Table of contents

An optical device is described by which the effect of rotation on the stereographic projection of a crystal can be observed directly. The application of the device to the construction of pole figures from x-ray data is described.

A general analysis of magnetic viscosity based on activation energy concepts is given. A particular case is considered of the application of the theory to the phenomenon occurring in materials in which bulk magnetization proceeds by the rotational movement of the vectors of single domains, which process, according to a recent theory of Stoner and Wohlfarth, may occur in certain high coercivity alloys. Experiments have been made, using a magnetometer method, with specimens of alnico maintained at various temperatures within the range - 187° c. to 250° c. The results obtained are found to be in good agreement with the theoretical analysis.

The radiations from the active isotopes ¹⁷⁰Tm and ¹⁸⁶Re have been investigated. ¹⁷⁰Tm is found to have a β-ray end-point of 1.00±0.005 Mev. with possible lower-energy groups at 0.90±0.015, 0.79±0.025, 0.45±0.05 Mev. γ-rays with energies 82.6±0.5, 205±10, 430±20 kev. were observed. The 430 kev. radiation is thought to be complex. ¹⁸⁶Re is found to have a β-ray end-point of 1.090±0.005 Mev. with other groups at 0.95±0.015 and 0.64±0.03 Mev. Three γ-rays were observed, having energies 700±50, 275±8 and 133±1 kev. The last is assumed to be a mean energy-value of the three low-energy γ-rays found by Cork, Shreffler and Fowler. Decay schemes are suggested for both isotopes.

It is difficult to explain the observed preponderance of transitions to the excited state of ⁷Li in the reaction ¹⁰B (n, α) ⁷L₁ in terms of the usual assumption that the ground state and first excited state of ⁷Li form a ²P_{fraction three-twos, ½} doublet. In addition the doublet separation (0.48 Mev.) would be much larger than expected theoretically. If the excited state of ⁷Li has total angular momentum other than 1/2, one would expect to find, in general, some angular correlation between the direction of emission of the α-particle, that of the subsequent γ-radiation and the polarization of the radiation. The correlations to be expected have been calculated on the assumption that the ground state of ⁷Li is (3/2, odd), that of ¹⁰B (3, odd), or (3, even), and that the compound nucleus ¹¹B has definite J=5/2 or 7/2. Results are given for excited states of ⁷Li with total angular momentum 1/2, 3/2, 5/2 and 7/2 and both even and odd parities.

The photographic plate method has been used in an investigation of the neutrons from the (dn) reactions in ¹⁰B and ¹¹B, separated isotopes being used in the targets.

The reaction ¹⁰B(dn)¹¹C gives neutron groups at 6.70 MeV. and 4.85 MeV.; these give an energy release for the transition to the ground state of 6.59±0.10 MeV., and show the existence of a level in ¹¹C at 2.02±0.10 MeV.

The reaction ¹¹B(dn)¹²C gives well-defined neutron groups at 13.51 MeV., 9.40 MeV. and 4.55 MeV., with a continuous distribution up to 6 MeV. and a small peak at 6.4 MeV. The 13.51 MeV. group gives an energy release of 13.92±0.15 MeV. for the transition to the ground state; the other groups confirm the existence of levels in ¹²C at 4.47±0.10 MeV., 9.72±0.15 MeV. and less certainly 7.7 MeV., while the continuous distribution is due to the reaction ¹¹B(dn)3α.

An analytical method for the design of a synchrotron pole-face is outlined, the method taking full account of the cylindrical symmetry. Relaxation methods are employed to determine the exact size and shape of the lips correcting for fringing, and are also used to give a final check on the characteristics of the magnetic field. Practical examples of these methods are then given.

Corrections to 1949 Proc. Phys. Soc. B 62 523