Response of NaI(T1) to Energetic Heavy Ions

Experimental values of the relative heights of scintillation pulses generated in NaI(T1) crystals, by heavy ions (Z\u3e5) of energy 1-10 MeV/amu, agree well with computed relative cross sections for photon production, from a theory based on the assumption of a one-hit response to the spatially distributed dose of ionization energy, and a characteristic dose of 4x107 erg/cm3 for this material Discrepancies between theory and experiment for He bombardments arise from the theoretical neglect of the nonlinear dose variation over the sensitive volume surrounding each TI atom. Similar discrepancies arising from the neglect of molecular volume occur in the theory of heavy-ion inactivation of dry enzymes and viruses, which forms the basis for the present work

Formation of Particle Tracks

The formation of particle tracks, and such phenomena as the detection of charged particles and the damage produced by charged particles, are intimately related to the spatial distribution of ionization energy deposited by δ-rays. Changes in the spectrum of δ-rays with the velocity of the primary particle imply that linear measures of the interaction of the primary particle with the medium, such as specific energy loss, or primary ionization, are unsatisfactory measures of effects produced in the medium, for they contain no knowledge of the spatial deposition of the lost energy

Energy Deposition by Electron Beams and δ Rays

The product of two empirical relations, for the practical range and the transmission probability of normally incident electrons through plane sheets of matter, may be differentiated to yield a simple formulation of the energy deposition by electron beams, in agreement with more complex formulations and with experimental data. When combined with the δ-ray distribution formula, these results provide a theory of the spatial distribution of ionization energy about the path of a rapidly moving ion, which is basic to theories of radiation damage and detection

Particle Tracks in Emulsion

A new theory of track formation in emulsion accounts for the tracks of charged particles on the basis of a theory developed earlier for the response of biological molecules and NaI(T1) to energetic heavy ions. The probability that an emulsion grain will remain undeveloped when exposed to δ rays depositing a mean energy E is assumed to be e-E/E0 where E0 is the dose at which l/e (37%) of the emulsion grains remain undeveloped, as in the one-or-more-hit cumulative Poisson distribution. The parameter E0 incorporates variations in emulsion properties and processing conditions. Calculation of the spatial distribution of the ionization energy deposited by δ rays is combined with the assumed emulsion response to yield the spatial distribution of developed grains about the path of the charged particle. Calculations are in agreement with experimental data for grain counts (up to the relativistic rise), blackness profiles, and track width

Width of Heavy-Ion Tracks in Emulsion

Profiles of the solid core of long, flat, ending tracks of heavy primary cosmic rays in Ilford G-5 emulsion have been measured by manually tracing their enlarged (3500X) photographic image. These measurements agree well in the ending 3000 μ of residual range (β \u3c0.3) with a reformulated theory of track width based on computation of the spatial distribution of ionization energy. The measured core width in G-5 emulsion is the sum of the sensitized cylinder diameter, at which 6000 erg/cm3 of ionization energy is deposited by δ rays, and the diameter of a developed grain

Response of Nuclear Emulsion to Electron Beams

A recent theory of particle tracks assumes that the probability P for grain development in nuclear emulsion depends on the local dose E of ionization energy deposited by secondary electrons (delta rays) in the neighborhood of the particle track. The response is assumed to be one of exponential survival; that is, if E0 is the dose for 37% survival, then P = 1 – exp (-E/E0). By calculation of the dose E(t) deposited at depth t in the emulsion by normally incident, monoenergetic electron beams, and applying the assumed dose-effect relationship, response curves giving blackness versus electron fluence are obtained, in terms of E0 and a second parameter combining the effects of the density of undeveloped grains, the developed grain size, densitometer optics, and light scattering. Calculated and measured curves are compared