Table of contents

On assuming that the exotic exchange reaction pi ^-p to Sigma ^-K⁺ occurs as a result of multiple non-exotic exchanges pi ^-p to rho ⁰n to Sigma ^-K⁺, the author finds that the imaginary parts of the invariant amplitudes A and B for the above reaction show Odorico zeros at almost fixed and small value of momentum transfer. The recent phase shift analysis of Langbein and Wagner supports his result.

Cross sections for alpha capture to the giant dipole resonances of 1d2s and 1f2p shell nuclei are shown to be in agreement with Hauser-Feshbach calculations. Isospin mixing in ²⁸Si, ³²S and ⁴⁰Ca is discussed. It is shown that alpha capture data do not provide a conclusive test for the proposed isosplitting of the ⁶⁰Ni and ⁴²Ca giant dipole resonances.

It has been suggested that particle-hole symmetry may be responsible for level energy systematics in the Z approximately=50 region but the measured quadrupole moments do not have a similar simple explanation.

Lifetimes have been measured for Coulomb excited states with 8⁺<or=J^pi <or=12⁺ in even A isotopes of Dy, Er and Yb. A significant retardation in E2 transition rates for the decay of 12⁺ states in ¹⁶⁰Dy, ¹⁶²Dy and ¹⁶⁴Er is observed.

A recent optical model analysis of ³He elastic scattering data has found evidence of target spin effects. The possible causes of these effects are examined and experiments are suggested which may reveal more information about the target spin effects.

There is experimental evidence favouring a flatter energy spectrum for primary iron nuclei than for the other charged components of the primary cosmic ray beam, at leat up to the highest energies at which measurements have been made ( approximately 10¹²eV/nucleon). The authors examine the consequences of extrapolating this flatter spectrum to much higher energies.

The author considers the Gel'fand-Yaglom equations for free fields of arbitrary spin, in the particular case when the field transforms according to a direct sum of inequivalent irreducible finite representations of the proper Lorentz group. Under the assumption that the theory carries neither physical states of zero charge or energy density and that the mass-spin states are non-degenerate, he obtains the precise forms of the minimal and characteristic polynomials of the s blocks of the L₀ matrix, which are then used to obtain new necessary and sufficient conditions that the theory be quantizable. The representation according to which the field transforms can be depicted graphically in a simple way and he takes advantage of this to use some simple ideas of graph theory to obtain results. The conclusion is that it will probably be necessary to allow repeated irreducible representations of the proper Lorentz group for theories of spin greater than eight to be quantizable.

The author deduces Green function equations and perturbation rules for chirally-invariant quantum field theory. The ordering problem is treated by a suitable time-like averaging in the operator interaction which at the same time prevents any occurrence of delta ⁴(0) terms and removes ambiguities in ( delta ³(0))² terms; these latter are known to cancel to lowest order. He also presents an equivalent lagrangian formulation which leads to the same results.

The energy-momentum tensor for a chiral-invariant theory of massless pseudoscalar mesons is 'improved' by the methods of Callan, Coleman and Jackiw. The improved tensor has a simple relation to the dilation current and nonvanishing triple-derivative terms in the equal-time commutators of its components.

Contributions of the rho ' meson are computed to various spectral function sum rules. The author concludes the possible existence of higher-mass axial vector mesons, isoscalar vector mesons and the importance of the higher-mass continuum, respectively.

The author presents theoretical and experimental evidence for a large d-wave pi Delta decay for the N_gamma (³/₂^-) (1520) resonance although the s-wave decay is kinematically preferred by a factor of about 19. The theoretical method here is a simple low energy bootstrap model, with resonance saturated dispersion relations (consistent with the Harari-Freund hypothesis). It agrees well with the dip structure required by rho -baryon duality and also with experiment.

The authors examine various reactions in which one might search for pi ⁰ to e⁺e^-; apart from the problem of the low branching ratio, the most serious observational difficulties arise from the competition of intermediate virtual photon states of close to the pion mass. They show that the obvious choice of pi ^-p to pi ⁰n at threshold is an unfavourable pion source but that the same reaction in the Delta (1236) resonance region seems currently to offer the best opportunity; it is analysed in detail K⁺ to pi ⁺ pi ⁰ seems the most hopeful alternative.

The static electric quadrupole moments of the first 2⁺ states of ^106,108Cd have been measured by Coulomb excitation. The measured moments are significantly smaller than previously reported values and indicate a gradual change in quadrupole moment across both the isotopes of Cd and the N=58 and 60 isotones.

Angular correlation measurements on levels in ²⁷Si have been made using the ²⁸Si ( tau , alpha )²⁷Si reaction at bombarding energies of 13.0 and 15.0 MeV. Spin restrictions and in some cases spin assignments have been made for several levels, namely 3.54 MeV (¹/₂, ³/₂) 3.81 MeV (³/₂, ⁷/₂), 4.14 MeV (¹/₂^-, ³/₂^-), 4.30 MeV (⁵/₂⁺), 4.72 MeV (⁵/₂, ⁷/₂), 5.08 MeV (⁵/₂). Calculations based upon an excited core model have been performed in which the states in ²⁷Si are obtained from coupling quasi-hole excitations from the d_5/2, s_1/2 and d_3/2 orbitals to the ground and first excited states of a ²⁸Si core. The results of the calculations have been compared with experiment.

The Oxford multigap spectrometer has been used in a study of the ²⁹Si(³He,d)³⁰P reaction at an incident ³He energy of 15 MeV. Twenty-eight states in ³⁰P have been identified up to an excitation energy of about 6 MeV. Parity assignments have been made from a DWBA analysis of the angular distributions spin restrictions have been placed on some levels while the 3.731 MeV level has been assigned J^pi =1⁺. Spectroscopic factors have been obtained and compared with theoretical values. The results are discussed with respect to model calculations.

Excitation energies, mean lifetimes, gamma -ray branching ratios, angular correlations, mixing ratios and linear polarizations have been measured for the first twelve levels of ³⁷Ar using the ³⁴S( alpha ,n gamma )³⁷Ar reaction. Parity assignments were made for the following levels: 3173 keV, ⁵/₂⁺, 3274 keV, ⁵/₂^-, 3527 keV, ⁷/₂^-, and 3602 keV, ³/₂⁺ or ⁵/₂^-. The spin and parity of the 3707 keV state ( tau _m=370+or-95 fs) was determined, J^pi =¹¹/₂^-. Three new low energy gamma -ray transitions were observed and six new mixing ratios were determined. The authors found that the negative parity levels which decay to the 1611 keV ⁷/₂^- state are represented qualitatively by the core excitation model.

Observations have been made of the transition from the 762 keV, 7/2^- level to the 207 keV, 9/2⁺ isomeric level in ⁷⁹Br. The 7/2^- level was populated by Coulomb excitation using alpha particles as the projectiles. Measurements were made on both the single gamma ray spectra and the delayed 9/2⁺ to 3/2^- (GS) isomeric transition. The strength of the transition was such as to give a branching ratio of (3.6+or-0.4)% from the 7/2^- level. An upper limit of 0.3% was obtained for the equivalent branch in ⁸¹Br.

Results are given for measurements of complete fusion cross sections in ⁴⁰Ar and ⁸⁴Kr induced reactions on medium and heavy targets. After complete fusion, composite nuclei decay by particle and gamma ray emission and also, in large proportions, by binary fission. Cross sections were measured on the residual nuclei and on binary fissions following full momentum transfer. In the case of Ar ions, the fusion cross section is still a large part of the total reaction cross section and the restriction due to high angular momentum is not severe. With krypton projectiles there is also a large proportion of complete fusion if the compound nucleus is in the medium masses. On the other hand with targets of bismuth and uranium a very small cross section was observed for fission events following a fusion process. An intermediate situation was found in the case of holmium and tungsten targets. Most of the reaction cross section goes into incomplete fusion channels, with a large loss of kinetic energy. A discussion is given on the dynamical aspects of the collision between two heavy nuclei.

An estimate is made of the gamma -ray spectrum resulting from an extragalactic, evolving source model of cosmic ray origin in the absence of intergalactic gas. The experimental situation does not at present appear to allow definite rejection of this theory, since the calculated spectrum lies between the extreme observational limits. It is possible that such a theory can explain the cosmic ray spectrum, the isotropy of cosmic rays and the diffuse gamma -ray spectrum.

At the Pic du Midi (730 g cm^-2) in France an air shower array has been operated to study high energy hadrons in air shower cores. The array consists of 13 scintillation counters of 0.25 m² each and a 14 m² high energy hadron detector. 2050 showers with a total of 1600 hadrons of energy E>100 GeV have been analysed. The energy spectrum of hadrons (E>300 GeV) is H(>E) approximately E^{- gamma} with gamma =1.7+or-0.2 independent of shower size in the size range 10⁵<N<10⁶. It is compared with results of different air shower simulations. The lateral distribution can be expressed by rho (>E,r) approximately exp(-r/r₀(>E)) with r₀=2.4(E/200 GeV)^-0.3+or-0.04 independent of shower size. It is not necessary to claim for large transverse momenta.

The sea level absolute vertical cosmic ray muon spectra at 12 degrees N (Calcutta) have been measured in the range 0.35-2.2 GeV/c with a range spectrometer. These spectra are, on the average, 12% higher than those of Bhattacharyya at the same place of observation. The lower value of intensities of Bhattacharyya might be due to underestimation of scattering corrections and rejections of a few per cent of 'single muons'. The measured differential spectrum may well be represented by a form-fit spectrum. The Durgapur spectrum of Nandi and Sinha at 12 degrees N at sea level is in agreement with the form fit spectrum up to 20 GeV/c. A comparison of this spectrum with the high latitude form-fit spectrum of De et al. gives 1.23, 1.25, 1.21 and 1.07 latitude effect at the momentum ranges 0.3-0.5, 0.5-1.0, 1.0-2.0 and 2.0 5.0 GeV/c respectively. These values are more or less in agreement with those predicted from Olbert. Above 5 GeV/c the latitude effect is observed to vanish.

The absolute sea level differential cosmic muon spectra at zenith angles 45 degrees and 60 degrees in the western azimuth have been determined near the geomagnetic equator (at 12 degrees N) by using the range spectrograph in the momentum interval 0.5-3 GeV/c. The experimental muon spectra after corrections agree well with the spectra, calculated after Jabs theory for the same location, above muon momentum 1.8 GeV/c. The results have been compared with others obtained at higher latitudes. It is found that the variation of differential muon intensity with 1g sec theta ( theta is the zenith angle of the spectrograph axis) diminishes slowly with the increase of muon momentum from 1 to 3 GeV/c. The variation of the cosine exponent in the expression I( theta )=I(0) cosⁿ theta agrees with that calculated after Jabs. The present spectra after latitude corrections for 55 degrees N agree well with that magnetic spectrograph result of Allkofer and Andresen for the same latitude at 45 degrees W and with that of Judge and Nash for 60 degrees W.