[1208] | 1 | \subsection {Pion absorption at rest} |
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| 2 | The absorption of stopped negative pions in nuclei is interpreted |
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| 3 | \cite{Gadioli}, \cite{Chiang}, \cite{Ashery}, \cite{Weyer} |
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| 4 | as starting with the absorption of the pion by two or |
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| 5 | more correlated nucleons; the total energy of the pion is transferred to |
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| 6 | the absorbing nucleons, which then may leave the nucleus directly, or |
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| 7 | undergo final-state interactions with the residual nucleus. The remaining |
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| 8 | nucleus de-excites by evaporation of low energetic particles. |
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| 9 | |
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| 10 | G4PiMinusAbsorptionAtRest generates the primary absorption component of |
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| 11 | the process through |
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| 12 | the parameterisation of existing experimental data; |
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| 13 | the primary absorption component is handled by class G4PiMinusStopAbsorption. |
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| 14 | In the current implementation only absorption on a nucleon pair is considered, |
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| 15 | while contributions from absorption on nucleon clusters are neglected; |
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| 16 | this approximation is supported by experimental |
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| 17 | results |
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| 18 | \cite{Gadioli}, \cite{Machner2} |
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| 19 | showing that it is the dominating contribution. |
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| 20 | |
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| 21 | Several features of stopped pion absorption are known from experimental |
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| 22 | measurements on various materials \cite{Hartmann}, \cite{Madley}, |
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| 23 | \cite{Schleputz}, \cite{Orth}, |
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| 24 | \cite{Pruys}, \cite{Heusi}, \cite{Isaak}, \cite{Isaak-ang}: |
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| 25 | \begin{itemize} |
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| 26 | \item the average number of nucleons emitted, as resulting from the |
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| 27 | primary absorption process; |
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| 28 | \item the ratio of nn vs np as nucleon pairs involved in the absorption |
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| 29 | process; |
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| 30 | \item the energy spectrum of the resulting nucleons emitted and their |
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| 31 | opening angle distribution. |
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| 32 | \end{itemize} |
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| 33 | The corresponding final state products and related distributions are |
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| 34 | generated according to a parameterisation |
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| 35 | of the available experimental measurements listed above. The dependence on |
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| 36 | the material is handled by a strategy pattern: |
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| 37 | the features pertaining to material for which experimental data are available |
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| 38 | are treated in G4PiMinusStopX classes (where X represents an element), |
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| 39 | inheriting from G4StopMaterial base class. In case of absorption on an element |
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| 40 | for which experimental data are not available, the experimental distributions |
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| 41 | for the elements closest in Z are used. |
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| 42 | |
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| 43 | The excitation energy of the residual nucleus is calculated by difference |
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| 44 | between the initial energy and the energy of the final state products of |
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| 45 | the primary absorption process. |
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| 46 | |
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| 47 | Another strategy handles the nucleus deexcitation; the current default |
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| 48 | implementation consists in handling the deexcitatoin component of the process |
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| 49 | through the evaporation model described elsewhere in this Manual. |
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| 50 | |
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| 51 | \begin{latexonly} |
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| 52 | |
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| 53 | \begin{thebibliography}{999} |
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| 54 | |
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| 55 | \bibitem{Gadioli} E. Gadioli and E. Gadioli Erba |
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| 56 | {\em Phys. Rev. C 36} 741 (1987) |
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| 57 | |
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| 58 | \bibitem{Chiang} H.C. Chiang and J. Hufner |
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| 59 | {\em Nucl. Phys. A352} 442 (1981) |
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| 60 | |
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| 61 | \bibitem{Ashery} D. Ashery and J. P. Schiffer |
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| 62 | {\em Ann. Rev. Nucl. Part. Sci. 36} 207 (1986) |
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| 63 | |
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| 64 | \bibitem{Weyer} H. J. Weyer |
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| 65 | {\em Phys. Rep. 195} 295 (1990) |
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| 66 | |
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| 67 | \bibitem{Hartmann} R. Hartmann et al., |
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| 68 | {\em Nucl. Phys. A300} 345 (1978) |
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| 69 | |
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| 70 | \bibitem{Madley} R. Madley et al., |
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| 71 | {\em Phys. Rev. C 25} 3050 (1982) |
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| 72 | |
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| 73 | \bibitem{Schleputz} F. W. Schleputz et al., |
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| 74 | {\em Phys. Rev. C 19} 135 (1979) |
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| 75 | |
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| 76 | \bibitem{Orth} C.J. Orth et al., |
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| 77 | {\em Phys. Rev. C 21} 2524 (1980) |
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| 78 | |
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| 79 | \bibitem{Pruys} H.S. Pruys et al., |
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| 80 | {\em Nucl. Phys. A316} 365 (1979) |
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| 81 | |
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| 82 | \bibitem{Heusi} P. Heusi et al., |
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| 83 | {\em Nucl. Phys. A407} 429 (1983) |
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| 84 | |
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| 85 | \bibitem{Isaak} H.P. Isaak et al., |
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| 86 | {\em Nucl. Phys. A392} 368 (1983) |
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| 87 | |
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| 88 | \bibitem{Isaak-ang} H.P. Isaak et al., |
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| 89 | {\em Helvetica Physica Acta 55} 477 (1982) |
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| 90 | |
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| 91 | \bibitem{Machner2} H. Machner |
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| 92 | {\em Nucl. Phys. A395} 457 (1983) |
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| 93 | |
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| 94 | \end{thebibliography} |
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| 95 | |
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| 96 | \end{latexonly} |
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| 97 | |
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| 98 | \begin{htmlonly} |
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| 99 | |
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| 100 | \subsection{Bibliography} |
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| 101 | |
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| 102 | \begin{enumerate} |
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| 103 | \item E. Gadioli and E. Gadioli Erba |
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| 104 | {\em Phys. Rev. C 36} 741 (1987) |
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| 105 | |
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| 106 | \item H.C. Chiang and J. Hufner |
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| 107 | {\em Nucl. Phys. A352} 442 (1981) |
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| 108 | |
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| 109 | \item D. Ashery and J. P. Schiffer |
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| 110 | {\em Ann. Rev. Nucl. Part. Sci. 36} 207 (1986) |
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| 111 | |
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| 112 | \item H. J. Weyer |
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| 113 | {\em Phys. Rep. 195} 295 (1990) |
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| 114 | |
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| 115 | \item R. Hartmann et al., |
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| 116 | {\em Nucl. Phys. A300} 345 (1978) |
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| 117 | |
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| 118 | \item R. Madley et al., |
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| 119 | {\em Phys. Rev. C 25} 3050 (1982) |
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| 120 | |
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| 121 | \item F. W. Schleputz et al., |
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| 122 | {\em Phys. Rev. C 19} 135 (1979) |
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| 123 | |
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| 124 | \item C.J. Orth et al., |
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| 125 | {\em Phys. Rev. C 21} 2524 (1980) |
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| 126 | |
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| 127 | \item H.S. Pruys et al., |
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| 128 | {\em Nucl. Phys. A316} 365 (1979) |
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| 129 | |
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| 130 | \item P. Heusi et al., |
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| 131 | {\em Nucl. Phys. A407} 429 (1983) |
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| 132 | |
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| 133 | \item H.P. Isaak et al., |
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| 134 | {\em Nucl. Phys. A392} 368 (1983) |
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| 135 | |
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| 136 | \item H.P. Isaak et al., |
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| 137 | {\em Helvetica Physica Acta 55} 477 (1982) |
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| 138 | |
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| 139 | \item H. Machner |
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| 140 | {\em Nucl. Phys. A395} 457 (1983) |
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| 141 | |
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| 142 | \end{enumerate} |
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| 143 | |
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| 144 | \end{htmlonly} |
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| 145 | |
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