Neutrons from nuclear capture of negative pions
Neutrons from nuclear capture of negative pions
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负π介子的核俘获中子
DOI：
10.1103/physrevc.25.3050
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发表时间：
1982
影响因子：
3.1
通讯作者：
F. Waterman
中科院分区：
文献类型：
--
作者：
R. Madey;T. Vilaithong;B. Anderson;J. Knudson;T. Witten;A. Baldwin;F. Waterman
我们测量了在C、N、O、Al、Cu、Ta和Pb靶中从负π介子慢化和停止的核俘获中超过1.2 MeV的中子的能谱和产额。每个中子谱被分解为蒸发部分和直接部分。对于所有靶，每个停止的π介子的直接中子数基本上是恒定的，平均值为1.74\ifmmode\pm\else\textpm\fi{}0.28，而蒸发中子的产额增加了一个数量级，从碳的约0.7增加到铅的约7。由中子带走的总动能对于所有靶也基本恒定，平均值为76.7\ifmmode\pm\else\textpm\fi{}2.0 MeV。蒸发中子带走的动能随质量数增加而增加，而直接中子带走的动能相应减少。我们获得了每个靶在蒸发过程中形成的第一个剩余核的核温度（MeV）：Pb（1.4），Ta（1.4），Cu（1.9），Al（2.3），O（2.2），N（2.2）和C（2.1）。来自光靶的光谱在60 MeV附近的区域中显示肩部，这与两核子吸收机制一致。直接中子能谱的特征在于，随着中子能量在从30 MeV下降到约10 MeV的区域中减小，产率上升。数据进行了比较与以前的测量和预测的核内级联和预平衡计算。
We measured the energy spectra and yields of neutrons above 1.2 MeV from nuclear capture of negative pions slowing down and stopping in C, N, O, Al, Cu, Ta, and Pb targets. Each neutron spectrum was decomposed into an evaporation portion and a direct portion. The number of direct neutrons per stopped pion is substantially constant for all the targets with a mean value of 1.74\ifmmode\pm\else\textpm\fi{}0.28, whereas the yield of evaporation neutrons increases by an order of magnitude from about 0.7 for carbon to about 7 for lead. The total kinetic energy carried away by the neutrons is substantially constant also for all the targets with a mean value of 76.7\ifmmode\pm\else\textpm\fi{}2.0 MeV. The kinetic energy carried away by evaporation neutrons increases with mass number with an associated decrease in the kinetic energy carried away by direct neutrons. We obtained the nuclear temperature (in MeV) of the first residual nucleus formed in the evaporation process for each target: Pb (1.4), Ta (1.4), Cu (1.9), A1 (2.3), O (2.2), N (2.2), and C (2.1). The spectrum from a light target displays a shoulder in the region around 60 MeV which is consistent with a two-nucleon absorption mechanism. The direct neutron spectra are characterized by a rising yield as the neutron energy decreases in the region from 30 MeV down to about 10 MeV. The data are compared with previous measurements and with the predictions of intranuclear cascade and preequilibrium calculations.