238 U (4.47  10 9 years) 226 Ra (1600 years) 222 Rn (3.82 days) 218 Po (3.10 mins) 214 Pb (26.8 mins) 214 Bi (19.9 mins) 210 Tl (1.30 mins) 214 Po (164  s) 210 Pb (22.3 years)  ~ 2.4MeV  ~ 2.3MeV Q  = 3.27MeV Q  = 7.83MeV 0.021%99.98% Extractable Isotope  -  delayed coincidence Potential Neutral Current Background

Membranes brought above ground for processing. Radioactivity washed from HTiO-loaded membranes using 15 litres of acid: –0.03M nitric acid for radium –0.5M hydrochloric acid for lead/thorium Efficiency of stage ~75%

The Elution Rig (situated above ground in Chemistry Laboratory)

232 Th (1.4  years) 228 Th (1.91 years) 224 Ra (3.66 days) 220 Rn (55.6 sec) 212 Pb (10.64 hours) 212 Bi (60.6 mins) 208 Tl (3.05 mins) 212 Po (0.299  s) 208 Pb  ~ 2.6MeV Q  = 2.25MeV Q  = 8.95MeV 36%64% Extractable Isotopes  -  delayed coincidence Potential Neutral Current Background

Two large ultra-filtration membranes are coated with the HTiO ion-exchanger These HTiO-loaded membranes are taken underground for deuteration The deuterated membranes are inserted into D 2 O circulation system in SNO Membranes extract: 228 Th, 226 Ra, 224 Ra and 212 Pb from hundreds of tonnes of D 2 O Efficiency of stage: ~90%

H. Heron for the SNO Collaboration Neutrino 2000, Sudbury, Canada

The SUF Assay System is an extractive assay system which has been used to assay the amount of 226 Ra and 224 Ra in the D 2 O in the SNO detector three times: –from ~50 tons in October 1999 (experiment RDA2) –from ~100 tons in November 1999 (experiment RDA3) –from ~200 tons in December 1999 (experiment RDA4) There are four stages: 1) extraction from D 2 O onto an ion-exchanger (HTiO); 2) the elution of this radioactivity into 15 litres of acid; 3) the concentration to a volume of just 10 milli-litres; and 4) measurement using low-level  -  delayed coincidence liquid scintillation counters.

Because a lower-strength acid can be used to wash radium from the HTiO this enables us to use a simple method to concentrate the radium into a 10 milli-litre sample The secondary concentration of radium uses two, small-scale, HTiO extraction and elutions. Efficiency of stage ~60%

The Heavy Water circulation system (under ground)

Systematic errors dominating results at present. It is expected that these will be significantly reduced by further checks. Preliminary results suggest levels of 238 U (as measured by extracting and assaying 226 Ra) are below target levels. Preliminary results suggest levels of 232 Th (as measured by extracting and assaying 224 Ra) are consistent with target levels.

The concentration of lead from 15 litres of 0.5M hydrochloric acid to 10 milli-litres is achieved using: –a solvent-solvent extraction; and –an ion-exchange separation. Total efficiency of stage ~85% The assay system is (at present) unable to measure levels of 212 Pb in the D 2 O of the SNO detector as procedural 212 Pb backgrounds are dominating.

Cuts on  energy and on pulse-shape give excellent identification of true  -  coincidences Data from Assay RDA3 Energy of  Pulse-shape of  True coincidences plotted against time (hrs) Fitted to decay chain True  -  coincidences shown in green.

The final sample of 10 milli-litres is mixed with ~42 grams of liquid scintillator. low-level  -  delayed coincidence liquid scintillation counters are used. The  -  coincidence is the 164  s decay of 214 Po for the 238 U decay chain and the  s decay of 212 Po for the 232 Th decay chain.

Samples are measured for a few weeks. Data then analysed to select true  -  coincidence from  -  and  -  background coincidences. Data then binned by hour and fitted to radioactive decay of isotopes in respective chains. Counting efficiency (including branching ratios): ~45% ( 232 Th); ~60% ( 238 U)

Cuts on  energy and on pulse-shape give excellent identification of true  -  coincidences Data from Assay RDA3 Energy of  Pulse-shape of  True coincidences plotted against time (hrs) True  -  coincidences shown in green. Fitted to decay chain