Ions In Foils Research Articles

Theory of average charge and energy loss of cluster ions in foils

We study the average charge and the electronic energy loss of the swift (but not relativistic) clusters in a solid. A self-consistent average-charge theory for clusters in foils is presented on the basis of the fluid-mechanical model. Here the electron stripping rate is evaluated not only for an isolated ion, but also for cluster ions under the same background by taking into account the binding effect of the surrounding ions. This theory can elucidate very well not only the reduction of the cluster average charge per ion, but also its cluster-size and foil-thickness dependences of the recent data for the MeV/atom carbon clusters $({\mathrm{C}}_{n})$ in carbon foils. The structure dependence is also proposed theoretically. In spite of the average-charge reduction, we can reconcile the enhancement of the energy losses of the corresponding clusters. The cluster energy losses with the inclusion of the Coulomb explosion by the wave-packet model is in much better agreement with the data at energies of 1--5.65 MeV/atom. Consistent agreement both in the diminution of average charge and in the enhancement of energy loss supports that the charge-state bulk effect is dominant in the cluster average charge.

Large energy loss straggling of protons and He ions in Mylar foils

Nuclear reaction analysis often requires polymer or thin metal foils to be inserted in front of the detection system to stop scattered incident ions from entering the detector. It is important to completely understand the straggling processes in the foil if true target depth profiles are to be extracted from the energy loss profiles of the reaction product particles. Generally Bohr straggling is used to account for energy spreads in these foils. This, however, has no ion energy dependence, is good mainly for energy losses much less than 20% and can underestimate straggling by a factor of 5 or more for large energy losses. This paper reports on proton and helium ion straggling in foils where the fractional energy loss ( ΔE / E ) exceeds the Bohr limit of 20% and gives simple methods of calculating the straggling from the stopping power of the ions in the foils.

Blisters in He+ ion implanted Nb-1%Zr alloy

Blister formation due to multi- and single energy He+ ions implanted in Nb-1%(wt)-Zr has been investigated by scanning electron microscopy. Foils implanted at room temperature to a concentration of 2 × 1028 He/m3 showed blistering whereas in foils with a concentration of 1028 He/m3 the blisters were only observed after annealing at 950°C for 2 h. It has been found that the blister size increases with increase in ion implantation energy, anneal temperature and, in general, anneal period. However, beyond a certain anneal period blister sizes do not increase with anneal period; they can even become smaller. The multi-energy implantation produces smaller blisters compared with those of the single ion energy imimplant. The blister skin thicknesses are approximately the same as the projected ranges of He+ ions in foils, and the blister formation may be due to the excessive gas pressure build up in the maximum gas concentration region of an implant foil.

Polarization Induced in a Solid by the Passage of Fast Charged Particles

A theoretical description is given of the polarization charge-density distribution induced in a solid by the passage of a fast charged particle. The stopping power of the solid (including the effects of close collisions) is well accounted for by the braking effect of the polarization charges. Calculations based on this model for the polarization give good agreement with the results of recent experiments on the dissociation of fast molecular ions in foils.