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Biomedical subjects

J W Baum

Publications and source records attributed to J W Baum.

At least 37 records · Page 2Linked to original sources
PubMed1980

Stopping power and radial dose distribution for 42 MeV bromine ions.

Linear energy transfer restricted in radius (LETr) and total linear energy transfer (LET infinity) were determined for 42 MeV bromine ions in tissue-equivalent gas. A variable pressure cylindrical ionisation chamber was used. Dose as a function of distance from the ion's path was also determined using a mesh wall ionisation chamber placed inside the cylindrical chamber. The range of distances studied was from 5 to 710 A in simulated tissue of unit density. Experimentally obtained values of radial dose were compared with calculations made using Paretzke's program. Stopping power for these ions in tissue-equivalent gas was extrapolated from proton stopping power in constituent gases. In this calculation the effective charge of the ions was obtained from the formula given by Dimitriev and Nikolaev. This calculated value was 6.3 x 10(4) MeV g-1 cm2. The experimentally determined value was 7.3 x 10(4) MeV g-1 cm2. The discrepancy between calculated and experimental values may be due to uncertainty in the determination of the effective charge of the incident ions. Uncertainty on the experimental value of LET infinity was estimated to be +/- 5% (one standard deviation).

Bromine↗
PubMed1979

Sensitivity of Drosophila melanogaster to low concentrations of the gaseous 1, 2-dibromoethane: I. acute exposures.

Drosophila melanogaster males were exposed to gaseous 1, 2-dibromoethane at concentrations lower than those used in aerosol treatments of suspected mutagens by other investigators. Premeiotic stages appear to be more sensitive than postmeiotic stages to gaseous mutagens. At an exposure of 125 ppm . hr, significant numbers of mutations were induced in spermatids, spermatocytes, and spermatogonia. Since this exposure increased the mutation rate in spermatogonial stages by a factor of 20--40 over the spontaneous rate, it appears that the lowest detectable exposures may be much lower than 125 ppm . hr for 1, 2-dibromoethane.

Aerosols↗
PubMed1979

Sensitivity of Drosophila melanogaster to low concentrations of gaseous mutagens. II. Chronic exposures.

Sex-linked recessive lethal mutations were induced in Drosophila melanogaster males by gaseous 1,2-dibromoethane at concentrations ranging from 0.2 to 2 parts per million. Significant numbers of mutations could be induced at all these concentrations. Pronounced germ-cell sensitivity differences were observed. For low exposures, spermatids and spermatocytes were about 10--20 times more sensitive than spermatozoa. The dose-effect relation was linear below 60 ppm . h for the 3 cell types. At higher exposures, sterility prevented mutation detection in spermatocytes and in spermatogonia. The lowest effective exposure for spermatozoa was 18 ppm . h (0.25 ppm for 72 h). In spermatids, the lowest exposure tested, 2.3 ppm . h (0.2 ppm for 11 h) induced 4 times the spontaneous mutation rate. Therefore, using prolonged exposure periods one may be able to detect concentrations in the range of parts per billion. Thus, Drosophila appears suitable as a system for detecting very low concentrations of gaseous mutagens in industrial, agricultural and environmental atmospheres.

Animals↗
PubMed1979

Relative determination of W-values for alpha particles in tissue-equivalent and other gases.

W (the average energy to form an ion pair) for 5.4 MeV 241Am alpha particles in a Rossi-type tissue-equivalent (TE) gas, argon and methane was determined to an accuracy better than 0.2% using a new automated data handling system. A vibrating reed electrometer and current digitiser were used to measure the current produced by completely stopping the alpha particles in a large cylindrical ionisation chamber. A multichannel analyser, operating in a slow multiscaler mode, was used to store pulses from the current digitiser. The dwell time, of the order of 60 min per channel, was selected with an external timer gate. Current measurements were made at reduced pressures (200 Torr) to reduce ion recombination. The average current, over many repeated measurements, was compared to the current produced in nitrogen and its previously published W-value of 36.39+/-0.04 eV per ion pair. The resulting W-values were, in eV per ion pair, 26.29+/-0.05 for argon, 29.08+/-0.03 for methane and 30.72+/-0.04 for TE gas, which had an analysed composition of 64.6% methane, 32.4% CO2 and 2.7% nitrogen. Although the methane and argon values agree within 0.1% with previously published values, the value for TE is 1.2% lower than the single previously reported value.

Alpha Particles↗
PubMed1978

Energy dependence of W for alpha particles in N2, CO2, CH4, Ar, H2 and Rossi-type tissue-equivalent gases.

Average energy required to form an ion pair (W) was determined in N2, CO2, CH4, Ar, H2 and Rossi-type tissue-equivalent gas. Alpha particles from a 241Am source were used. W was determined at alpha energies of 5.37, 3.12, 1.08 and 0.46 MeV. The ratio of total ionisation produced (for fixed alpha particle energy) in experimental gas to that produced in argon was measured. This ratio was then multiplied by the previously determined W value for argon gas (26.29 eV per ion pair) to yield W for various experimental gases. Energy of the 241Am alpha particles was degraded by using air as an absorbing material. Empirical relations W = alpha + betaE-1/2 and W = alpha1 + beta1E-1 were fitted to the experimental data. Both functions fit reasonably well in the range 0.4--5.37 MeV. Below about 0.4 MeV the first function provides a better fit to the data of Boring et al. (1965).

Alpha Particles↗
PubMed1975

Experimental determination of W for oxygen ions in nitrogen.

'Differential' and integral measurements were made of the W value (average energy required to form an ion pair) for oxygen ions in nitrogen gas. A variable pressure cylindrical ionization chamber with a differential pumping section was employed. The average energy deposited per particle in the chamber was determined by integrating the energy spectrum measured with a heavy ion solid state detector. In the integral measurement of W, the particle was completely stopped in the chamber and the total ionization produced in the chamber was measured. The integral W value for 34-5 MeV oxygen ions was found to be 38-6 +/- 0-54 eV per ion pair. For 'differential' measurements, the pressure in the chamber was raised to 0-003, 1, 5, 15 and 20 Torr; and measurements of ionization currents and average energy deposited per particle were made at each pressure. From differences between these measurements 'differential' W was found. The average value of fifteen 'differential' W values was found to be 38-6 +/- 1-16 eV per ion pair.

Ions↗