title: Contamination of ionization chambers by talcum powder.
abstract: This is a word of caution to anyone using ionization chambers protected by thin rubber sheaths in water. Four Farmer-type ionization chambers contaminated with talcum powder were received for calibration by the Accredited Dosimetry Calibration Laboratory at the University of Texas M. D. Anderson Cancer Center. The chambers show a marked energy dependence (5% to 20%) to soft orthovoltage x rays. The response of the contaminated chambers is compared with the chambers' response before contamination and after cleaning. Techniques for identifying contaminated chambers and suggestions for cleaning them are presented.
authors.affiliation: Accredited Dosimetry Calibration Laboratory, University of Texas M. D., Anderson Cancer Center, Houston 77030.
authors.forename: W F
authors.initials: WF
authors.lastname: Hanson
authors.forename: D J
authors.initials: DJ
authors.lastname: Arnold
authors.forename: R J
authors.initials: RJ
authors.lastname: Shalek
authors.forename: L J
authors.initials: LJ
authors.lastname: Humphries
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D006801:Humans; D011874:Radiometry / Q000295:instrumentation* / Q000592:standards; D012408:Rubber; D013627:Talc
chemical_list: D013627:Talc; D012408:Rubber