TY - JOUR
AU - Warner, Arthur H.
AB - A Rugged, Direct-Reading Iontoquantimeter of High Sensitivity Leo P. Delsasso and Arthur H. Warner , Ph.D. University of California at Los Angeles, Los Angeles, California University of California at Los Angeles, Los Angeles, California Soiland Radiological Clinic, Los Angeles, California Excerpt THE two most important parts of an iontoquantimeter are the ionization chamber and the instrument attached thereto for measuring the amount of ionization. It is the purpose of this paper to describe a new type of instrument to measure this ionization. In order to understand the requirements such an instrument must meet, a brief discussion of the instruments now in use must be given. The ideal ionization chamber has been the subject of exhaustive research. As a result, several types are in general use. The majority of commercial iontoquantimeters use a small “thimble” chamber made of materials of light atomic weight. The second type, as used by Duane, also employs light materials, but obtains greater volume by a construction in which the ionization occurs in air between flat plates of which there may be a considerable number. The third type was developed by Dauvillier, who employs several hundred cubic centimeters of the rare gas, xenon, in order to obtain sufficient ionization to actuate a microammeter. The use of the small chamber is of advantage in mapping the distribution of intensity in a beam, particularly in a water phantom. Its chief disadvantage lies in the type of instrument necessary in order to measure the extremely small amount of ionization produced in its restricted volume. The current must be guarded with care, and only costly amber, protected from contamination, will maintain the necessary insulation. The string electrometer is usually used to measure the current. Although it is very sensitive, it is quite rugged and consequently lends itself well to use in a portable instrument. The leads to the instrument must be kept short to maintain the sensitivity, prevent current leakage, and keep down expense. It is usually necessary for the operator to use the device in the treatment room, unavoidably exposed to some secondary radiation. It has the further disadvantage that it is not direct-reading. The rate of fall of the string must be determined by means of a stop watch. The greatest errors in timing occur when the beam is most intense, as the time of discharge is then quite short. The difficulties of the string electrometer have been eliminated by one manufacturer, who has substituted a vacuum tube and relays by means of which the instrument is made to sum up the total dose. The insulation difficulties still remain, and something of ruggedness is lost. With the use of the larger ionization chambers it becomes possible to use the less sensitive but more fragile galvanometer, or the microammeter, instead of the string electrometer, since the currents are considerably larger. The insulation given by high quality ignition cable is adequate, and the sensitivity of the instrument is not diminished by long leads. It is, therefore, possible to place the galvanometer and scale permanently in some convenient location suitable for it, where the operator will be protected from radiation. It is also possible to use the same galvanometer for any number of ionization chambers, if suitable switches are provided to connect them one at a time. Copyrighted by the Radiological Society of North America, Inc.
TI - A Rugged, Direct-Reading Iontoquantimeter of High Sensitivity
JF - Radiology
DO - 10.1148/16.1.39
DA - 1931-01-01
UR - https://www.deepdyve.com/lp/radiological-society-of-north-america-inc/a-rugged-direct-reading-iontoquantimeter-of-high-sensitivity-0kjbaUIwZW
SP - 39
VL - 16
IS - 1
DP - DeepDyve
ER -