TRANSFER-FACTOR OF I-131 FROM THE FALLOUT TO HUMAN THYROID DOSE EQUIVALENT AFTER THE CHERNOBYL ACCIDENT

A similar pattern of variation with time in observed maxima of daily d ose equivalent rates in human thyroids (TD - mu-Sv.d-1) and of daily f allout radioactivities (FR - kBq.m-2) has been found after the Chernob yl accident. An estimate of the time-lag between the maxima in TD line s and the preceding FR peaks was made of about seven days for adult an d nine days for juveniles. Applying this time-lag it was possible to e stimate transfer factors from the fallout to thyroid dose equivalent: the highest estimated values were 221-mu-Sv/kBq.m-2 for adult and 641- mu-Sv/kBq.m-2 for juvenile thyroids. These values differ from those pu blished by UNSCEAR (United Nations 1988), which have been calculated f or various regions of Czechoslovakia, from ingestion and inhalation in take estimates. A broad variation of transfer factor values could be e xpected to result from such transfer calculations using ingestion and inhalation estimates. The findings also support the concept of a need for prolonged iodine prophylaxy after emissions of radioiodine into th e environment.