in fhe frrtrrro f$^h 61! hr'-l ^^- +^^+^ -^-t^-*^r nuclear tests performed. In its 197T report to the ceneralAssenbry, eV tne conr:nitt ee surnmarized the d.oses conrmitted by all nuclear testscarried. out before 1976. These are estimated to have caused a g1oba1 dispersionof radioactive debris from about Ll+5 l.{t. of fission yield. part of the rad.iationreceived. by nan is external, coming from debris deposited on the ground. rmportantdoses to d.ifferent org€ns of the body also cone from several radio-nucl-ides(notably strontiun-lO and cesium-f3]) which enter man via food. or throushinhalation, and act as internal sources of radiation durine their combinedphysical and biological l"ifespan. 260. The radiation doses averaged ove" the world population fron external- andinternal- sources are estimated. to be roughfy equal, the totaf whole-body d.ose(up to the year 20oo) being about rao rniiriraa.- zg/ rinis means that past nucleartests which have contaninated. the biosphere have-Eonmitted of the order of1 miflirad per lllt. fission averaged over the world population. !o quantify thisin terms of possibfe cancer deaths and. serious hereditary i11 hearth one can usethe uncertain but conmonl;. cited estimate of 2 to 3 deaths due to cancer orgenetic damage for each 10,000 nanrad collective dose. For the vorld populationthis woufd lead to one d.eeth for each kiloton fission exp1od.ed.. With this rneasu.Teall past atmospheric tests coul-d. be equiva]-ent to about 15OrO0O premature deathsworld-vide, and approxilnat ely 90 ler cent of these would be e:rpected to occur inthe llorthern Hemisphere, llorever, it should be noted. not only that this figureis based on an estimate of the risks associated with -Iow radiation d.oses vhich initself is a matter of scientific controversy, but also that even if that estinxateis correet, there is no way of identifying these cases a.nong the msny nillions ofother cancer d.eaths during the same period of tirne. 26\, I,flren a nuclear device d-etonates underground an almost spherical- cavity isformed and. at soltrewhat larger d.istances the rock is cracked. The radius of the 28/ Sources and Effects of TonizinE nadiation (United llations publi cat ion, Safes No.8.7?.IX.]).
**Analysis**
The text discusses the effects of nuclear tests on the environment and human health, specifically the dispersion of radioactive debris and the estimated radiation doses to different organs of the body. The text also mentions the potential risks of cancer deaths and serious hereditary damage due to these radiation doses. Given the focus on the environmental and health impacts of nuclear tests, it is likely that the text falls under the categories related to natural resources and environment, as well as health.

**Category**
Natural resources and environment, Health