotope 135 I using the technique of nuclear magnetic resonance on oriented nuclei (NMR/ON). The magnetic moment of the 7 2 + ground state has been measured to be μ( 7 2 + 135 I ) = 2.940(2) μ N , thereby extending the known data on these states in odd- A I isotopes up to the neutron shell closure at N = 82. Shell-model calculations have been performed for the magnetic moments of 7 2 + states in the N = 82 isotones using free-nucleon and effective g -factors. The effective g -factors are obtained from a perturbation calculation that includes corrections for core polarisation and meson-exchange currents. The proton number dependence of the magnetic moments in the sequence of N = 82 isotones 133 Sb 139 La is discussed in terms of blocking of the Og 9 2 to Og 7 2 core polarisation with increasing Og 7 2 occupancy. Systematics of all measured 7 2 + odd-proton moments for 74 ⩽ N ⩽ 82 are reviewed.

We report a new method for the measurement of quadrupole moments of radioactive nuclei which were not accessible with other techniques until now: modulated adiabatic fast passage on oriented nuclei (MAPON) after recoil implantation into hcp Co. Quadrupole moments of Zr and Nb isotopes were determined which are interesting in the context of the proton and the neutron effective charge at $A\ensuremath{\sim}90$.

The β+ decay of 50Fe ( t 1 2 = 155 ± 11 ms ) has been observed for the first time; it exhibits a superallowed branch (77 ± 6%) to the 0+ ground state of 50Mn and an allowed branch to the 650.99 ± 0.06 keV 1+ state. The energy of the latter state has been precisely determined in order to reduce the uncertainties in a previous measurement of the QEC-value difference between the superallowed branches of 50Mn and 54Co, an important datum in determining the value for the Vector Coupling Constant in nuclei. Precise energies have also been determined for β delayed γ rays from the decay of 50mMn.

Nuclear magnetic resonance on oriented nuclei was applied to 89Nb ( I π = 9 2 + ; T 1 2 = 2.0 h ) and 89Zr ( I π = 9 2 + ; T 1 2 = 78 h ). The zero-field hyperfine splitting frequency μ m = | gμ n B hf /h |, was determined to be 278.55(12) MHz for 89Nb Fe and 51.57(3) MHz for 89Zr Fe . With the known magnetic hyperfine fields B hf (Nb Fe ) = −264.54(19) kG and B hf (Zr Fe ) = −284(6) kG, the magnetic moments are deduced to be μ(89Nb) = 6.216(5) μ n and μ(89Zr) = −1.072(23) μ n .

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}

The magnetic moments of ( $\mathrm{double}\mathrm{magic}+1\mathrm{proton}$) nuclei having a ``jack-knife'' $j\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}l\ensuremath{-}s$ configuration form crucial tests for the theoretical treatment of mesonic exchange currents and core polarization effects in finite nuclei. The reported precision measurement and analysis of the magnetic moment of ${}^{133}\mathrm{Sb}$ ( ${}^{132}\mathrm{Sn}+\mathrm{one}{g}_{7/2}\mathrm{proton}$) $\ensuremath{\mu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3.00(1){\ensuremath{\mu}}_{N}$ provides the first such test in medium-heavy nuclei. In addition, new data on the N dependence of the ${7/2}^{+}{}^{123\ensuremath{-}133}\mathrm{Sb}$ ground state moments are presented. Analysis in terms of particle-core coupling indicates slightly negative collective g factors of heavy Sn core nuclei.

We have studied the prevously unknown β + decay branches from 44,44m V and 52 Co to particle-bound states in 44 Ti and 52 Fe, respectively. These intense branches populate a few states in the daughters from an excitation energy of about 1 MeV up to the isobaric analogue states at about 6 MeV. We have measured the first precise energy values for the latter states as well as the β-branching ratios to all states in this excitation energy region. We have calculated the β + decay of 44,44m V in the full fp shell model space as well as in a truncated space. Renormalized transition operators are constructed for the truncated space and tested against experimental data in 44 V and 52 Co. In general there is good agreement between theory and experiment for the half-lives, level energies and beta branches, but not all the states found are reproduced by the calculations.

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.

A search for excited ${0}^{+}$ states in ${}^{62}$Zn was conducted via the ${}^{64}$Zn($p,t$)${}^{62}$Zn reaction. Four such states in ${}^{62}$Zn were observed up to an excitation energy of 5.4 MeV. The measured angular distribution for the previously assigned ${0}_{2}^{+}$ 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 $\ensuremath{\beta}$ decay, ${\ensuremath{\delta}}_{C1}$ for ${}^{62}$Ga is reduced by nearly a factor of two. This result shifts the theoretical value closer to previous experimental determinations of the same quantity through ${}^{62}$Ga superallowed $\ensuremath{\beta}$-decay branching-ratio measurements.

With the recent inclusion of core orbitals to the radial-overlap component of the isospin-symmetry-breaking (ISB) corrections for superallowed Fermi $\ensuremath{\beta}$ 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 ${}^{63}$Zn, one neutron away from ${}^{62}$Zn, the superallowed daughter of ${}^{62}$Ga. 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 ${10}^{\ensuremath{\circ}}$ and ${60}^{\ensuremath{\circ}}$. Angular distributions and vector analyzing powers were obtained for all 162 observed states in ${}^{63}$Zn, 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.

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.

Results from superallowed 0+→0+ nuclear beta decays today provide the best value for Vud, with an uncertainty of ±0.02%. Some 150 independent measurements of 13 separate superallowed transitions covering a wide range of parent nuclei from 10C to 74Rb constitute a very robust data set. Excellent consistency among the average results for all 13 transitions - an expected consequence of the conservation of vector current (CVC) - also confirms the validity of the small transition-dependent theoretical corrections that have been applied to account for isospin-symmetry breaking. With CVC consistency established, the value of the vector coupling constant, GV, has been extracted from the data and used to determine |Vud| = 0.97425 (22).

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.

A measurement of the superallowed 0[sup +][r arrow]0[sup +] branching ratio in [sup 10]C performed with the 8[pi] gamma-ray spectrometer is described. From the measured branching ratio, we extract a new precise value of [ital Ft]([sup 10]C)=3076.7(6.0)s. This does not support previously suggested [ital Z]- or [ital Z][sup 2]-dependent corrections to the superallowed 0[sup +][r arrow]0[sup +] data set, which removed the apparent nonunitarity of the Cabibbo-Kobayashi-Maskawa matrix.

The nucleus $^{49}\mathrm{Sc}$, having a single ${f}_{7/2}$ proton outside doubly magic $^{48}\mathrm{Ca}$ ($Z=20$, $N=28$), is one of the very few isotopes which makes possible testing of the fundamental theory of nuclear magnetism. The magnetic moment has been measured by online $\ensuremath{\beta}$ NMR of nuclei oriented at milli-Kelvin temperatures to be $(+)5.616(25)\text{ }\text{ }{\ensuremath{\mu}}_{N}$. The result is discussed in terms of a detailed theory of the structure of the magnetic moment operator, showing excellent agreement with calculated departure from the ${f}_{7/2}$ Schmidt limit extreme single-particle value. The measurement completes the sequence of moments of Sc isotopes with even numbers of ${f}_{7/2}$ neutrons: the first such isotopic chain between two major shells for which a full set of moment measurements exists. The result further completes the isotonic sequence of ground-state moments of nuclei with an odd number of ${f}_{7/2}$ protons coupled to a closed subshell of ${f}_{7/2}$ neutrons. Comparison with a recent shell-model calculation of the latter sequence is made.

Studies of 6He beta decay along with tritium can play an important role in testing ab initio nuclear wave-function calculations and may allow for fixing low-energy constants in effective-field theories. Here, we present an improved determination of the 6He half-life to a relative precision of 3×10(-4). Our value of 806.89±0.11(stat)(-0.19syst)(+0.23) ms resolves a major discrepancy between previous measurements. Calculating the statistical rate function we determined the ft value to be 803.04(-0.23)(+0.26) s. The extracted Gamow-Teller matrix element agrees within a few percent with ab initio calculations.

Background: Models to calculate small isospin-symmetry-breaking effects in superallowed Fermi decays have been placed under scrutiny in recent years. A stringent test of these models is to measure transitions for which the correction is predicted to be large. The decay of ${}^{32}$Cl decay provides such a test case.Purpose: The purpose of this paper is to improve the $\ensuremath{\gamma}$ yields following the $\ensuremath{\beta}$ decay of ${}^{32}$Cl and to determine the $ft$ values of the the $\ensuremath{\beta}$ branches, particularly the one to the isobaric-analog state in ${}^{32}$S.Method: Reaction-produced and recoil-spectrometer-separated ${}^{32}$Cl is collected in a tape and transported to a counting location where $\ensuremath{\beta}\ensuremath{-}\ensuremath{\gamma}$ coincidences are measured with a precisely calibrated high-purity germanium detector.Results: The precision on the $\ensuremath{\gamma}$ yields for most of the known $\ensuremath{\beta}$ branches has been improved by about an order of magnitude, and many new transitions have been observed. We have determined ${}^{32}$Cl-decay transition strengths extending up to ${E}_{x}\ensuremath{\sim}11$ MeV. The $ft$ value for the decay to the isobaric-analog state in ${}^{32}$S has been measured. A comparison to a shell-model calculation shows good agreement.Conclusions: We have experimentally determined the isospin-symmetry-breaking correction to the superallowed transition of this decay to be ${({\ensuremath{\delta}}_{C}\ensuremath{-}{\ensuremath{\delta}}_{\mathrm{NS}})}_{\mathrm{exp}}=5.4(9)%$, significantly larger than for any other known superallowed Fermi transition. This correction agrees with a shell-model calculation, which yields ${\ensuremath{\delta}}_{C}\ensuremath{-}{\ensuremath{\delta}}_{\mathrm{NS}}=4.8(5)%$. Our results also provide a way to improve the measured $ft$ values for the $\ensuremath{\beta}$ decay of ${}^{32}$Ar.