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...
The Evaluation of the X-Ray Pastille Dose in Rontgen (r) Units
(1) A calibration in Rontgen r. units has been made of the B dose indicated by barium platinocyanide pastilles backed with lead and irradiated by unfiltered X rays from a Coolidge tube excited by voltages between 50 and 100 KV. from an induction coil. (2) About eight years ago a provisional ionisation standard based on an electroscope was set up at the National Physical Laboratory for the purpose of calibrating pastilles. It was then found that the product I.t of the ionisation (I) per unit time produced in the electroscope and the time (t) required for a pastille B dose was constant for a constant exciting voltage (70 KV.), on the X-ray tube. This work has now been extended over a range of from 50 to 100 KV. and I.t for the electroscope in question is found to increase with increasing kilovoltage. (3) A standard ionisation chamber (with graphite walls and using air at atmospheric pressure), has been designed and constructed, and by its aid the I.t readings of the electroscope in question have been expres...
Chemical, biological, and immunological characterization of mono- and diiodothyrotropin releasing factor.
Abstract Iodination of thyrotropin releasing factor (TRF) with chloramine-T and NaI at pH 7.5 produces both mono- and diiodo-TRF as well as unreacted TRF and I − . The four compounds can be separated by ion-exchange chromatography on SP-Sephadex C-25, using a stepwise gradient of 0.01 m MH 4 OAc at pH 3.5, 5.2 and 7.2. The monoiodo-TRF was characterized by nuclear magnetic resonance, mass spectra, and elemental analysis as [Im-5-iodo-His 2 ]-TRF while the diiodo-TRF was similarly characterized as [Im-2,5-diiodo-His 2 ]-TRF. Both iodination products showed no thyrotropin releasing activity at doses up to 1 μg in the in vivo mouse bioassay. The specific binding of mono- and diiodo-TRF was measured against three different TRF antisera. In the absence of TRF, antisera A and C bound more diiodo-TRF than monoiodo-TRF while antiserum B seemed to bind both tracers equally. In all cases steeper curves were produced when diiodo-TRF was displaced by synthetic TRF.