The EFFECT OF ELECTRIC FIELDS, AND a RELATED DEPENDENCE ON DOSE RATE, IN THE Γ-Radiolysis OF HYDROCARBON GASES

Abstract

The effect of electric fields on the y-radiolysis of ethane, propane, and the butanes has been investigated briefly a t 800 mm pressure, with dose rates between 2X101° and 400X1010 ev/cc sec. Yields of hydrogen were reduced when a saturation field was applied, except with ethane a t low dose rate, where a slight increase in hydrogen yield was observed. With propane and n-butane, the yield of hydrogen in the presence of a saturation field was independent of dose rate, while with ethane, it decreased with decreasing dose rate. A t the same time, a dose rate dependence was discovered in the simple radiolysis, in the absence of any field, of ethane, propane, and n-butane, a decrease in the yield of hydrogen a t low dose rates being observed. An explanation of these observations is suggested in terms of a competition between neutralization of ions in the gas phase and diffusion of ions to the wall. High dose rates should favor the former process, and low dose rates the latter. At sufficiently high dose rates, all ions should be neutralized in the gas phase. A t sufficiently low dose rates, all ions should diffuse t o the wall before neutralization, and it is suggested that the radiolysis under these conditio~ls should closely reseinble that ill the presence of a saturation field a t higher dose rates.The application of an electric field to a gas during irradiation offers a potential means of -distinguishing between products arising from ions and those forined from neutral species. In practice, the interpretation of the results is very complex, and except for the work of Essex and his collaborators a t Syracuse (I), mostly concerned with a-radiation, the method has not been widely used in radiation chemistry. The present work was undertaken to study the effects oi electric fields on the 7-radiolysis of some simple hydrocarbon gases, using a saturation-current method (2) to measure absolute product yields. In the course of the work, a hitherto unsuspected dependence of hydrogen yield on dose rate was discovered, which appears to be closely related to the action of applied fields on --the radiolysis. EXPERIMENTALThe preparation and purification of hydrocarbon samples for irradiation have been previously described (2, 3). Gases were irradiated in cylindrical vessels of 60-mm 0.d. and about 500-to 600-cc volume. Two experiments with propane were done in a smaller vessel of the same design and length, but with about one-half the diameter and one-quarter the \~olume. The measurement of saturation ion current and of hydrogen yield has been described (2). Electric fields were always applied with the central electrode positive, so that the positive ions were drawn to the other electrode, the graphite-coated wall of the cylindrical vessel. Hydrogen was the only product measured, and the extent of decomposition was always small enough that "internal" scavenging was negligible, and the measured yields were very close to their true initial values (3). Ethylene scavenger was added in some experime~lts, in which case the hyd...

Ion neutralization reactions in irradiated hydrogen chloride, hydrogen bromide, and nitrous oxide

“…Graphite coated electrodes were therefore en~ployed, the cells being baked under vacuum at 250 ' C for 12 h prior t o each experiment. Most experiments were performed in cells similar to those previously described (1,5). The cylindrical collecting surface was 40 mm long and 33 mm in diameter with a coaxially mounted 7 mm tube serving as the high voltage electrode.…”

Pulse radiolysis of neopentane in the gas phase

“…The yields of the meas ured products are given as molecules , M, of product X produced per ion pair, N +, (M(X)/N+) [9]. A W-value of23.2 eV for neopentane was chosen to convert number of molecules per e V to the number of molecules per ion pair [10].…”

Effect of Electric Fields on Gamma Radiolysis of Methanol Vapor

“…On the other hand, the process (2) will be greatly suppressed by the fast collection of electrons to the anode. If the above assumption is allowed, the observed reduction of the scavengeable hydrogen yield in the saturation region, about 20% of the total hydrogen yield in no field region, may correspond to this suppression of the process (2).…”