Geant4 is a software toolkit for the simulation of the passage of particles through matter. It is used by a large number of experiments and projects in a variety of application domains, including high energy physics, astrophysics and space science, medical physics and radiation protection. Over the past several years, major changes have been made to the toolkit in order to accommodate the needs of these user communities, and to efficiently exploit the growth of computing power made available by advances in technology. The adaptation of Geant4 to multithreading, advances in physics, detector modeling and visualization, extensions to the toolkit, including biasing and reverse Monte Carlo, and tools for physics and release validation are discussed here.

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Recent developments in GEANT4

Following the introduction of GUPIXWIN in 2005, a number of upgrades have been made in the interests of extending the applicability of the program. Extension of the proton upper energy limit to 5 MeV facilitates the simultaneous use of PIXE with other ion beam analysis techniques. Also, the increased penetration depth enables the complete PIXE analysis of paintings. A second database change is effected in which recently recommended values of L-subshell fluorescence and Coster–Kronig yields are adopted. A Monte Carlo code has been incorporated in the GUPIX package to provide detector efficiency values that are more accurate than those of the previous approximate analytical formula. Silicon escape peak modeling is extended to the back face of silicon drift detectors. An improved description of the attenuation in dura-coated beryllium detector windows is devised. Film thickness determination is enhanced. A new batch mode facility is designed to handle two-detector PIXE, with one detector measuring major elements and the other simultaneously measuring trace elements.

The Guelph PIXE software package IV

The K, L, and higher atomic shell x‐ray fluorescence yield measured data, covering the period 1978 to 1993, following the major previous compilations by Bambynek et al. (1972) and Krause (1979), are reviewed. An annotated bibliography of x‐ray fluorescence yield measurements, analyses, fits and tables 1978–1993 is presented. Comparisons of the fluorescence yields ωk, ωL, and ωM, based on measurements, and on theoretical models, are presented. Values of ωK, ωL, and ωM, fitted to standard empirical parametric formulations, are presented. In addition, selected well‐characterized measured ωK, ωL, and ωM results restricted to the period 1978–1993 are listed. These selected measured values are fitted by least squares to polynomials in Z of the form ∑nanZn and compared with theoretical and with earlier fitted values. A section on application of fluorescence yield data to computations of x‐ray energy‐absorption coefficients is included.

A Review, Bibliography, and Tabulation of K, L, and Higher Atomic Shell X‐Ray Fluorescence Yields

A second X-ray production database is introduced into GUPIX to complement the existing theoretical (ECPSSR–DHS) database and to provide some estimate of analytical uncertainty due to this aspect of GUPIX; it is based on published compilations and analyses of large numbers of measured K and L subshell X-ray production cross-sections. The two databases are compared through analysis of single-element standards and standard reference materials. Good agreement is observed for the case of K X-rays. In contrast, neither the theoretical nor the “reference” database appears to be entirely satisfactory in the case of L X-rays. New work is required on L subshell X-ray production cross-sections using protons. The tools in GUPIX for film thickness determination are expanded, and tested using the two alternative databases.

The Guelph PIXE software package III: Alternative proton database

K- and L-shell ionization cross sections for protons and helium ions calculated in the ecpssr theory

The influence of the energy loss of slow projectiles during inelastic collisions on the inner-shell ionization cross sections is treated analytically. The result agrees with available experimental cross sections for $K$-shell ionization by protons. Residual trends in the data may gauge the quality of wave functions employed in calculations of Coulomb ionization cross sections.

Energy-loss effect in inner-shell Coulomb ionization by heavy charged particles

The theory of Coulomb ionization of $L$ shells by low-velocity heavy charged particles whose atomic number is small compared to the atomic number of the target atom is extended to projectiles with velocities comparable to or larger than the $L$-shell orbital velocities. At large impact parameters projectiles polarize the shell, and at small impact parameters they increase the binding energies of the electrons to be excited. The polarization effect is incorporated in accordance with the perturbed stationary-state (PSS) approximation. The effect of the repulsion between the projectile and the target nucleus is accounted for by a Coulomb-deflection factor (C). This CPSS theory is developed further to include relativistic effects (R) of the target wave function through a procedure that reproduces the results of numerical calculations for heavy target atoms. With electron capture by the projectiles as an additional channel of ionization, the CPSSR theory is compared with experiment.

L-shell Coulomb ionization by heavy charged particles

Experimental cross sections for $L$ -shell ionization by heavy charged particles, of atomic number small compared to the target atomic number and with velocities low compared to the $L$ -shell orbital velocities, can be smaller by more than an order of magnitude than the quantum-mechanical predictions in the plane-wave Born approximation (PWBA). The contribution of two effects, not contained in the PWBA, is derived. These effects are the binding of the $L$ -shell electrons to the moving particle during collision and the Coulomb deflection of the particle in the field of the target nucleus. As developed here for $L$ shells and previously for $K$ shells, the theory treats the excitation of inner shells from perturbed stationary states (PSS) and incorporates the effect of the Coulomb-distorted wave of the heavy charged projectile semiclassically. It agrees well with experimental $L$ -shell cross sections of 16 different target atoms for protons, and accounts for the isotope effect observed on various targets with protons and deuterosn of equal velocities.

Binding and Coulomb-deflection effects in L -shell Coulomb ionization by heavy charged particles. Low particle velocities

Cross sections for electron capture from inner atomic shells by fully stripped ions, of velocities high compared to the electron velocities in the inner-shell orbits, are calculated in the second Born approximation. The theory of Drisko for electron capture by protons from hydrogen is generalized to projectiles and targets of arbitrary atomic numbers ${Z}_{1}$ and ${Z}_{2}$, respectively. For ions of low velocity, the effects of binding and Coulomb deflection are accounted for in a manner similar to that of Brandt and his co-workers in the theory for direct ionization to the continuum of the target atom. The results are in good agreement with experimental capture cross sections, whereas the Oppenheimer-Brinkman-Kramers approximation overestimates such cross sections. The contribution of electron capture to inner-shell ionization cross sections increases with increasing $\frac{{Z}_{1}}{{Z}_{2}}$ and brings them into agreement with experiment.

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Electron capture from K shells by fully stripped ions

Experimental cross sections for K‐shell x‐ray production by hydrogen and helium ions (Z1=1,2) in target atoms from beryllium to uranium (Z2=4–92 ) are tabulated as compiled (7418 cross sections) from the literature (161 references were found) with the search for the data terminated in January 1988. These cross sections are compared with predictions of the first Born approximation and ECPSSR theory for inner‐shell ionization. The ECPSSR accounts for the energy loss (E) and Coulomb deflection (C) of the projectile ion as well as for the perturbed stationary state (PSS) and relativistic (R) nature of the target’s inner‐shell electron. While the first Born approximation generally overestimates the data by orders of magnitude, the ECPSSR theory is confirmed to be, on the average, in agreement with the experiment to within 10%–20%. For light and heavy target atoms, however, systematic and opposite deviations are found in the low projectile‐velocity regime. These deviations are associated with the influence of m...

Grzegorz Lapicki

Papers

Energy-loss effect in inner-shell Coulomb ionization by heavy charged particles

L-shell Coulomb ionization by heavy charged particles

Binding and Coulomb-deflection effects in L -shell Coulomb ionization by heavy charged particles. Low particle velocities

Electron capture from K shells by fully stripped ions

Cross Sections for K-shell X-ray Production by Hydrogen and Helium Ions in Elements from Beryllium to Uranium