Table of contents

Gamma rays have been detected in coincidence with delayed neutrons following the decay of ⁹⁵Rb, ⁹⁰Br and ⁸⁵As. The energies of the first excited states of ⁹⁴Sr and ⁸⁹Kr are identified as 837 keV and 424 keV respectively.

A method is given for computing the equal-time commutators of a Bose-Einstein field with constraints directly from the lagrangian density, without necessitating the introduction of conjugate variables or solving equations of motion. The method is illustrated by the vector meson field.

Shell-model calculations have been performed for a number of nuclei in the sd shell to obtain binding energies and energy spectra. The realistic interactions of Kuo (1967), and Elliott et al (1968), and the empirically determined matrix elements of Preedom and Wildenthal (1972) were used in the full sd shell basis. Comparison with experiment shows that the Preedom-Wildenthal interaction works well in the lower part of the shell, whereas the other two give rise to shifts of whole rotational bands in most nuclei.

For pt. I see ibid., vol.7, 1374 (1974). Calculations of binding energies and energy spectra have been performed for a number of neutron- and proton-rich (exotic) nuclei in the sd shell using the Kuo (1967) and Preedom and Wildenthal (1972) interactions. It is found that the Preedom-Wildenthal interaction reproduces the binding energies very well even when used for masses greater than those for which it was derived. A number of mass and spin predictions are made in cases where as yet no data are available.

Gamma-ray angular distributions have been measured following the ²⁸Si( alpha ,p gamma )³¹P reaction using both NaI(Tl) crystals, in coincidence with an annular particle telescope, and GeLi detectors. Lifetimes have been determined using the DSAM and gamma -ray polarizations measured using a 3 GeLi Compton polarimeter. Several new definite spin assignments are given. Many multipole mixing ratios, lifetimes and new branching ratios are reported. An interpretation of the positive parity states is proposed based on the strong coupling and rotation-vibration models. A striking feature in the spectrum of the negative parity states is pointed out which suggests particle-phonon coupling is important. Shell-model calculations based on the MSDI interaction have been extended to include the transition strengths from higher spin positive parity states.

Excitation energies, mean lifetimes, gamma-ray branching ratios, angular correlations and linear polarizations have been measured for levels below 5.3 MeV in ³⁷Cl. The states were populated using the ³⁴S( alpha ,p gamma )³⁷Cl reaction at bombarding energies between 9.0 MeV and 12.2 MeV. A gamma-gamma coincidence experiment was performed at 11.5 MeV to obtain the decay scheme. New measurements were made for the following levels: E_x( tau _m)J^pi ; 3087 keV (<40 fs) ⁵/₂⁺; 3105 keV (48+or-5 ps) ⁷/₂^-; 3626 keV (40+or-20 fs) ³/₂, ⁵/₂, ⁷/₂⁺; 3708 keV (<25 fs) ³/₂⁺, ⁵/₂^-; 3740 keV (<20 fs) ⁵/₂^-; 4011 keV (31+or-3 ps) ⁹/₂^-; 4547 keV (2.7+or-0.6 ps) ¹¹/₂^- and 5271 keV (2.7+or-0.4 ps) ¹³/₂^-. The results are compared with the properties of high-spin negative-parity states in neighbouring nuclei and are discussed in terms of recent shell-model calculations.

The reaction ⁴³Ca( alpha ,n)⁴⁶Ti was used to populate levels in ⁴⁶Ti at alpha particle energies of 6.5 and 7.5 MeV. Gamma rays in ⁴⁶Ti were observed in a Ge(Li)-NaI(Tl) escape-suppressed spectrometer. The Doppler shift attenuation method was used to measure the mean lifetimes of 10 levels in ⁴⁶Ti. The J^pi =0⁺ 2.61 MeV level is shown to have an enhanced E2 transition to the first excited 2⁺ state.

The gamma-ray spectrum of ⁷⁵Se below 30 keV has been recorded with a guard-ring Si(Li) spectrometer. No evidence was found to support a recent observation of a 14.9 keV gamma ray; the upper limit for its intensity was 0.0017 relative to I_gamma (264.6 keV)=100.

The total negative muon capture rate in deuterium has been calculated using the closure approximation and results are compared with those of Pascual et al. (1972) who use the impulse approximation for computing the capture rate.

Published experimental (n,2n) cross sections at E_n=14 to 15 MeV have been obtained. Weighted average of the total (n,2n) cross sections reported and the probable error in it are tabulated for each nuclide in the region A=2 to 238. (n,2n) cross sections at E_n=14.5 MeV have been calculated using Pearlstein's formulae based on the statistical model with new constants; these theoretical cross sections are also tabulated for nuclides A=23 to 209. A comparison shows that (a) the statistical model values in general agree well with the experimental values; (b) the theoretical cross sections agree well with the experimental cross sections even for target nuclides having neutron shell closures except in the case of ³⁹K and ⁵⁴Fe which have high (n,2n) thresholds comparable to the incident neutron energy. It is concluded that there are no shell effects other than those manifested in Q values and the level density parameters.

Spin-dependent sum rules for spectroscopic factors have been fitted to proton s_1/2 and d_3/2 spectroscopic factors obtained from (d,³He) and (³He,d) reactions on ^35,37Cl. The fits with suggested spin assignments show deep minima in a plot of expected error in relative spectroscopic factors against absolute magnitude of the spectroscopic factors. Thus, if the relative spectroscopic factors have a 10% error, the absolute magnitudes are determined to about +or-6%. The reduction in pick-up spectroscopic factors on ³⁷Cl found by analysing one set of experimental data is in agreement with more recent (d,³He) data. Theoretical wavefunctions for ³⁵Cl are examined in the light of the results obtained.

A plot of the declination against right ascension of 2598 observed air showers has been divided into a grid of 5 degrees declination against 5 degrees right ascension. A distribution of the number of showers along each declination band is then constructed. In each declination band those groups of showers (bins within the grid) which are above 2 standard deviations in the distribution are selected for further analysis. There are 36 such groups and among these 19 coincide with the known positions of pulsars while 7.5 are expected from accidental coincidence. The results obtained from this preliminary analysis do not rule out the possibility that some at least of the cosmic ray primaries in the energy range studied originate in pulsars.

The coupling functions for underground cosmic ray muon component variations have been calculated, applying the CKP interaction model and allowing for the effect of muon energy loss fluctuations. For that purpose, the survival probabilities of muons have been calculated for standard rock for the range of depth 20-1000 hg and sea level energies 3.8-3000 GeV using a Monte Carlo method. The average effect of range fluctuations was found to reduce the coupling functions by a factor between 0.96 and 0.45 over the range of depths considered. At a depth of 60 hg, the influence of such fluctuations on the diurnal variation in the muon component was found to decrease the amplitude by 0.34% and to increase the phase by 0.26%.

A model is presented in which the bulk of the cosmic rays comprises two components: one, from galactic sources (probably pulsars) and the other having a universal, i.e. extragalactic, origin. Attention is directed particularly towards the particles above about 10¹⁷ eV which, like those below 10¹⁴ eV, are proposed to be of universal origin, it is shown that if these particles have a production spectrum having constant exponent (differential value=-2.75) then interaction with the black-body radiation gives a spectrum at the earth not inconsistent with observation. In this model the extragalactic sources of cosmic rays do not increase in total number or in intensity at high red shifts.