Luo Zhengming

An overview of the transport theory of charged particles

Abstract An unified description of the transport theory for charged particles including electrons, ions and atoms has been formulated and is presented. The main content of the paper includes: the Boltzmann equation and its different approximations, the theory of electron slowing down spectra, multiple scattering theory, the theory of deep penetration and the theory of secondary particle emission. The scaling properties of the transport of charged particles are also presented. Although some discussion of stochastic (Monte Carlo) methods is included, the main focus of this review is on analytical approaches. Finally, some important unsolved problems in the transport theory for charged particles are discussed.

On the possibility of determining an effective energy spectrum of clinical electron beams from percentage depth dose (PDD) data of broad beams

Experiments have already shown that obvious differences exist between the dose distribution of electron beams of a clinical accelerator in a water phantom and the dose distribution of monoenergetic electrons of nominal energy of the clinical accelerator in water, because the electron beams which reach the water surface travelling through the collimation system of the accelerator are no longer monoenergetic. It is evident that, while calculating precisely the dose distribution of any incident electron beams, the energy spectrum of the incident electron beam must be taken into consideration. In this note we shall present a method for determining an effective energy spectrum of clinical electron beams from PDD data (percentage depth dose data). It is well known that there is an integral equation of the first kind which links the energy spectrum of an incident electron beam with PDD through the dose distribution of monoenergetic electrons in the medium, as a kernel function in the integral equation. In this note, the integral equation of the first kind will be solved by using the regularization method. The bipartition model of electron transport will be used to calculate the kernel function, namely the energy deposition due to monoenergetic electron beams in the medium.

The L-shell ionization of Ho and Os induced by electron impact

The electron-induced L-shell X-ray partial production cross sections, total production cross sections and mean ionization cross sections for Ho and Os have been measured as functions of electron energies from near threshold up to 36 keV by using a thin target with thick substrate technique. The influence of the electrons reflected from the substrate was corrected by using the electron transport bipartition model. Also, the corrected measured results were compared with theoretical predictions proposed by Gryzinski and McGuire.

Measurement of Zinc K-Shell Ionization Cross Sections by Electron Impact

Electron-induced Zn ionization cross sections, which are scarce, have been obtained from measurement of Kα x-ray emission at energies from near threshold to 25 keV. The influence of substrate of thin target on ionization cross sections has been corrected by using the bipartition model of electron transport. The experimental results are satisfactory as compared with empirical formula of Green and Cosslett.

An Empirical Formula of Atomic K-Shell Ionization Cross Sections by Electron Impact

An empirical formula is proposed to describe the K-shell ionization cross sections by electron impact over a wide range of atomic numbers and overvoltages U (the ratio between the electron incident energy and the binding energy of the electrons in the K-shell). The study is based on the analysis of existing experimental data of K-shell ionization cross sections. The expression shows the results in good agreement with the data for Z<6 atoms as well as for 6≤Z≤79.

Measurement of L-shell ionization cross sections for niobium by electron impact

L-shell ionization cross sections of Nb by electron impact in the energy range from 3 to 40 keV have been determined with an Si(Li) X-ray detector. Influence of reflected electrons from backing on the measurement was corrected using an electron transport model. The experimental results are compared with the theoretical calculations of Gryzinski (1965 Phys. Rev. A138 336) and McGuire (1977 Phys. Rev. A16 73).

Measurements and calculations of absorbed dose in electron beam radiation processing

Abstract An electron beam current densimeter has been described and used for dose measurement in EB radiation processing. An improved bipartition model of electron transport is applied to calculate the reflection coefficients and energy deposition distributions produced by 0.2–3 MeV electrons in semi-infinite media of Al, C, MAR and nylon, and the energy deposition produced by 2 MeV electrons in the two-layer medium consisting of copper and polystyrene. In addition, the depth dose distribution of 300 keV electrons in Ti-air-nylon composite-layer has been evaluated. The calculation results are in good agreement with the measurement data.

L-Shell X-Ray Production Cross Sections of Au and Ir Atoms by Electron Impact near the Threshold Region

L-shell production cross sections Lα, Lβ and Lγ for Au and Ir atoms have been measured by electron impact at incident electron energies of about one to three times of the threshold energy. The total production cross section and mean ionization cross section were obtained from the experimental results and by using mean fluorescence yield, respectively. The influence of electrons reflected from the substrate and multiple electron scattering inside the target have been corrected. The experimental results are compared with the existing measured results and the theoretical predictions.

Measurement and Multiple Scattering Correction of K-Shell Ionization Cross Sections of Silver by Electron Impact

The K-shell ionization cross sections of silver have been measured by electron impact. In order to overcome the difficulties in preparing a self-supporting thin targets, a thin target with a thick substrate was used in our experiments. The influence of electrons reflected from the substrate was corrected by means of a detailed calculation of electron transport. The path of the electrons passing through the silver target of 31.2 µg/cm2 was calculated by the EGS4 Monte Carlo program. This method of correction for the measurement is reported for the first time.

Measurement and Correction of K-Shell Ionization Cross Sections for Copper and Gallium by Electron Impact

The K-shell ionization cross sections of Cu and Ga are measured by electron impact and the data of Ga are reported for the first time. The method of a thin chemical compound target with a thick substrate is formally used in the experiment. The influence of electrons reflected from the substrate is corrected by means of a calculation of electron transport.