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A Feldman

Publications and source records attributed to A Feldman.

106 records · Page 6Linked to original sources
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60Co dosimetry.

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Cobalt Radioisotopes↗
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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↗
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Lipowitz metal shielding thickness for dose reduction of 6-20 MeV electrons.

The relative dose reduction by Lipowitz metal of 6 to 20 MeV electrons from a Varian Associates Clinac-20 linear accelerator has been measured using a parallel plate thin wall ionization chamber. Metal thickness required for a 5% attenuation level for a 10 X 10 cm2 field are as follows: 6 MeV-2.3 mm, 9 MeV-4.4 mm, 12 MeV-8.5 mm, 16 MeV--18.0 mm, 20 MeV-25.0 mm.

Humans↗
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Threshold-duration function of the acoustic reflex in man.

The threshold-duration function of the acoustic reflex was investigated in 5 male and 5 female adult, normal-hearing humans and in 3 adult male subjects with hearing loss of cochlear etiology. Reflex threshold was obtained at stimulus durations of 10, 20, 50, 100, 200, and 500 msec and at frequencies of 500, 1 000, 2 000, 3 000, and 4 000 Hz. Three commercially available acoustic bridges were employed, the Madsen ZO-70 and Grason-Stadler 1720 electroacoustic bridges, and the Grason-Stadler-Zwislocki model 3 mechanical-acoustic bridge. A probe-tone frequency of 220 Hz was used in all measures. The reflex threshold-duration function for normal-hearing subjects was found to encompass a much greater range of intensity than the psychophysically assessed auditory threshold temporal integration function. A sex difference was found which may be explained by subclinical noise-induced cochlear pathology in the male subjects with subsequent truncation of the reflex threshold-duration function. The function was also found to be truncated in the 3 subjects with hearing loss diagnosed to be of cochlear etiology. The implications of these findings for control of stimulus duration in clinical reflex measurement was discussed.

Acoustic Stimulation↗