The status of x-ray standards in the United Kingdom.
Recent intercomparisons between the medium voltage X-ray standards of N.P.L. and of Sweden and USA (National Bureau of Standards) are described. The results confirm the work of Kemp and indicate that the original N.P.L. and N.B.S. standard free-air chambers have inadequate dimensions for the measurement of X-rays excited above 100 kV. In the case of the N.P.L. chamber the error has been about 0.4 per cent at 100 kV and 3 per cent at 200 kV. After allowing for the errors revealed by these intercomparisons, the calibration of secondary by the three laboratories concerned was found to be in agreement to about 1 per cent.Details are given of the installation at N.P.L. of a 2 MV Van de Graaff X-ray generator and of the dose measuring equipment constructed for use with this machine. Comparisons of the calibration of Victoreen chambers when exposed to X-rays generated at 1 to 2 MV or to radium gamma rays at N.P.L. and to 60Co gamma rays at N.B.S. indicate agreement to 1 per cent provided the conditions of stem i...
An International Comparison of the Röntgen—The Unit of Quantity of X Rays
An account is given of a comparison carried out at the National Physical Laboratory of the rontgen (the unit of quantity of X rays) as realised by the portable guarded-field ionisation chamber of the Bureau of Standards and the primary free-air standard ionisation chamber of the National Physical Laboratory. The Bureau of Standards subsequently carried out a similar comparison with the standard chamber at the Physikalisch-Technische Reichsanstalt. The ultimate agreement between the results for the three National Laboratories is within 0·5 per cent. The main factors regarded as important in the experimental realisation of the rontgen are summarised in the paper.
Correlations for mass transfer between fluidized spheres and a liquid
Abstract Data on mass transfer between the solid particles and the liquid in a fluidized bed have been analyzed. After a convenient selection, various correlations have been derived. They show that for a given fluidized system, the Sherwood number is independent on the Reynolds number.