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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