Robin The cross-section for alpha emission from carbon is way too small for the explanation you suggest.
Wiki sez: in the radiation detection application, CR-39 material is exposed to proton recoils caused by incident neutrons. The proton recoils cause ion tracks, which are enlarged by an etching process in a caustic solution of sodium hydroxide. The enlarged ion tracks are counted under a microscope (commonly 200x), and the number of ion tracks is proportional to the amount of incident neutron radiation. -----Original Message----- From: mix...@bigpond.com AFAIK fast neutrons are detected by the fact that they occasionally break a C12 nucleus into 3 alpha particles. It is the three alpha particles that produce three cone shaped tracks in the CR39, with a common origin. Note that only charged particles create tracks, because the tracks are formed from chemical changes in the CR39 caused by the CR39 molecules being ionized, and only energetic photons and charged particles cause ionization (not neutral particles). Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/project.html
