Cesium pre-implantation of embedded biological sections

An ion implantation system which allows the implantation of a large surface of a specimen has been used to obtain an homogeneous enrichment with cesium of embedded biological tissues sections. In such a specimen, containing already oxygen at a high concentration, the addition of cesium allows both positive and negative secondary ions to be studied with the highest sensitivity, using the same primary ion source.     

Restricted cross sections

Multiparticle processes with only neutral final state particles are shown to be useful to study multiperipheral dynamics without the presence of recently introduced corrections due to diffraction, clusterings, multi-Pomeranchukon contribution, etc.     

On the calculation of scattering cross sections from absorption cross sections

A dispersion-type relation between photon scattering and absorption cross sections is derived. It is shown that the relation gives the correct scattering cross section in the low and high frequency limits, and is consistent with the Kramers-Heisenberg formula in the vicinity of a resonance. The practical application of the relation is illustrated by calculations of the scattering cross section and refractive index of He and Ne at STP and dry air at 1200°K from known absorption cross section data. The method is useful for obtaining scattering cross sections, polarizabilities, and refractive indices at elevated temperatures.     

Heavy-ion fusion cross sections

The absolute cross sections for heavy-ion induced reactions in the rare earth region are studied systematically as functions of projectile energy, charge and mass. Targets and projec-tiles are chosen so that the same final states are fed in erbium, holmium and dysprosium nueleides with mass numbers A = 159–162. As the low lying states in these final nucleides are well known, the cross sections for the various reaction channels can be determined from singles γ-ray spectra. By summing these cross sections, the heavy-ion fusion cross sections are determined, and compared to theoretical calculations based on the Bass model as well as to total reaction cross sections deduced from optical model fits to elastic scattering data.     

Integrated pion-nucleus cross sections

We propose an improved analysis for transmission experiments which determines uniquely, up to statistical error, the imaginary part of the forward nuclear amplitude. The analysis we propose takes the Coulomb interaction into account and is especially useful when the Coulomb-nuclear interference effects are large. In some cases the real part of the forward nuclear amplitude may also be extracted.     

Rising total cross sections

As two hadrons pass one another the vacuum between them becomes polarised. It is shown that quark-loop contributions to the vacuum polarisation account for most, if not all, of the rise of the total cross section with energy.     

Quasi-elastic reaction cross sections

Starting from the idea that a critical phenomenon separates deep-inelastic from quasi-elastic reactions, we introduce a simple procedure to calculate quasi-elastic cross sections. The results are compared with experimental data.     

The study of interaction potentials and differential cross sections for collisions between He atoms and hydrogen halide molecules

In this paper, we present the uniform interaction potentials for helium atoms and halogen hydride molecules (HF, HCl and HBr). The differential cross sections are calculated using the above interaction potentials for the He－HF, HCl and HBr systems, respectively, and the results of the calculations are found to be in agreement with the existing theoretical results and experimental data.     

Energy integrated photonuclear cross sections

Energy integrated photonuclear cross sections are calculated in the electric dipole approximation for the nuclei ²H, ⁴He, ¹²C, ¹⁶O, ²⁸Si, ³²S and ⁴⁰Ca. The ground-state wave functions are calculated by the Brueckner-Hartree-Fock procedure. The dependence of the cross sections on the different types of realistic nucleon-nucleon potentials is discussed as well as the dependence on the underlying harmonic oscillator states. The enhancement factors κ are also given.     

Heavy-ion total reaction cross sections

A one-parameter expression has been found which predicts with a smaller χ² than previous expressions, the total reaction cross sections for a large number of heavy-ion systems covering a wide energy range. The expression uses an interaction radius which is a sum of the equivalent uniform matter radii of the interacting nuclei plus and energy-dependent term.     

Double pomeron jet cross sections

We treat hadron-hadron collisions where the final state is kinematically of the kind associated with double-pomeron-exchange (DPE) and has large transverse momentum jets. We show that in addition to the conventional factorized (FDPE) contribution, there is a nonfactorized (NDPE) contribution which has no pomeron beam jet. Within a simple model we compute DPE-two-jet total and differential cross sections at Tevatron energy scales, and show that the NDPE contribution is dominant.     

Photoionization cross sections of Fe XXI

Total and partial photoionization cross sections for (Fe XXI+hν→Fe XXII+e) are presented for the ground and excited bound states with n?10 and l?9. Fe XXI is prevalent in high-temperature astrophysical plasmas as well as in photoionized plasmas excited by hard X-rays. Results are reported for the first time for the high-energy photoionization with core excitations to n=2,3 states. Details of photoionization, especially the high-energy features that often dominate considerably over the low energy ones, are illustrated. These prominent features will affect the photoionization and the recombination rates in high-temperature plasmas. Calculations are carried out in the close coupling (CC) approximation using the R-matrix method. A large CC wavefunction expansion for Fe XXII which includes the ground and 28 excited core states from n=2 and 3 complexes and spans over a wide energy range is used. A total of 835 discrete bound states of Fe XXI in the singlet, triplet, and quintet symmetries are obtained. Total photoionization cross sections, σ_PI(nLS), for ionization into all 29 states are presented for all 835 final bound states and partial photoionization cross sections, σ_PI(g,nLS), for ionization into the ground ²P⁰ state of the core are presented for 685 states. While the n=2 core excitations are at relatively lower energy range (within 15 Ry from the ionization threshold), the n=3 excitations lie at considerably higher energy, 73 Ry and above, yet introduce resonant features and enhancements more prominent than those of n=2 states. Larger numbers of resonances are formed due to Rydberg series of autoionizing states converging on to the 29 core states. However, most noticeable structures are formed in the excited state cross sections by the photoexcitation-of-core (PEC) resonances in the photon energy range of 73-82 Ry. All these high-energy features are absent in the currently available results. The present results should enable more accurate modeling of the emission spectrum of highly excited plasma from the optical to far-ultraviolet region.     

165Ho fast neutron cross sections

Total neutron cross sections of¹⁶⁵ Ho were measured from 0.1 to 1.5 MeV with resolutions of ? 2.5 keV. The observed total cross sections varied slowly with energy and displayed no significant structure. Differential neutron elastic and inelastic scattering cross sections were determined at intervals of ?50keV from 0.3 to 1.5 MeV. The inelastic excitation of states in¹⁶⁵Ho at; 98, 214, 371, 460, 517, 586, 712, 824, 995, 1104 and 1143 keV was positively observed with probably identification of several additional states. The observed excited structure and the respective cross sections were correlated with known single-particle and collective states and with excited structure postulated from systematics. The measured cross sections were compared with calculated values based upon spherical and deformed optical-potentials, and compound-nuclear processes. Total cross sections were best described by a spherical potential while the differential elastic angular distributions were better represented by deformed-potential calculations. Resonance interference effects were found small and, at the energies of the present experiments, the contribution of direct processes was not large.     

Singular cross sections in muon colliders

We address the problem that the cross section for the collisions of unstable particles diverges, if calculated by standard methods. This problem is considered for beams much smaller than the decay length of the unstable particle, much larger than the decay length and finally also for pancake- shaped beams. We find that in all cases this problem can be solved by taking into account the production/propagation of the unstable particle and/or the width of the incoming wave packets in momentum space. Received: 4 March 2003 / Revised version: 8 April 2003 / Published online: 23 May 2003 RID="a" ID="a" e-mail: chrisd@sci.kun.nl RID="b" ID="b" e-mail: kleiss@sci.kun.nl     

Electron-impact excitation cross sections for neon

An analytic atomic independent particle model adjusted to experimental single-particle energy levels is used to generate wavefunctions for the excited states of neon. Using these wavefunctions in conjunction with the Born approximation and the Russell-Saunders LS-coupling scheme, we calculate generalized oscillator strengths and cross sections for electron-impact excitation of neon from the 2p⁶(¹ S ₀) ground state.