Journal of Physical Chemistry, Vol.98, No.15, 4043-4049, 1994
Track Effects in Water Radiolysis - Yields of the Fricke Dosimeter for Carbon-Ions with Energies Up to 1700 MeV
The radiation chemical yields of the Fricke dosimeter have been determined for carbon ions with energies up to 1700 MeV. These yields can be described by a general relation of the form G(0) = G(B) + (G infinity-G(B)) (1 - E(B)/E(0))F where G infinity and G(B) represent the limiting yields at high energy and at the Bragg peak, respectively, and Fis a dimensionless factor given by a(E(0) - E(B))(m)/(1 + a(E(0) - E(B))(m)). The initial value of the carbon ion energy is E(0) in MeV while E(B) is the energy at the Bragg peak, 3 MeV in the case of carbon ions. Taking G infinity as the yield observed with fast electrons (15.5 molecules/100 eV) and G(B) as 2.65 molecules/100 eV, the yields observed for aerated solutions are fitted very well for carbon ions by values of the empirical parameters a = 0.0258 and m = 0.520. It is shown that the differential yields are never more than 25% greater than the yields averaged over the track. Comparative measurements made in deaerated solutions provide information on the energy dependence of the hydrogen atom yield which increases from small values at low energies to only similar to 2 H atoms/100 eV for 1000-MeV carbon ions. Since the latter value is only 55% of the hydrogen atom yield observed for fast electrons, it is clear that intratrack reactions are still of major importance at carbon ion energies of similar to 1000 MeV where the LET is similar to 20 eV/nm, i.e. only 10 times that of fast electrons.
Keywords:HEAVY-IONS