Document q3kJ9EDMxwenOG0MbEXv8DORx

Ionizing radiation FI9. 42-10. Deposition of materials in haled Into the bronchialtree, according to particle size in microns. Adopted tram "Atomic Radiation," O 1957 by RCA Service Co , tnc 000 p = 1 meter) in size are of health sig nificance, because they do not settle out even over long periods of time and are suffi ciently small that they are not removed in the nasal passages as are the larger parti cles. Tarbcles smaller than 5 to 10 p, then, can penetrate deep into the lung (Fig 42-10). The volume of a 10 p (10** centimeters) sphere is 0524 X 10** cubic centimeters (cu cm). For plutonium (sp gr 19.74) the weight of the 10-p diameter particle is 104 X 10** gm. Hie amount of activity in a particle 10 p m diameter can be calculated. The cunes per gram (a constant) is known as the "specific activity'' of an radionuclide and may be ob tained from tables (for example m Radio logical Health) ox calculated horn the ex pression: Curies/gram m ___________1.308 X 10* (atomic weight) (half-life in days) For plutonium, with a half-life of 8 8 X 10* days and the atomic weight 239, the formula yields a specific activity of 0062 cune per gram. The 10-p plutonium particle weighs 1 04 X 1** gm with 8.4 X 10*" cune m the particle. The number of these particles which may be breathed m a day at the permissible level can now be calculated. A man at work is considered to breathe 10 cu m (10T cu cm) per eight-hour shift Then, 1 particle per day = 64 X 10~" = 10* 6 4 X 10*" cune per cu cm or 64 X 10"" microcune (pc) per cu cm. Since the guide level is 2 X 10*" (pc) per cu cm (from NBS Handbook 69, p. 87 under mPu** "Borne0), it is found that one such particle per shift is 32 times too much Plutonium is one of the more hazardous radioisotopes that be inhaled. Since the volume vanes as the cube of the diameter, a particle 10 p in diameter has the same weight as 1,000 particles 1pm diameter or the same weight as 1,000,000 particles 01 p in diameter. Therefore, the guide daily level would be 00314 of 1 particle 10 p in di ameter, 314 particles 1pm diameter, or 31,400 particles 1/10 p m diameter. As shown in Table 43-C, similar calculations can be made for other radioisotopes Particles in the range of sizes shown in Table 43-C are commonly found around in dustrial operations Since the particle size greatly affects the nsk of operations with radioactive materials, the volume of air m a sample must be large enough not only to ensure collection of particulates in the distribution of sizes probably present but also to yield an amount of activity above the minimum detectable quantity of the analytical method The sampled air vol ume should be large enough to place the concentration below the limit of the radio activity concentration guide (RCG) for the minimum detectable quantity. Therefore a knowledge of the actual particle size distri bution is important For instance, it is necessary to sample 10 cu m of air during the tame that the work operation is being conducted to trap 31.4 one-p particles of plutonium. Thirtyone is a reasonable number of 1-p particles to collect to give confidence to the measure ments, but for 1 ten-p particle, 320 cu m of air are needed to yield a guide level con centration 42-26