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J B Smathers

Publications and source records attributed to J B Smathers.

43 records · Page 3Linked to original sources
PubMedDate not supplied

Neutron energy spectra of d(49)-Be and p(41)-Be neutron radiotherapy sources.

Zero-degree neutron energy spectra for the p(41)-Be and d(49)-Be reactions were measured by time-of-flight for neutrons with energies above 1.9 and 1.4 MeV, respectively. Spectral changes resulting from the addition of copper, aluminum, and polyethylene filters to unfiltered beams were determined. Integral yields, average energies, filter material attenuation coefficients, and kerma fractions were computed for these spectra. Calculated spectra for neutron beams filtered by various thicknesses of polyethylene compared favorably with experimental results

Fast Neutrons↗
PubMedDate not supplied

Calorimetric and ionimetric dosimetry intercomparisons I: U.S. neutron radiotherapy centers.

In the U.S. neutron radiotherapy trial centers, absorbed dose is routinely measured using commercially available A-150 tissue equivalent (TE) plastic ionization chambers. The collecting volumes of these chambers are filled with either methane-based tissue equivalent gas or air. Absorbed dose in A-150 plastic, determined with these ionization chambers, was compared to that measured by an A-150 plastic calorimeter in an A-150 plastic phantom. These comparisons have yielded the following information: (1) Agreement of the total absorbed dose measured using the ionization chambers was within 2.5% of the calorimeter at all the centers visited to date. (2) For all the neutron fields measured, the product of the stopping power ratio (sw,g)N' between the A-150 plastic chamber wall and TE gas, and the average energy expended in the gas per ion pair formed, WN/e, was computed assuming Bragg-Gray theory and found to be 31.0 +/- 0.7 J/C. (3) The displacement correction factor employed to normalize measurements at a depth in a phantom using the type IC-17 ionization chamber was verified to be approximately 0.97 +/- 0.01.

Calorimetry↗
PubMedDate not supplied

Modification of the 50% maximum dose depth for 41-MeV (p+,Be) neutrons by use of filtration and/or transmission targets.

Several target configurations for the 41-MeV (p+,Be) reaction have been evaluated for the characteristics of the radiation field produced; depth dose, dose rate per microA, From analysis, it is concluded that to achieve the desired 13.2-cm depth for 50% of maximum dose and acceptable dose rate at a target-to-skin distance (TSD) of 125-150 cm, the neutron spectra must be filtered to preferentially absorb the lower-energy neutrons. Further increases in depth of 50% of maximum dose and a significant reduction in beryllium heating problems result if a partial transmission target is used with the terminal 30% of proton energy being deposited in a copper target backing.

Beryllium↗
PubMedDate not supplied

Skin-sparing effects of neutron beam filtering materials.

The skin-sparing effects of several filtering materials for fast neutron beams were studied under various conditions. A parallel-plate ionization chamber was used for the measurements. The parameters which were studied included field size, distance from filter to ion chamber, filter material, and filter thickness. On the basis of this work, Teflon (polytetrafluoroethylene) was chosen for fabrication of flattening filters and wedges.

Humans↗
PubMedDate not supplied

Radiation quality investigations around a neutron therapy beam, using a high-pressure ionization chamber.

The mean quality factor (Q) and the dose mean linear energy transfer [LET (LD)] a few centimeters outside a neutron therapy beam have been measured using a high-pressure ionization chamber. Measurements have been carried out in air, 5 and 100 cm outside the treatment field edge on the patient plane for p(46)-Be neurons and are compared with the results obtained at the same points with a low-pressure proportional counter (Rossi counter) and a Bonner spheres system. General agreement is found between these independent methods. The dose equivalent at 5 and 100 cm distances outside the field edge is 2% and 0.4% of the dose equivalent at the isocenter. Measurements were also performed at the same points as a function of proton energy on the Be target. Proton energies of 25-46 MeV on Be were applied. The results indicate increase in the mean quality factor at proton energies below 30 MeV.

Humans↗
PubMedDate not supplied

Anthropomorphic radiation therapy phantoms: a quantitative assessment of tissue substitutes.

Compositional analyses of samples of soft tissue and lung substitutes used in the construction of anthropomorphic radiotherapy phantoms were performed for products from Alderson Research Laboratories Inc., Kyoto Scientific Specimens Company/Capintec Inc., Humanoid Systems Inc., Radiology Support Devices Inc., and The Phantom Laboratory Inc. To assess quality control in the manufacture process, the results of these compositional analyses were compared with individual manufacturer's design specifications and electron densities measured by computed tomography analysis of actual phantom slices. A comparison of the manufacturers design specifications against reference tissue parameters from Tissue Substitutes in Radiation Dosimetry and Measurement (International Commission on Radiation Units and Measurements) indicates marked differences in the basic design of commercially available anthropomorphic phantoms.

Evaluation Studies as Topic↗