Electron capture and loss

Charge exchange is important all along the high-LET tracks. The effective ionic charge is determined by cross sections of electron capture and loss, which depend predominantly on the ionic velocity. Electron loss may be simply described by an ionization of the incident ion in its own reference frame due to the impact of medium electrons and nuclei. Following Bohr (1948), Mozumder et al. (1968) wrote the cross section for this process as1... 

Although an accurate theory of equilibrium and nonequihbrium charge-state populations must presumably be based on a quantal description of electron capture and loss, a simple estimate of the equilibrium charge state... 

Cemy et al (Ref 109) calcd range-eneigy relations for protons and a - particles in RDX and HMX, Pb styphnate and Pb azide, as shown in Fig 1. The a - particle ranges were obtained from established proton ranges the difference in range caused by variations in electron capture and loss were estimated from the known value for air by assuming that this effect depended only on the molecular electron density... 

Before proceeding to calculate the stopping cross section, we calculate the fraction of protons,/(H ), and the fraction of neutral hydrogens,/(H), in the beam during the collision according to equation (9). With the calculated values obtained for the electron capture and loss cross sections as shown in Fig. 3, we present in Fig. 4 the fraction of and in the hydrogen beam... 

In Fig. 8, we present the total, St, electronic, S, and nuclear, S, contributions to the stopping cross section as a function of the initial projectile velocity, for the case of He" colliding with atomic Ne. In the same figure we compare with the experimental data of Chu and Powers [52], of Fukuda [53], and of Baumgart et al. [54]. For the case of He Ne, and following the Dalgarno approach, we require the cross section for electron capture and loss for He , He. and He in order to determine the fractional... 

Cross-Section for Electron Capture and Loss Energy Loss in Charge Exchange Processes... 

Both electron capture and loss represent special cases of energy loss of the incident particle. In the case of electron capture, an electron must be ionized from the water molecule and it must be given a minimum speed v. The energy to effect this process must come from the particle. The energy requirement is somewhat reduced because of the binding of the electron in the ion. Hence, the energy loss in the electron capture process is given approximately by... 

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