Table of contents

The production of charged pions at complex nuclei is calculated on the basis of a simple independent particle model for the nucleus. The primary photoproduction is assumed to be a single nucleon process in which the struck nucleon undergoes transitions into discrete or continuum states. Two points of view are adopted, (a) that production may take place inside the nucleus; (b) that only surface production is allowed, according to the model of Wilson and of Butler. Cross sections are obtained for two nuclei, ¹¹B and ⁴⁰Ca. Available experimental data are inconsistent with surface production.

Measurements of neutron flux in the neutron energy region 0.03 MeV to 3.0 MeV have been made using a proton recoil counter and a Hanson-McKibben type long counter. Several proton recoil counters filled with different gases at different pressures have given flux measurements self-consistent to 2%. The long counter has been calibrated against photo-neutron sources at a number of energies and also against the recoil counter. The variation of its efficiency as determined by the two methods is in satisfactory agreement. The absolute calibration of the long counter with respect to a RdTh-D₂O source whose strength was known to ±2½% agreed with the calibration with respect to the recoil counter to 1%. A similar cross check with an Ra-Be source gave an initial discrepancy of 15% but this was traced to an error in the source strength and variation with energy in the response of the long counter. These cross checks are satisfactory and over the major portion of the energy range the standard error is not more than ±3%.

The methods of a previous paper are applied in a theoretical analysis of the spectra of nitrogen derivatives of naphthalene and stilbene. The results provide, in every case, a satisfactory account of the main absorption bands and of the effects of nitrogen substitution. A simplified method, which permits very rapid estimates of shifts due to substitution in terms of data for the parent hydrocarbon, is found to be satisfactory and should be of general value.

The ¹⁵N(α, γ)¹⁹F reaction has been examined with bombarding energy from 1.2 to 2.35 MeV. Three resonances have been found, two narrow and one of measurable width. The cascade schemes at each of the resonances have been partly elucidated, and the partial radiative widths of the resonances have been determined, except for a statistical factor. Some of the angular distributions have been measured, and conclusions have been drawn about the possible values of the spins and parities of the levels concerned. The relation of these results to the predictions of Elliott and Flowers is briefly discussed.

The relation of the complex well which is used to describe average features of the scattering to dispersion theory is discussed. A model is employed in which the compound states have an underlying single-particle structure. It is shown that a complex well can be defined which reproduces the average scattering phase. The imaginary part of this well is simply related to the absorption.

The scattering in a complex well of the type used in optical model calculations is described by dispersion theory. The positions and widths of the resonances are found.

The problem of inelastic scattering of several MeV nucleons is formulated in nuclear dispersion theory. The case where the residual nucleus is left in a state of low excitation is considered in detail. Contributions from the distant compound-nucleus levels can be summed explicitly, and give an expression similar to that usually employed in the theory of direct interaction to calculate differential cross sections. Contributions from the near compound-nucleus levels contribute in a complex fashion, and cannot explicitly be summed. It is assumed that phase relations can usually be neglected for them, and they, then, are responsible for the compound-inelastic scattering.

Possible proton-proton polarization experiments and the information that can be gained from them are reported here. In this paper we write down the formalism and list formulae from which a quantity which can be measured in such experiments can easily be obtained in terms of the theoretical quantities. We employ the formalism of the statistical matrix for spin ½ particles and the representation of the scattering matrix in spin space. The chief aim of this paper is to present a complete set of formulae covering all experiments which appear to be possible in the near future. In a second paper we shall discuss in more detail a group of experiments which are now of great interest, namely, those involving analysis in coincidence.

In § 1 we introduce the formalism to be employed and give an elementary discussion of polarization phenomena.

In § 2 results of the algebra needed to carry out the analysis of experiments are given, and in § 3, these are used to show what quantities the experiments determine.

An elementary discussion of experiments involving analysis in coincidence is given. The case in which the incident beam is unpolarized is discussed in detail. Additional information that can be obtained if the incident beam is polarized is indicated, and the additional information which can be obtained with a magnetic field is briefly summarized.

Corrections to 1957 Proc. Phys. Soc. A 70 515.