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Abstract

The natural ²²⁶Ra activity in human foetal bone ash remains constant from the fourth to the tenth month of pregnancy. The ²²⁶Ra content is equal to that determined in the bone ash of adults, found to be 1.3 * 10⁻¹⁴ c/g of bone ash. An analogous identity in the ²²⁶Ra content of soft tissue of foetuses and adults has also been found. For both embryonic and adult tissues the specific activity is 1 * 10⁻¹⁶ c/g of fresh tissue. From comparison of the specific values of the ²²⁶Ra content in bone and soft tissue it may be derived that the major portion of the ²²⁶Ra content of the foetus is in the skeleton. Therefore the specific ²²⁶Ra activity of ashed total foetuses is of the same order of magnitude as the value in foetal bones. The ²²⁶Ra activity of placental tissue is about 2 * 10⁻¹⁶ c/g of fresh tissue. The discrimination factor between the placenta and the foetal bones, and the placental transfer of ²²⁶Ra are discussed. The specific radium level of both the placenta and the embryonic tissue proved to be comparable. In consequence the placenta does not act as a barrier for the natural ²²⁶Ra content, that is to say there seems to be no discrimination in the passage of this radionuclide.