Biomaterial Database

Energy dependence of W for alpha particles in N2, CO2, CH4, Ar, H2 and Rossi-type tissue-equivalent gases. 1978

M N Varma, and J W Baum

Average energy required to form an ion pair (W) was determined in N2, CO2, CH4, Ar, H2 and Rossi-type tissue-equivalent gas. Alpha particles from a 241Am source were used. W was determined at alpha energies of 5.37, 3.12, 1.08 and 0.46 MeV. The ratio of total ionisation produced (for fixed alpha particle energy) in experimental gas to that produced in argon was measured. This ratio was then multiplied by the previously determined W value for argon gas (26.29 eV per ion pair) to yield W for various experimental gases. Energy of the 241Am alpha particles was degraded by using air as an absorbing material. Empirical relations W = alpha + betaE-1/2 and W = alpha1 + beta1E-1 were fitted to the experimental data. Both functions fit reasonably well in the range 0.4--5.37 MeV. Below about 0.4 MeV the first function provides a better fit to the data of Boring et al. (1965).

UI	MeSH Term	Description	Entries
D007477	Ions	An atom or group of atoms that have a positive or negative electric charge due to a gain (negative charge) or loss (positive charge) of one or more electrons. Atoms with a positive charge are known as CATIONS; those with a negative charge are ANIONS.
D008697	Methane	The simplest saturated hydrocarbon. It is a colorless, flammable gas, slightly soluble in water. It is one of the chief constituents of natural gas and is formed in the decomposition of organic matter. (Grant & Hackh's Chemical Dictionary, 5th ed)
D009584	Nitrogen	An element with the atomic symbol N, atomic number 7, and atomic weight [14.00643; 14.00728]. Nitrogen exists as a diatomic gas and makes up about 78% of the earth's atmosphere by volume. It is a constituent of proteins and nucleic acids and found in all living cells.
D011854	Radiochemistry	The study of the chemical and physical phenomena of radioactive substances.	Radiochemistries
D002245	Carbon Dioxide	A colorless, odorless gas that can be formed by the body and is necessary for the respiration cycle of plants and animals.	Carbonic Anhydride,Anhydride, Carbonic,Dioxide, Carbon
D005740	Gases	The vapor state of matter; nonelastic fluids in which the molecules are in free movement and their mean positions far apart. Gases tend to expand indefinitely, to diffuse and mix readily with other gases, to have definite relations of volume, temperature, and pressure, and to condense or liquefy at low temperatures or under sufficient pressure. (Grant & Hackh's Chemical Dictionary, 5th ed)
D006859	Hydrogen	The first chemical element in the periodic table with atomic symbol H, and atomic number 1. Protium (atomic weight 1) is by far the most common hydrogen isotope. Hydrogen also exists as the stable isotope DEUTERIUM (atomic weight 2) and the radioactive isotope TRITIUM (atomic weight 3). Hydrogen forms into a diatomic molecule at room temperature and appears as a highly flammable colorless and odorless gas.	Protium,Hydrogen-1
D000512	Alpha Particles	Positively charged particles composed of two protons and two NEUTRONS, i.e. equivalent to HELIUM nuclei, which are emitted during disintegration of heavy ISOTOPES. Alpha rays have very strong ionizing power, but weak penetrability.	Alpha Rays,Alpha Radiation,Radiation, Alpha,Alpha Particle,Alpha Ray,Particle, Alpha,Particles, Alpha,Ray, Alpha,Rays, Alpha
D001128	Argon	A noble gas with the atomic symbol Ar, atomic number 18, and atomic weight 39.948. It is used in fluorescent tubes and wherever an inert atmosphere is desired and nitrogen cannot be used.	Argon-40,Argon 40