RMI Nuclear Justice Documents

og rs * jase BN lh lalallala UPTAKE OF RADIOACTIVE NUCLIDES “LL stable caesium i by the addition of sues observation 79). The latter thong 289 radium 228. Little experimental work on the absorption of thorium by plants has been carried out. However, in water culture experiments lasting 24 hr Mercer & Morrison (85) found no detectable quantities of thorium potassium, milar to that for that the w (81). There is evidence caes1um of the availability in shoots, but more prolonged studies must be carried out before it can be concluded that this element cannot move upwards in plants to any appreciable extent. and that Thus, wheres ‘o or more years (82). 137 usua Y caesium s suggest that the extent ° soil to about one-tenth may years » after three or more t a assumed was itively recently it This, howeve yle degree in all soils. series oO extensive an nm conducted Radium.—Twoisotopes of radium have sufficiently long half lives to deserve consideration from the viewpoint of absorption by plants, namely radium 228 (thorium series; half life 6.7 years) and radium 226 (uranium series; half life 1620 years). Numerous measurements of radium have been made in plant tissue and very widely ranging values have been found (2). Turner e¢ al. (86) found that the content of different edible plant tissues ; many of t <t eas in South America © ranged from less than 1 to 17,000 pe alpha activity/kg. The highest values were for Brazil nuts, cereals were intermediate (up to 580 pc/kg) while other fruits and leaf vegetables contained low quantities. The existence of an unusual accumulation mechanism in the Brazil nuts was suggested both by this observation and by the fact that the same species also accumulate barium to an unusual extent (87}. However, as soil samples were not no evidence of clay minerals and llowt.—The relative rom world-wide fa ect con- of the dir plants as a resu It the soil, has been to absorption fro m the ium 90. Because ian that of stront extent the d an l, soi the absorbed from it would be Cx elatively similar, : more closely im ate nts would be much n 0 l, era gen in s 1s, te past. While thi i caesium 137 in m ition the levels of available from the areas where the nuts were collected for alpha assay, the possibility could not be excluded that the results were due to abnormal levels of activity in the soil. More recently a preliminary report has been made on different tissues of Brazil nuts and the underlying soil in British Guiana (88). The soil contained 22,000 to 24,000 pc alpha activity/kg which is within the normal range for many areas (83). The endosperm and peri- ected, relative ° se in the manner exp . : lined in 1960 (2) ite of fallout dec ° ms is an ch me ing” oy the two “delay Caen carp of the nuts, however, sometimes contained more than 30,000 pc/kg, twice the previously reported figure; the values for the epicarp were lower than those for other tissues. Although the full spectrum of the alpha activi- retention of made, namely the ties in these tissues has not yet been reported, radium 226 was the pre- relationship idertaken before iv e and the cumu * ; and both the rat been s ha h ic wh ent i, even to the ext plant is therefore established. The ratios of alpha activity to calcium were also examined in the Brazil nut samples from British Guiana. The values for the endosperm and epicarp appreciably exceeded those for leaves or such stem tissues as were examined. These findings do not, however, prove that radium is transferred preferentially to calcium in any step of the ARTO TYEeT EE encouraged by the observation that strontium may be retained to a considerably greater extent than calcium in plant stems and that under some experimental conditions a higher ratio of strontium to calcium in grain than in other tissues can be induced, though the reverse usually occurs (13). The study of these relationships in the Brazil nut is rendered difficult both by the laborious procedures necessary to identify specific alpha-emitting substances in the low levels in which they occur in nature and by the ‘ a r . T “or ree aye EET OT subsequent release at the time of fruit development. This suggestion is SM sy tte ep eetre Sr pit ce teey em ae “3 eee Ta upward transfer mechanism. The higher ratio in the endosperm than other aerial tissues could be due to the preferential retention of radium in some stem tissues during the process of upward transfer to leaves and to its fs ES AND THORIUM SERI tting nuclides betong yecurring alpha-emi is much less abu . the actinium series series, measuremen'® y schemes of these Uncertainties as ° total alpha activity. the interpretatio in can cause difficulties m is the elementPri parent that radium e mh parent me 84). Thorium 232, the thorium s; sue tis ing liv etected in y of the paren ca de 1 be attributed to the dominant nuclide; its accumulation to an unusual degree in the fruits of this © PRIA=!Ne EE APTS ' ' ontium 90 an “ne mger period than str Considerably m re yroceed in the soil. s betwe "