-I
100-
Table
11.
Sample Ge poKder Ge dioxide
Comparison o f Spectrographic and Chemical Standard and Unknown Samples
Arsenic, P.P.M. Doped std. Chem. Gutaeit 0.15 0.50
Blank Blank 0.50 1.0
50y' of the rutheiiiuin in the uridoppered flask remained. nhile 97% of the ruthenium in the stoppered vessel was recovered. Extraction of Zirconium. The extraction is decidedly superior in separation efficiency to the distillation method. Examination of a large number of carbon tetrachloride extracts b y gamma spectrometry showed no other fission activities from samples aged 4 to 10 days after irradiation, as well as samples aged up to 6 months, rvhen the above procedure was folloii-ed. I n t h e absence of zirconium holdback carrier, traces of radiozirconium were found in the earbon tetrachloride. Addition of zirconium carrier piior to the extraction. and washing of the carbon tetrachloi d e Ivith n-ater, effectively prevent tontaminatiori by zirconium. This freedom from contamination is in contrast t o that of ruthenium tetroxide distillates, which are usually contaminated 111th iodine, molybdenum, and technetium. Contamination by Other Fission Products. Experiments were performed t o determine t h e decontamination from other fission products. T h e complete procedure was followed on a 4-day-old solution of irradiated plutonium from which all radioruthenium had previously been removed b y distillation. T h e final precipitates were counted for beta and gamma activity. Only 4 X lo2 to 8 X lo3 of a n original 6 X lo7 counts per minute per milliliter were found. Gamma pulse height analysis and decay curves
showed this residual activity to be due t o a mixture of tellurium-132 and zirconium-97. The decontamination factor for these elements is between l o 3 and lo4. Decontamination from other fission products is greater than 104. Isotopic Exchange. T h e fission product ruthenium is not oxidized as rapidly a s is t h e carrier ruthenium. Experiments in which t h e extraction was made immediately following t h e addition of t h e sodium hypochlorite gave low, a n d variable. count rates for t h e ruthenium actirity, indicating incomplete isotopic exchange. This difficulty was overcome b y allowing the samples t o stand for 1 hour after addition of the oxidizing agent prior to the eutraction. The count rates of samples treated in this manner were identical TT ith samples prepared by the distillation method, shon ing that complete equivalence of carrier and tracer i- achieved by this: treatment. KO ruthenium ia lost by Yolatilization prior t o the re-acidification a t pH 4, since hypochlorite in alkaline medium oxidizes ruthenium mainly to perruthenate. Ruthenium tctroside is fornied when the sample is brought to pH 4 n i t h acid. Reproducibility. Table I1 coiiipares ruthenium analyses in irradiated plutonium (about 10’5 fissions per gram) b y extraction a n d by distillation. These analyses were performed n ithin 1 week following irradiation t o test for interference from short-lived fission product activities. Within experimental error t h e same gamma activity and t h e same precision are obtained by both methods. The relative standard deviation of the extraction method is less than 1.5y0 by gminia counting, and 3% or less by beta counting. Gamiiia counting is preferred because of greater detection sensitivity. The alpha decontamination factor is 105. Quadruplicate analyses b y the extraction method may be performed in about 3.5 hours, of which 1 hour is used for isotopic exchange. With a n experienced operator yields of about 95% may be achieved consistently. As in other radiochemical methods, 100% yield is not required s o long as the yield of each sample is mensured and the count rate is corrected for that yield. Carbon Tetrachloride Purity. Ruthenium tetroxide is sensitive t o reduction, especially b y organic substances. Reagent grade carbon tetrachloride was found to contain sufficient impurities t o cause a slow reduction of t h e ruthenium tetroxide during t h e extraction, which tended t o produce low yields of 90 t o 95%. KO reduction was observed when redistilled carbon tetrachloride was employed in t h e extractions.
I.
Table
Recovery of Ruthenium from Carbon Tetrachloride Extractions
% Ru Recovered Determined by
Sample No.
In aqueous
1
2.8 2.8 2.5 2.8
Spectrophotometric absorbance
2 3 4
Gamma counting
a
1
2 3 4
In
In
cc1, a
a (I (1
1.6 1.6 2.8
