Accurate evaluation of stopping and straggling mean excitation energies for N, O, H/sub 2/, N/sub 2/, O/sub 2/, NO, NH/sub 3/, H/sub 2/O, and N/sub 2/O using dipole oscillator strength distributions. A test of the validity of Bragg's rule

Journal Article · Sun May 01 00:00:00 EDT 1977 · Radiat. Res.; (United States)

DOI:https://doi.org/10.2307/3574587· OSTI ID:7323281

Zeiss, G D ^[1]; Meath, W J; MacDonald, J C.F.; Dawson, D J

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1. Univ. of Western Ontario, London

Accurate values of the mean excitation energy I/sub 0/ (occurring in the Bethe stopping cross section equation for fast charged particles) and the dipole oscillator strength sum S/sub 1/ and mean excitation energy I/sub 1/ (appearing in the equation for straggling given by Fano) have been determined for N, O, H/sub 2/, O/sub 2/, O/sub 2/, NH/sub 3/, H/sub 2/O, NO, and N/sub 2/O using dipole oscillator strength distributions. For energies for which the Bethe stopping theory is valid these results allow a quantitative test to be made of the reliability of Bragg's rule and of the analogous additivity rule for straggling. Difficulties arising from problems associated with the use of experimental stopping cross sections and the treatment of shell corrections, that have introduced uncertainty in previous studies of Bragg's rule, are avoided in the present work. Using the accurate results obtained for H/sub 2/, N/sub 2/, and O/sub 2/ as elemental values in the additivity relations, the additivity estimates of S/sub 1/, I/sub 1/, and I/sub 0/ obtained for N, O, NH/sub 3/, H/sub 2/O, NO, and N/sub 2/O agree with the accurate results to within 0.4, 0.9, and 4%, respectively. On the other hand, for the H atom large discrepancies (20--30%) between the accurate values for S/sub 1/, I/sub 1/, and I/sub 0/ and the estimates obtained by additivity occur and are due to major modifications in the electronic wavefunction in regions close to the proton that are caused by chemical binding. For heavier atoms this effect is relatively unimportant. For H/sub 2/, N/sub 2/, and O/sub 2/ calculated Bethe stopping cross sections are compared with experimental results and are used to discuss shell corrections to the Bethe stopping cross section equation.

• OSTI ID: 7323281
• Journal Information: Radiat. Res.; (United States), Vol. 70:2
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ALPHA PARTICLES
ABSORPTION
SLOWING-DOWN
AMMONIA
CHARGED-PARTICLE TRANSPORT
HYDROGEN
NITRIC OXIDE
NITROGEN
NITROUS OXIDE
OXYGEN
PROTONS
WATER
CORRECTIONS
CROSS SECTIONS
DISTRIBUTION
EXCITATION
OSCILLATOR STRENGTHS
BARYONS
CHALCOGENIDES
CHARGED PARTICLES
CRYOGENIC FLUIDS
ELEMENTARY PARTICLES
ELEMENTS
ENERGY-LEVEL TRANSITIONS
FERMIONS
FLUIDS
HADRONS
HYDRIDES
HYDROGEN COMPOUNDS
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NITROGEN OXIDES
NONMETALS
NUCLEONS
OXIDES
OXYGEN COMPOUNDS
RADIATION TRANSPORT
654001* - Radiation & Shielding Physics- Radiation Physics
Shielding Calculations & Experiments