Author/Authors :
Andersen، نويسنده , , T.C. and Blevis، نويسنده , , I. and Boger، نويسنده , , J. and Bonvin، نويسنده , , E. and Chen، نويسنده , , M. and Cleveland، نويسنده , , B.T and Dai، نويسنده , , X. and Dalnoki-Veress، نويسنده , , F. and Doucas، نويسنده , , G. and Farine، نويسنده , , J. and Fergani، نويسنده , , H. and Ferraris، نويسنده , , A.P. and Fowler، نويسنده , , M.M. and Hahn، نويسنده , , R.L and Hallman، نويسنده , , E.D and Hargrove، نويسنده , , C.K. and Jagam، نويسنده , , P. and Jelley، نويسنده , , N.A and Knox، نويسنده , , A.B. and Lee، نويسنده , , H.W and Levine، نويسنده , , I. and Majerus، نويسنده , , S. and McFarlane، نويسنده , , K. and Mifflin، نويسنده , , C. and Miller، نويسنده , , G.G. and Noble، نويسنده , , Mark A.J and Palmer، نويسنده , , P. and Rowley، نويسنده , , J.K and Shatkay، نويسنده , , M. and Simpson، نويسنده , , J.J. and Sinclair، نويسنده , , D. and Wang، نويسنده , , J.-X. and Wilhelmy، نويسنده , , J.B and Yeh، نويسنده , , M.، نويسنده ,
Abstract :
We describe a method to measure the concentration of 224Ra and 226Ra in the heavy water target used to detect solar neutrinos at the Sudbury Neutrino Observatory and in the surrounding light water shielding. A water volume of 50–400 m3 from the detector is passed through columns which contain beads coated with a compound of manganese oxide onto which the Ra dissolved in the water is adsorbed. The columns are removed, dried, and mounted below an electrostatic chamber into which the Rn from the decay of trapped Ra is continuously flowed by a stream of N2 gas. The subsequent decay of Rn gives charged Po ions which are swept by the electric field onto a solid-state α counter. The content of Ra in the water is inferred from the measured decay rates of 212Po, 214Po, 216Po, and 218Po. The Ra extraction efficiency is >95%, the counting efficiency is 24% for 214Po and 6% for 216Po, and the method can detect a few atoms of 224Ra per m3 and a few tens of thousands of atoms of 226Ra per m3. Converted to equivalent equilibrium values of the topmost elements of the natural radioactive chains, the detection limit in a single assay is a few times 10−16 g Th or U/cm3. The results of some typical assays are presented and the contributions to the systematic error are discussed.
