Approaches to Track Structure

In attempting to understand the chemical and biological effect* of ionizing radiation it is natural to consider first the most characteristic feature of the energy transfer process, namely, the concentration of energy along the tracks of charged particles whether these are the primary radiation itself /fast electron beams, alpha particles, heavy ions/ or the secondaries produced within the material /Cornpton recoil electrons, recoil protons, e tc , / . This feature of ionizing radiation has been recognised from the earliest period and was made explicit by BRAGG . Early theories of the biological and chemical action of radiation were based on certain simple aasumptions about the primary absorption events . The information on track structure available to these early workers came chiefly from cloud chamber pictures of the tracks of fast particles found by H. A. WILSON and later workers, notably E. J. WILLIAMS 7 . A quantum mechanical theory of the energy loss of charged particles o was developed by BETHE and his theory has remained the principal support for subsequent attempts to calculate energy concentration