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...
Note on International Comparison of X-ray Standards
A RECENT paper1 gave a description of comparisons of the Bureau of Standards X-ray ionization standard with that of the National Physical Laboratory, Physikalisch-technische Reichsanstalt, and Le Service d'Etalonnage de l'Hopital St. Antoine. In these comparisons it was necessary in all cases to make corrections for the absorption of X-rays in air, for which absorption coefficients were obtained by extrapolation from available data. These coefficients are, as pointed out, uncertain. Unfortunately, corrections for this paper, suggested by Dr. Kaye, were received after it was too late to insert them. He informs us that their recent determinations of the air absorption correction under the conditions used in the comparisons give values somewhat different from those used in the published paper. For 110 K.V. unfiltered radiation Dr. Kaye finds a correction of 2.2 per cent as against 1.5 per cent used in the published paper. For 143 K.V., 1.4 mm. copper, his correction agreed with the published value. Applying ...
Experimental energy barriers to anions transporting through nanofiltration membranes.
Environmentally relevant contaminants fluoride, chloride, nitrate, and nitrite face Arrhenius energy barriers during transport through nanofiltration (NF) membranes. The energy barriers were quantified using crossflow filtration experiments and were in the range of 7-17 kcal·mol(-1), according to ion type and membrane type (Filmtec NF90 and NF270). Fluoride faced a comparatively high energy barrier for both membranes. This can be explained by the strong hydration energy of fluoride rather than other ion properties such as bare ion radius, fully hydrated radius, Stokes radius, diffusion coefficient, or ion charge. The energy barrier for fluoride decreased with pressure, indicating an impact of directional force on energy barriers. The influence of temperature-induced pore radius variability and viscosity on energy barriers was considered. The novel link between energy barriers and ion properties emphasizes the importance of ion hydration and/or partial dehydration mechanisms in determining transport in NF.