title: Track studies in water vapor using a low-pressure cloud chamber. I. Macroscopic measurements.
abstract: Techniques have been developed to operate a low-pressure cloud chamber with pure water vapor. Photographs have been obtained of the tracks arising in this medium from the passage of ionizing radiation. The sources used were low-energy X rays, 242Cm alpha particles, and low-energy protons. Track lengths of the electrons were similar to those found previously in tissue-equivalent gas. W values of 35.6 +/- 0.4 and 32.6 +/- 0.6 eV per ion pair for carbon and aluminum X rays also compare closely with those in tissue-equivalent gas, but are somewhat higher than the predictions of Monte Carlo calculations. Differential w values were obtained: for alpha particles of energy 5.3 MeV the value was 33.0 +/- 3.0 eV per ion pair; for protons of energy 390, 230, and 85 keV the values were 30.6 +/- 1.9, 31.9 +/- 2.0, and 33.6 +/- 3.4 eV per ion pair. The energy losses of protons in water vapor were measured in a second (dummy) chamber used for energy calibration. Results support Janni's values of stopping power for protons in the energy range 40-480 keV.
authors.affiliation: A.E.A. Technology, Harwell Laboratory, Didcot, Oxon, United Kingdom.
authors.forename: G P
authors.initials: GP
authors.lastname: Stonell
authors.forename: M
authors.initials: M
authors.lastname: Marshall
authors.forename: J A
authors.initials: JA
authors.lastname: Simmons
mesh_terms: D000512:Alpha Particles; D004583:Electrons; D011312:Pressure; D011522:Protons; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods; D014835:Volatilization; D014867:Water; D014965:X-Rays
chemical_list: D011522:Protons; D014867:Water