Abstract. 0 2 -free aqueous solutions of 0.05 mol dm -3 rmmonium bicarbonate were studied after receiving vnrious doses of so Co gammas (0.001-170 Mrd) or krd pulses of 10 MeV electrons. Formate, oxalate, formaldehyde and an unidentified polymer (M W 14000-16000 daltons) were found to be the main radiolytic products. A large initial yield of formate in the Y-radiolysis, G(HC00 -) = 2.2, is due to the reaction CO* + HCO7 t HC00~ + CO3. The efficiency of organic synthesis within the large dose range studied is low and is explained by efficient pathways to the reformation of bicarbonate, where the reaction

We have examined a water-dominated multicomponent system after irradiation in the multimegarad dose range with gamma rays from a 60Co source at both 77 and 310 K. The constituents were simple organic compounds in the proportions in which they appear in a dense interstellar cloud: HCN/CH3OH/CH3CN/C2H5CN/HCOOH = 1:0.6:0.2:0.1:0.05. The total amounts were adjusted to correspond to a carbon to nitrogen ratio of 1.8 and a water content of about 50% in a cometary nucleus where the dust to volatiles ratio is 1; the total amount of CN-bearing compounds was taken to correspond to 0.4% of the cometary mass. In experiments at 310 K about 40 radiolytic products are identified, among them aldehydes and amino and carboxylic acids. Abundant polymeric material (Mw up to 80,000 daltons) is formed. The basic aspects of radiolysis of the liquid system are present also at 77 K, although at radiation-chemical yields that are lower by one to two orders of magnitude. We have considered the relevance of the present findings to the chemistry of a liquid-water core and the icy layers of a cometary nucleus.

Ultrafiltration of a laboratory-made hematite sol was studied in a batch cell with an Amicon PM 10 membrane at 298 K. The effects of hematite bulk concentrations (2 to 10 k g .~~-~) , stirring conditions (0 and 400 rpm), and pressure (50 to 350 kPa) were investigated. The permeate flux increases with increasing pressure and stirrer speed, and decreases with increasing hematite bulk concentration. The polarization resistance increases with an increase in pressure and hematite concentration. The polarization resistance is greater under unstirred conditions.