fy, 156 the absorbed dose delivered to the stomach in i hour ig small. The absorbed dose in the top portion of the small intestine is the same as that to the stomach, but decreases during the 4 hours there due to the 60 percent uptakeinto the bloodstream. ‘The absorbed dose to the large intestine is much greater than that to the small intestine because the radioactive material speuds 8 hours in the upper and 18 hours in the lower large intestine compared with only 4 hours in the small intestine. Also, the mass of material in (he upper or lower large intestine is aboutone-eighth of (hat in the small intestine ONy=150 gg, Mu (35 g, Mg=1100 g, Mytomsen*= 250g). In the case of Ra”the 6-hour daughter, Ac”, makes a large contribution to the dase. Therise in the dese in the small intestine is accentuated by the fact that the effective energy of Ac? is 80 times that of the parent, Ra?*, and there is only 20 percent absorption from the small intestine into the blood, ct THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD The slow rise in the absorbed dose in the upper and lower large intestines in the case of SP°+¥", and Ra**-+-Ac is the result of the growth of the 61-hour Y®*, and 6-hour Ac™® respectively. In the case of the 17.5minute Pr, the absorbed dose is delivered mostly to the stomach. The dose to the large intestine is negligible because Pr' passes through17 radioactive half-lives in the stomach and small intestine. The foregoing tables of MPC values maybe useful in dealing with hazards associated with the fallout material from the testing of nuclear weapons as well as the contaminationresulting from a laboratory spill or accident. However, manyof the radionuclides of great interest that comprise fallout during the early periods follow- ing the detonation of an atomic weapon were not included in these tables. There are many factors that determine the type of fallout material from the detonation of a nuclear weapon, e. g., height of burst, distance from ground zero, typo of weapon, weapon yield, meteorological conditions, ete. Likewise it has been found that there maybe factors (physical, chemical, and biological) which tend to frac- tionate and concentrate certain of the radio- INTERNAL DOBE FROM SHORT-LIVED RADIONUCLIDES 157 nuclides. For example, at the first Bikini underwater test I made a numberof surveys on the target ships and nearbyislands of the 8/y dose rate rrtio and found it to range from 1 to several hundred. This high 6/y dose rate ratio was, in part, a consequence of the fact that on the. average there are about twice as many radiation. In any case, the record should speak for itsclf- namely, the damage to man and animals (cattle, horses, deer, etc) that unless measurements have been made of the absorbed dose from # and soft + radiation. Having called attention to the many factors exposure to hard gamma radiation but from have risked setting up Table III which lists the more important U-fission radionuclides that. disintegration of the U-fission mixture, and most of the beta particles have a range of less than a meter in air whereas a large fraction of the gamma photons have a range in air of manymeters, i. e., the fraction of photons with an absorption coefficient d that travel a distance cautious not to overlook the seriousness of fractionation. beta particles as gamma rays emitted per has been observed from the fallout material from nucleartests to date has resulted not from exposure to beta radiation. In assessing the hazard from fallout, therefore, one must be exposure to beta radiation, and one should not rely on a theoretical estimate of the isotopic distribution or one should not reach final conclusions regarding the radiation hazard greater than x is given approximately by the tain circumstances this fractionation maybe of considerable importance because overexposure to beta radiation can lead to serious erythema, burns, ulcera, and even death. Yet the most commonly used field survey equipment is designed to measure the absorbed dose from relatively hard gammaradiation and may give little or no response to beta radiation. Following the test of a thermonuclear weapon by the United States in the South Pacific in 1954, the more serious cases of radiation damage among the natives and operating personnel from the United States: resulting from contact with the fallout’ materials were the consequence of exposure to beta radiations. It is sometimes stated that beta exposureis oflittle importance compared to the gamma dose from fallout material and that one would have to be partly naked or lie prone on the ground before the beta exposure should be a matter of concern.* T do not agree with this point of view and dare say some among the Marshallese, the Japanese fishormen, and the Americans who received painful and disfiguring beta burns as a cansequence of exposure to fallout material in the “South Pacifie would not be inclined to underestimate the seriousness of exposure to beta “Thereader is referred 1o the final summary ofthis Conference by Dr. K.P. Cronkite. would be presentas a function of time following the detonation of a weapon if there were no The radionuclides are listed in order of decreasing availability (assuming no selective deposition or separation of the radio- elements) for 5 time intervals—1 hour to 1 day, 1 day to 1 week, 1 week to 1 month, 1 monthto Tante IIT.--AVAILABILITY OF U-FISSION RADIONUCLIDES equation (1—e>*). In addition, many common materials such as tar, resin, rusi, paint, metals, etc., seemed to retain selectively certain of the beta-emitting radionuclides. Under cer- which may change the isotopic distribution, I (Listed in order of decreasing yield) Thour to 1 dey Radionuclide t week to 1 month T day to 1 week 1 monthto I yeur 1 year to 70 years Yield Radionuclide Yield Rudionuclide Yield Radionuelide 559 519 458 454] 451 Mo... 8s. Cel... 2] Nb? 1.) DR... pit. 360 360 250] 241 937) Lal__ re Bato ~w--f Pri@ __ Cettt__. DH. 444 427 423 414 387 376 363 351) 314 294 250 233 222 206 164 163 161] Zr"... Tet?, Bat®_.. Lave. -| Palo... -] Pri®. 2...) Y%_Srt._ Pmt. Nd¥7___ Rho [5_. Celt, Zr. ¥"__ ¥e_. Sri. ~ 229 228 160 128 122 U1 Hid 9G 92 77 70 48 40 39 37 37 35 Nd¥7_ Zr%6___ Y%_. Sree_. Mom, Rue. Rhee, 132 | . Tet?___ wees Obes, e weee Cet4... Pret. Cela... Pm'@.. 337 293 284) 216 160 128 127 Nb... 2...) Zr... 22) Yo. Sriv_. Cem, Ces... Prt _. 586 483 374 311 284 271 271 Sr. 12... } Ye Cet? . -. Bat7_ Pm Cems. Pris, 480 430 406 406 215 214 214 96 93) 87 79 Lave. _ Baio __ Pm¥?.. _... Nd... 150 Rhtes_ 135 Zr%__ 44 ya . et 27 14 9 4 28 Rhis_ 72 71 70 67 61 Rh 2. Pris. oo... 31 7 126 37 34 2 Ru... 2.) 32 122 109 102 4h] 28 14} 12) Vield Rus _ Rnie__ Pri___ ym le Ruts, . Sr -| - ¥8_. Cit a Bat?__.. 197 189 154 34 22 22 13 13 10 10 Radionuetide Smit Nb®. Ruts, Yield 44 31 27