Relative Partial Cross Sections Research Articles

Comment on the interpretation of repellar curves obtained with Nier type electron impact ion sources

It is shown that, under the usual operating conditions, it is impossible to measure accurate relative partial ionisation cross section functions with this source.

Single and double ionization of nitrogen dioxide by electron impact from threshold up to 180 eV

Electron impact ionization of nitrogen dioxide has been studied as a function of electron energy up to 180 eV with a double focussing mass spectrometer Varian MAT CH5 and an improved Nier type electron impact ion source. We report the first observation of NO2++ produced via electron impact. Relative partial ionization cross section functions have been obtained for the processes NO2+e→NO2++2e and NO2+e→NO2+++3e. An accurate measurement of the cross section ratio q (NO2++/NO2) /q(NO2+/NO2) has been performed. In addition an estimate of the absolute partial cross sections has been made normalizing the measured relative cross section against the Ar+ cross section with the method of molecular effusive flow. Using the nth root extrapolation the following ionization potentials have been derived from the cross section functions near threshold: NO2+ = (10,4±0,3) eV and NO2++ = (35,0±0,5) eV.

An instrument for measuring branching ratios in photoionizing processes

An instrument using photo-electron spectrometry has been developed to measure branching ratios and relative partial cross-sections for photoionizing processes in gases, with particular emphasis given to measuring variation of these parameters as a continuous function of wavelength. The instrument is described together with a consideration of sources of errors and a method of calibration.

Phenomenological analysis of high energy nuclear fragmentation based on the diffractive excitation model

A phenomenological study of fragmentation of beam nuclei in the Bevatron energy region is made based on the diffractive excitation model. Two body dissociation and fragmentation are assumed. It is shown that because of the slight energy transfer between colliding nuclei, the interfragment binding energy of the beam nucleus plays an important role in the fragmentation even in the high energy region and that the main features of relative partial cross sections and momentum distribution widths of fragments can be understood with the diffractive excitation model. Some implications of our results for the cluster structure of the beam nuclei are discussed.NUCLEAR REACTIONS Analysis of data on the partial cross sections and momentum width distributions of fragments from $^{16}\mathrm{O}$ and $^{12}\mathrm{C}$ at 2.1 and 1.05 GeV/N, diffractive excitation model.

Modes of Atomic Motions in Liquid Helium by Inelastic Scattering of Neutrons

The wavelength distribution of ${4.03}_{9}$A neutrons scattered inelastically by specimens of liquid helium has been measured at 30 angles of scattering in the range 10\ifmmode^\circ\else\textdegree\fi{} to 140\ifmmode^\circ\else\textdegree\fi{}. At each angle of scattering there is a discrete peak which shows little broadening, and little if any excess scattering outside this peak. The changes in energy and momentum corresponding to the change in wavelength of the scattered neutrons have been calculated for each angle of scattering. The dispersion curve in the liquid is similar in form to that predicted theoretically but there are differences in detail. For momentum changes ($\ensuremath{\hbar}Q$) in the range $0.26 {\mathrm{A}}^{\ensuremath{-}1}\ensuremath{\le}Q\ensuremath{\le}0.6 {\mathrm{A}}^{\ensuremath{-}1}$, the measurements fall on a straight line which has a slope given by the velocity of sound. The maximum and the minimum of the curves occur at 1.10 ${\mathrm{A}}^{\ensuremath{-}1}$ and 13.7\ifmmode^\circ\else\textdegree\fi{}K and at 1.91 ${\mathrm{A}}^{\ensuremath{-}1}$ and 8.65\ifmmode^\circ\else\textdegree\fi{}K, respectively. Beyond the minimum the curve starts to rise with a slope equal to or less than the phonon branch and then falls below this, suggesting the possible existence of a second maximum. The relative partial differential cross section for the production of a single phonon excitation is low at low momenta, has a maximum in the region of 2.0 ${\mathrm{A}}^{\ensuremath{-}1}$ and then decreases rapidly to low values in the region of 2.68 ${\mathrm{A}}^{\ensuremath{-}1}$. The position of the maximum may be compared with 2.05 ${\mathrm{A}}^{\ensuremath{-}1}$, the maximum in the total differential cross-section curve and 1.91 ${\mathrm{A}}^{\ensuremath{-}1}$, the minimum of the dispersion curve, respectively. The widths and mean energy change of neutrons scattered through 80\ifmmode^\circ\else\textdegree\fi{} have been measured at 13 temperatures in the range 1.78\ifmmode^\circ\else\textdegree\fi{}K to 4.21\ifmmode^\circ\else\textdegree\fi{}K. Scattering at this angle corresponds to the production of excitations at the minimum of the dispersion curve. The mean energy change decreases rapidly from a value of ${8.6}_{5}$\ifmmode^\circ\else\textdegree\fi{}K at 1.1\ifmmode^\circ\else\textdegree\fi{}K to 5.6\ifmmode^\circ\else\textdegree\fi{}K at the $\ensuremath{\lambda}$ temperature where there is a marked change in slope and only a much slower decrease above the $\ensuremath{\lambda}$ temperature to 4.9\ifmmode^\circ\else\textdegree\fi{}K at 4.2\ifmmode^\circ\else\textdegree\fi{}K. The widths of the spectra increase rapidly from a value of 1\ifmmode^\circ\else\textdegree\fi{}K at 1.1\ifmmode^\circ\else\textdegree\fi{}K to 11\ifmmode^\circ\else\textdegree\fi{}K at the $\ensuremath{\lambda}$ temperature where there is also a marked change in slope and only a much slower increase to about 15\ifmmode^\circ\else\textdegree\fi{}K at 4.2\ifmmode^\circ\else\textdegree\fi{}K. The measured widths are compared with theoretically calculated widths.