John E. Steigerwalt

Changes in the frequency distribution of energy deposited in short pathlengths as a function of energy degradation of the primary beam.

The frequency distributions of event size in the deposition of energy over small pathlengths have been measured after penetration of 44.3 MeV protons through various thicknesses of tissue-equivalent material. These distributions have been measured over a range of penetration extending from zero thickness to thicknesses of muscle-equivalent plastic close to that corresponding to the total range of the protons. These distributions are those associated with the passage of the proton through

Frequency distributions of energy loss by fast charged particles after passage through large thicknesses of tissue-equivalent materials.

0.667\times 10^{-4}\ {\rm g}/{\rm cm}^{2}

The calculation of proportional counter energy-deposition spectra from experimental data.

of a tissue-equivalent gas. The transition from the region where statistical fluctuations dominate to that where a significant spread in beam energy has taken place is clearly demonstrated. In no instance does it appear that the concept of dose based upon a value of the stopping power or average energy deposited adequately defines the energy delivered to a structure having the dimensions usually associated with those of biological significance if only a relatively small number o...

The calculation of proportional counter energy deposition spectra from experimental data. II - Very small energy losses and high energy delta rays

Frequency distributions of the energy deposition by 600 MeV protons in small volumes as a result of their traversal of a tissue-equivalent gas have been measured after the beams passage through various thicknesses of a tissue-equivalent plastic. The pathIength examined is equivalent to 1.75 ,u of unit density tissue (muscle). Comparisons of the energy deposition distribution functions after passage through 0, 5 and 21 cm of tissue-equivalent plastic (muscle) are given. Through the use of a coincidence gate, spectra depicting energy deposition due only to direct proton ionization in the gas were compared with those combined with contributions due to the nuclear interaction products.

The relative influence of geometry and statistical fluctuations of energy loss on the distribution function of energy deposition by charged particles in proportional counters

Experimental energy-deposition frequency distributions, measured by means of a proportional counter, have been transformed to those of other pathlengths, under a compound Poisson process, and the results have been compared with the corresponding experimental spectra. The computational technique, in the form of a computer program, was written by Kellerer. The input distributions were produced by ∼45 MeV and 600 MeV protons passing through tissue-equivalent gas mixtures whose areal densities are on the order of

A multiwire proportional counter designed for microdosimetric studies.

1\times 10^{-4}\ {\rm g}/{\rm cm}^{2}

The Radiobiological Implications of Statistical Variations in Energy Deposition by Ionizing Radiations

. For transformations which produce calculated spectra whose mean energies lie sufficiently close to those of the input spectra (shift factors of ∼0.75), reliable predictions of experimental energy-deposition spectra can be made. Calculations of this type potentially could reduce considerably the experimental work which must be done to define distributions needed for the folding of such distributions into those corresponding to volumes of interest.

Frequency distributions of energy deposition by 44 MeV protons at bone-soft tissue interfaces

BS>It is shown that a convolution technique, developed by Kellerer can be used to generate energy deposition spectra, by either forward or reverse shifts, for many pathlengths from a limited set of experimental data for low energy fast protons ( approximates 45 MeV) corresponding to pathlengths of radiobiological interest. For medium energy fast protons ( approximates 600 MeV) the method fails if shifts based upon the expected average energy losses are used as the base for these calculations. However, if shifts based on an experimental determination of the average energy loss in the volume of interest are used then good agreement with experiment is obtained. This reflects the effect of energy transport into and out of the counter volume by high energy secondary particles, resulting in a significant loss of energy from the volumes in which the measurements have been made and the high probability for a significant number of incident particles not undergoing collisions over the test pathlength. This results in experimental values of average energy which are different than those calculated using stopping power theory. (auth)

Frequency distributions of energy deposition by fast charged particles in very small pathlengths

If the energy loss for a charged particle traversing a fixed pathlength were a single valued function of the parameters governing energy loss by charged particles, then the pathlength distribution through a given volume would completely describe the distribution of energy losses found for particles traversing that volume. This would be true for either parallel or isotropically incident beams. In many instances of interest in micradosimetric measurement, statistical variations of energy losses by individual particles will play a significant role in determining the character of the resultant energy deposition distribution function obtained in a proportional counter. This has been investigated with an approximate analytical method for isotropically incident particle beams having various energies and masses traversing a number of differently shaped volumes, namely, the sphere and cylinders of different heightto-diameter ratios. Corrections for delta ray losses or contributions have not been considered.

Frequency distributions of energy deposition by 44 MeV protons at bone-soft tissue interfaces.

A multiwire proportional counter has been constructed for use in microdosimetric studies. Its physical details and special preamplifiers are described. The dependency of its operational characteristics with respect to wire diameter, wire spacing, electrode spacing, and gas pressure are discussed. Experimentally determined performance levels are shown. Finally, experimental data depicting typical frequency distributions of energy deposition associated with the passage of 5.5-MeV ..cap alpha.. particles through the chamber are shown for both individual wires and the high-voltage planes.