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#### Radiometric Assay System for Radioactive Isotopes in Neutrino Experiment ####

The Radiometric Assay System is a comprehensive method for extracting, concentrating, and measuring radioactive isotopes, such as 238U and 232Th, in the SNO neutrino experiment. Various stages, including Extraction, Elution, and Counting, are involved to accurately assess the levels of isotopes in D2O. The system aims to reduce systematic errors, achieve target levels of isotopes, and provide detailed measurements essential for the experiment's success. ####

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#### Radiometric Assay System for Radioactive Isotopes in Neutrino Experiment ####

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  1. The238U Decay Chain 238U (4.47109 years) 226Ra (1600 years) Extractable Isotope 222Rn (3.82 days) 218Po (3.10 mins) - delayed coincidence Potential Neutral Current Background 214Pb (26.8 mins)  ~ 2.3MeV 214Bi (19.9 mins) Q = 3.27MeV 0.021% 99.98% 210Tl (1.30 mins) 214Po (164s) Q = 7.83MeV  ~ 2.4MeV 210Pb (22.3 years)

  2. Stage 2: Elution • 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%

  3. Stage 2: Elution The Elution Rig (situated above ground in Chemistry Laboratory)

  4. The232Th Decay Chain 232Th (1.41010 years) 228Th (1.91 years) Extractable Isotopes 224Ra (3.66 days) 220Rn (55.6 sec) - delayed coincidence Potential Neutral Current Background 212Pb (10.64 hours) Q = 2.25MeV 212Bi (60.6 mins) 36% 64% 212Po (0.299s) 208Tl (3.05 mins) Q = 8.95MeV  ~ 2.6MeV 208Pb

  5. Stage 1: Extraction • 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 D2O circulation system in SNO • Membranes extract: 228Th, 226Ra, 224Ra and 212Pb from hundreds of tonnes of D2O • Efficiency of stage: ~90%

  6. The Seeded Ultra-Filtration (SUF) Assay System for the SNO Experiment H. Heron for the SNO Collaboration Neutrino 2000, Sudbury, Canada

  7. Overview • The SUF Assay System is an extractive assay system which has been used to assay the amount of 226Ra and 224Ra in the D2O 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 D2O 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.

  8. Stage 3: Concentration (Radium) • 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%

  9. Stage 1: Extraction The Heavy Water circulation system (under ground)

  10. Preliminary Results

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

  12. Stage 3: Concentration (Lead) • 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 212Pb in the D2O of the SNO detector as procedural 212Pb backgrounds are dominating.

  13. Data from Assay RDA3 Cuts on  energy and on pulse-shape give excellent identification of true - coincidences Energy of  Pulse-shape of  True - coincidences shown in green. Example Counting Fitted to decay chain Data (232Th) True coincidences plotted against time (hrs)

  14. Stage 4: Counting • 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 214Po for the 238U decay chain and the 0.299s decay of 212Po for the 232Th decay chain .

  15. Stage 4: Counting • 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% (232Th); ~60% (238U)

  16. Data from Assay RDA3 Cuts on  energy and on pulse-shape give excellent identification of true - coincidences Pulse-shape of  Energy of  Example True - coincidences shown in green. Counting Fitted to decay chain Data (238U) True coincidences plotted against time (hrs)

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