Alpha-radioactivity in the human body

Plastic track detectors are used to make measurements of the microdistribution of low level and natural alpha radioactivity in human autopsy or biopsy tissues and teeth. The data are used to determine the mechanisms of retention and clearance of radioactive particles by the human body as well as the radiation dose to the target cells for the induction of cancer. It is also of interest to look at geographical variations.

(a) (b) (c) (d)

The photomicrographs a, b, c and d show a cluster of ~160 tracks of alpha particles emanating from a volume of a few cubic microns of bronchial epithelium from a 79 year old female. A second cluster similar to this one was found a few mm away. The illustrations are photomicrographs taken at (a) the surface and at depths of (b) 13 microns, (c) 23 microns, and (d) 28 microns into the cluster. They show the end parts of alpha particle trajectories at these depths. Detailed measurements of track lengths in the cluster show four tracks significantly longer than the remainder suggesting that the source particle contains Uranium and its daughter nuclei. This is substantiated by estimates of the particle size both from the geometry of the cluster and the degree of activity present.

A major source of enviromental alpha radioactivity arises from radon in the home. Owing to its short half-life, its presence in the human body cannot be measured directly. Body uptake is modelled mathematically and this is a key area of research.

In 1990 we reported a series of geographical correlations between domestic radon exposure and the incidence of leukaemia and several other cancers in children and adults. As a result of these findings, we are examining the hypothesis that natural alpha radioactivity is an important initiator of some cancers in man.

Plastic detectors are used to map the distribution of 'hot' plutonium particles in the environment and to study alpha-radionuclides in the local population using biological samples such as teeth and breast milk.

These two pictures show tracks of 'hot' plutonium particles found in the soil near Chernobyl.