Primary Energy Loss Research Articles

On the mechanism of molecular ion formation from organic solids by ion impact

The general behaviour of transitions from bound molecular surface states into dissipative gaseous states in an externally dc-field-free region is reviewed. Adiabatic and non-adiabatic processes have to be distinguished. It is shown that non-adiabatic interactions may be responsible for various phenomena of molecular ion formation by heavy ion induced desorption, in the inelastic as well as in the elastic primary ion energy loss regime. The implications of this non-adiabatic desorption model are compared with experimental data as primary ion energy loss dependence, secondary ion yields, and energy distributions. The organic ion types are shown to be representative for the condensed phase acidity or basicity, respectively, being desorbed by the very sudden process of ion impact.

Secondary electron yield in the Bendix channel electron multiplier

Abstract The secondary emission yield of the emissive layer of a Bendix channel electron multiplier was measured using an electron beam for energies between 100 eV and 1 keV. This yield reaches δ = 3.6 at about 350 eV in a channel electron multiplier at the end of the desorption phase. The variation of δ as a function of the electron energy is in agreement with semiquantitative theories using a power law to describe the primary electron energy loss.

Physics of an active region loop system

The structure of the active region loops is investigated by the study of a loop complex which undergoes a dramatic evacuation of most of the mass it contains. The need for continual energy deposition in loops is emphasized by the apparent cessation of energy input to the loops studied and their subsequent behavior. Estimates are made of the energy necessary to form and to maintain the loops, and of the relative importance of radiation and thermal conduction as energy loss mechanisms. Models based on the observed EUV emission are used to place limits on the size of loops seen in various lines and on the density and temperature structure. We find that the cool cores of active region loops are likely to be no more than a few hundred kilometers in radius and that several such cool threads may be imbedded in a common hot outer sheath. The primary energy loss on a large scale is radiation with thermal conduction contributing to local disturbances. There is a tendency for the development of apparently unstable condensations or knots along the length of a loop. Higher resolution observations will be necessary to confirm some of our predictions.

Production of Displacement Radiation Effects by Recoils from Photoneutron Reactions

The photoneutron method of producing displacement radiation effects has been established. The displacement effects produced by recoils from $\mathrm{Si}(\ensuremath{\gamma},n)$ reactions have been detected by measurement of the change in excess-carrier lifetime. The change in the reciprocal of the lifetime is approximately proportional to the total number of primary reactions at various irradiating bremsstrahlung energies between 15 and 38 MeV, with a proportionality constant of (2.0\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$\ifmmode\pm\else\textpm\fi{}25%)${\mathrm{cm}}^{3}$ ${\mathrm{sec}}^{\ensuremath{-}1}$. The data can be explained on the basis that the primary energy loss of the recoil atoms is due to ionization. Other possible explanations are offered and a comparison of the results with those of 30-MeV electron irradiations is made.

XXX. Theory of ionization fluctuations

Summary The distributions of the loss of energy by ionization of a fast primary and of the numbers of ion pairs it produces are derived. It is shown that down to quite small values of the primary ionization. both can be represented by the same “universal’ distribution if the variables are reduced by a proper choice of scale and origin, which accounts for the experimental fact that ion pair numbers are proportional to primary energy loss. These conclusions remain valid when one takes into account quantum resonance effects and the details of atomic structure of the absorber.

Fundamentals of Secondary Electron Emission

Secondary electron emission is of great importance to the physicist because of its bearing upon the problem of the interactions between fundamental particles and to the radio engineer because of its applications, as well as its effect, upon the operation of electronic tubes. A complete theoretical picture capable of accounting quantitatively for all observed phenomena does not exist. Secondary electron emission differs from other modes of emission in many respects. The essential characteristics can best be evaluated by considering a typical experimental arrangement for investigating the phenomenon. Three categories of emitted electrons are recognized. The yield may depend upon various factors, such as the primary energy, collector voltage, target temperature, time, angle of incidence, atomic properties of target, and the composition of the target. The difficulties of propounding a satisfactory theory are evident from an individual consideration of each of the various processes involved. The primary interaction, primary energy loss, escape of secondaries, and integration over the range of the primary must each be treated to arrive at a final solution. In several previous attempts at formulating a theory, only the most loosely bound electrons in the solid have been regarded as constituting the source of secondary electrons. Normalizations are required for comparison of the results with existing experimental data. There are cogent reasons for regarding bound electrons as a very important source of secondaries.

The Specific Primary Ionization and Energy Loss of Fast Electrons in Matter

By utilizing the dependence of the efficiency of a Geiger-Mueller counter upon the primary ionization of a counted particle, the primary ionization by electrons in hydrogen has been determined for energies in the range 0.2 Mev to 9.0 Mev. The relative stopping powers of carbon and ${\mathrm{H}}_{2}$O have also been investigated, the results yielding evidence for the existence of a polarization effect which reduces the energy loss of fast particles in condensed matter. Experimental results are compared with those of the Bethe-Bloch theory and the Halpern-Hall theory which takes into account the polarization properties of the medium.