Angular Correlation Experiments Research Articles

A search for parity mixtures in nuclear states

The gamma radiation emitted from nuclear states which are polarized by beta decay can show a 90 degree asymmetry if parity conservation in nuclear states does not hold strictly. A beta-gamma angular-correlation experiment yields linearly the quantity R F , where F is the relative amplitude of the irregular wave functon with respect to the regular one and R is the matrix-element ratio of the gamma transitions. The measurement are performed with the beta-gamma decays of A 41 → K 41, Xe 133 → Cs 133, and Lu 177 → Hf 177 and result in the following upper limits for F : 6 × 10 − for A 41, 2 × 10 −4 to 8 × 10 −6 for Xe 133, and 3 × 10 −3 for Lu 177.

Determination of the Beta-Decay Interaction from Electron-Neutrino Angular Correlation Experiments

The methods used to obtain a series of measurements of the angular correlations in the allowed beta decay of described. Schematic diagrams of the apparatus used in various experiments are given. The results prove that the dominant interactions are vector for the Fermi type of decay and axial-vector for the Gamow-Teller decays with the dominant interaction form being VA. The present experiments do not exclude a possible tensor admixture of 10% or less. A scalar mixture of the same magnitude may also be present. (C.J.G.)

SPINS OF EXCITED STATES OF Os188

Seven excited states of Os188 populated through the beta decay of Re188 have been studied by gamma–gamma angular correlation experiments. The data for the various cascades fit the following theoretical functions: (all gamma-ray energies are in kev and the description following each cascade refers to the first transition) 478–155 (2–2–0, 99.7% E2, δ +ve), 931–155 (0–2–0), 672–633 (2–2–0), 97% M1, δ −ve or 3–2–0, 94% M1, δ −ve or conceivably 4–2–0), 828–633 (2–2–0, 98% M1, δ −ve or conceivably 3–2–0, 80% M1, δ −ve), 1132–633 (0–2–0), and 1308–633 (2–2–0, 98% M1, δ −ve). Some attenuation occurred in the correlations involving the 155-kev gamma ray. The K-conversion coefficients for the 478- and 633-kev transitions have been measured as 0.023 ± 0.003 and 0.010 ± 0.002 respectively, confirming the E2 character for these transitions obtained by angular correlation. These results, coupled with data concerning log ft values and gamma-ray intensities, lead to the following spin and parity assignments for levels in Os188: 155 (2+), 633 (2+), 1086 (0+), 1306 (2+ or 3+), 1461 (2+), 1765 (0+), 1941 (2+), and 1958 (1+ or 2+).The 631–137 correlation data in Os186 was found to fit an attenuated 2–2–0 function with the first transition 99% E2 and δ −ve. This result supports the established decay scheme for this nucleus.

E2-M1 mixing ratios in 2′ → 2 → 0 transitions

The results of twelve published angular correlation experiments have been analyzed, and the E2-M1 mixing ratios of the 2′ → 2 transitions have been obtained for twelve different even nuclei. Particular attention has been given to evaluation of the errors in the measured values of the mixing ratios. The available data range from A = 56 to A = 198. When ( δ/ E γ ) 2 is plotted against Z 2 A 4 3 , three of the experimentally observed points, those for Fe 56, Zr 92 and Hg 198, deviate sharply from a curve calculated from the theoretical considerations of Davydov and Filippov.

Instrument for electron-gamma directional correlation experiments with magnetic momentum selection

A medium thick lens spectrometer was adapted for electron-gamma angular correlation experiments. The requirements to be filled are discussed. It has been found that the necessary mutual independence between spectrometer and gamma-counter can be obtained by suitable iron and mu-metal shielding. A transmission of 1.5% at 3% resolution has been obtained, when utilizing a mean emission angle of 11°.5.

A new method in gamma-ray spectroscopy: A two crystal scintillation spectrometer with improved resolution

A new method has been developed to measure the spectra of gamma radiation emitted in cascade disintegrations. Use is made of a two-crystal scintillation spectrometer and a gated multi-channel analysing device. The pulses produced by summing the outputs of the two crystal-photomultiplier combinations are selected by a single-channel differential discriminator. The output of this differential discriminator gates the multi-channel analyser whenever the sum pulse corresponds to the release in the crystals of the full energy available in the cascade. The spectrum displayed is that of either of the two detectors. The most important features of the technique are: 1. (a) only “full-energy” peaks are detected; 2. (b) improved resolution is obtained especially at higher gamma-ray energies; 3. (c) one γ-γ or p-γ-γ angular correlation experiment determines the angular correlation of the gamma rays of all double cascades deexciting a given level. Details of operation and typical spectra are presented. It is suggested that the technique be called the “sum-coincidence” method.

A resonance model for pion production in nucleon-nucleon collisions at fairly low energies

Cross-sections for pion production in nucleon-nucleon collisions are calculated on the assumption that the production takes place into a few angular momentum states only, and that the matrix element for each particular transition is constant except for factors due to the final-state pion-nucleon and nucleon-nucleon interactions. The outgoing pion is assumed to be in a resonant (3/2, 3/2) state with one of the nucleons. The angular momentum states introduced are compared with those of Rosenfeld (1954) and Gell-Mann & Watson (1954). It is found that a three-parameter theory can give a good account of most of the experiments on pion production, both total and differential, up to 660 MeV, except near threshold when non-resonance production is important and further parameters are necessary. Energy distribution and angular correlation experiments bring out the importance of the pion-nucleon resonance. The cross-section for neutral pion production is predicted fairly accurately in terms of that for positive pion production from threshold to 660 MeV; at 660 MeV, the calculated positive:neutral ratio is 3⋅9. The difference between this value and that of Peaslee (1954) is partly due to the mass difference between the positive and neutral pion and partly to the inclusion of interference effects between the outgoing nucleons.

Measurements on isotope separated β-ray sources of Re 186 and Re 188

Isotopically pure β-ray sources of Re 186 and Re 188 were prepared from pile irradiated natural Re in an isotope separator. The spectrum of the β-rays from Re 188 to the ground state of Os 188 was found not to have the allowed shape. The deviations are of the type earlier observed in the decay Re 186 → Os 186. Both transitions probably proceed from a 1 − to a 0 + state. The K-conversion lines for the transitions from the 633 keV level in Os 188 to the ground state and to the 155 keV 2 + level were observed. The conversion coefficients indicate E2 nature for these transitions in agreement with an angular correlation experiment. The level schemes of Os 186 and Os 188 indicate that these nuclei lie in the transitional region between the strongly deformed nuclei and those of spherical equilibrium shape.

The internal Compton effect: A determination of cross section and angular correlation

The internal Compton effect, a nuclear transition in which there is a simultaneous ejection of a bound electron and emission of a gamma ray, has been unambigously demonstrated. The experiment concerned the 662 keV transition in Ba 137m and was carried out with a gamma scintillation spectrometer and a beta-ray spectrometer in coincidence. The presence of other effects was carefully considered. The experimental cross section was found to be 1.86 × 10 −5 photons in the energy region 97 keV – 120 keV per conversion electron at 90° between the electron and photon directions. Angular correlation experiments were carried out. Comparison with various theories shows that the theory by Spruch and Goertzel does fit the experimental results excellently both regarding absolute cross section and angular correlation.

Decay ofIr192

Gamma-gamma angular correlation experiments have been performed for the 604-316, 588-613, and 468-316 kev cascades in ${\mathrm{Pt}}^{192}$ and the 485-206 kev cascade in ${\mathrm{Os}}^{192}$. The data are consistent with a spin of 3 for the 690-kev level in ${\mathrm{Os}}^{192}$ and the 921- and 1201-kev levels in ${\mathrm{Pt}}^{192}$. The assignment of spin 3 to the 1201-kev level in ${\mathrm{Pt}}^{192}$ requires an admixture of about 8.5 percent $M1$ radiation in the 588-kev transition. Spin 5 for the ground state of ${\mathrm{Ir}}^{192}$ is indicated.

Decay ofA35

The positron decay of ${\mathrm{A}}^{35}$ has been investigated with a magnetic lens beta-ray spectrometer and a NaI(Tl) scintillation spectrometer. A maximum beta-ray energy of 4.96\ifmmode\pm\else\textpm\fi{}0.04 Mev was found, which is 0.5 Mev higher than the previous values determined by cloud-chamber measurements. The new value is in good agreement with the end point predicted from Coulomb energy considerations. Two weak gamma rays were found with energies of 0.19\ifmmode\pm\else\textpm\fi{}0.04 and 1.73\ifmmode\pm\else\textpm\fi{}0.04 Mev; both are in good agreement with reported levels in ${\mathrm{Cl}}^{35}$. Analysis of the complex beta spectrum shows that approximately 7% of the ${\mathrm{A}}^{35}$ decays to two excited states in ${\mathrm{Cl}}^{35}$. The $\mathrm{ft}$ value of the ground-state, mirror transition is 6200\ifmmode\pm\else\textpm\fi{}400 seconds. From this $\mathrm{ft}$ value and the $\mathrm{ft}$ value of ${\mathrm{O}}^{14}$, the ${|\ensuremath{\int}\ensuremath{\sigma}|}^{2}$ for this transition was estimated to be less than 0.13; the $e\ensuremath{-}\ensuremath{\nu}$ angular correlation coefficients were calculated to be +0.96\ifmmode\pm\else\textpm\fi{}0.04 and -0.93\ifmmode\pm\else\textpm\fi{}0.09 for the $V$, $T$ and $S$, $T$ beta interactions, respectively. These coefficients are indistinguishable from those expected in the case of a pure Fermi transition, indicating that ${\mathrm{A}}^{35}$ would be very suitable for identifying the Fermi invariant in the beta-decay interaction by an angular correlation experiment.

On Source Scattering in Angular Correlation Experiments with Soft Electrons

On Source Scattering in Angular Correlation Experiments with Soft Electrons

LVIII. The effects of finite size and decentring of the source in an angular correlation experiment

Summary In a first approximation any extended source behaves like a point source situated at the ‘centre of gravity’ of the given activity distribution. The first-order errors caused by bad centring of a point source are rather large and exhibit a strong angular dependence. They can be minimized by a randomized block design when it is impossible to avoid them altogether owing to technical reasons.

On the Geometry of Angular Correlation Experiments

On the Geometry of Angular Correlation Experiments