Energy loss of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>α</mml:mi></mml:math>particles in gaseous C-H and C-H-F compounds

Abstract

The stopping powers of six gaseous compounds ${\mathrm{C}}_{2}$${\mathrm{H}}_{2}$${\mathrm{F}}_{2}$, ${\mathrm{C}}_{2}$${\mathrm{H}}_{4}$${\mathrm{F}}_{2}$, ${\mathrm{C}}_{3}$${\mathrm{H}}_{8}$, ${\mathrm{C}}_{4}$${\mathrm{H}}_{6}$, ${\mathrm{C}}_{4}$${\mathrm{H}}_{10}$, and ${\mathrm{C}}_{3}$${\mathrm{H}}_{4}$ (allene) for $\ensuremath{\alpha}$ particles of energies 0.3 to 2.0 MeV have been measured in a differentially-pumped gas-cell system with probable random errors ranging from 0.7% to 1.3%. An ambiguity in the interpretation of previous stopping-power measurements in hydrocarbon and halogen-carbon compounds has been resolved, and it is shown that all the previous data, as well as the present data involving straight-chain single-bond compounds, can be fitted by an atomic stopping power for carbon identical to the vapor-deposited solid-carbon stopping power. A rule has been obtained to predict the molecular stopping power of aliphatic saturated hydrocarbons. It is found that due consideration must be given to molecular structure when predicting molecular stopping powers from atomic stopping powers for double-bonded compounds.