226Ra in Human Embryonic Tissue, Relationship of Activity to the Stage of Pregnancy, Measurement of Natural 226Ra Occurrence in the Human Placenta

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Abstract
The natural Ra226 activity in human fetal bone ash remains constant from the 4th to the 10th month of pregnancy. The Ra226 content is equal to that determined in the bone ash of adults, found to be 1.3 [center dot] 10-14 c/g of bone ash. An analogous identity in the Ra226 content of soft tissue of fetuses and adults has also been found. For both embryonic and adult tissues the specific activity is 1 [center dot] 10-16 c/g of fresh tissue. From comparison of the specific values of the Ra226 content in bone and soft tissue it may be derived that the major portion of the Ra226 content of the fetus is in the skeleton. Therefore the specific Ra226 activity of ashed total fetuses is of the same order of magnitude as the value in fetal bones. The Ra226 activity of placental tissue is about 2 [center dot] 10"16 c/g of fresh tissue. The discrimination factor between the placenta and the fetal bones, and the placental transfer Ra226 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 R226 content, that is to say there seems to be no discrimination in the passage of this radionuclide.

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