Naslov
Mean energy required to form an ion pair (W value) for various ionizing particles in air

Autori
Krajcar Bronić, Ines

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Abstracts. Third European IRPA Congress: Radiation protection - science, safety and security / - Helsinki : International Radiation Protection Association (IRPA), 2010, 107-107

ISBN
978-952-478-549-5

Skup
Third European IRPA Congress: Radiation protection - science, safety and security

Mjesto i datum
Helsinki, Finska, 14.06.2010. - 18.06.2010

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
W value; radiotherapy; electrons; protons; heavy ions

Sažetak
The mean energy required to form an ion pair (W value) is defined as the mean energy spent by the incident particle of energy E for the formation of an electron - ion pairs after complete dissipation of the initial energy, W = E/N, where N is the total number of produced electron-ion pairs. For high-energy particles in thin media, when only a fraction of the particle energy (dE) is deposited in a medium, it is necessary to consider the differential w value, w = dE/dN. For sufficiently high incident energy, W value is approximately constant, and w = W is a good approximation. Available data on W or w are often fragmented, dispersed, and missing systematic. Several compilations and reviews, such as ICRU Report 31 and IAEA TECDOC 799, provide a basis for assessing the present knowledge of W values for different charged particles in various gases. Most available data exist for electrons. The W value for high-energy electrons (>10 keV) in dry air is well defined, 33.97 ± 0.05 eV, and also a dependence on air humidity has been studied. W and w values for high-energy protons (>20 MeV) have been also carefully analyzed. The value of 34.23 eV, with ±0.4%, has been recommended. The existing W or w data for heavy ions used in radiotherapy (He, C, Ne, Si, Ar) are fragmentary and most of them are measured for relatively low energies (<1 MeV/amu) where major variations in energy dependence are observed. There is a lack of experimental data at energies >1 MeV/amu of interest for radiotherapy. For carbon ions a few sets of experimental data on W exist at low energies and have been recently extended to higher energies. The average W value for C ions at energies >10 MeV/amu is 34.7 ± 0.9 eV, which is slightly higher than the recommended value (34.5 ± 0.5 eV) for all ions at energies >1 MeV/amu. There is a need for new W value measurements for heavy-ions in air at energies >10 keV/amu, and especially for C ions of several hundreds of MeV/amu that are of interest in carbon-ion therapy.

Izvorni jezik
Engleski

Znanstvena područja
Fizika, Geologija

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