Collisional mechanisms for single and double ionization of He by protons and antiprotons.
Collisional mechanisms for single and double ionization of He by protons and antiprotons.
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DOI：
10.1103/physreva.36.1519
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发表时间：
1987-08
期刊：
影响因子：
--
通讯作者：
Olson
中科院分区：
文献类型：
--
作者：
Olson
用经典的轨道蒙特卡罗计算解释了250-1000keV能量范围内质子和反质子在He原子的单电离截面和双电离截面上不同的碰撞机制。计算采用包含1/r/sub12/电子-电子相互作用的玻尔氦原子模型。意想不到的巨大观测差异(Andersen等人，Phys.莱特牧师。57,2149(1986))，通过计算重现了质子和反质子碰撞的双电离与单电离比R。计算表明，由于两种效应，反质子的双电离截面大于质子的双电离截面。第一个效应是，反质子可以从比质子更大的撞击参数将一个电子推入另一个电子，质子必须位于原子核和第一电子之间，才能将其拉入与第二电子碰撞的轨道。然而，最重要的影响是，在较小的撞击参数下，反质子屏蔽了氦原子核，导致库仑爆炸，而质子增加了两个电子的结合。计算还表明，在低能(小于或等于500keV)时，比值R的差异的一个组成部分是由于质子的单电离截面，预计质子的截面比反质子大(在250keV时相差36%)。
Classical trajectory Monte Carlo calculations have been used to elucidate the collision mechanisms responsible for the differences in the single- and double-ionization cross sections of He atoms by protons and antiprotons in the energy range from 250 to 1000 keV. The calculations employed the Bohr helium-atom model which includes the 1/r/sub 12/ electron-electron interaction. The unexpected large observed difference (Andersen et al., Phys. Rev. Lett. 57, 2149 (1986)) in the ratio R of double to single ionization for proton and antiproton collisions is reproduced by the calculations. The calculations indicate that the antiproton double-ionization cross section is larger than that for protons because of two effects. The first effect is that the antiproton can push one electron into the other from larger impact parameters than for protons which must be between the nucleus and the first electron in order to pull it into a trajectory which collides with the second electron. The most important effect, however, is that at small impact parameters the antiproton screens the helium nucleus causing a Coulomb explosion while the proton increases the binding of the two electrons. The calculations also show a component of the difference in the ratio R at low energies (Eless thanmore » or equal to500 keV) is due to the single-ionization cross sections with protons predicted to have a larger cross section than antiprotons (36% difference at 250 keV).« less