1978, British Journal of Radiology, 5/, 931

NOVEMBER

1978

Correspondence person could be persuaded to become periodically lefthanded. The Task Group report led one to expect that the latest ICRP recommendation would give a categorical ruling on finger doses, keeping in view the urgency of the problem of protection while handling radionuclide generators. Yours etc.,

The design of the detector and collimators of a hybrid scanner {In reply) THE EDITOR—SIR,

We have read the comment of Mr. H. Propp (1978). In later measurements our group has noticed a similar deviation from the exponential attenuation law, especially at both ends of the crystal. If a correction is not made for this nonlinearity, it will cause distortion in the picture. We feel that Mr. H. Propp's solution is a good way to eliminate the effect. On the other hand the deviation from an exponential law does not make our statistical estimation of accuracy invalid, as the estimation procedure can be readily modified for any arbitrary attenuation law. Yours, etc.,

A. NAGARATNAM, A. R. REDDY.

Institute of Nuclear Medicine & Allied Sciences, Probyn Road, Delhi—110007, India. REFERENCES ICRP, 1966. Recommendations of the International Commission on Radiological Protection (adopted September 17,1965), ICRP Publication 9, Pergamon Press. 1969. Radiosensitivity and Spatial Distribution of Dose, Reports prepared by two task groups of Committee 1., ICRP Publication 14, Pergamon Press. ICRP, 1977. Recommendations of the International Commission on Radiological Protection (adopted January 17, 1977) ICRP Publication 26, Pergamon Press.

E. VAURAMO, A. VIRJO.

Department of Medical Physics, Central Hospital of Tampere, SF-33520 Tampere 52, Finland. REFERENCE PROPP, H., 1978. The design of the detector and collimators of a hvbrid scanner. British Journal of Radiology, 51, 930.

The discovery of X rays THE EDITOR—SIR,

ICRP 1977 recommendations and handling of radionuclide generators THE EDITOR—SIR,

The problem of high doses to the finger tips in the handling of ii^In m and 99Tcm generators and during injection of the radiopharmaceuticals into the patient has been of concern to the health physicist over the last decade. One naturally turns to ICRP for guidance on dose limits. Paragraphs 182 and 183 of the latest ICRP recommendations (ICRP, 1977) deal with skin monitoring. It is mentioned that for external radiation there is not likely to be any problem of averaging and that a representative dosimeter reading could be related to the dose-equivalent limit; for surface contamination of the skin, notably the hands, the irradiation will not be uniform and for routine purposes it is adequate to regard the contamination as averaged over 100 cm2 and the limit applied to the dose-equivalent so averaged. In the case of accidents or suspected accidents it is recommended that an estimate be made of the average doseequivalent over 1 cm2 in the region of the highest dose equivalent and this value compared with the dose-equivalent limit. Now in the case of handling of generators, the problem is external irradiation and not contamination, and not an accident but part of normal operations. However the dose distribution will be extremely non-uniform and there is no question of a representative dosimeter reading being adequate in the sense used in para 182. In this case are we to average over 100 cm2 or 1 cm2? If the averaging is over 2 1 cm , the non-stochastic annual dose limit of 50 rem will severely restrict the scope of work with generators. Incidentally this non-stochastic limit is less than the 75 rem allowed by the earlier recommendation to hands and forearms (ICRP, 1966). The report of the task group on "Radiosensitivity and spatial distribution of dose" (ICRP, 1969) has something relevant to say on this point. After a discussion of the radiobiological aspects, paragraph 34 says that "when small areas of skin are irradiated, the Task Group recommends that the present limit of 30 rem in a year, averaged over 1 cm2 of skin, be increased to at least 100 rem in a year, with the proviso that irradiation of the same area year after year should be avoided if possible". Of course the proviso cannot be adhered to in the present instance unless a right-handed

The interpretation placed by E. Fischmann (Fischmann, 1978) on alterations contained in Wilhelm Conrad Rontgen's original manuscript, "A New Kind of Rays", is indeed convincing in so far as it seeks to establish historical authenticity. Moreover, Sir James Mackenzie Davidson in his account of a discussion with Rontgen held not long after the discovery of X rays, recalled that Rontgen referred specifically to the use of a Hittorf tube (Kaye, 1914). However, it would be unfortunate if this point caused the significance of Lenard's own work to be underestimated. At the suggestion of Hertz, Lenard constructed aa ingenious form of vacuum tube, equipped with a thin aluminium window which allowed the cathode rays to be transmitted outside the tube. It was Lenard's systematic study of these "emergent cathode rays", or "Lenard rays" as they were then described, that subsequently enabled Rontgen to recognize the "X rays". The suggestion that the contribution of Lenard (Freund, 1946), or of other researchers of electricity in high vacua such as Varley, Hittorf, Crookes, and Hertz, be accorded greater recognition does not detract from Rontgen's achievements. In his paper entitled "A New Kind of Rays" (Rontgen, 1896), first published after seven weeks of intensive research, Rontgen not only described the absorption properties of X rays and their ability to produce fluorescence in a variety of materials, but also established that X rays do not obey the laws of optics, are not deviated by magnetic forces, and that the X rays originate wherever the cathode rays strike the wall of the vacuum tube. Rontgen even anticipated X ray diffraction by suggesting that "the geometrical arrangement of the molecules might affect the action of a body upon the X rays". The scientific significance of Rontgen's discoveries was placed in perspective as early as March 1896 when Sir James Dewar remarked " . . . Of course they (critics of Rontgen) always felt that somebody else might have discovered something and that it was a pity he missed it; but really one man could not monopolise everything, and there was plenty yet to be found out". Yours etc., C. B. SMITH.

Department of Clinical Physics and Bio-Engineering, 11 West Graham Street, Glasgow G4 9LF.

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ICRP 1977 recommendations and handling of radionuclide generators.

1978, British Journal of Radiology, 5/, 931 NOVEMBER 1978 Correspondence person could be persuaded to become periodically lefthanded. The Task Grou...
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