High resolution alpha particle spectroscopy using CR-39 plastic track detector

Abstract

We present a technique for high resolution alpha particle spectroscopy using CR-39 plastic. An energy resolution, δE, close to the range straggling limit is reported on particles of energy ≳3 MeV under typical etch conditions. For 6 MeV α-particles δE is ∼35 keV on individual tracks. For groups of particles δE∼20 keV can be achieved using certain data selection criteria. The technique is based on the determination of track length in the plastic from measurement of the etch track parameters. The etch track data can be analysed by two methods. Method 1 employs all five parameters of the etched track: track depth, Z; major axis M j; minor axis, M i overall track length, X and the diameter of the etched out end, m, which is equal to zero in the case of a non-etched out track. Method 2 employs only the horizontal measurements of the projected parameters X, M i and m. The experimental data presented include (1) V T-range curves at etch temperatures of 50, 75 and 100°C in 6.25N NaOH for CR-39 available commercially and for material manufactured to specific temperature-time curing profiles. (2) The variation of etch induction time with etch temperature and α-particle energy. The theoretical analysis includes (1) a full discussion of α-particle track structure in CR-39 as a function of particle energy, dip angle and degree of etching including a comparative simulation of etched tracks, (2) a description of the methods of track analysis. The energy resolution attainable using the methods of analysis described is discussed fully. As an example of the best resolution achievable using selection criteria on a group of tracks the energy distribution of α-particles from a 252Cf source is considered. The 6.076 and 6.119 MeV α-particles are clearly resolved: δE=±20 keV.