A description is given of a hydrogen condensation pump of output 3·7 × 104 sec−1 which has its own liquifier. The limiting vacuum is 10−8–10−9 mm Hg. The total power consumed (allowing for the liquid nitrogen) is 17 which is less than for oil-diffusion pumps of the same performance.
Two distinct ways in which the variational method may be used to obtain approximate solutions of the equations which are involved in neutron transport theory are discussed. In the first, a method is given whereby an estimate of an eigenvalue or some weighted average of the solution of the equation is obtained. Whilst the second way is a method whereby a relatively complicated equation involving multi-dimensional variables is reduced to a number of simpler equations each in a fewer number of independent variables. Examples to illustrate both methods are given.
The scattering of neutrons from a rotating rigid molecule has been analysed for incident neutron energy of the same order of magnitude as the rotational level separations, without making any approximations.
When the energy of the incident neutron is large, the method of Zemach and Qlauber (1956) of using the rotator as a model for a spherical top molecule, has been justified.
The inclusion of zero-point vibrations have been considered briefly.
The yields of 188Ba, 138Sr, 90Sr, 89Y and of five zirconium isotopes formed in the fission of 233U have been measured. There is a fine-structure in the yield as a function of mass number. The independent yield of 136Cs has been measured, while that of 86Rb has been estimated, thus completing important parts of the yield curve. The boundary between the region where a light fragment emits one neutron and the region where it emits two is established from the curve. It is concluded that the structure is determined by events at the instant of fission.
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