Radiochemical neutron activation analysis for trace chlorine in steels and alloys.

Chlorine is usually present at low concentrations in reactor materials and thermal neutron activation of (35)Cl produces (36)Cl, which has a long half-life and is a radionuclide of significance in nuclear waste disposal. This paper describes a radiochemical method that has been developed to measure low concentrations of Cl in reactor stainless steels, so that the amount of (36)Cl in radioactive wastes can be estimated. The method is based on the irradiation of a 1 g sample in a thermal neutron flux of 10(16) n m(-)(2) s(-)(1), followed by dissolution in HNO(3) with the addition of stable KCl carrier/tracer. The Cl is precipitated as AgCl, and the recovery is measured gravimetrically. The (38)Cl, which has a half-life of 37 min, is measured with γ-ray spectrometry. The entire process, from irradiation to the end of counting, takes ∼1.5 h. The recovery is near-quantitative, and the detection limit for Cl in most stainless steels is below 1 mg/kg.

The determination of 129I in milk and vegetation using neutron activation analysis.

A new method has been developed to measure 129I in the environment with detection limits below 10 mBq/kg of vegetation and 10 mBq/l of cows' milk. The method is based on extraction of 129I from the milk or vegetation sample, onto an ion exchange resin. An inactive carrier of 127I is added to the sample before separation, to monitor losses throughout the entire procedure. The ion exchange resin is irradiated for 7.5 h in a neutron flux of 10(16) n m-2 s-1 to induce the 129I(n, gamma) 130I reaction with thermal neutrons. The 127I carrier undergoes a (n,2n) reaction with fast neutrons to produce 126I. Iodine is extracted from the ion exchange resin after irradiation with an elution scheme which removes contamination from the radionuclide 82Br, the main interference in the analysis. Finally iodine is precipitated as AgI for gamma ray analysis. The sample is counted for 3 h on a Ge semiconductor detector to measure the radionuclide 130I, which has a half life of 12.4 h and 126I, which has a half life of 13.0 days. The measured 130I activity is compared to a known standard to deduce the amount of 129I in the sample, and the concentrations are corrected for losses during processing using the measured activity of 126I. The detection limits for 129I by this method are below 10 mBq/l for milk samples and 10 mBq/kg for vegetation. In addition to routine monitoring of milk and grass samples the method has been used to measure 129I deposition on grass and soils in a field near the Sellafield plant. Results of these analyses, along with measurements of 129I in air and rainfall using the same methodology, have been used to determine deposition velocity and retention coefficients of 129I to grass.

Environmental and personnel monitoring for uranium by delayed neutron counting.

At the Imperial College Reactor Centre we have developed a fully automated, large sample, high sensitivity delayed neutron counting system for routine analysis of environmental samples and personnel monitoring. Two-hundred fifty samples with a maximum volume of 30 ml can be analysed each working day. The detection limits (3 sigma) for uranium of natural isotopic abundance in our routine samples are typically 1 microgram/kg (0.05 Bq/kg) for dry samples and 1 microgram/l (0.05 Bq/l) for aqueous samples. Daily analysis of BNFL uranium standards, 'in house' uranium standards and weekly analysis of IAEA Soil-7 reference material are used to ensure constant system sensitivity and accuracy.

A simple automatic gamma counter based upon the IAEA radioimmunoassay instrument.

A relatively inexpensive modification is described to the IAEA automatic gamma counter based upon the Kodak Carousel projector. The instrument is capable of counting up to three energies simultaneously, ranging from 30 keV to 1 MeV.