Total Interaction Cross Sections Research Articles

The interactions of high-energy, highly charged Xe ions with fullerenes

Ionization and fragmentation have been measured for C 60 molecules bombarded in the vapor phase by Xe 35+ and Xe 18+ ions with energies in the range 420–625 MeV. The CM energies exceeded those used in previous studies by several orders of magnitude. We present the observed mass distribution of positively charged fragments together with a theoretical model indicating that the total interaction cross section contains roughly equal contributions from (a) excitation of the giant plasmon resonance, and (b) large-energy-transfer processes that lead to multiple fragmentation of the molecule.

The interactions of high-energy, highly charged Xe ions with buckyballs

Ionization and fragmentation have been measured for C 60 molecules bombarded by highly charged (up to 35 +) xenon ions with energies ranging up to 625 MeV. The observed mass distribution of positively charged fragments is explained in terms of a theoretical model indicating that the total interaction cross section contains roughly equal contributions from (a) excitation of the giant plasmon resonance, and (b) large-energy-transfer processes that lead to multiple fragmentation of the molecule. Preliminary results of measurements on VUV photons emitted in these interactions are also presented.

One- and two-neutron removal from the radioactive secondary projectiles 56Ni and 52Fe

Abstract A method for measuring the cross sections for the neutron removal from relativistic secondary projectiles by means of a two-stage magnetic spectrometer is presented. Its application to the 1n- and 2n-removal from 56 Ni and 52 Fe at 470 A ·MeV in an aluminum target is described. The results are compared to the intranuclear-cascade plus evaporation model and to the statistical abrasion-ablation model. The influence of the nuclear surface on the few-nucleon removal reactions is discussed. The neutron-removal cross sections are combined with total charge-changing cross sections to obtain the total interaction cross sections of 56 Ni and 52 Fe.

Doubly differential and total ionization cross sections of alkali atoms

A variant of the Born approximation is used to calculate doubly differential and total ionization cross sections for the (e, 2e) interaction between an electron and the alkali atoms, lithium through rubidium. The calculation is done for the ionization of the valence electron. A primary purpose of the work is to establish the basic features of the doubly differential cross sections. The total cross section results compare well with the few experimental data available.

Cross sections for the interaction of multiply charged Ta and Ti ions with H2 and He at low collision energies

Total interaction cross sections for collisions of multiply charged Ta and Ti ions with H2 and He as targets have been determined in a gas chamber experiment. A laser produced plasma has been used as the ion source. Energy spectra of total cross sections are obtained by the combined time-of-flight/retarding potential method for collision energies from several eV amu-1 to about 30 eV amu-1. This energy range is of particular interest in the plasma edge region of fusion reactors. Generally it is found that the cross sections for H2 range from about 3*1015 cm2 to 10-14 cm2 while those for He are smaller by about an order of magnitude. There is experimental evidence that the essential contribution to the measured total cross sections can be attributed to electron capture.

Total charge-changing cross sections for neutron-deficient isotopes from58Ni fragmentation

At the projectile-fragment separator FRS of GSI, relativistic secondary beams of about 520 MeV/nucleon were produced by fragmentation of a primary beam of58Ni at 650 MeV/nucleon in a beryllium target. By means of aΔE—Bρ—TOF measurement, the fragments have been identified and their charge-changing probabilities in targets of CH2, C, Al, and Pb have been determined. We describe the results for the total charge-changing cross sections in this first paper, whereas a second article deals with the partial charge-changing cross sections. At the drip line, the measured charge-changing cross sections exhaust close to 100% of the total interaction cross sections as calculated with semiempirical models. The measurements at the proton drip line with low-Z targets indicate that only a very small increase of the cross sections may be observed, whereas the measurements with a lead target show that no significant increase of the total charge-changing cross sections is present which would be a hint for low-lying dipole strength. Our experimental data are compared to Glauber-type calculations.

Ionization and Multifragmentation ofC60by High-Energy, Highly Charged Xe Ions

Ionization and multifragmentation have been observed in ${\mathrm{C}}_{60}$ molecules bombarded by ${\mathrm{Xe}}^{35+}$ and ${\mathrm{Xe}}^{18+}$ ions with energies in the range 420-625 MeV. The c.m. energies exceeded those used in previous studies by several orders of magnitude. We present the observed mass distribution of positively charged fragments together with a theoretical model indicating that the total interaction cross section contains roughly equal contributions from (a) excitation of the giant plasmon resonance, and (b) large-energy-transfer processes that lead to multiple fragmentation of the molecule

Statistical abrasion of nucleons from realistic nuclear-matter distributions

A description of peripheral nuclear collisions at high energies in terms of quasi-free nucleon-nucleon collisions is proposed. The statistical removal of nucleons from diffuse nuclear-density distributions is formulated in the framework of the abrasion model. Based on the nucleon-nucleon cross sections, energy-dependent partial and total abrasion cross sections are obtained. The total abrasion cross section is found to be equivalent to the total interaction cross section resulting from a microscopic Glauber-type calculation. In contrast to geometrical and optical abrasion models, the statistical abrasion formalism describes the fluctuations of the prefragment neutron-to-proton ratio without need for further assumptions. The predictions of the statistical abrasion model are compared to experimental data.

Secondary radiations in spacecraft shieldings

Some problems are discussed which relate to the generation of secondary radiation under the effects of heavy charged cosmic ray particles in spacecraft shielding and in biological tissue. Methods for obtaining the total and differential inelastic interaction cross sections are recommended for use in the calculation of heavy charged particle transport in the shielding. The most extensively used methods for calculating heavy charged particle passage through matter are appraised. The results of calculating cosmic ray doses in biological tissue behind shielding, which allow for the secondary particle contribution, are presented. All the calculations have been made using the set of radiation protection standards approved by the Russian State Committee for Standards. The set of standards has been verified experimentally on board satellites of the Cosmos series.

Total Interaction Cross Sections of Several Sugars for133Ba Photons

Total attenuation cross sections of several sugars have been measured for 133Ba photons in a narrow-beam geometry setup, by using a hyperpure germanium detector. The values are compared with the va...

Total and 2n-removal cross sections of the neutron-rich isotopes 8,9,11Li

Total interaction cross sections have been measured for 8Li on C and Pb targets, for 9Li on C, Al, Cu, Sn and Pb targets, as well as for 11Li on C, Sn and Pb targets at about 80 MeV/nucleon. In addition, 2n-removal cross sections for 11Li have been extracted. These measurements are used to determine the nuclear and the electromagnetic part of the cross sections for the different projectile-target combinations. The experimental results are compared to different model calculations. These comparisons allow one to draw conclusions on the matter density distribution of the neutron-rich lithium isotope 11Li. By comparing our data on the electromagnetic dissociation of 11Li with all the other data available in the literature, we are able to put constraints on the dipole-strength distribution in 11Li.

DYNAMICAL STRING MODEL ON THE BASIS OF A SEMICLASSICAL UNIFIED STRING-FLUX TUBE MODEL

We present the dynamical string model of high-energy hadronic processes, developed by us recently. To describe the dynamical aspects of the decay of hadrons and those of the hadron-hadron interaction correctly, a semiclassical unified string-flux tube model of hadrons is used. Specific aspects of this model are discussed: (i) the transverse extension of gluon flux tubes, (ii) the decay of highly excited flux tubes, (iii) the gluon structure functions of hadronic flux tubes and their connection with the total cross section of the flux tube-flux tube interaction at high energies. The dynamical string model is applied to the numerical simulation of e+e− annihilation and pp collision at high energies.

Reaction cross section measurements of the neutron-rich isotopes8,9,11Li at 80 MeV/nucleon

Total interaction cross sections have been measured for8Li on C and Pb targets, for9Li on C, Al, Cu, Sn and Pb targets as well as for11Li on C, Sn and Pb targets. For each beam, we also used a plastic scintillator as target. The measurements with the scintillator targets are used to extract reduced nuclear radii of the lithium isotopes. These radii are then used for the calculation of the nuclear part of the total cross section for the other targets. The total electromagnetic-dissociation (EMD) cross sections have been deduced and are compared to different models. A strong target-charge-dependent EMD cross section is measured for11Li reaching 2.96−0.82+0.84 b for the Pb target. In the9Li case, a large EMD cross section for high-Z targets has been observed which amounts to 0.75 ± 0.45 b for the Pb target. The EMD cross sections of both,9Li and11Li, may be understood by the giantdipole-resonance model.

Is the cosmic-ray hadron shower a fractal?

The possible fractal nature of trajectories drawn by cosmic-ray particles in the atmosphere is investigated. In the course of the propagation of a primary cosmic-ray particle from the top of the atmosphere to sea level, it develops a ramified hadron shower, which is constituted mainly of pions and kaons. These hadrons are multiply produced at every collision of the hadron with an air nucleus. If the cross section corresponding to a definite multiplicity of hadrons decreases with the increase of energy E, in such a manner as to be reciprocally proportional to some powers of E, the resultant pattern of the shower possibly becomes fractal. Since the total interaction cross section is considered to be a superposition of many fundamental cross sections each of which corresponds to a definite multiplicity, the actual hadron shower can be interpreted as a superposition of many fractals each of which has an unique fractal dimension. The total energy of the shower has appeared to obey Laplace's equation under a quasi-stationary condition. Some ramified patterns of the cosmic-ray hadron shower are derived with computers.

Charge, mass, and energy changes during fragmentation of relativistic nuclei.

We have examined the fragmentation of relativistic lanthanum and gold nuclei incident on targets of polyethylene, carbon, aluminum, and copper. Attention has been concentrated on those fragments whose atomic numbers were only changed by +1 to -3 from those of the incident nuclei. The cross section for the production of fragments with increased charge is about 10% that for fragments that have lost one charge, or about 1% of the total interaction cross section. We find that the velocity distributions of these fragments can be explained by assuming that they also lose significant numbers of neutrons when they pick up or lose charge, without a need to invoke any energy or momentum loss in the interaction, although we cannot exclude small losses. In particular, we cannot confirm the recent report of large energy losses during the charge pickup process. The relative numbers of neutrons lost can be represented by a simple Gaussian model, and, for those fragments with decreased charge, are much larger than the proton losses. These fragments consequently have large proton excesses and will be highly unstable.

The status of PNC experiments on nucleon-nucleon and few-nucleon systems at low energies

The history of studies of parity nonconserving (PNC) effects in nuclear interactions was initiated nearly 25 years ago by the first successful observation of two such effects in electromagnetic nuclear decays, namely, gamma -radiation asymmetry in the capture of polarized neutrons by nuclei and gamma -ray circular polarization in the decay of polarized nuclei. In recent years a number of other effects have been observed including: (a) parity-forbidden alpha -decay of 16O; (b) asymmetry in nuclear fission fragment ejection with respect to spin direction of captured neutron; (c) spin rotation of neutrons passing through matter; (d) dependence of total thermal and resonant neutron interaction cross sections on neutron helicity; (e) gamma -ray asymmetry and circular polarization in the integral gamma -ray spectrum of the (n, gamma ) reaction on nuclei; (f) asymmetry of proton ejection in the (n,p) reaction on polarized neutrons.

Effective atomic number studies in different soils for total photon interaction in the energy region 10–5000 keV

Effective atomic numbers ( Z eff) of 12 different soil samples were computed for total photon interaction cross sections using theoretical data over a wide energy region from 10 to 5000 keV. It is seen that Z eff of a composite material, like soil, changes with a change in energy. With an increase in energy from 10 to 20 keV, Z eff increases, then remains nearly constant up to 40 keV but decreases sharply from 40 to 400 or 500 keV, and a further comparatively small rate of decrease up to 1500 keV. However, there is a small but continuous increase in Z eff with photon energy increases of 1500–5000 keV. This significant change in Z eff of soil is due to variations in the domination of different interaction processes in different energy regions as well as to the large number of elements present in the soil.

Photon scattering from 90Zr below neutron emission threshold.

Cross sections for elastic and inelastic scattering of monochromatic photons from /sup 90/Zr have been measured for excitations between 8.1 and 10.5 MeV. The observed inelastic cross sections sigma/sub el//sub el//sub i/ correspond to transitions to the 02 , 21 , 22 , and 23 states. A simple theoretical description using the Brink-Axel hypothesis and estimates of the level density and of the total photon interaction cross section sigma/sub el//sub T/ gives predictions for the individual cross sections that are in very good agreement with data. The E1 strength corresponding to the inferred sigma/sub el//sub T/ amounts to about B(E1up-arrow)--0.5 eS fmS for the energy range under consideration.

Effective atomic numbers for low-energy total photon interactions in human tissues.

A new method is introduced in which the total photon interaction cross sections per electron of human tissues are used to define effective atomic numbers for blood, bone, brain, fat, heart, kidney, liver, lung, muscle, ovary, pancreas, spleen, and water. These effective atomic numbers are equal within 4% from 10 to 200 keV in each soft tissue, whereas for bones of different chemical compositions the variation ranges from 2.86% to 5.03%. This effective atomic number definition is less energy dependent than a previous definition based on the total photon interaction cross section per atom averaged over all elements in the tissue, from which the computed effective atomic numbers varied by as much as 50% (in bone) as a function of photon energy over the energy range from 10 to 200 keV.

Photoelectric cross-sections for Cd and In at 22.2, 59.6 and 88.8 keV

The total photon interaction cross-sections for Cd and In at photon energies of 22.2, 59.6 and 88.8 keV have been measured. The photoelectric cross-sections at these energies have been deduced by subtracting the scattering cross-sections (coherent plus incoherent) from the measured values of total interaction cross-sections. The results have been compared with corresponding theoretical values in the literature.