Energy determination for electron beam calibration.
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Calibration↗
Biomedical subjects
J O Freim
Publications and source records attributed to J O Freim.
Ultraviolet irradiation of the vegetative cells of Dictyostelium discoideum.
Experiments on the effect of ultraviolet (UV) light on the survival of vegetative Dictyostelium discoideum cells indicate that this is a relatively UV-resistant organism. Several factors suggest the presence of some type of repair process. Experiments to test for liquid-holding recovery and simple photoreactivation yielded negative results. Acriflavine and caffeine were utilized to possibly interfere with dark repair. Acriflavine produced no UV sensitization, but caffeine did cause a concentration-dependent decrease in survival of irradiated cells. When UV-irradiated cells were illuminated with photoreactivating light while suspended in caffeine, the survival increased above that for cells treated with caffeine alone, suggesting an overlap between lesions repaired by photorepair and dark repair. Growth experiments showed that UV light induced a dose-dependent division delay, followed by a period of retarded growth characterized by the presence of a constant fraction of nonviable cells in the irradiated population. The delayed exposure of cells to caffeine after irradiation showed that the magnitude of the caffeine sensitization diminished throughout the division-delay period. An action spectrum indicated probable nucleoprotein involvement in the induction of division delay. UV light retarded ribonucleic acid and protein synthesis and temporarily blocked deoxyribonucleic acid synthesis. However, synthesis of all three accelerated prior to the end of the division-delay period and then closely paralleled the increase in cell number.
Acridines↗
Cobalt-60 dose calibration: a comparison of methods.
Cobalt-60 dose determination can be accomplished by a variety of methods. This study investigates dose determination by actual "at-depth" measurement for the depths and field sizes desired as well as by "in-air" or "in-water" calibration measurements for both constant SSD and isocentric techniques. Comparison of the above dose determination methods reveals the existence of both depth-dependent and field size-dependent dose discrepancies between the individual methods studied. For many teletherapy units, the source of these discrepancies lies in the inapplicability of the tabulated percent depth dose and tissue-air ratio values employed. Appropriate percent depth dose and tissue-air ratios can be obtained by performing a series of at-depth dose determinations for a variety of depths and field sizes. When the appropriate values are employed, excellent agreement is found between all of the dose determination methods investigated.
Cobalt Radioisotopes↗