Document 71JDx13O81rmRBLokvqqrZp78

710 LEON F. CURTISS Table 4, taken from Handbook H-23 of the National Bureau of Standard Radium Protection, which shows permissible daily exposures (based on till now discarded tolerance level of 0.1 r per 8-hour day) with contingent sail distances of a technician during these exposures. Total daily exposure (mg.-hr.) 100 200 400 TABLE 4 Safe Working Distances from Radium Safe distance Meters Feet Total daily exposure (mg.-hr.) 13 1.6 4 26 800 1600 3200 Safe distance Meters Feet 2.5 8 3.5 11 6. 15 The next factor in order of importance is reduction of the time of exposurj'- Therefore, provisions should be made to permit all operations involving unusuA levels of gamma ray intensity to be carried out in the shortest time consist^ with the nature of the operation and with the personnel as far from the radip^ active material as can be arranged. Under no circumstances should sourcef the order of a millicurie or greater come into contact with any part o: worker's body, especially the fingers. It should `be obvious that techniciil should not remain in the immediate vicinity of an unshielded source longest necessary, a precaution that also applies to those not directly concerned;., the work in hand. This is particularly important in gamma ray radiograph^Mp. very strong sources are often used to reduce the time required to obtai satisfactory negative. Finally, consideration should be given to protective screens of dense majeri having a high coefficient of absorption for gamma rays. This material may iron, or concrete. Screens must be provided whenever operations with s sources, millicurie level and above, are to be carried out at short rangeft. thickness of the screens should be adequate to reduce the radiation to a'!~ well below the average tolerance for continuous exposure. Where viewif source is essential to the operation, thick transparent screens or periscopes^ be provided to make the screening complete. _____ ... Xn^mployees in the ra'diation area, or having access to-it, shbuld' personnel radiation meters continuously, and these should be collected at the end of each day by someone in charge of radiation safety. This asj| early detection of any violations of regulations or accidental overexposures! ecord-of-these-readmgs-is-valuable-also-as-proof-of-absenee-of-ssPisfT exposures. ,,j Regular medical examinations should be given individuals engagedi| work. The examination should include a blood count as well as a careful#! of each of the known possible symptoms of overexposure to radiation. Iff! . RADIANT ENERGY 711 )an examination for evidences of injury to fingers should be made. The iirequpqpy with which medical examinations should be made depends somewhat r^lie|eonditions of work. Where gamma ray sources of . the order of a curie cpjsniore are involved, an examination every month would seem to be required, '.^operations are substantially below this level, and particularly if possibilities 'ftcxpcisure to radiation are infrequent, an examination every six months might Jeofail equate. S. Storage of Radioactive Sources storage of radioactive sources, emitting penetrating gamma radiation iwitlijehergies of the order of 1 Mev. or greater,, presents something of a problem, x^arTicUlarly where large amounts are involved. Industrial radiography is an exv, general, the inverse-square law provides the most economical and effec^Tvc'jmcans of solving this problem. However, a certain amount of lead, or itd juyalent, shielding is required to permit approach to the storage vault and to ifotf%t,.thse who may require to be temporarily in its vicinity. Where the ^ccupincy of the space about the vault can be rigidly controlled, the thickness -vcMhV.shieMing in any particular direction will depend, for a given amount of !^|||pye material, upon the distance to the person to be protected, the period p^^g|or which protection is required, and the effect that the required protec- t^^freen may have on the intensity of the radiation in other directions where ig?^Sn may be required. In other words, the scattered radiation must be taken ^ritS labcount and in some cases this can_J)e done only by actual measurement. In n^^^ittie combined protective arrangements must reduce the whole body exffl^ffi. the tolerance dose. |||irage vaults should be designed with an interior cavity no larger than cmufegpo accommodate the sources to be stored. Not only is this more economiqtfjjbut,y3y reducing the size of the exterior, it also reduces the amount of ^^Kradiation in the vicinity. When material other than lead is used for this fil.hj|l'ead equivalent (see Table 5) must be known un|fer. conditions similar Byifmjjgih which the material is to be used. In general, ih'e lead equivalent for can be computed by multiplying the thickness'of the material by the i^S??ity to that .of lead. In computing reqiiireiphTck'n'essesjlt'is 'advisthe thfqknesspf.matierial,,by,a^p.ut:.;50.-per cent of the, value ob- iren assigning storage vaults ior a numoer oi sources it. is aesiraoie to *^^pfitagparate-lead screening for individual preparations. This reduces the ex- technician who must remove sources from the vauit^Tt is equally sSPMt-th reduced to a minimum. Identifying -------- "----------------------------- illustrate one method of-expediting the ^gttibmfOf a preparation. Another suggestion is to code with distinctive colors -"''litis themselves to permit instant identification. In no case should the dose