Gamma-ray transitions in Bi following the decay of Po

The decay of 5.7 h ²⁰⁷Po to levels in ²⁰⁷Bi has been studied using a Ge(Li) detector. Combining the relative gamma-ray intensities with previously established conversion electron intensities, K-conversion coefficients are determined. The multipolarities of 29 transitions are deduced from a comparison with theoretical conversion coefficients, thus establishing the following spins and parities for the excited levels:

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. A comparison with a recent shell-model calculation shows good agreement for all negative parity levels.     

The decay of 23.0 min Rb to levels in Kr

The radioactive decay of ⁷⁹Rb(23.0±0.5 min) has been studied with the aid of semiconductor radiation detectors. Both singles and coincidence spectra have been recorded. The decay energy: 3520±45 keV was determined by measuring the endpoint of the positon spectrum in coincidence with prominent γ-rays. A decay scheme is proposed incorporating most of the measured γ-rays. The following energies in keV and parities of levels are assigned: ground state ( ), , , , , 383.71±0.18, 532.82±0.33, 688.21±0.09, , 934.0±1.4, 1089.4±0.4, 1474.7±0.3. The spin and parity of the ⁷⁹Rb ground state is most probably .     

Levels and transitions in 131Xe studied by the decay of oriented 131I

Sources of ¹³¹I were prepared by implantation in iron foils. Nuclear orientation of these sources was obtained by cooling them to temperatures of 30 to 50 mK using a dilution refrigerator and saturating the iron by an external magnetic field. Anisotropies of angular distributions of eleven γ-transitions in ¹³¹Xe have been measured, yielding the following results: the levels at 405 and 637 keV are $\text{3}\text{2}$⁽⁺⁾ and $\text{7}\text{2}$⁽⁺⁾ states and the assignment $\text{5}\text{2}$⁽⁺⁾ for the level a keV is confirmed. Deduced values of E2/M1 multipole mixing ratios are (energies in keV): ?0.5 ≦ δ(318) ≦ + 0.2; δ(364) = ?4.53±0.12; + 0.2 ≦ δ(405) ≦ +2.0; δ(723) = +0.207 ± 0.005. The allowed β-decay branch to the level at 637 keV is for at least 90% of the Gamow- Teller type.     

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 decay schemes of Y and Y and γ-rays observed in the decay of Y

Active yttrium was separated from ²³⁵U fission products and the decay of ⁹⁴Y, ⁹⁵Y and ⁹⁶Y to the levels of ⁹⁴Zr, ⁹⁵Zr and ⁹⁶Zr, respectively, has been studied with the aid of a 17 cm³ Ge(Li) detector. Gamma-ray energies and intensities were accurately determined. In the decay of ⁹⁴Y four new transitions at 1232.78 ± 0.35, 1324.97 ± 0.35, 1363.48 ± 0.35 and 2467.00 ± 2.75 keV were observed. The data obtained support the level scheme proposed for ⁹⁴Zr by Knight et al. and that deduced from more recent reaction data. Evidence supporting the location of the 0⁺ excited state at 1300 keV is presented. Branching ratios are calculated and a modified level scheme for ⁹⁴Zr is proposed. In the decay of ⁹⁵Y the energies of 13 γ-rays, previously identified with the decay of this nuclide, have been accurately measured and are presented in a partial level scheme for ⁹⁵Zr. The data obtained in this work support the level structure deduced from reaction data by Cohen and Chubinsky and by other workers. New γ-transitions at 550.10 ± 0.23, 1723.30 ± 0.90 and 1805.0 ± 1.0 keV were measured in the decay of ⁹⁶Y.     

After-effects in the decay of As and Hg

After-effects following internal conversion processes in the decay of ⁷⁵Se and ^197mHg are investigated. Time differential electron-γ and time integral electron-γ, γ-electron and γ-γ directional correlation measurements are performed, and a magnetic decoupling technique is used. For certain insulating source backing materials after-effects are found. Relaxation time constants for the time-dependent perturbation and recombination time constants for the ionized atoms, as well as the strength of the time-dependent internal magnetic fields are deduced.     

On the theory of auto-ionization in electron-capture decay

Existing theories of auto-ionization in electron-capture decay are reviewed. It is proved that the theoretical model recently developed by Law and Campbell is identical with an earlier theory due to the author. Disagreement between the final results obtained from these two theories is traced to additional approximations introduced by Law and Campbell in the course of their calculations. These approximations are critically examined and found to be invalid thus explaining the reported disagreement. The results of various theoretical calculations previously reported by the author are evaluated for several nuclei of interest.     

The decay of the Co isomers

The single and coincident γ-ray spectra following the decay of the ⁶²Co isomers were measured. New γ-transitions in the decay of the 13.5 min respectively 1.4 min isomer with energies: 0.7778, 0.8749, 1.1291, 1.7535, 2.3020 and 2.8826 MeV respectively 1.8863, 2.3458, 3.271 and 3.370 MeV have been observed. The intensity of the direct feeding from the 1.4 min isomer to the ground state of ⁶²Ni was determined to be < 0.5 %.     

Studies of the alpha decay of U

The decay of ²³³U through the first and second excited states of ²²⁹Th has been studied using a uranium oxide source. The half-life of the first excited state of ²²⁹Th was found to be less than 1.9 nsec; it decays by an almost pure M1 transition. The half-life of the second excited state of ²²⁹Th was found to be 0.5±0.2nsec; this level de-excites by E2 cross-over radiation in 96% of events. Contrary to expectations, an anisotropic alpha-gamma angular correlation was not found, and the probable reason for this is discussed.     

Alpha decay of Cm

An enriched sample of ²⁴⁷Cm (99.4 %) has been used to investigate the -decay scheme of ²⁴⁷Cm. Seven -groups with energies and intensities 5.265 (13.8 %), 5.210 (5.7 %), 5.145 (1.2 %), 4.983 (2.0 %), 4.941 (1.6 %), 4.868 (71.0 %) and 4.818 (4.7 %) were observed. Gamma-singles and γ coincidence spectra showed the presence of 278.0, 287.5, 346.0 and 402.4 keV γ-rays. A two-parameter coincidence experiment established that the sources of the 402.4 and the 287.5 keV γ-rays were 4.868 and 4.983 MeV -groups, respectively. The multipolarity of the 287.5 keV transition was found to be M1. The K conversion coefficient of the 402.4 keV γ-ray indicates an E1 multipolarity for this transition. The levels at 287.5 and 402.4 keV have been assigned to the and Nilsson states, respectively. The half-life of ²⁴⁷Cm was found to be (1.56±0.05) ×10⁷ y from the pulse analysis and mass spectrometric analysis of the sample.     

The decay of Se

The gamma-ray spectrum associated with the electron capture decay of ⁷⁵Se has been studied with Ge(Li) spectrometers. Coincidence spectra were taken with a Ge(Li)---Ge(Li) combination. The data do not support a recent report of several new gamma rays in the decay of ⁷⁵Se. Gamma-gamma angular correlation experiments were performed with a NaI(Tl)---Ge(Li) combination. The value obtained for δ(280 keV) is in excellent agreement with one recently reported value but in poor agreement with another. The ratio P_K/P_tot for the electron capture branch to the 401 keV level of ⁷⁵As has been determined, and the result agrees with previous experimental determinations.     

The decay of Ag

The γ-radiation following the decay of ¹¹²Ag has been studied with a Ge(Li) detector. A total of 76 γ-rays was observed. The γ-γ coincidence and angular correlation relations involving the 617 keV 2⁺-0⁺ transition have been measured using Ge(Li)-NaI(Tl) and NaI(Tl)-NaI(Tl) detectors. These results have been used to confirm spins and parities of some levels of ¹¹²Cd in the proposed decay scheme. Cross sections for ¹¹²Ag production by ¹¹⁵In(n,α) and ¹¹²Cd(n, p) reactions have been measured; the ¹¹²Ag half-life has been determined as 3.14 ± 0.02 h.     

The decay of Cs

In a study of the level scheme of ¹³¹Cs, we have measured the γ-γ and the ce-γ directional correlations of the 496-123.7 keV and 486-133.5 keV cascades. The linear polarization at φ=90° was measured for the 496-123.7 keV and 486-133.5 keV cascades. The L-subshell ratios for the 123.7 keV transition were determined. The g-factor of the 133.5 keV level and the half-lives of the 78.7, 123.7, 133.5 and 216 keV levels were re-investigated. The spin and parity assignments derived for the 620, 133.5 and 123.7 keV levels are , respectively. The 620, 496, 486, 133.5 and 123.7 keV transitions are found to be of pure E2, pure M1, pure E2, (M1+(22±2)%E2) and pure E2 multipolarity, respectively. An upper limit of 192 ps for the half-life of the 216 keV level is obtained. The results are compared with theoretical estimates from the calculations of Kisslinger and Sorensen, of Freed and of Freed and Miles.     

The decay scheme of Ag

The γ-radiations following the decay of ¹¹²Ag have been studied with Ge(Li) detectors. The ¹¹²Ag half-life has been measured as 3.16±0.02 h; twenty gamma radiations ranging in energy from 606.7 keV to 2829.6 keV have been observed.

Gamma-gamma coincidence measurements have been performed with Ge(Li) and NaI(Tl) detectors. A decay scheme consistent with the present data is proposed.     

Multipole mixing ratios of transitions in Te

Gamma-gamma directional correlation measurements were made on nine transitions in ¹²⁴Te with a NaI(Tl)-Ge(Li) detector arrangement and multichannel analysis. The multipole mixing ratios obtained were δ(646) = 0.000±0.001, δ(714) = 1.5_−0.3^+0.6, δ(723) = −3.3±0.2, δ(1437) = 3.7_−2.0^+2.7, δ(1489) = −3.4_−1.5^+0.9, δ(968) = −0.03_−0.05^+0.06, δ(1368) = −0.045±0.090, δ(1045) = 0.041_−0.041^+0.047, δ(1691) = −0.02±0.01, and δ(2091) = 0.00_−0.03^+0.02. The first δ is M3/E2, the next three are E2/M1, and the last five are M2/E1. The retardation (a factor of approximately 50) of the crossover to cascade transitions from the 2039 keV, third 2⁺ level to the second and first 2⁺ levels is essentially the same for both the M1 and E2 components. In addition, spin and parity assignments of 2⁺ were made for the 2039 and 2092 keV levels.     

The ratio of K-capture to positon emission in the decay of P

The ratio of K-capture to positon emission in the 2.5 min decay of ³⁰P has been measured by a proportional counter-flow technique. The experimental value of the K/β⁺ was found to be (1.24 ± 0.04) × 10⁻³ in agreement with the conventional theoretical ratio i.e. apparently supporting the view that exchange and overlap effects are small.     

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.     

Multipole mixing ratios of electromagnetic transitions in Gd

Using γ-γ(θ), γ(θ) (nuclear orientation) and e_k-γ(θ) directional correlation techniques, we have determined the multipole character of some transitions connecting the quadrupole and octupole quasi-vibrational bands to the ground state quasi-rotational band in ¹⁵²Gd following the decay of ¹⁵²Tb. For the γ-γ directional correlation measurements a high-energy resolution system employing a Ge(Li) and a NaI(Tl) detector was used while for the e_k-γ correlation we used a NaI(Tl) and magnetic lens spectrometer system. The nuclear orientation measurements were carried out at low temperatures obtained with a ³He-⁴He dilution refrigerator. The results show that the 2⁺ → 2⁺ transition between the β-vibrational and the ground state bands contains ≈ 10% Ml admixture, δ = − 3.05 ± 0.14, and a large E0 contribution while the similar transition from the γ-vibrational band has δ = 4.3 ± 0.7. These results are compared with Kumar's predictions for similar transitions in ¹⁵²Sm. Three other mixing ratios were also determined.     

The decay of Sc and V

The decays of ⁴⁸Sc and ⁴⁸V have been studied with Ge(Li) diodes, scintillation spectrometers and a double focussing beta-ray spectrometer. The 3507 keV level, from which originates the quadruple cascade (9.4±0.5)% in the ⁴⁸Sc decay, is also de-excited by a 1212 keV cross-over transition to the 2295 keV (4⁺) level and supports the assumption, that the 3507 keV level has a spin 6⁺. The first member of the reported triple cascade in the ⁴⁸V decay is shown to be a doublet of 928.9±0.7 (1.2±0.2)% and 944.3±0.5 keV (8.0±0.5)% gamma rays, both followed by the 1311.4–983.3 keV cascade. Evidence was found, that the 2421 keV (2⁺) level is excited by weak gamma rays from high-energy levels. The K/β⁺ ration in the ⁴⁸V decay is 0.69±0.05 The Q-values of ⁴⁸Sc and ⁴⁸V are calculated to be 3986±7 keV and if 4015±4 keV, respectively. The energy of the gamma ray of ⁴⁷Sc, which is present as an impurity, is 159.2±0.5 keV.