Determination of the amounts and kinds of radioactivity in a biological
sample is a process wholly dependent on instruments, since radiation
usually cannot be detected by the senses.
A biological sample is any material of measurable biological
significance. A sample of tissue or similar organic material usually is
dried or reduced to ash in a muffle furnace before it is examined with a
radiation counting device.
Improved instruments now permit the counting of radioactivity at levels
so low as to have been imperceptible a few years ago. The samples,
placed in lead chambers for maximum shielding from background
radiations, are examined by multichannel analyzers capable of recording
radiation emissions continuously over long periods of time.
Data-processing techniques have been employed in the handling and
interpretation of information from long-range biological sampling and
analysis programs. Analog computers have been used experimentally for
theoretical projections of results.
[Illustration: _Instruments record radiation, weather, sunlight, and
other factors transmitted from remote sensors to this data center
established for a long-range terrestrial ecology study program._]
Scientists at the AEC’s Oak Ridge National Laboratory, for example, have
developed experiments in which an analog computer is programmed to keep
a running balance of the net changes—simultaneous gains and losses—of
radioactivity in the various compartments of a representative ecosystem.
The computer becomes an electronic image of the biosphere, using known
or assumed rates of energy transfer and photosynthesis to predict
probable radiological results of tracer experiments of environmental
contamination.