Recent publications ( 1 4 ) have dealt with the effect of electron scavengers on the radiolysis of simple inorganic gaseous hydrides. We would like to present some results of a preliminary study on the radiolysis of gaseous H2S that are, in general, quite different from those above (14).Matheson C.P. grade H,S (99.7 %) was found to contain CO, (-0.2 %) and CS, (< 0.001 %) as impurities when checked by gas chromatography. A 3 m Poropaq Q column maintained at 65 "C, helium carrier gas, and thermal conductivity detection were used (5). After several freezepump-thaw cycles at -130 "C, the concentration of CO, was reduced to -0.005 %. Some of this H,S was irradiated to a dose of about 4 x lo2, eV g-l. After degassing at -196 "C, this H,S was found to contain -0.005 % CO, and no detectable amount of CS,. Radiolysis experiments with the pre-irradiated H,S gave identical results to the untreated H,S, and so the latter was used for the bulk of the work presented here. SF, and N,O (Matheson) were degassed several times by freeze-pump-thaw cycles at liquid nitrogen temperature and were used without further purification.Dosimetry was effected by ion current measurements in vessels similar to those described by Back et al. (6), the extrapolation method of Scott and Greening (7) being used to obtain saturation ion currents. The same vessels were also used as irradiation vessels, as were ordinary Pyrex vessels of similar geometry. All vessels were baked out at 400 "C, to a pressure of less than lo-' Torr prior to filling and irradiating.

Ion currents produced in hydrogen sulphide in a cylindrical ion chamber by y-radiolysis have been measured. Saturation points on the ion current curves were located by application of general recombination theory. These saturation currents were then used to estimate that the average energy W(H2S) required to produce an ion pair in hydrogen sulphide is 25.3f0.4 eV. Other values determined were W(CH3SH) = 25.1 f0.4 eV, W(N20) = 32.7f0.4 eV and W(SFs) = 35.0f0.4 eV. Hydrogen and sulphur are produced upon irradiation, with radiation yields (molecules per 100 eV energy absorbed, or G values) G(H,) = 7.0k0.2 and G(S) = 7.0f0.4 relative to W(HzS) = 25.3 eV. Possible use of the production of hydrogen from the radiolysis of hydrogen sulphide as a gas dosimeter is discussed.

In they-radiolysis of H2S with added buta-1,3-diene, H atoms appear to react before they become thermalised. With added benzene, propene, and but-1-ene insufficient scavenging occurs to say with certainty whether a similar situation applies, but indications are that it may be so for propene, and but-1-ene. Investigation of the effect of but-1-ene on the sulphur yield, indicates a dose rate effect which is explained by a competition between ion-recombination and diffusion to the wall enhanced by convection currents. Yields of G(H2) = G(S) = 0.5 unscavengable by buta-1,3-diene are indicated, and evidence is given that excited sulphur atoms (S*) and S+ ions are probable precursors of these yields. Nitric oxide appears to react with SH radicals in a chain process producing H20, N20 and S. Electric fields do not affect the radiation yields until electron acceleration just before saturation occurs, causes increased decomposition. The ratio of sulphur scavengable in the presence of a field is -4 : 1, which is much lower than in the absence of a field (13 : 1). This is evidence for production of excited S atoms by field accelerated electrons.

Measurement of G(ion) (= 1 0 0 / W ~) and G(H& in H2S+SF6 mixtures, where WM is the average energy required to produce an ion pair in the mixture, and G(ion) and G(H~)M are the total ion yield and hydrogen yield respectively, enables energy partition parameters a to be calculated. These were found to be a = 1.44 for mixtures of stopping power fraction 2 = P1/(Pl+S2P2/Sl), (where P and S refer to pressure and stopping power of gases 1 and 2) between -h 0.2 and 1 .O. Below 2 -I I . 0.2 each mixture has its own particular a value and these values, in the main, decrease smoothly with decreasing 2 to a e 0.70 at 2 = 0.02. The hydrogen produced in the mixtures from energy deposited in H2S alone, G(H~)H~s, is independent of SF6 concentration when energy partition is calculated using these a parameters.Sulphur yields in the mixture G(S)M are much greater than G(H& ; the imbalance is accountable by HF production. At low SF6 concentration (high Z), G(S)M inneases rapidly with SF6 concentration fram 7.0 in pure H2S to 11.0 at 2 = 0.98 (3; mol % SF6).Recent work on the a-particle and y-ray irradiation of gaseous H2S has demonstrated that electron scavengers such as 02, N20, SF6, do not lower the radiation yield of hydrogen, G(H,). In fact, as the SF6 concentration is increased to 7 mol %, G(H,) increased from 7.0 to 8.0.2 In experiments using very high dose rates from a 600 kV electron pulse, Perner and Franken observe the lowering of G(H2) by the addition of SF6.The effect of SF6 on G(H,) observed by us may be due to energy transfer from SF6 to H2S. To test this possibility and perhaps gain information on the radiolysis mechanism, we decided to measure the W values and product yields, G(H2) and G(S), of binary mixtures of H2S and SF6 over the whole concentration range. EXPERIMENTALThe treatment of H2S, SF6 and all other materials used, irradiation equipment and procedure, ion current measurements, and hydrogen and sulphur analyses, have all been described previously. 3 SiF, was detected by I.R. and mass spectroscopy. Infra-red measurements were carried out on a Unicam SP200 spectrophotometer, using a 0.1 m gas cell having sodium chloride windows.Mass spectra were obtained on an A.E.I. MS12 instrument.

Measurement of ion yields Gm(= lOO/W,), where W, is the average energy required to produce an ion pair in the mixture) in gaseous H2S-N20 mixtures indicates that the energy partition parameter " a " = 0.53 holds for mixtures of stopping power fraction Z = P1[P1+(S2/S1)P21 from 0.15 41.0, and perhaps over the whole range of 2. PI and P2 are the partial pressures and S1 and S2 are the stopping powers relative to air of H2S and N20 respectively. The radiation yields of H2 and N2 in the mixtures G(H,), and G(N2)m yield this value of " a " = 0.53 probably restricted to the range 2 = 0.45 +1.0. A scheme of energy transfer from an excited state of N 2 0 to H2S is suggested for the deviation below 2 = 0.45. For 2 ~0.45 an excited state of N20 is postulated that does not transfer energy to H2S. A mechanism of ionization energy transfer plus reactions of 0 and NO2 with H2S is suggested as an explanation of the high sulphur yields at low 2.Recent articles 1v have shown that N 2 0 does not appear to lower the yield of H,, G(H2), in the radiolysis of H,S. However, at a gas pressure of 106 kN m-2, N2 was produced with a G(NJ fi 1.7 for > 2 % N,O. This figure is well below the value of G (ion) Because of this lack of effect on G(H,) in H2S, and the rather peculiar value of G(N,). we decided to investigate the energy partition between the two gases. 4.0 in H,S, expected if N,O captures all the electrons. EXPERIMENTAL Details of materials used, irradiation equipment and procedure, ion current measurements and hydrogen and sulphur analyses have been given previ~usly.~ Dosimetry in Pyrex vessels was based on G(H2) = 7.0 in pure H2S.3Gaseous products not condensable at 77K, H2, N2 and 02, were collected in a gas burette and the total observed. H2 was diffused away through a palladium thimble, and the remaining N2 and O2 measured and analyzed by mass spectroscopy. N2 yields were '