The GT matrix elements in the decay of the mirror nuclei 47Cr, 51Fe and 55Ni

Three new mirror nuclei, ⁴⁷Cr, ⁵¹Fe and ⁵⁵Ni, have been identified in (³He, 2n) reactions. The measured half-lives were as follows: ${}^{47}\text{Cr}\text{, 452 ± 18}\text{ms}\text{;}{}^{55}\text{Fe}\text{, 245 ± 7}\text{ms}\text{;}{}^{55}\text{Ni}\text{, 189 ± 5}\text{ms}$. Known mass data were utilized to deduce log $\text{?t}$ values and Gamow-Teller matrix elements for the three mirror β-decays. The experimental GT matrix elements are compared to the results of shell-model calculations.     

Internal bremsstrahlung in the electron capture decay of 145Sm

Internal bremsstrahlung (IB) emitted in the non-unique first-forbidden electron capture decay of the $\text{7}\text{2}{}^{\mathrm{?}}$ ground state of ¹⁴⁵Sm to the $\text{7}\text{2}{}^{\mathrm{+}}\text{61}\text{keV}$ first excited level of ¹⁴⁵Pm has been studied. The total IB spectrum and the IB spectrum for captures proceeding via the 1s shell were measured for photons in the energy range of 100–580 keV and the spectra were normalized to the non-radiative capture rate. The experimental data agree with theoretical predictions.     

Search for virtual electron capture in the investigation of the internal bremsstrahlung from the decay of 59Ni

The internal bremsstrahlung spectrum from the non-unique second-forbidden pure electron capture decay of ⁵⁹Ni was studied in a limestone low-background chamber using a 20 cm³ Ge(Li) detector, searching for the effects of the virtual electron capture in the spectrum shape of internal bremsstrahlung. Comparing the experimental data with the Cutkosky, Zon-Rapoport and virtual capture theories, the best fit was found for the Zon-Rapoport theory and thus the virtual capture theory is not indispensable to the interpretation of the experiment. Some additional results are also obtained in the present study. Thus, the combination of the nuclear matrix elements λ has been determined, λ = 0.028 ± 0.006, as well as the total disintegration energy $\text{Q(}{}^{59}\text{Ni}\text{-}{}^{59}\text{Co}\text{) = 1075.1 ±1.3}\text{keV}$. The existence of a positive β-branch was proved with an estimated value of 1.05 × 10^?7 for the branching.     

Internal bremsstrahlung in the unique first-forbidden electron capture decay of 41Ca

The spectrum of internal bremsstrahlung photons has been measured for the unique first-forbidden decay of ⁴¹Ca. The experimental shape factor essentially deviates from the theoretical ones. Also, the overall photon intensity per K-capture is higher than predicted.     

Allowed electron-capture branches in the decay of 34mCl

The decay of ^34mCl has been studied with 36 and 100 cm³ Ge(Li) detectors and with a high-resolution large volume Ge(Li)-NaI(Tl) Compton-suppression spectrometer. The ^34mCl activity was produced with the reaction ²⁴Mg(¹²C, pn)³⁴Cl at $\text{E(}{}^{12}\text{C}\text{) = 35}\text{MeV}$ by bombarding thick natural Mg targets. The half-life was measured to be $\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 32.06 ± 0.08}\text{min}$. Nine γ-ray transitions were observed including four γ-rays not seen previously. The measured γ-ray intensities determine new electron-capture branches of (0.030 ± 0.006) % and (0.032 ± 0.003) % to ³⁴S levels at 4.69 and 4.88 MeV with log ft values of 5.48 ± 0.08 and 5.26 ±0.04, respectively. These log ft values imply allowed transitions and are consistent with the known J_π values of J_π = 4⁺ and 3⁺ of the 4.69 and 4.88 MeV levels, respectively. A lower limit of log ft ? 6.9 is obtained for the allowed electron-capture branch to the J^π = 2⁺, 4.89 MeV level. Other previously observed decay branches have been confirmed. Since the decay of ^34mCl proceeds (46.9 ± 1.0)% to the ³⁴Cl ground state, the latter decay was studied concurrently; ³⁴Cl(0)with J^π = 0⁺, T = 1 decays exclusively to its analog ³⁴S(0) and the sum of the intensities of four other allowed branches is less than 1.2 × 10^?4 of the intensity of the ground-state branch. The experimental results are compared with recent shell-model calculations performed in a large configuration space.     

A new critical study of the internal bremsstrahlung spectrum from 35S

A new precise measurement has been carried out for the internal bremsstrahlung from ³⁵S, together with control measurements to clear up the probable reason of deviations from the theory in earlier studies. It is found that there is good agreement between the most precise theories and experiment for the IB spectrum of ³⁵S under proper experimental conditions.     

Double internal bremsstrahlung in electron capture

Double internal bremsstrahlung has been observed in the electron capture decay of ³⁷Ar. The energy distribution of the two photons has been investigated, using a dual parameter pulse-height analysis system, at an angle of θ = 90° between two photon propagation vectors. For sum photon energies in the interval of 210–810 keV and at θ = 90° the ratio of the transition probabilities of double to single bremsstrahlung emissions was found to be (4.8±0.4)×10^?5.     

On the decay of 201Bi and 199Bi

Level schemes for ²⁰¹Pb and ¹⁹⁹Pb, studied from the radioactive decay of bismuth isobars, are proposed on the basis of γ-ray, electron spectra and γ-γ coincidence measurements. The experimental results are compared mainly with those of two theoretical approaches.     

Gamma transitions in 59Ni following the β+ decay of 59Cu

The γ-ray decay spectrum of 82 s ⁵⁹Cu produced by the ⁵⁸Ni(p, γ) ⁵⁹Cu reaction has been studied with a 40 cm³ Ge(Li) detector. The number of γ-rays now known for this decay has more than doubled. Additional direct β⁺ branches to the 1679.7($\text{5}\text{2}{}^{\mathrm{?}}$), 2414.8($\text{3}\text{2}{}^{\mathrm{?}}$) and 2681 keV states of ⁵⁹Ni have been identified with log ft values of 5.5, 5.5 and 6.0, respectively. A major change is the reassignment of the 1340.4 keV γ-ray to a 1679.7 → 339.3 keV transition. A limit of log $\text{ft ≧ 6.9}$ is given for the direct feeding of the 1337($\text{7}\text{2}{}^{\mathrm{?}}$) keV state, together with limits for direct population of other energetically available states. The new weak γ-ray branches found for the 878.0, 1301.5 and 1679.7 keV levels are in excellent agreement with the recent theoretical calculations of Glaudemans et al.     

The β− decay of 102Mo

The ¹⁰²Mo activity was obtained by photofission of natural U and thermal-neutron induced fission of ²³⁵U, with subsequent chemical separation of the molybdenum fraction. In addition, nuclei with mass 102 were separated from fission products of ²³⁵U(n_th, f) using the mass separator LOHENGRIN. A decay scheme and absolute γ-intensities are deduced from measured γ-ray, X-ray and γ-coincidence spectra. Logftvalues are calculated. Shell-model calculations for a $\text{(πlg}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)}{}^3$$\text{(νlg}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{)}{}^3$ multiplet have been carried out using effective nucleon-nucleon interactions. The γ-decay between low-lying, low-spin members of this multiplet was studied in detail and compared with the experimental data.     

The decay of 44Sc

The 3.9 h decay of the ⁴⁴Sc ground state has been investigated with a ⁴⁴Ti source. In a singles experiment with a Ge(Li) detector and a γ-γ coincidence experiment with a NaI(Tl)-Ge(Li) detector arrangement a (0.010 ± 0.002)% EC branch to the 3.30 MeV level of ⁴⁴Ca has been found. The γ-decay branching ratio of the 3.30 MeV level has been determined.     

Beta decay of 28P

The β⁺ decay of ²⁸P has been studied with a Ge(Li)-NaI(Tl) escape-suppression spectrometer. The number of ²⁸Si γ-transitions observed following ²⁸P decay has been increased from 15 to 34. New β⁺ branches were observed to ²⁸Si levels at 7416, 9796 and 10209 keV and sharper limits were placed on unobserved gb⁺ transitions.     

The decay of 74Kr

The decay of ⁷⁴Kr has been studied. Its half-life was determined to be $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 11.50 ± 0.11}\text{min}$. A decay scheme is proposed, based on γ-γ and β⁺-γ coincidence measurements, which takes account of 99 % of the strength of 57 observed γ-rays. The total decay energy was measured to be Q_EC = 3327 ± 125 keV. The decay feeds the (0, 1)^?, $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 25.3}\text{min}$ isomer of ⁷⁴Br.     

The decay of 101Ag

The decay of ¹⁰¹Ag have been studied using β- and γ-spectrometers in singles and coincidence modes. A half-life of 11.4 ± 0.3 min was obtained and a decay scheme was proposed. The first excited state was established at 80.3 keV and a half-life of 4.8 ± 0.5 ns was suggested. The resultant level structure of ¹⁰¹Pd is compared to a theoretical calculation with strong band mixing.     

The decay of 235U

Twenty-eight γ-rays, ten of which are reported for the first time, have been observed in the decay of ²³⁵U, and all have been placed in a revised level scheme for ²³¹Th. Three new levels at 390.27, 317.42 and 240.82 keV respectively have been proposed and the data are in accord with he results of coincidence studies. Reduced transition probabilities of inter-band γ-ray transitions are calculated from the data and compared with theory and an estimate of the intrinsic quadrupole moment, Q_O has been computed.     

The decay of 192Ir

The decay of ¹⁹²Ir has been studied with Ge(Li) spectrometers. Gamma-ray energies and relative intensities are reported. Four previously unreported transitions at 329, 420, 593 and 703 keV have been identified by half-life and a level in ¹⁹²Os at 909 keV has been established on the basis of energy considerations. Upper limits are given for the γ-ray intensities of previously reported transitions at 110, 212, 280, 739, 765 and 1055 keV.     

Vibrational band structure in 184W populated in the decay of 184Re

The decay of ^184mRe has been investigated through γ-ray and conversion electron studies. The band head of the K^π = 2^? octupole band has been established at 1130.0 keV. The E2/M1 mixing ratios of three transitions from the γ-vibrational band to the ground state band have been determined by angular correlation measurements. A mixing of El, M2 and E3 multipolarity has been derived for the 921 keV transition combining angular correlation and conversion electron data. A value B(E3, 0⁺ → 3^? = (25 ± 5) × 10⁴e² · fm⁶ was obtained from the measured E2/M1 mixing of the 91 keV 3^? → → 2^? transition and γ-branchings. The data are discussed in terms of the collective model taking into account band mixing.     

Levels in 161Tm excited in the decay of 4.2 min 161Yb

The decay of ¹⁶¹Yb ($\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 4.2}\text{min}$) has been investigated with Ge(Li) and Si(Li) detectors and a toroidal β-spectrometer. Isobarically separated samples produced by the YASNAPP facility at Dubna Institute were used. The singles γ-ray spectrum, the conversion electron spectrum, γ-γ-τ and e-γ coincidences have been measured. In all, 67 γ-ray transitions have been observed. A decay scheme for ¹⁶¹Yb is proposed involving 12 excited states in ¹⁶¹Tm. The $\text{7}\text{2}$⁺[404], $\text{7}\text{2}$^?[523] and $\text{5}\text{2}$⁺[402] levels have been identified. The interpretation of the high-lying levels is discussed. The Q-value of ¹⁶¹Yb decay has been determined to be 3850 ± 250 keV. The A-dependence of the energies of the one-quasiparticle states in odd-A Tm isotopes is demonstrated.     

Properties of 81Kr levels populated in the decay of 81Rb isomers

The β⁺ decay of ⁸¹Rb ground and isomeric states (4.58 h and 30.25 min) have been studied with Ge(Li) detectors in both singles and coincidence modes. The decay of the ⁸¹Rb isomer ($\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 30.25 ± 0.25}\text{min}$) has been investigated for the first time. The relative electron intensities of fourteen transitions in ⁸¹Kr have been measured with a magnetic Si(Li) spectrometer and an iron-free toroidal magnetic spectrometer. The internal conversion coefficients have been determined by the normalized electron-to-γ-ray ratio method. The multipolarities of the transitions were deduced. The spin-parity assignments have been made from the consideration of the logft values, the transition multipolarities and the γ-rays branching ratios. The structure of some of the excited states in the ⁸¹Kr nucleus is discussed.     

Measurement of the parity non-conservation in nuclear forces in 75As, 171Tm,and 175Lu and of the polarized bremsstrahlung from 51Cr, 170Tm, 177Lu,and 198Au

The circular polarization P of γ-rays from unpolarized sources of ⁷⁵Se, ¹⁷¹Er, and ¹⁷⁵Yb of strengths ? 500 Ci has been measured with a Compton polarimeter of the radial transmission type. Eight NaI crystals and a four-fold current integration system were used to simultaneously record the data in four independent channels. The results are: P = ?(1.8 ± 6.0) × 10^?5 for the 401 keV transition in ⁷⁵As (the experimental error is ± 1.5 × 10^?5, the remaining part is due to the uncertainty in the decay scheme of ⁷⁵Se), P = (0.8 ± 1.5) × 10^?4 for the 296 keV and 308 keV transition in ¹⁷¹Tm, and P = (5.7 ± 0.8) × 10^?5 for the 396 keV transition in ¹⁷⁵Lu. The last value confirms the parity non-conservation in nuclear forces. The polarimeter was calibrated with bremsstrahlung from ¹⁷⁰Tm. The correction for polarized bremsstrahlung was given special attention. Correction factors are derived for ⁵¹Cr, ¹⁷⁷Lu, and ¹⁹⁸Au from a comparison of the measured and calculated bremsstrahlung yields.