Low-velocity Ions Research Articles

Elastic and Inelastic Scattering of Low-Velocity Ions: Ne+ in A, A+ in Ne, and A+ in A

Elastic and charge-exchange cross sections have been measured in the energy range 4 to 400 ev for Ne+ in A, A+ in Ne, and A+ in A. Charge exchange was observed only for A+ in A. No evidence was found for the existence of the diatomic ion NeA+. Constants for empirical potential functions have been evaluated and the functions tabulated.

The nature of the taper tracks of heavy ions in nuclear emulsions

The thinning down of the tracks of heavy ions as they approach the end of their range in electron sensitive photographic emulsion, can he quantitatively explained on the assumption that the thickness of the developed track is due mainly to δ-rays which no longer have sufficient range at low ion velocities to broaden the track.

Elastic and Inelastic Scattering of Low-Velocity Ions: He+ in Ne, Ne+ in He, and Ne+ in Ne

Experimental results are presented for collisions in the energy range 4 to 400 electron volts of He+ ions in neon and of Ne+ ions in helium and in neon. Charge exchange was observed only in the case of Ne+ in neon. Empirical potential functions for the interactions are tabulated and discussed. It is concluded that the HeNe+ ion, if formed, would probably separate if subjected to impact at thermal energies.

Scattering Cross Sections and Interaction Energies of Low-VelocityHe+Ions in Helium

It is pointed out that the determination of ion-molecule forces from results of measurements of scattering of low-velocity ion beams in gases can be seriously in error unless some a priori knowledge of the nature of the forces is available. The scattering of ${\mathrm{He}}^{+}$ in He is chosen as an illustration. The elastic and charge exchange cross sections calculated from Moiseiwitsch's theoretical force laws are shown to be in good agreement with the experimental values of Cramer and Simons. The force law determined by the latter authors directly from their measurements is in error because of the assumption of an incorrect form and the failure to consider the two interaction states involved.

Sputtering at Low Ion Velocities

Low sputtering rates are measured by means of the probe technique in a plasma. The displacement of the probe curve along the voltage axis (and its change in shape) when the probe is covered with a material of different work function, sputtered from a sputtering electrode, is a dependable measure for the thickness of the sputtered layer. The method is very sensitive, generally applicable, and was applied especially to answer the question of a threshold voltage U0 for sputtering. The sputtering rate for Pt in Xe, in the region of low ion energies (50<Us<200 ev) is roughly proportional to (Us−U0)2 with U0=40 ev.

XV. Slow inelastic collisions between atomic systems

Abstract The physical mechanisms of the various processes which may occur as a result of encounters between low velocity atoms or ions are discussed, particular attention being paid to the factors which determine whether or not a collision is likely to be near-adiabatic. The following are the processes considered :

The Low Velocity Scattering of H+ and H3+ in Hydrogen

The theory of the elastic scattering of a low velocity ion in a gas is examined in some detail. More precise measurements are reported on the elastic scattering of H+ and H3+ in hydrogen in the velocity range of 2 to 135 volts. The simple exponential form of a potential law is shown to change with the velocity of the ion, i.e., with distance of closest approach of the interacting particles. For H+ in H2 this is—V=−20.37×10−32r4from 2 to 24 volts (ra>1.74A)and V=−8.68×10−14r1.74from 24 to 135 volts (ra=1.74 to 1.5A).The interaction energy calculated on this basis is 3.0 electron volts instead of the 3.5 previously reported. For H3+ in H2 an average taken from 5.4 to 130 volts is V=−1.145×10−36r4.60(ra=2.12 to 1.07A);but between 10.5 and 28 volts (ra = 1.85 to 1.48A) V=−5.98×10−32r4.Both inverse fourth-power potential laws are compared with a similar law evaluated on the basis of the interaction being due solely to that of the charge on the ion interacting with the induced dipole of the hydrogen molecule. The H3+ law is seen to approximate this closely whereas the H+ law does not.

An Apparatus for the Measurement of the Scattering of Low Velocity Ions in Gases at Low Pressure

An apparatus is described for the measurement of the scattering of low velocity ions in gases. This consists essentially of an ion source, focusing devices, a magnet for velocity and species selection, and a measuring chamber. Technique of construction and operation is described which enables scattering curves to be obtained where the effective cross-sectional area is plotted against ion velocity down to a velocity of two volts. This apparatus has been found useful for condensable gases such as water, as well as for non-condensable gases. It has been constructed in such a way that ion neutralization as well as elastic scattering can be quantitatively determined as a function of velocity.