(a) Milk For the purpose of sampling, the area around the station is again divided into three annuli of radii 1 to 5 km, 5 to 10 km and 10 to 25 km in which are situated inner, outer and control farms respectively. Normally four farms are chosen in each category, disposed at approximately equal intervals of arc in the land sector.

Milk samples are obtained once every two weeks from each farm which is currently in production, and analysed for iodine-131 and sulphur-35. From these samples, a bulked sample (together with for­malin solution) is made up for each category over three months, and this bulked sample is ana­lysed quantitatively for strontium-90 and caesium — 137, and qualitatively for gamma-emitting nu­clides. Some bulking of samples may also take place for iodine-131 and sulphur-35. While every attempt is made to sample continually the same farms, they have sometimes to be changed because of cessation of milk production.

(b) Soil cores Ten of these are obtained from around each farm site; sites are sampled on a rota basis

such that at least one farm is sampled each year and each farm is sampled at least once every five years. Core samples are taken to a depth of 150 mm using a sampling tool about 100 mm in diameter. A bulked sample is analysed quantitative­ly for gross beta, strontium-90 and caesium-137, and qualitatively for other gamma emitters.

(c) Deposition collectors For the purpose of these samples, two concentric circles are drawn around the station, the inner having a radius of about 1 km and the outer about 10 km. Inner sites are disposed at approximately equal intervals of arc around the land sector of the inner circle, and outer sites are similarly distributed around the outer circle.

Deposition collectors consist of rectangular wire frames covered with muslin, the total area of cloth exposed being about 2000 cm2. The collectors are suspended some 3 metres above ground level. During exposure, particulate matter adheres to the muslin. The collectors are exposed in pairs at each site for a period of two months then replaced. The exposed collectors are analysed quantitative­ly for gross beta, and qualitatively for gamma emitters.