Energy Loss Per Ion Pair for Protons in Various Gases

The w-value in air for proton therapy beams

“…These measurements were made at low energies (o4 MeV) and the values for air have been deduced here from measurements in argon (Parks et al, 1972) and nitrogen (Thomas and Burke, 1985) using appropriate conversion factors, viz., (W air /W Ar ) p ¼ 0.963 and (W air / W N 2 ) p ¼ 1.313. These ratios are the means of those measured by Hiraoka et al (1989) and Larson (1958). No additional uncertainties were assigned to the data because of the use of these ratios.…”

“…Eight sets of data (Bakker and Segre´, 1951;Delacroix et al, 1997;Denis et al, 1990;Hiraoka et al, 1989;Larson, 1958;Petti et al, 1986;Palmans et al, 1996 (the same result is given in Seuntjens et al, 1994); Siebers et al, 1995) were used In the ICRU 59 assessment of (w air ) p values. The same data sets were used in the TRS 398 evaluation (IAEA, 2000).…”

“…In the latter case a median (w air ) p value of 34.23 J C À1 in dry air was determined with a relative standard uncertainty of 0.4% (0.13 J C À1 ) from (w air ) p -values supplied by the IAEA (S. M. Vatnitsky, personal communication, 2005) and using the method of weighted medians (Muller, 2000). For the Larson (1958) data point at 1.83 MeV (35.18 J C À1 ) an uncertainty of 70.21 J C À1 was used in TRS 398, although the uncertainty given in the original publication is 70.42 J C À1 . Bakker and Segre´(1951) do not give an uncertainty for their data point measured at 340 MeV, which was derived by comparing measurements in air to measurements in argon made by Chamberlain et al (1951).…”

“…Larson (1958) measured the (W air ) p -value (i.e. the protons lose all their energy in the gas cavity) and therefore made an absolute measurement not dependent on the stopping power in air.…”

Determination of the airw-value in proton beams using ionization chambers with gas flow capability

“…The first method measures the energy of particles by time-of-flight, magnetic deflection, or residual range, both before and after they pass through a long column-shaped ionization chamber. [2][3][4] The energy lost in the column is divided by the charge produced and collected in the column. Corrections for delta-rays and scattered particles are extremely important when using this energy loss method.…”