Sj. Parry et al., THE DETERMINATION OF I-129 IN MILK AND VEGETATION USING NEUTRON-ACTIVATION ANALYSIS, Science of the total environment, 173(1-6), 1995, pp. 351-360
A new method has been developed to measure I-129 in the environment wi
th detection limits below 10 mBq/kg of vegetation and 10 mBq/l of cows
' milk. The method is based on extraction of I-129 from the milk or ve
getation sample, onto an ion exchange resin. An inactive carrier of I-
127 is added to the sample before separation, to monitor losses throug
hout 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 I-129 (n,g
amma) I-130 reaction with thermal neutrons. The I-127 carrier undergoe
s a (n,2n) reaction with fast neutrons to produce I-126. Iodine is ext
racted from the ion exchange resin after irradiation with an elution s
cheme which removes contamination from the radionuclide Br-82, the mai
n interference in the analysis. Finally iodine is precipitated as AgI
for gamma ray analysis. The sample is counted for 3 h on a Ge semicond
uctor detector to measure the radionuclide I-130, which has a half lif
e of 12.4 h and I-126, which has a half life of 13.0 days. The measure
d I-130 activity is compared to a known standard to deduce the amount
of I-129 in the sample, and the concentrations are corrected for losse
s during processing using the measured activity of I-126. Th, detectio
n limits for I-129 by this method are below 10 mBq/l for milk samples
and 10 mBq/kg for vegetation. In addition to routine monitoring of mil
k and grass samples the method has been used to measure I-129 depositi
on on grass and soils in a field near the Sellafield plant. Results of
these analyses, along with measurements of I-129 in air and rainfall
using the same methodology, have been used to determine deposition vel
ocity and retention coefficients of I-129 to grass.