[1211] | 1 | \section{Ionisation} |
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| 2 | \label{secioni} |
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| 3 | |
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| 4 | The total cross section at a given incident kinetic energy T is calculated by |
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| 5 | summing the partial cross sections at such energy for all the subshells of an |
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| 6 | element. The partial subshell cross sections at incident energy T are obtained |
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| 7 | from an interpolation of the evaluated cross section data in the EEDL library, |
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| 8 | according to the formula \ref{eqloglog}. |
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| 9 | |
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| 10 | The subshell from which the electron is emitted is randomly selected according |
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| 11 | to the cross sections of the subshells, determined at the energy T by |
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| 12 | interpolating the evaluated cross section data from the EEDL data library. |
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| 13 | |
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| 14 | The probability of emission of an electron ($\delta$ ray) with kinetic energy |
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| 15 | $t$ from a subshell of binding energy $B_i$ as the result of the interaction of |
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| 16 | an incoming electron of kinetic energy $T$ is described by: |
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| 17 | \begin{equation} |
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| 18 | \label{eqionihigh} |
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| 19 | Prob(T, t, B_i) = {\sum^7}_{j=2}{a_j(T)\over(t+b_i)^j} |
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| 20 | \end{equation} |
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| 21 | for $t < t_0$ and |
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| 22 | \begin{equation} |
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| 23 | \label{eqionilow} |
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| 24 | Prob(T, t, B_i) = {c(T)\over t^2} |
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| 25 | \end{equation} |
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| 26 | for $t > t_0$, where $t_0$ is a parameter. |
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| 27 | Both formulas result from empirical fits to the EEDL data and |
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| 28 | are normalized to 1. |
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| 29 | The $a$, $b$ and $c$ coefficients are |
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| 30 | determined by fitting the data; their energy dependence is evaluated from a |
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| 31 | semilogarithmic interpolation of the fitted data. |
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| 32 | |
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| 33 | The sampling of the final state proceeds |
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| 34 | through two steps: first the range of the energy ($t < t_0$ or $t > t_0$) is |
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| 35 | determined by a random number extraction, taking into account the relative area |
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| 36 | determined by the two functions \ref{eqionihigh} and \ref{eqionilow}, then the |
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| 37 | energy of the $\delta$ ray is generated according to the corresponding |
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| 38 | probability distribution. |
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| 39 | |
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| 40 | The angle of emission of the scattered electron and of the $\delta$ ray |
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| 41 | is determined by energy-momentum conservation. |
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| 42 | |
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| 43 | The interaction leaves the atom in an excited state, with excitation energy |
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| 44 | equal to the binding energy of the subshell from which the electron has been |
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| 45 | emitted. The deexcitation of the atom proceeds via the emission of fluorescence |
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| 46 | photons, as described in section \ref{secphoto}. |
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| 47 | |
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| 48 | \section{Status of the document} |
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| 49 | 30.9.99 created by Alessandra Forti |
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| 50 | |
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| 51 | |
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