Angular Correlation Studies Research Articles

Time differential perturbed angular correlation studies with154Gd in a liquid environment at different temperatures

The perturbation of gamma-gamma angular correlations in the 1.17 ns 2+ state of154Gd has been studied by using the154Eu activity dissolved in 6N HClO4. Time differential measurements were performed at five different temperatures between 0 °C and −80 °C. The environment remains in the liquid phase in the whole temperature range and the attenuation of the angular correlations can be described by the theory of Abragam and Pound5. The observed attenuation parameters λ2 and λ4 were used to derive separately the strengths of the magnetic dipole interaction and the electric quadrupole interaction between the nuclei and their environment. The observed temperature dependence of the magnetic dipole and electric quadrupole interaction strength can be understood by a simple model of the attenuation mechanism.

Angular correlation studies for α-particle excitation of the 1.78 MeV 2 + state in 28Si

The α-γ in-plane angular correlations of the reaction 28Si(α, α 1γ) 28Si have been measured at 10, 12, 14 and 18 MeV. Correlations were obtained for c.m. scattering angles from 20° to 170° in 3° steps. Extracted angular-correlation parameters show a strong energy dependence, with a more rapid variation of the correlation pattern as a function of scattering angle with bombarding energy increase. Detailed coupled-channels analyses of the 18 MeV data with coupling of the first three excited states to the ground state of 28Si were performed and a prolate deformation β R = 0.3 was deduced.

A study of the low-lying states in 22Mg

New states have been found in 22Mg at E x = 5006±2, 5317±5 and 5837±5 keV with spins of J = (≦ 4), (1, 2, 3) and (≧ 2) , respectively, in coincidence and angular correlation studies of the reaction 20Ne( 3He, nγ) 22Mg at E( 3 He) = 4.3–11.5 MeV . For the known states below E x = 6.3 MeV the following information has been obtained: E x(keV){ J π } = 1247 (2 +), 3308 (4), 4402 (2), 5037 (1, 2), 5290 (2, 3, 4), 5464 (2, 3, 4), 5714 (1, 2) and 6298 (≦ 6). Branching and mixing ratios are reported. The mean-life of the 1247 keV state has been determined to be 1.0 +2.2 −0.5 ps with the use of the Doppler-shift attenuation method.

Differential perturbed angular correlation study of quadrupole coupling of 181Ta in neutral octocoordinated d° hafnium (IV) complexes

The differential perturbed angular correlation of 181Ta 133−482 keV γ-γ cascade was studied in Hf(IV) d° neutral complexes. The quadrupole coupling parameters were shown to be sensitive to the nature of increasingly covalent ligands. The occurrence of several isomeric forms and their interconversions is discussed in the light of the experimental evidence.

Electron momentum distribution in silicon

Abstract X-ray Compton profiles of silicon were measured, using Mo Kα (Λ = 0·709 A) and Ag Kα (0·559 A) along the [100], [110] and [111] directions. After subtracting the 2s 22p 6 Hartree-Fock core contributions in the impulse approximation (1δ2 not excited the Compton profile for the four valence electrons averaged over these three directions agreed with the averaged theoretical profile calculated by Stroud and Ehrenreich (1968) and with the averaged profile determined by Erskine and McGervey (1966) from their positron annihilation angular correlation studies. The small departures from spherical symmetry in the Compton profiles did not agree with the theoretical calculations nor with the positron measurements (which agree with each other) but rather appeared to be similar to the anisotropies in the diamond Compton profile. The disparity between the x-ray and positron work may be due to the local positron shielding of the electron-electron correlation effect.

Investigation of the Electronic Structure ofα′-Cerium by Angular-Correlation Studies of Positron-Annihilation Radiation

Investigation of the Electronic Structure of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi>α</mml:mi></mml:mrow><mml:mrow><mml:mo>′</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>-Cerium by Angular-Correlation Studies of Positron-Annihilation Radiation

Angular-correlation studies in the decay of198Au

The angular correlation of the γ-γ cascade 676-412 keV in the decay of198Au is studied, with the aid of a high-efficiency sum-peak coincidence arrangement. The resultant correlation pattern isW(θ) =1 −- (0.272 ± 0.01)P2 cos ϑ + (0.143 ± 0.006)P4 cosθ. Under the assumption of a 2+-2+-0+ spin sequence connecting the cascade, the present correlation coefficients are used to obtain the mixing ratio of the 676 keV transition to be 0.85 ± 0.06. The results indicate monopole contribution and an admixture of particle and collective excitations in the 676 keV transition in198Hg. Vibrationlike wave functions furnished by Covello and Sartoris, and Ialongo and Alaga, for the 2+ states are used and the mixing ratios are estimated to be 5.03 and 0.143, respectively. It is concluded that the vibrationlike wave functions based on microscopic models are not adequate for describing the second 2+ state in198Hg.

A new approach to positron angular correlation studies

A new kind of apparatus is described for carrying out positron angular correlation measurements. The apparatus employs a spark chamber as a two dimensional gamma -ray detector and is able to determine two components of the momentum of photon pairs produced by annihilating electron positron pairs. The results of an experiment on a copper single crystal are described and it is shown that the experimental data show the effect of the necks of the copper Fermi surface. Various possibilities for improvements to the apparatus are discussed. Finally a mathematical method is proposed which it is believed would permit the complete momentum for photon pairs to be derived from a single experiment at a mirror plane orientation. If this method were operated successfully then it would allow a Fermi surface to be derived which was correct for electrons in the region of the positron. This has been shown to be very similar to the true Fermi surface.

Spins of Levels in 32P by Angular-Correlation Studies

The spectroscopic properties of the 1.75, 2.66, 2.74, and 3.00 MeV levels of 32P have been studied by the particle–gamma angular-correlation method II of Litherland and Ferguson applied to the reaction 29Si(α,p)32P at 10.3 MeV. The decay scheme was observed with a Ge–Li detector in coincidence with the protons. The spin of the 1.75 MeV level was determined to be 3. The restrictions imposed on J by the analysis of the angular correlations combined with other information lead to the following most probable assignments: 2.66 MeV, J = 1,2; 2.74 MeV, J = 1,2; 3.00 MeV, J = 1,2,3.

Gamma-gamma-gamma angular correlation method and triple gamma angular correlation studies in 133Cs from the decay of 133Ba

A gamma-gamma-gamma angular correlation method for radiations from radio-active nuclei has been described. Three NaI(Tl) detectors are used for the detection of gamma-radiations. Two geometries have been used for the mounting of these three detectors. Angular correlation studies for the cascade 276 keV → 79.6 keV → 81 keV in 133 Cs from the decay of 133Ba have been made. The multipolarity of the 79.6 keV gamma transition has been discussed.

Sign of 'δ', the Amplitude Mixing Ratio of Gamma Transitions, and Gamma–Gamma–Gamma Angular Correlation Studies in 160Dy

The importance of gamma–gamma–gamma angular correlation in order to study the absolute sign of 'δ', the amplitude mixing ratio of gamma transitions, independent of phase convention is given. A study of the triple gamma-rays cascade of 298 keV → 879 keV → 87 keV in 160Dy from the decay of 160Tb has been done.

Angular correlation studies of electromagnetic transitions following the 16O(τ, α)15O reaction

Abstract A particle-gamma angular correlation coincidence technique enabling the measurement of 0° coincidences was used to study levels in 15 O at 5.24 MeV (J π = 5 2 + ) , 6.18 MeV (J π = 3 2 − ) , 6.79 MeV (J π = 3 2 + ) and 6.86 MeV (J π = 5 2 + ) . The multipole mixing ratios of the de-excitation γ-rays were determined as the following: x (5.24→ 0) = +0.08±0.08 an E3/M2 mixture; x (6.86 → 5.24) = +0.04±0.03, an E2/M1 mixture; x (6.79 → 0) = −0.02±0.02, an M2/E1 mixture and x (6.18 → 0) = −0.121 ±0.008 an E2/M1 mixture. The latter value is to be compared with x (( E 2/ M 1) = +0.13 ±0.02 for the mirror 6.323 MeV transition in 15 N indicating |x( 15 O )| ≦ |x( 15 N )| contrary to previous findings (10). The results obtained, together with those corresponding to mirror transitions in 15 N are compared with recent IPM and core polarization theoretical investigations.

An associated gamma ray time of flight spectrometer with high neutron efficiency

A high efficiency, associated gamma ray time of flight spectrometer for the study of (n, γ) angular correlations following (charged particle, n) reactions is described. The neutron detector employs eight XP1040 photomultiplier tubes viewing four tanks of NE213 liquid scintillator, and subtends a solid angle of 0.092 sterad at the target when the neutron flight path is two metres. Neutron events in the scintillator are identified by means of pulse shape discrimination. The use of constant fraction pulse height discriminators to provide fast timing pulses, enables the use of a wide dynamic pulse height range in both the neutron and gamma ray detectors. This method of timing enables the gamma ray detector to be changed from a Ge(Li) counter, to a NaI(Tl) or other type of scintillation detector with only a minimal rearrangement of the electronic system.

Gamma-ray angular correlation measurements in 30Si

A particle-gamma angular correlation study using the reactions 30Si(p, p'γ) 30Si and 30Si(α, α'γ) 30Si has enabled spin and parity assignments to be made in 30Si up to an excitation energy of 7.9 MeV. Major electromagnetic decay modes have been established for levels up to 8.6 MeV, the more complex cases by a proton-gamma coincidence method using the 27Al(α, pγ) 30Si reaction. Spin and parity assignments have been made for levels at 4809 (2 +), 4830 (3 +), 5230 (3 +), 5280 (4 +), 5487 (3 −), 5612 (2+), 5951 (4 +), 6503 (2 −, 4 −), 6537 (2 +), 6745 (1 −), 6865 (2 −, 3 +) 6914 (2 +), 7044 (3 −, 5 −), 7223 (4 +), 7256 (2 +), 7610 (2 +) and 7899 keV (2 +). A new level is proposed at 7590±10 keV. Multipole mixing ratios have been measured for most of the observed decay modes. The results are discussed in terms of collective and shell-model excitations.

Studies of 37Ar via the 36Ar(d, pγ) 37 Ar reaction

The 37Ar states below an excitation energy of 3.7 MeV have been studied via the 36Ar(d, pγ) 37Ar reaction at deuteron bombardment energies in the vicinity of 3 MeV. Direct γ-ray spectra were recorded in Ge(Li) spectrometers at θ γ = 0° and 90° with gas target pressures in the range 25 to 3000 Torr. The following excitation energies were observed for the low-lying levels of 37Ar: E x = 1408.8 ± 1.5, 1611.2 ± 0.8, 2218.2 ± 1.5, 2490.6 ± 1.3, 2796.3 ± 1.8, 3171.3 ± 1.7, 3186.4 ± 1.7, 3273.4 ± 1.6, 3516.1 ± 1.8, 3526.1 ± 2.1 and 3607.7 ± 2.9 keV. An upper limit on the mean lifetime of τ ≦ 30 ps was deduced from the Doppler shift for all of the above states except the relatively long-lived 1611 keV state. Proton-gamma angular correlation studies were performed in a collinear geometry at E d = 2.800, 2.975 and 3.100 MeV. The following spin restrictions resulted therefrom: E x (J) = 1611 ( 5 2 , 7 2 ), 2218 ( 5 2 , 7 2 ), 2491 ( 3 2 , 5 2 ), 2796 (≦ 7 2 ), 3171 ( 3 2 , 5 2 ), 3273 ( 3 2 , 5 2 ), 3516 ( 3 2 ), 3526 ( 7 2 ), and 3608 ( 3 2 , 5 2 ) . The results of the present and previous studies on the low-lying levels of the 37Ar structure are synthesized and compared with existing shellmodel calculations.

Angular correlation studies in 34S

The states of 34S up to 5.4 MeV excitation have been studied by particle-γ-ray angular correlation experiments using the reaction 31P(α, p) 34S. Spin assignments of 4, 3 2 and 1 have been made to the levels at 4.688 MeV, 4.874 MeV, 5.318 MeV and 5.380 MeV, respectively. Spin assignments to levels below 4.9 MeV have been confirmed. Branching ratios have been determined for all but one of the states and multipole mixing ratios for all but one of the observed transitions. The results are discussed in relation to various models.

The spins and lifetimes of some low-lying states of 58Ni

Particle-gamma-ray angular correlation studies of the 58Ni(p, p'γ) reaction have been used to determine the spins of the following states of 58Ni: 2.775 MeV (2), 2.943 MeV (0), 3.038 MeV (1, 2), 3.263 MeV (2), 3.420 MeV (3, 4), 3.531 MeV (0), 3.593 MeV (1), 3.620 MeV (2, 3, 4), 3.774 MeV (2, 3, 4), and 4.108 MeV (2). Gamma-ray branching ratios and mixing ratios were also measured. The Doppler-shift attenuation method has been used to measure the lifetimes of the states of 2.902 MeV (100−19+22 fs) and 3.774 MeV (400−100+200 fs) while the mean life of the 2.943 MeV level was found to be 2.9 ± 0.1 ns by direct timing. The internal conversion coefficient of the 2.943 (0+) MeV to 2.902 (1+) MeV has been measured to be 0.48 ± 0.05 and an upper limit of 2 % has been placed on the 2.943 MeV to ground state EO transition. The experimental energy level spectrum of 58Ni and electromagnetic transition rates are compared to shell-model predictions calculated using the two-body interaction matrix elements of Kuo.

An angular correlation study of the low-lying levels of 29P

Abstract The low-lying levels of 29P have been investigated by 32S(p, αγ)29P angular correlation measurements using a collinear geometry. The spin assignments for the 1.38 and 1.96 MeV levels are in agreement with the known values of 3 2 and 5 2 respectively. A J π = 3 2 + assignment is made to the third excited state at 2.40 MeV. Branching ratios for these levels are presented as well as γ-ray multipole mixing ratios for some of the transitions. Predictions of the vibrationparticle coupling model are compared with these results.

Electromagnetic transitions in 19Ne

The Doppler shift attenuation observed with a Ge(Li) γ-ray detector was used to gain information on the decay rates of some of the bound states of 19Ne. The values τ = 4.1 −1.4 +3.5 ps, τ = 28±15 fs, τ = 180±60 fs and τ = 330±130 fs have been determined for the 1508, 1536, 1615 and 2795 keV levels respectively. Level energies and decay schemes are reported and angular correlation studies taken together with the lifetime results and mirror level arguments show that the spin-parity sequence for the levels studied is 5 2 −, 3 2 +, 3 2 − and 9 2 + respectively. The results are compared with model calculations.

A new type of double-focusing magnetic spectrometer

A double-focusing magnetic spectrometer was built for beta-gamma angular correlation studies. The magnetic field was obtained by double wedge shaped iron polefaces. The resulting electron trajectories are trochoidal in nature, and the central trajectory covers an angular range of approximately π√ 2 rad. Numerical calculations of the focusing properties indicate that the magnetic field gives first-order double-focusing that is very similar to the π√2 first-order double-focusing principle.