A systematic study is made of the Cd isotopes [110][111][112][113][114][115][116] Cd by making use of available experimental data and interacting boson model calculations incorporating both normal vibrational levels and intruder excitations. At the two-phonon level, the calculations appear to reproduce the data reasonably well in 110-114 Cd, whereas they break down completely for the 0 + states in 116 Cd. At the three-phonon level, systematic deviations occur across the Cd isotopic chain, revealing the breakdown of vibrational motion in low-spin states. Combined with the failure to reproduce 116 Cd at the two-phonon level, it is possible that the Cd isotopes may not represent vibrational systems and that the essential physics of their motion has been missing.

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A study of the β + /EC decay of 110 In into levels of 110 Cd is combined with a reanalysis of data from a previous study of 110 Cd with the (n, n ′ γ) reaction with monoenergetic neutrons. The γγ coincidences from the 110 In decay leads to many new assignments of γ rays observed in the (n, n ′ γ) reaction, permitting the observation of weak low-energy transitions, and setting stringent upper limits on unobserved decay branches. The uncertainties on many of the lifetimes from the (n, n ′ γ) reaction are significantly reduced, and limits are established for the lifetimes of levels too long for a direct measurement. The absence of enhanced transitions between the previously assigned phonon states and the deformed intruder states strongly suggests that mixing between the configurations is generally weak, refuting the strong-mixing scenario as an explanation of the decay pattern of the excited 0 + states in 110 Cd. The decay pattern of the non-intruder states is suggestive of a γ-soft rotor, or O(6) nucleus, rather than a vibrational, or U (5) pattern. The existence of a 4p − 6h proton excitation in 110 Cd is also suggested.

A high-precision half-life measurement for the superallowed þ emitter 26 Al m was performed at the TRIUMF-ISAC radioactive ion beam facility yielding T 1=2 ¼ 6346:54 AE 0:46 stat AE 0:60 syst ms, consistent with, but 2.5 times more precise than, the previous world average. The 26 Al m half-life and ft value, 3037.53(61) s, are now the most precisely determined for any superallowed decay. Combined with recent theoretical corrections for isospin-symmetry-breaking and radiative effects, the corrected F t value for 26 Al m , 3073.0(12) s, sets a new benchmark for the high-precision superallowed Fermi -decay studies used to test the conserved vector current hypothesis and determine the V ud element of the CabibboKobayashi-Maskawa quark mixing matrix. DOI: 10.1103/PhysRevLett.106.032501 PACS numbers: 23.40.Às, 24.80.+y, 27.30.+t High-precision ft values for superallowed Fermi decay transitions between spin J ¼ 0 þ and isospin T ¼ 1 states have proven to be an invaluable probe of the standard model [1]. The validity of the conserved vector current (CVC) hypothesis [2], which states that the vector coupling constant G V is not renormalized in the presence of strong interactions, has been established by the superallowed data at the level of 1:3 Â 10 À4 [3]. Combined with the Fermi coupling constant for purely leptonic decays G F , G V from the superallowed data also currently provides the most precise determination of V ud ¼ G V =G F ¼ 0:974 25ð22Þ [1], by far the most precisely determined element of the Cabibbo-Kobayashi-Maskawa (CKM) matrix relating the quark weak eigenstates to their mass eigenstates. To achieve this precision, the 13 superallowed ft values measured to better than AE0:3% must be corrected to obtain transition-independent F t values [1]:where K is a constant, Á V R is the nucleus-independent component of the radiative correction, 0 R and NS are, respectively, the nuclear-structure-independent and dependent components of the radiative correction for each transition, and C accounts for the breaking of isospin symmetry by Coulomb and charge-dependent nuclear forces [4].Applied to the world superallowed data evaluated in Ref. has led to a reduction of its uncertainty by a factor of 2. The calculations of the nuclear-structure-dependent ISB corrections, on the other hand, have undergone significant revisions in the last decade [4,7], leading to shifts as large as 50% of their own values in some cases, and to a general increase in their individual quoted uncertainties. A further reduction in the uncertainty assigned to Á V R could potentially be achieved via lattice QCD calculations [8], ultimately leading to a value of V ud limited by the nuclear-structure-dependent correction terms. The ISB corrections in superallowed Fermi decays have thus become the focus of intense study in recent years from a variety of theoretical approaches [3,4,[9][10][11][12], as well as semiempirical analysis [13]. Continued development, and refinement, of independent first principles approaches to ISB corrections, and the tes...

Properties of low-spin states in 114 Cd have been studied with the (n, n γ ) reaction. Gamma-ray angular distributions and excitation functions have been used to characterize the decays of the excited levels. Level lifetimes have been obtained with the Doppler-shift attenuation method. Sixteen new levels and many new transitions have been suggested below 3.5 MeV in excitation energy. Levels belonging to the phonon multiplets have been proposed based on their decay patterns and collectivity, and the existing intruder structure has been extended. A two-phonon 1 + ms state has been suggested. Excitation of the hexadecapole moment has been considered. Data have been compared with the theoretical calculations of the interacting boson model.

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High-statistics β-decay measurements of112 Ag and 112 In were performed to study the structure of the 112 Cd nucleus. The precise energies of the doublet of levels at 1871 keV, for which the 0 + member has been suggested as a possible daughter state following neutrinoless double electron capture of 112 Sn, were determined to be 1871.137 (72) One of the most pressing issues in subatomic physics today is the question of the nature of the neutrino. The observation of neutrino oscillations [1][2][3] has revealed neutrino mixing and that neutrinos are massive particles or, more precisely, that at least two of the mass eigenstates are nonzero. However, it is still unknown if neutrinos are their own antiparticles (Majorana) or distinct from their antiparticles (Dirac). Furthermore, the oscillation experiments yield information on ( m) 2 , and thus the masses and their orderings remain unknown. Observation of neutrinoless double-β-decay, ββ(0ν), would reveal the Majorana nature of neutrinos, and a measure of the decay rate, λ 0ν , would provide information on the neutrino masses viaThe G 0ν (Q ββ ,Z) factor is the phase-space integral including the Fermi function, M 0ν is the nuclear matrix element, and For ββ(0ν) searches, the typical signature is a peak at Q(ββ) in the sum-β-energy spectrum. However, such searches must strongly suppress the backgrounds from natural radioactivity and cosmic rays. A new class of ββ(0ν) experiments will attempt to surmount these problems; however, the neutrinoless double electron capture, ECEC(0ν), process offers a potentially attractive alternative.The basic physics of the ECEC process was outlined some time ago [4] and included an estimate of the radiative ECEC(0ν) process, which was further refined in Ref. [5]. Following the formation of a virtual capture state with two electron holes in the 1s shell, an internal bremsstrahlung (IB) photon is emitted accompanied by an electron transition from the 2p to the 1s shell. The IB photon is emitted at an energy E IB ofwhere m is the difference in the initial and final atomic masses, E ex is the excitation energy in the daughter nucleus, and E(e i ) is the binding energy of the resulting electron hole in the final state. The normal IB process involves a transition of one of the electrons to an intermediate state from which it is captured, and this process dominates for large Q values. However, for small Q values, where both electrons may be captured leading to a virtual two-electron-hole atom, the process has a resonant enhancement when Q ≡ m − E(1S) − E(2P ) − E ex = Q res ≡ E(2P ) − E(1S); i.e., the radiative IB photon energy matches the K α hypersatellite x-ray energy [6]. In this case,and for favorable cases where Q = Q res , λ 0ν may be enhanced by several orders of magnitude [6].

With the recent inclusion of core-orbitals to the radial-overlap component of the isospinsymmetry-breaking (ISB) corrections for superallowed Fermi β 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 9 angles between 10 • and 60 • . 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.