High-energy Bombardment Research Articles

Cosmic-ray-produced 53Mn in thirty-one meteorites

Cosmic-ray-produced 53Mn (t ½ = 3.7 × 10 6years) has been determined by neutron activation analysis in twenty-two chondrites including three Antarctic meteorites: Yamato-7301 (j), -7305 (k) and -7304 (m). 53Mn was also measured in four mesosiderites, three iron meteorites, Bencubbin (unique) and Udei Station (iron with silicate inclusions). In addition, preliminary results for 10Be (1.6 × 10 6 years) were obtained in the Yamato meteorites using a low-background needle GM counter. Based on published values of rare gas ages, corrections were made for undersaturation; the average specific saturation activities of 53Mn were found in the range 450 ± 90dpm 53Mn/kg Fe in most of the chondrites and 490 ± 75dpm 53Mn/kg Fe in the mesosiderites. Two meteorites had extremely low contents of 53Mn: 102 ± 6 in Yamato-7301 and 48 ± 3dpm 53Mn/kg Fe in Bondoc. The Bondoc mesosiderite was already known to have a low concentration of cosmogenic radionuclides due to its large pre-atmospheric size. Several possible mechanisms are discussed to explain the low 53Mn activity in Yamato-7301: (1) long terrestrial age of about 7 m.y.; (2) low production rate of 53Mn due to heavy pre-atmospheric shielding (>70cm); (3) multi-stage irradiation history resulting in an undersaturation of 53Mn; and (4) a mechanism in which two or three of the above factors are combined. The ratio of 53Mn production rate in Ni to that in Fe has been estimated to be 1/3, based on the measurements of 53Mn in the metallic and silicate phases of St. Séverin meteorite, as well as on published results of some high-energy bombardment experiments.

The chemical evolution of molecular clouds

view Abstract Citations (149) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The chemical evolution of molecular clouds. Iglesias, E. Abstract The nonequilibrium chemistry of dense molecular clouds (10,000 to 1 million hydrogen molecules per cu cm) is studied in the framework of a model that includes the latest published chemical data and most of the recent theoretical advances. In this model the only important external source of ionization is assumed to be high-energy cosmic-ray bombardment; standard charge-transfer reactions are taken into account as well as reactions that transfer charge from molecular ions to trace-metal atoms. Schemes are proposed for the synthesis of such species as NCO, HNCO, and CN. The role played by adsorption and condensation of molecules on the surface of dust grains is investigated, and effects on the chemical evolution of a dense molecular cloud are considered which result from varying the total density or the elemental abundances and from assuming negligible or severe condensation of gaseous species on dust grains. It is shown that the chemical-equilibrium time scale is given approximately by the depletion times of oxygen and nitrogen when the condensation efficiency is negligible; that this time scale is probably in the range from 1 to 4 million years, depending on the elemental composition and initial conditions in the cloud; and that this time scale is insensitive to variations in the total density. Publication: The Astrophysical Journal Pub Date: December 1977 DOI: 10.1086/155727 Bibcode: 1977ApJ...218..697I Keywords: Chemical Evolution; Cloud Physics; Interstellar Chemistry; Interstellar Gas; Molecular Spectra; Chemical Equilibrium; Interstellar Matter; Organic Compounds; Astrophysics full text sources ADS |

Use of Li(d,n) Neutrons for Simulation of Radiation Effects in Fusion Reactors

In this paper we show that the neutron spectrum from high-energy deuteron bombardment of a thick Li target is suitable for simulation of radiation effects in a fusion reactor. Neutron spectra from 15, 20, 25, 30 and 35-MeV deuterons incident, respectively, on a 2-cm thick Li target are reported. For these spectra, a recently-developed computer code was used to evaluate damage-energy cross sections, primary recoil energy distributions, and spectrum-averaged reaction cross sections in several metals. The results indicate that a (d,n) source can simulate the energy dependence of the recoil spectra, and the rate of helium production anticipated in a real fusion reactor

Luminescence in High-Energy-Irradiated Alkanes at Low Temperature

Abstract High-energy bombardment is well-known to produce luminescence in condensed systems which contain suitable scintillators. Such light emission has been observed for weak scintillators like benzene in sufficiently dilute solutions in aliphatic hydrocarbons and, more recently, even in pure liquid benzene. It is not observed in pure liquid alkanes. However, when suitable alkanesare reduced to sufficiently low temperature (e.g., 77 °K), irradiation with 60Co gammas produces a persistent luminescence, the decay curves of which show peculiar behavior characteristics. This report reviews the decay characteristics and spectra of glassy 2-methylpentane and 3-methylpentane as well as of glassy and crystalline i-pentane, reexamines the kinetics and the mechanism of the luminescence process, interprets the applicability of the decay law Io/I = 1 + αt, demonstrates that an excited state of the system (probably a charge-separated state) and not of an individual molecule is involved, presents evidence that the number of available (A and B type) luminescence sites is limited and depends on the history of the system and suggests that the nature of the emitting state may change with temperature. An important aspect of the theoretical considerations is that they suggest that at sufficiently low temperatures such luminescence can be observed even for hydrocarbons as simple as methane. The most recent work of Janssen, Lang, Hebert, and the authors shows that, although luminescence can be induced in hydrogen and the lower alkanes by irradiation of polycrystalline material at sufficiently low temperature, it appears only when the temperature is raised to certain definite temperatures characteristics of each of the alkanes. Some of these temperatures correspond to know transition points; others may correspond to other solid-state changes.

Yields and isomeric yield ratios of antimony isotopes from the interaction of 159 MeV to 18·2 GeV protons with uranium

Relative cross-sections have been measured for the formation of antimony isotopes of A = 115–131 by bombarding uranium with protons of energies from 159 MeV to 18·2 GeV. Absolute cross-sections have been measured at 570 MeV and 18·2 GeV. The isotopic yield distributions show a broadening towards lower mass numbers when the bombarding energy increases, but also a remaining structure at the highest mass numbers A = 128–131. Isomeric yield ratios have also been determined at the same energies for the isomeric pairs of antimony at mass numbers 116, 120, 124, and 126. Each of these ratios remains constant throughout the energy range. Qualitative arguments are presented suggesting that structure observed in isotopic yield distributions in the mass region 115–140 from high-energy proton bombardments of uranium is due to a combined effect of the breadth of the spectrum of energies deposited in the target nucleus by the protons, and the large and rapid variations in the deformabilities of the nuclei when crossing the 82 neutron shell. The assumption that the fragments are “cold” in the scission configuration seems to be necessary. An attempt to calculate the angular momentum distribution of the primary fragments from knowledge of the isomeric yield ratios only leads to a demand for more, and accurate, recoil measurements giving kinetic energies and excitation energies of the fragments. In the course of this work, new determinations of the half-lives of seventeen nuclides from 115Sb to 131Sb were made on isotope-separated samples.

The application of diffusion theory to inert-gas motion in ion-bombarded solids: Diffusion theory for discrete media, part III

In spite of the growing recognition that the motion of inert gases in ion-bombarded solids constitutes a solid-state probe of potentially wide applicability, the relevant diffusion theory has been to some extent neglected. The present work attempts to extend this theory. Use is made of the equation for true diffusion, ∂C 1/ ∂t = ( D/ gl 2) ( ∂ 2 C 1/ ∂x 2, the equation for single-jump diffusion, dC 1/ dt = − k' C 1, as well as the modified equation of Hurst and Gaus, ∂C 1 ∂t = ( D gl 2 ) ( ∂ 2C 2 ∂x 2 )−(D/L 2λ 2)C 2 , where the final term takes permanent trapping into account. Various geometries and types of diffusion appropriate for ion bombardments are considered, namely the plane source (for very low or very high bombardment energies and for amorphous targets), the peaked or “ xe − x ” distribution (for low-mass, polycrystalline targets), the exponential or “ e − x ” distribution (for high-mass, polycrystalline targets and for bubble motion), the homogeneously labeled sphere (for high-energy bombardments of fine powders), and single-jump diffusion (for gas-release of the type “damage diffusion” or stage I). Expressions are given for analyzing integral depth distributions, measurements of cumulative gas-release and measurements of the rate of gas release.

Yields of potassium isotopes in high energy bombardments of vanadium, iron, cobalt, nickel, copper and zinc

Potassium isotopes 38K, 42K, 43K, 44K and 45K have been measured in interactions of protons at 590 MeV and 18·3 GeV with vanadium, iron, cobalt, nickel, copper and zinc. Absolute cross-sections were determined with reference to the Al(p,3pn) 24Na reaction and estimates were made of the yield of 39K, 40K and 41K. The results show a preferential loss by evaporation and spallation of about twenty nucleons in the bombardments at 18·3 GeV, an effect consistent with published Monte Carlo calculations. Predictions of the 39K, 40K and 41K cross sections should be of relevance to studies of the potassium content of iron meteorites.

THE ABSORPTION OF HIGH-ENERGY RADIATION, A MONTE CARLO STUDY: III. DENSITY AND TRANSPARENCY DISTRIBUTIONS

Random spherical arrays of rigid spheres are being studied as a model for a nucleus under high-energy bombardment. This paper reports on the distribution of sphere centers, the matter distribution, and the transparency for such arrays. Low (12.5%) and high (42.2%) nominal densities are treated for arrays numbering 27 and 216 spheres. At high densities a strong surface correlation of geometric origin is observed. Analytic formulas are presented which in general adequately represent the Monte Carlo data.

Cosmogenic Rare Gas Ratios in Iron Meteorites

Rare gas abundances in iron meteorites are compared with cross section ratios from high energy bombardments. A meteoritic low-energy flux (below 1 Gev) of about 13 times the high energy flux (above 1 Gev) is found. About half the helium is produced by this low energy flux.

Excitation Functions up to 980 MeV for Proton-Induced Reactions in some Light Elements

A study has been made of some of the active products from the high energy bombardment of carbon, nitrogen, oxygen and fluorine. The ratios of cross sections to the 12C(p, pn)11C cross section were found and the excitation functions estimated. Deviations from a monotonic decrease of cross section with energy for some reactions have been found and are discussed. Evidence exists for a marked dependence of the (p, pn) cross section on the energy level structure of the residual nucleus.

Production of Deuterons in High-Energy Nucleon Bombardment of Nuclei and Its Bearing on Nuclear Charge Distribution

A study has been made of deuterons produced at wide angles to a beam of 300-Mev neutrons and a beam of 300-Mev protons. The cross-section dependence on atomic number for these deuterons for light elements can be written as $\ensuremath{\sigma}=k{A}^{1.2}$. This fact and the energy spectra and angular distribution of the deuterons show that the process that forms these deuterons is related to the indirect pick-up process described by Bransden. This is a two-step process in which the incident nucleon, or its collision partner, is scattered and then picks up a deuteron-forming partner in the same nucleus. A yield of tritons has also been observed which has the same $A$-dependence and is presumably made by a similar process. The $A$-dependence of the deuteron-production cross section also suggests that these deuterons are made on the nuclear surface. Because of this $A$ dependence, a comparison of the deuteron yields using an incident neutron beam and an incident proton beam can give information about the relative numbers of neutrons and protons on the surface of the nucleus. An analysis of this sort leads to a possible conclusion that for heavy nuclei there is a nuclear skin rich in neutrons. For light nuclei the effect is not observed. If this skin is composed only of neutrons its thickness must be about 0.8\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ cm for lead.

Studies on the luminescence efficiency of biological compound solutions

All biological compound solutions tested under high-energy gamma bombardment quenched the water luminescence by no more than a factor of two. The values for relative luminescence of the 10 −2 molar solutions ranged from 94% for glycine to 56% for uric acid. Typical concentration-effect curves indicated definite quenching of the luminescence with increasing solute concentration. Two of the biological compound solutions, tryptophan and glutathione, showed a marked relation between solution pH and luminescence efficiency.

Analysis of Secondary Particles Resulting from High-Energy Nuclear Bombardment

Experimental studies have been made of the low-energy yields of secondary particles resulting from high-energy bombardment. For this purpose, thin foils of Be, Al, Ni, Ag, Au, and U have been bombarded by an internal beam of 375-Mev alphas, 332-Mev protons, and 187-Mev deuterons. Secondary particles emerging from the disintegration of the nucleus at 0\ifmmode^\circ\else\textdegree\fi{} to the incident beam direction are magnetically analyzed and detected in nuclear emulsions located beneath the median plane of the 184-inch cyclotron. There are three specific positions for these emulsions corresponding to energies of the secondary protons and of alpha particles of approximately 6, 10, and 20 Mev. This apparatus was modified to make a special study of the secondary alpha and proton yields by including two extra plates so that 10 energy points could be taken in the range from approximately 5 to 22 Mev. The angular distribution of secondary particles has also been measured for 240-Mev alpha bombardment of Be, Al, Ni, and Ag. Here, secondary particles emitted at 0\ifmmode^\circ\else\textdegree\fi{}, 45\ifmmode^\circ\else\textdegree\fi{}, and 135\ifmmode^\circ\else\textdegree\fi{} are detected in nuclear emulsions at positions for which the secondary proton and alpha energy is approximately 6 Mev. A secondary particle is identified by measurement of its radius of curvature upon entering the emulsion and its range and specific ionization in the emulsion. A considerable yield of hydrogen and helium isotopes as well as of particles of higher atomic number is found. The relative yields of the secondary protons and alpha particles for each element and for each bombardment are shown as a function of energy. The results, while found to be consistent with the predictions of an evaporation model, also indicate that a large percentage of secondary protons and alphas are directly knocked out of the nucleus.

Yields of Low-Energy Protons and Alphas Resulting from High-Energy Bombardment of Ag

Yields of Low-Energy Protons and Alphas Resulting from High-Energy Bombardment of Ag

Chemical State of Radioactive Phosphorus (32P)

NUCLEAR reactions initiated by heavy nucleons involve the transfer of considerable energy from the incident particle to the target nucleus. The amount of energy carried off by the recoiling nucleus is generally sufficient to break chemical bonds, or in irradiated crystalline substances to move the atom to a new site in the lattice. Little information is available about the chemical form in which these recoil atoms come to rest, but useful surveys of previous work have been given by Libby1, and by Edwards and Davies2. A study of the literature shows that the knowledge of chemical behaviour following high-energy particle bombardments is especially lacking, the well-known Szilard–Chalmers effect having been mainly studied with slow neutrons.