W.D. Hamilton

Angular correlation measurements in 192Pt

Abstract Gamma-gamma and gamma linear polarized gamma angular correlation measurements were used to determine the E2 : M1 multipole mixing ratio of the 296 (2 + → 2 + ) 308 (3 + → 2 + ) and 604 (3 + → 2 + ) keV transitions in 192 Pt. A Ge detector was used in conjunction with a NaI detector to resolve the complex spectra of the γ-γ correlations. The linear polarization measurements were carried out at a correlation angle of 90° using a summing polarimeter. The measurements are consistent with the accepted spins of the levels involved and yield the following values of the E2: M1 mixing ratio σ: δ(296) = −9.0 to −11.0 , δ(308) = −6.5 to − 8.3 , δ(604) = +1.9 to + 2.4 .

Parity mixing in the 482 keV state in 181Ta

Abstract A search has been made for a parity-violating component in the 482 keV level of 181 Ta by measuring the degree of circular polarization of the ground state transition. Two Compton transmission analysers were used. The design of the experiment required extreme care because of the small degree of polarization expected, i.e. P γ ≈ 10 −4 , and the low efficiency of the Compton analysers. The minimization or elimination of possible causes of a false effect is discussed; control experiments with 60 Co and 181 Hf sources were used to evaluate any residual asymmetry in the measuring system. Considerable care was taken in the analysis of the data especially as regards the removal of trend effects. A careful investigation of the various sources of systematic error was made; the only significant one found was due to bremsstrahlung. The results obtained were P γ = − ( 0.8 ± 1.4 ) × 10 − 4 ( a n a l y s e r e f f e c i e n c y 0.6 % ) , P γ = − ( 0.9 ± 0.6 ) × 10 − 4 ( a n a l y s e r e f f e c i e n c y 1.6 % ) . The second result is significantly larger than the calculated effect due to bremsstrahlung ( P γ = −1.6×10 −5 ). It is consistent with the theoretical estimates, which lie in the range P γ = −(0.4to2.7)×10 −4 .

The mean life and nuclear deformation of the 98 keV level in 153Eu

Abstract The nuclear resonant scattering cross-section for 98 keV γ-rays has been evaluated relative to that for Rayleigh scattering. The resonant condition was provided by the overlap of the thermally broadened emission and absorption levels. The scattering cross-section gave a mean life for γ-decay of (2.28±0.18) × 10 −10 sec and on the basis of the Nilsson model the deformation parameter of the 98 keV level was found to be δ = 0.20±0.01 when δ = 0.30 for the ground state, and the parameter μ has the values 0.55 and 0.70 for the ground and excited states respectively.

The low energy levels of 211Bi

Abstract The gamma-ray spectrum of the excited levels of 211 Bi populated following the β-decay of 211 Pb was examined using both NaI(Tl) and germanium detectors. Coincidence, component sum coincidence and sum coincidence techniques were used to evaluate the spectra and the possible cascades which occur. Evidence is presented for several new transitions and the results of previous work are largely confirmed with respect to the decay scheme. There are however some disagreements with previous measurements of the γ-decay relative intensities. In particular the 405:427 keV intensity is 1:0.40±0.03 and together with the relative intensities of K-shell conversion electrons implies that the 427 keV transition is essentially pure M1. The conversion coefficients for other dominant transitions are evaluated.

The multipole mixing ratio of 2′+ → 2+ transitions in 194Pt and 196Pt

Abstract Gamma-gamma and gamma-linear polarized gamma angular correlation measurements were used to determine the E2 : M1 multipole mixing ratio of 2′ + → 2 + transitions in 194 Pt and 196 Pt. The γ-γ measurements were made with a good resolution detector and the transitions were unambiguously identified. A summing polarimeter with a correlation angle of 90° was used for the linear polarization measurements. The results obtained are [2′ + (294)2 + ; 194 Pt ] = −(30 +39 −11 ) , [2′ + (333)2 + ; 196 Pt ] = +(4.03±0.12. The magnitude and sign of δ for 194 Pt is in agreement with Kumars theoretical value, while the result for 196 Pt disagrees markedly.

Multipole mixing ratios of electromagnetic transitions in 152Gd

Abstract 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 152 Gd following the decay of 152 Tb. 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 3 He- 4 He 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 Kumars predictions for similar transitions in 152 Sm. Three other mixing ratios were also determined.

Spin assignments and multipole mixing ratios in 211Bi

Abstract The spins of the 405, 832 and 1106 keV excited states in 211 Bi and the multipole mixing ratios of the cascade transitions which link them with the ground state have been determined from γγ and γ-linear polarization γ-angular correlation measurements. The level spins have been uniquely determined and the results for the multipole mixing ratios are as follows: 9 2 (405 keV, Q = 0.30 to 0.87) 7 2 (427 keV, Q = 0.00 to 0.03) 9 2 , 9 2 (405 keV, Q = 0.30 to 0.87) 7 2 (702 keV, Q = 0.98 to 1.00) 9 2 ,where Q is the fractional E2-M1 admixture, i.e. Q= δ 2 (1 + δ 2 ) . This set of results is consistent with internal conversion coefficient measurements. These results also recent theoretical calculations of the level scheme by Gabrakov.

The linear polarization of the 482 keV transition in 181Ta

Abstract The 482 keV E2-M1 transition in 181 Ta is important in nuclear penetration and parity violation experiments. A critical analysis of previous experiments indicates discrepancies and inconsistencies in the analysis of the experimental data for the determination of the mixing ratio for this transition. A new determination has been made of the mixing ratio using a method which is independent of perturbing effects which have been present in all previous determinations. This method depends on the comparison of results obtained from γ-γ directional and linear polarization correlation experiments, using the same source for both experiments. The method of analysing this type of experiment is presented. The value δ = 7.2 −1.5 +1.8 is in agreement with the presently accepted value.

Monopole mixing ratio of the 793 keV 2+ → 2+ transition in 184W

Abstract The amplitude mixing ratios of the E2 to M1 and E0 to E2 components of the 2 + (793 keV) 2 + transition in 184 W were obtained from γγ, and gamma-conversion electron angular correlation measurements. The γγ measurements used a Ge(Li) detector in some cases; the eγ correlations were performed using a magnetic lens spectrometer. The results obtained are δ (E2:M1) = + 18.7 +4.6 −3.1 + 0.38 ≧ q( E 0: E 2) ≧ − 0.28 for + 53 ≧ λ ≧ − 113 . Agreement with Kumars theoretical values for δ and q is contradictory: the former favours a 2″ assignment, the latter a 2prime; assignment to the 904 keV level.

The linear polarization of the 279 keV transition in 203Tl

Abstract The 279 keV E2-M1 transition in 203 Tl is important in nuclear penetration and parity violation experiments. Straightforward γ-γ angular correlation measurements do not provide a method of determining the mixing ratio of this transition accurately. The special methods which have been used to determine the mixing ratio do not give results in complete agreement. A new determination of the magnitude and sign of the mixing ratio has been made by combining results obtained from γ-γ directional and linear polarization correlation experiments. The result obtained δ (279) ≦ 1.1, is in agreement with the presently accepted value. In addition, the spin of the 680 keV level in 203 Tl has been shown explicitly to be 5 2 as is commonly assumed.