title: Ultrasonic absorption in polymer gel dosimeters.
abstract: Ultrasonic absorption in polymer gel dosimeters was investigated. An ultrasonic interferometer was used to study the frequency (f) dependence of the absorption coefficient (alpha) in a polyacrylamide gel dosimeter (PAG) in the frequency range 5-20 MHz. The frequency dependence of ultrasonic absorption deviated from that of an ideal viscous fluid. The presence of relaxation mechanisms was evidenced by the frequency dependence of alpha/f(2) and the dispersion in ultrasonic velocity. It was concluded that absorption in polymer gel dosimeters is due to a number of relaxation processes which may include polymer-solvent interactions as well as relaxation due to motion of polymer side groups. The dependence of ultrasonic absorption on absorbed dose and formulation was also investigated in polymer gel dosimeters as a function of pH and chemical composition. Changes in dosimeter pH and chemical composition resulted in a variation in ultrasonic dose response curves. The observed dependence on pH was considered to be due to pH induced modifications in the radiation yield while changes in chemical composition resulted in differences in polymerisation kinetics.
authors.affiliation: Centre for Medical, Health and Environmental Physics, Queensland University of Technology, GPO Box 2434, Brisbane, QLD 4001, Australia.
authors.forename: Melissa L
authors.initials: ML
authors.lastname: Mather
authors.forename: Anthony F
authors.initials: AF
authors.lastname: Collings
authors.forename: Nick
authors.initials: N
authors.lastname: Bajenov
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Whittaker
authors.forename: Clive
authors.initials: C
authors.lastname: Baldock
mesh_terms: D000180:Acrylic Resins; D005782:Gels; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007368:Interferometry; D011874:Radiometry / Q000295:instrumentation*; D014465:Ultrasonics
chemical_list: D000180:Acrylic Resins; D005782:Gels; C016680:polyacrylamide gels