Document aJ4Qaprwvb2yr46gvYer5Nb

722 LEON F. CXJRTISS In fact, where slow and fast neutrons are encountered, in practice, potenti^ gamma ray exposure will also be present, therefore, it is important to control exposures in terms of all three radiations. Thus, if the ordinary gamma ray of pocket ionization chamber is designed to measure fast neutrons it will b sufficient whenever the total reading gives a value well below tolerance lev| In some installations, where alterations of equipment or procedures are infrequeif this condition can be ascertained by survey measurements, which can be mad more accurately than by pocket meters. In some cases monitoring instrumeiSlj located at strategic points and operated continuously during working hours mil be desirable. Such monitoring arrangements may be a necessity where a varisH of different operations are performed or where accidental increases in the lejj|[ of the radiation may be anticipated. S. Shielding Shields for the two types of neutrons, swift and slow, are as different as thei properties would indicate. Since fast neutrons are reduced in energy and final! stopped only by more or less direct collisions with atomic nuclei, most effective! with hydrogen nuclei, a shield for fast -neutrons should contain plenty:, hydrogen. Water and paraffin are good examples. When these neutrons have-tl reduced to thermal velocities their properties are the same as those of any ah thermal neutrons. Boron and cadmium are quite opaque to thermal neutrons so that thickn|' of these metals of the order of 0.040 inch will screen them off completely. In case of cadmium, gamma rays are generated by the capture of neutrons,^ whenever high intensities are involved, a layer of lead or other dense ma$| must be placed between the cadmium layer and personnel to be protected*1. t adequacy of this layer should be checked by measurement of the radiation; V. Poisoning from Radioisotopes The discussion of radioactive poisoning will be based on the facts devela in connection with the poisoning of radium dial painters in this country folltfwti World War I. The principles involved apply to any other radioisotopes tha concentrated in the bone structure, such as radioactive strontium or cSl However,.the .presence.of_these..artificialLy_radioactiy,e..substancesJs-nofai^ to detect and measure because with radium the radon gas can be used . radioactive tracer. Therefore, greater precautions are required to ensurfe "fffi environmental conditions of the employees preclude the possibility of ingestiSfi inhalation of potentially dangerous amounts. A. RADIUM POISONING 1. Historical Summary Radium poisoning as a definite source of injury was first brought to jig this country through a report, in 1924, by Blum, a New York dentist, wB RADIANT ENERGY 723 uifered a case of chronic osteomyelitis in the mandible of a girl engaged in Bg radioactive paint to instrument and clock dials. Without any knowledge |kind of material with which this girl worked, he concluded that the jiof the affliction was so. unusual that it must result from some type of HPiional poisoning, and published a statement to this effect.10 MfH|the following year, Hoffman,11 who was asked to investigate the plant _rNejfeJersey where the girls were employed to apply radioactive paint, found 4n examination of death certificates of deceased former employees that Certificates were strikingly similar, although made out by different- family Spim8. who were entirely ignorant of the true cause of death. There> was l|&t mention of jaw necrosis, anemia, and buccal lesions, although the cause of death was usually given as some well-known disease that fsome of these symptoms; It was highly improbable, in Hoffman's opinion, iris could be accidental. After he had assembled data on five deaths and Jlajliving cases, where infeoted jaws and anemia wjere predominant features, ubhcluded that they represented a new type of occupational poisoning, since had worked at the same plant. From his investigations of the working is and the nature of the material applied by these employees, he also ;he opinion that the mesothorium in the paint had something to do with fmptoms observed. This opinion was further confirmed in his mind by the "ation that after dipping their brushes in the radioactive paint the girls [My pointed them between their lips. This practice would give an excellent jfunity for ingestion of the paint. JJtese preliminary repbfts~le"d to a series of investigations, sometimes with fjf&ictory conclusions. In many cases the radioactive constituent of the rc|was ignored and some other source of the disease was sought. However, Bsame year Martland12 examined two girls who were suffering from extensive rjfecrosis and anemia. Both girls died and, as a result of autopsies that he s&ed and of investigations on living patients suffering from the; same pjjqms and engaged in the same work, he was able- to$formulate an,';,extensive pifflrhich clearly, for the first time, traced the .disease* to its >trugr origin.18 m-an examination of the expired air, he was able to detect the presence of r. the large number,, qfalpha,-particles -revealed^by-a^zinc sulfide 'screen listened room when.the subj,ect,%breathed^again.sjt..it.^rqm--ftthev8keletons, ^^Bl^inproved^he''presencn6l,ra'3ioaeti^mat'eriaBimiEKnBoiKsJ^ysei?ctro- Jupand autoradiographic tests. By chemical extraction metho'ds'.-he-recovered 'Sl'o01ro|crograms of radium from one.skeleton. At the same time, from.examinations Sijents suffering with the disease,.die-was Able to describe nfote accurately p^mcifmiieima7asLweU^aszthematureiantptQgrsa_QLtlie_honedfesions-:In-thi "ml SfT. Blum, J. Am. Denial Atsoe. (1924). E. Hoffman, J. Am. Med. Assoc., 85, 961 (1925). t ".51. 8. Martland, P. Conlon, and J. P. Knef, J. Am. .Med. Assoc., 85, 1769 (1925). $H. 8. Martland, J. Am. Med. Assoc., 92, 466, 552 (1929).