A review of the program in space-radiation protection at the Langley Research Center is given. The relevant Boltzmann equations are given with a discussion of approximation procedures for space applications. The interaction coefficients are related to the solution of the many-body Schrodinger equations with nuclear and electromagnetic forces. Various solution techniques are discussed to obtain relevant interaction cross sections with extensive comparison with experiments. Solution techniques for the Boltzmann equations are discussed in detail. Transport computer code validation is discussed through analytical benchmarking, comparison with other codes, comparison with laboratory experiments, and measurements in space. Applications to missions to the Moon and Mars are discussed.

Transport Methods and Interactions for Space Radiations

Energy loss, range, path length, time-of-flight, straggling, multiple scattering, and nuclear interaction probability: In two parts. Part 1. For 63 compounds Part 2. For elements 1 ⩽ Z ⩽ 92

When an energetic ion traverses a polymer medium, it loses its energy by electronic and nuclear processes. In the past, considerable research efforts have been devoted to understand the effects of the electronic and nuclear processes in materials. There have been, however, some conflicting reports regarding the roles of electronic and nuclear stopping in producing property changes in polymeric materials, namely the magnitude of cross-linking and scission. A consensus derived from the work conducted at ORNL indicates that electronic stopping is largely responsible for cross-linking and nuclear stopping for scission, although both processes can cause cross-linking as well as scission. The most important parameter for cross-linking is found to be the energy deposited per unit ion path length or linear energy transfer (LET). The mechanisms involved with property changes are discussed by clarifying the concepts of nuclear and electronic stopping, LET, tracks, and spurs. Experimental evidence to support the views are presented. Also addressed are specific property changes induced by ion-beams, which may be of use for industrial applications.

Ion-beam modification of polymeric materials – fundamental principles and applications

A wide range of gas, liquid and solid state properties are calculated using most of the presently available potential functions for the water pair interaction. It is shown that no one model gives a satisfactory account of all three phases. We propose a new semi-empirical model that has some success as an effective pair potential in all three phases.

Intermolecular potential functions and the properties of water

Accurate values for the orientation-averaged long-range dipole-dipole dispersion energy coefficients, C 6(A, B), have been determined for all possible pair interactions involving ground state H, Li, N, O, H2, N2, O2, NH3, H2O, NO, and N2O. The calculations have been carried out by employing dipole oscillator strength distributions for these species that have been constructed (except in the case of H) by using discrete oscillator strength, photo-absorption, and high energy inelastic scattering data and by requiring the distributions to reproduce the Thomas-Reiche-Kuhn sum rule and, in the case of the molecules, available accurate refractivity and dispersion measurements for the relevant dilute gases. These oscillator strength distributions were also used to evaluate the refractivity R(λ), as a function of wavelength λ in the visible and ultra-violet region below the ultra-violet absorption thresholds, and the dipole oscillator strength sums S -2l , l = 1, 2, …, 7, for each atom and molecule. The calculated...

Dispersion energy constants C 6(A, B), dipole oscillator strength sums and refractivities for Li, N, O, H2, N2, O2, NH3, H2O, NO and N2O

Dipole oscillator strength distributions (DOSDs) have been constructed for ground state Li, N, O, H2, N2, O2, NH3, H2O, NO, and N2O by using experimental and theoretical photoabsoiption and high energy electron inelastic scattering cross sections Each DOSD is required to satisfy the Thomas–Reiche–Kuhn sum rule and additional constraints derived from available accurate experimental refractivity and dispersion measurements The DOSDs, the data and procedure used to construct the DOSDs, and the values of the dipole oscillator strength sums Sk and Lk (for a variety of k values) and related atomic and molecular properties obtained from the DOSDs are reported The discussion includes comments regarding the importance of the constraints imposed on the DOSD with respect to the evaluation of various dipole sums and properties and the accuracy of the results

Dipole oscillator strength distributions, sums, and some related properties for Li, N, O, H2, N2, O2, NH3, H2O, NO, and N2O

Dipole oscillator strength distributions (DOSDs) have been constructed for ground state ethane, propane, n-butane, n-pentane, n-hexane, n-heptane, and n-octane. Each DOSD is constructed by using available experimental and theoretical photoabsorption cross sections and by constraining the resulting dipole oscillator strength data to satisfy the Thomas–Reiche–Kuhn sum rule and molar refractivity constraints. The latter were obtained using available experimental refractive index measurements of relevant dilute gases. The recommended DOSDs, and the values of integrated "band" oscillator strengths and the dipole oscillator strength sums Sk and Lk (for a variety of k values) obtained from them, are reported. The discussion includes an analysis of the accuracy of the results and a comparison with available literature values, which are scarce, for the dipole properties of the alkanes.

Dipole oscillator strength distributions and sums for C2H6, C3H8, n-C4H10, n-C5H12, n-C6H14, n-C7H16, and n-C8H18

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 04, 09, and 4%, respectively On the other hand, for the H atommore » 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« less

Accurate Evaluation of Stopping and Straggling Mean Excitation Energies for N, O, H 2 , N 2 , O 2 , NO, NH 3 , H 2 O, and N 2 O Using Dipole Oscillator Strength Distributions: A Test of the Validity of Bragg's Rule

Experimental and theoretical photoabsorption and photoionization cross sections and quantum mechanical sum rules are used to construct nonrelativistic dipole oscillator strength distributions for the following ''processes'' involving the ground state water molecule: total absorption, total ionization, total excitation to neutral species, and partial ionization to the ions H$sub 2$O$sup +$, OH$sup +$, and H$sup +$. These distributions are used to evaluate a number of dipole oscillator strength sums that are important in the radiation physics and chemistry of the water molecule and in the evaluation of the dipole properties of H$sub 2$O. Various parameters that occur in the Bethe--Born approximation for the total inelastic scattering cross sections that characterize the energy loss spectrum of fast-charged particles in water vapor are also evaluated and, where possible, compared with experimental results. The dipole oscillator strength sums are also used to evaluate the mean excitation energies for the stopping power and straggling of fast-charged particles in water vapor; I$sub 0$ = 70.8 eV and I$sub 1$ = 935 eV. (2 figs, 5 tables, 67 refs)

Dipole spectrum of water vapor and its relation to the energy loss of fast-charged particles.

The zeroth-order theory of intermolecular forces is used to derive additivity relations for rotationally averaged molecular dipole properties and dispersion energy constants by assuming that a molecule is comprised of non-interacting atoms or molecules. Some of the additivity rules are new and others, for example the mixture rule for dipole oscillator strength distributions (DOSDs), Bragg's rule for stopping cross sections and Landolt's rule for molecular refractivities, are well known. The additivity rules are tested by using previously constructed DOSDs and reliable values for the dipole oscillator strength sums Sk , Lk and Ik , and dispersion energy constants C 6, for H, N, O, H2, N2, O2, NO, N2O, NH3 and H2O as models. It is found that additivity is generally unreliable for estimating molecular properties corresponding to k < -2. Generally for k ≥ -2 and for C 6, and if the hydrogen molecule is used to represent the hydrogen atom in the additivity rules, the additivity relations yield results that are...

J. C. F. MacDonald

Papers

Dipole oscillator strength distributions, sums, and some related properties for Li, N, O, H2, N2, O2, NH3, H2O, NO, and N2O

Dipole oscillator strength distributions and sums for C2H6, C3H8, n-C4H10, n-C5H12, n-C6H14, n-C7H16, and n-C8H18

Accurate Evaluation of Stopping and Straggling Mean Excitation Energies for N, O, H 2 , N 2 , O 2 , NO, NH 3 , H 2 O, and N 2 O Using Dipole Oscillator Strength Distributions: A Test of the Validity of Bragg's Rule

Dipole spectrum of water vapor and its relation to the energy loss of fast-charged particles.

On the additivity of atomic and molecular dipole properties and dispersion energies using H, N, O, H2, N2, O2, NO, N2O, NH3 and H2O as models