title: W values for helium particles in nitrogen and argon in the energy range from 10 keV to 10 MeV.
abstract: An analytical model is presented that facilitates the calculation of the mean energy W expended to produce an ion pair upon complete slow-down for heavy particles in gases. This model is applied to the calculation of the W values for helium beams of energies from 10 keV to 10 MeV in argon and nitrogen gas. Good agreement of the theoretical W values with the experimental ones is found in the case of nitrogen. The theoretical results for argon are about 15% higher than the experimental values throughout the entire energy range. However, they show a similar energy dependence. The theoretical and the experimental W values for nitrogen exhibit an extraordinary energy dependence at energies around 300 keV, at which the cross-section for charge exchange cycles reaches the maximal value. Such a phenomenon was also observed in the case of the W values for protons, which show a clear minimum at the energy of the maximal cross-section for charge exchange cycles.
authors.affiliation: Physikalisch-Technische Bundesanstalt, Braunschweig, Germany.
authors.forename: W Y
authors.initials: WY
authors.lastname: Baek
authors.forename: B
authors.initials: B
authors.lastname: Grosswendt
mesh_terms: D001128:Argon; D005740:Gases; D006371:Helium; D006801:Humans; D008433:Mathematics; D008962:Models, Theoretical; D009584:Nitrogen; D011878:Radiotherapy / Q000295:instrumentation* / Q000379:methods; D011879:Radiotherapy Dosage
chemical_list: D005740:Gases; D006371:Helium; D001128:Argon; D009584:Nitrogen