. Biophysical research methods. Biophysics -- Research. XIV. X RAYS AND X IRRADIA'JION 457 other existed. This gap has been filled through the work on Droso- phila eggs (4-8,44) followed by that of genetics workers on gene muta- tion and on survival of Drosophila sperm (26). The measurements are in agreement and show that the total energy absorbed in the tis- sues as the X rays pass thi-ough them is the important element in producing the effects. The physical unit of X radiation, r. unit or roentgen, is the quantity of X rays "such that the associated corpus- cular emission per g
. Biophysical research methods. Biophysics -- Research. XIV. X RAYS AND X IRRADIA'JION 457 other existed. This gap has been filled through the work on Droso- phila eggs (4-8,44) followed by that of genetics workers on gene muta- tion and on survival of Drosophila sperm (26). The measurements are in agreement and show that the total energy absorbed in the tis- sues as the X rays pass thi-ough them is the important element in producing the effects. The physical unit of X radiation, r. unit or roentgen, is the quantity of X rays "such that the associated corpus- cular emission per gram of air produces, in air, ions carrying 1 electrostatic unit of quantity of electricity of either ; The dose in r. units, therefore, is not a measure of the total energy in an. L M N Fig. 3. Sectional view of an X-ray dosimeter oi' r. meter (courtesy Victoreen Instrument Co.): A, chamber tube containing condenser and chamber; B, chamt)er tube cap (for end opposite chamber); C, ionization chamber; D, insulating button to cover insulation at E; F, discharge switch; G, static charger wheel; H, scale; I, objec- tive; J, ocular; L, lamp; M, battery; N, light switch. X-ray beam, but only that fraction which can be dissipated by the ionization process in a thin layer of air. This can be related to the energy dissipated in tissue by ionization. For a further discussion, the reader should consult the following chapter. A diagram of a small dosimeter based on this ionization principle is shown in Figure 3. The ionization chamber is a small thimble- shaped structure at the end of the tube. Its walls are easily pene- trated by X rays, the charge being taken by the wire to the electro- scope. The current causes the electroscope to discharge; the amount of the discharge is measured on an r. unit scale, which is read by look- ing through the microscope. This type of dosimeter must be cali- brated for the quality of X rays absorbed, however, by comparison. Please note that these i
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