Quasi-free Electron Bremsstrahlung Research Articles

Development of a 20MeV proton particle-induced X-ray emission analysis method in a helium atmosphere

We developed a 20[Formula: see text]MeV particle-induced X-ray emission (PIXE) analysis method using a medical cyclotron, which is conventionally used for positron emission tomography analysis performed in vacuo, during which the target sample is damaged. For non-destructive analysis and ease of switching between target samples, we developed a technique allowing 20[Formula: see text]MeV proton PIXE analysis to be performed at the atmospheric pressure. We filled the PIXE analysis chamber with helium and checked that the continuous background of the Compton tails of nuclear reaction [Formula: see text]-rays increased only minimally, and that the quasi-free electron bremsstrahlung (QFEB) did not increase at all, in the X-ray energy spectrum.

CONTINUOUS X-RAY PRODUCTION CROSS-SECTION IN THIN POLYMER FILMS

We have calculated the production cross-sections of continuous X-rays for commonly used thin polymer films on the basis of the theories of quasi-free electron bremsstrahlung (QFEB), secondary electron bremsstrahlung (SEB), atomic bremsstrahlung (AB) and nuclear bremsstrahlung (NB). These results are compared with that of experimental one. We found that SEB is the main contributing factor and the contribution of QFEB, AB and NB is negligible. This work would facilitate choice among available polymer materials and lay down well-defined standard data against which new candidates might be judged.

Continuous X-rays produced in light-ion–atom collisions

Continuous X-rays produced in light-ion–atom collisions producing continuous backgrounds and therefore determining the detection limit of PIXE, have been experimentally and theoretically studied. It is shown that the experimental results over the wide range of projectile-ion energy from 0.5 to 40 MeV are well explained by four sources of radiative processes: nuclear bremsstrahlung (NB), atomic bremsstrahlung (AB) (or polarization bremsstrahlung), secondary-electron bremsstrahlung (SEB), and quasi-free-electron bremsstrahlung (QFEB).

A study of PIXE continuum polarization properties

AbstractThe continuum radiation emitted after the proton bombardment of a solid or gaseous target can be described mainly by three mechanisms: the secondary electron bremsstrahlung (SEB), the quasi‐free electron bremsstrahlung (QFEB) and the atomic bremsstrahlung (AB). Each background mechanism exhibits a different relative contribution in the PIXE continuum according to the projectile energy, the x‐ray region and the atomic number of the target element. The anisotropy of the SEB and AB continuum, peaking at 90° with respect to the beam axis, has been confirmed and studied experimentally in the past. In the present work, the degree of polarization of the PIXE continuum was determined experimentally in the energy region 3–5 keV for a solid, thick carbon target and for 2.5 and 3 MeV proton energies. Copyright © 2005 John Wiley & Sons, Ltd.

PIXE spectrum analysis taking into account bremsstrahlung spectra

Continuous background appearing over the wide region of X-ray energy in the PIXE spectrum is very troublesome presence in the peak fitting. In the usual manner, the spectrum of continuous background is predicted as a function of polynomial and is subtracted from the X-ray spectrum. However, the parameters of the polynomial are determined with difficulty in the case that the continuous background exists under many peaks of characteristic X-rays. We calculated the production cross sections of continuous X-rays for several elements on the basis of the theories of quasi-free electron bremsstrahlung (QFEB), secondary electron bremsstrahlung (SEB) and atomic bremsstrahlung (AB), and obtained the continuous X-ray spectrum as a function of atomic number and X-ray energy. X-ray spectra of a standard sample and of a bovine liver sample were analyzed by a pattern analysis method assuming the reference spectra consisting of characteristic X-rays and continuous X-rays for each element. The results of analysis are quite satisfactory. By the present method, the PIXE spectra can be analyzed under little influence of the background subtraction, and it enables us a full auto-analysis of PIXE spectrum.

CONTINUUM X RAYS IN HIGHLY CHARGED ION-ATOM COLLISIONS

Continuous X rays produced by highly charged heavy ion-atom collisions have been studied experimentally. 2–5.5 MeV/u F, Si, S and Cl ions with zero or one electron were bombarded with a thin gas target of H 2 and He. Emitted X-ray spectra were measured by using a Si(Li) X-ray detector at 90°. The characteristic X rays and radiative electron capture X rays were observed clearly, which were superimposed on the continuum X rays. The continuum X rays can be well explained by two types of radiative processes: mainly quasi-free electron bremsstrahlung (QFEB), and partly atomic bremsstrahlung (AB). It should be noticed that QFEB is predominant at low X-ray energy region and AB at high X-ray energy region in highly charged heavy ion-atom collision process.

High energy limit of atomic bremsstrahlung

Atomic bremsstrahlung and nuclear bremsstrahlung produced by ion-atom collisions are discussed on the basis of PWBA theory, and the high energy limit of atomic bremsstrahlung is estimated. The production cross sections of continuous X-rays from a carbon target bombarded with 2 MeV protons are compared with the predictions of quasi-free electron bremsstrahlung, secondary electron bremsstrahlung, atomic bremsstrahlung and nuclear bremsstrahlung.

CONTINUOUS BACKGROUNDS IN PIXE

Continuous X rays produced by light-ion·atom collisions, which mainly form continuous backgrounds and determine the detection limit of PIXE, have been experimentally and theoretically studied, and it is shown that the experimental results over the wide range of projectile-ion energy from 0.5 MeV to 40 MeV can be well explained by three kinds of radiative process: atomic bremsstrahlung (AB), secondary-electron bremsstrahlung (SEB), and quasifree electron bremsstrahlung (QFEB). Results on the X-ray spectra, the projectile-energy dependence and the projectile-charge dependence, and on the angular distribution of these bremsstrahlungs will be summarized and the importance of AB in heavy-ion atom collision is presented. Discussions are also given on the other origins of continuous backgrounds such as the Compton scattering background, cosmic rays, the Rutherford scattering background, piling up of signals and response functions of detector, charge up effect of the target and natural backgrounds. On the basis of analyses of continuous backgrounds, the detection limit of PIXE is estimated.

Scaling law for a continuum of X-rays produced by light-ion-atom collisions

Production processes for a continuum of X-rays in light-ion-atom collisions are surveyed. Scaling laws for secondary-electron bremsstrahlung, quasi-free electron bremsstrahlung, and atomic bremsstrahlung are derived and compared with experimental results. A fairly good agreement is found.

Continuum X-rays produced by a few MeV proton bombardment

Production cross sections of continuum X-rays for quasi-free electron bremsstrahlung (QFEB), radiative ionization (RI), secondary electron bremsstrahlung (SEB), radiative elastic scattering (RES), and nuclear bremsstrahlung (NB) have been estimated for carbon and aluminum targets bombarded with 1, 3, and 6 MeV protons. Contributions of these processes to the sensitivity of PIXE are discussed. It is shown that, in the case of PIXE using 1–3 MeV protons, RES strongly influences the detection limit for those elements for which the K X-ray energy is larger than the energy T m, which is the maximum energy transferred from the projectile to a free and rest electron.

Quasifree electron bremsstrahlung induced by 20-MeV-proton impact

Energy spectra and angular distributions of quasifree electron bremsstrahlung (QFEB) induced by 20-MeV-proton bombardments of a Be target have been measured with a Si (Li) detector. The Doppler shift of QFEB is clearly observed in the energy spectra and depends on the observation angle. The production cross section calculated from a free-electron approximation is compared with the experimental result and the agreement is quite satisfactory. The spectral shape near the high-energy end point of the QFEB definitely reflects the velocity distribution of the orbital electrons of the target atom. Angular distributions of secondary-electron bremsstrahlung were also measured and are compared with a calculation which includes relativistic retardation effects.