Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science and Technology, Sichuan University, China Research Coordination Meeting, IAEA, Vienna, 4-6 March 2009

Contents 1. Introduction 2. Our experimental method 3. Experiment results 4. Summary

 main experimental methods ： to measure the characteristic x-rays to measure the Auger electrons  targets ： self-supporting thin targets （ △ E/E~0.01 ） Experimental sketch ： 1 Introduction

Si(Li) detector X-ray e Thin target

Problems of the self-supporting thin targets: 1) preparing the self-supporting thin targets, is the main difficulty: 20 keV electrons d= Fe: 300Å Cu: 276Å Mo: 270Å W: 179Å Pb: 166Å 30 keV electrons d= Fe: 602Å Cu: 553Å Mo: 537Å W: 351Å Pb: 330Å 2) not easy to making use of it

2. Our experimental method Application of vacuum coating technique to prepare thin target on thick film. Advantage: easy to prepare the targets. Detecting the characteristic x-rays by a Si(Li) detector. However, ionization contribution in thin target by electrons reflected from the substrate must be corrected.

e¯ Si (Li) detector Thin target Thick substrate Experimental sketch :

Bipartition model

a. Calculation of electron reflection energy spectrum ： —Bipartition model Electron reflection energy spectra calculated by the bipartition model for 20 keV electrons from Mylar （ solid line ） and Al （ dashed line ） substrates. The incident angle is 45 degrees.

b. Correction for multiple scattering by Monte Carlo method d’/d: ratios of electron mean track length to straight target thickness

c. Thickness measurements of thin targets By Rutherford Backscattering Spectrometry （ RBS) （ The accuracy can be about 5% ）

RBS experimental spectrum of thin Ti target on thick Al substrate and the simulation curve using GISA3.3 code. The 2 MeV 4 He + ions were impacted vertically on the target. The backscattered particles were detected at a scattering angle of by a Si surface-barrier detector. RBS example: Al

d. Efficiency calibration of Si(Li) detector:  the shape of the efficiency calibration curve was determined from the ratio of experimental and theoretical thick carbon target (PENELOPE code) bremsstrahlung spectra produced by incident electrons.  the absolute value for the efficiency calibration was obtained from the use of 241 Am radioactive standard source.

Experimental set-up for RBS

Experimental set-up for ionization cross-sections

3.Experiment results 3.1 Thin target method By using the method for thin targets on a thick substrate, we have measured the electron-impact inner-shell ionization cross sections near the threshold energies for the following elements and shells: S-K, Cl-K, Ca-K, Zn-K, W-L ,L , Bi-L ,L , Ba-L  and Gd-L .

The present experimental data of K-shell ionization cross sections by electron impact for S element are compared with the results from the PWBA-C-Ex theory and the Luo and Joy’s theory as well as the results from the empirical formulae of Casnati and co-workers and of Hombourger. S-K

The present experimental data of K-shell ionization cross sections by electron impact for Cl element are compared with the results from the PWBA-C-Ex theory and the Luo and Joy’s theory as well as the results from the empirical formulae of Casnati and co-workers and of Hombourger. Cl-K E(keV)

The present experimental data of K-shell ionization cross sections by electron impact for Ca element are compared with the results from the PWBA-C-Ex theory and the Luo and Joy’s theory as well as the results from the empirical formulae of Casnati and co-workers and of Hombourger. The experimental data of Shevelko and co-workers for Ca element are also plotted for comparison. Ca-K

The present experimental data of K-shell ionization cross sections by electron impact for Zn element are compared with the results from the PWBA-C-Ex theory and the Luo and Joy’s theory as well as the results from the empirical formulae of Casnati and co-workers and of Hombourger and of Gryzinski. The experimental data of Tang and co-workers for Zn element are also plotted for comparison. Zn-K

The present experimental data of L α, L β x-ray production cross sections by electron impact for W element are compared with the PWBA-C-Ex theory and the experimental data of Campos et al. W-L α,L β

The present experimental data of L α, L β x-ray production cross sections by electron impact for Bi element are compared with the PWBA-C-Ex theory. Bi-L α,L β

The present experimental data of L α x-ray production cross sections by electron impact for Ba element are compared with the PWBA-C-Ex theory. Ba-L α

The present experimental data of L α x-ray production cross sections by electron impact for Gd element are compared with the PWBA-C-Ex theory. Gd-L α

3.2 Thick target method By using the thick-target method, we measured the K-shell ionization cross sections near the threshold energies for Ni and Si element. ( Physical Review A 77, 2008, )

The measured K-shell ionization cross sections for Si element by the thick- target method. The predictions of DWBA and PWBA-C-Ex theories and the values of Casnati empirical formula [18] are also shown for comparison. Si-K

The K-shell ionization cross sections for Ni element determined by the Tikhonov regularization method (circles, in red) and the classical molecular dynamics (CMD) method (triangles, in blue) for the real experimental data. The experimental data of Llovet et al (squares, in black) and the predictions of DWBA (dashed line) and PWBA-C-Ex (solid line) theories are also shown for comparison. Ni-K

3.3 Effect of surface roughness Studied using Monte Carlo simulations. The effect of surface roughness increases as the roughness increases. The surface roughness of the target should be limited to less than 100 nm if the experimental error originated from the surface roughness would be kept less than 2%. ( NIM B 266(23), 2008, )

4. Summary: By using the method for thin targets on a thick substrate, we have measured the electron-impact inner-shell ionization cross sections near the threshold energies for the following elements and shells: S-K, Cl-K, Ca-K, Zn-K, W-L ,L , Bi-L ,L , Ba- L  and Gd-L . By using the thick-target method, we measured the K-shell ionization cross sections near the threshold energies for Ni and Si element. The effect of surface roughness increases as the roughness increases and the surface roughness of the target should be limited to less than 100 nm if the experimental error originated from the surface roughness would be kept less than 2%.