238U (4.47109 years)

226Ra (1600 years)

222Rn (3.82 days)

218Po (3.10 mins)

214Pb (26.8 mins)

214Bi (19.9 mins)

210Tl (1.30 mins) 214Po (164s)

210Pb (22.3 years) ~ 2.4MeV

~ 2.3MeVQ = 3.27MeV

Q = 7.83MeV

0.021% 99.98%

Extractable Isotope

- delayed coincidence

Potential Neutral CurrentBackground

•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%

10 PSI N2

5 PSI N2

H2

6 UF

H2

6 UF

TO WASTE DRUMTO ACID WASTE LINE

TO SINK

LOW ISOTOPIC

DRAINTANK

SOLVENT-SOLVENT

TANK

ACIDWASTETANK

ELUTIONTANK

LEVE

L IN

DIC

ATO

R

RESERVOIR

UPWHTiO

STOCK5M HCl

COVER GAS

ELUTION ACIDFROM 20L CARBOY

UPW TOWORKSPACE

ELUTION FEED TO WORKSPACE

WASTE FROMWORKSPACE

SUPPLY OF5M HCl

SAMPLE PORT

½“

1“

The Elution Rig (situated above ground in Chemistry Laboratory)

232Th (1.41010 years)

228Th (1.91 years)

224Ra (3.66 days)

220Rn (55.6 sec)

212Pb (10.64 hours)

212Bi (60.6 mins)

208Tl (3.05 mins) 212Po (0.299s)

208Pb ~ 2.6MeV

Q = 2.25MeV

Q = 8.95MeV

36% 64%

Extractable Isotopes

- delayed coincidence

Potential Neutral CurrentBackground

• 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%

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 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.

•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 (underground)

grams 232Th per gram D2O

grams 238U per gram D2O

TARGET VALUES 3.7 10-15 4.5 10-14

RDA2(~50 tons D2O) 6+6

-4 10-15 <0.2 10-14

RDA3(~100 tons D2O) 6+6

-2 10-15 <0.2 10-14

RDA4(~200 tons D2O) 5+4

-3 10-15 <0.1 10-14

• 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.

•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.

Cuts on energyand on pulse-shapegive excellentidentification oftrue - coincidences

Data from Assay RDA3E

nerg

y of

Pul

se-s

hape

of

True coincidences plotted against time (hrs)

Fit

ted

to d

ecay

cha

in

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 164s decay of 214Po for the 238U decay chain and the 0.299s decay of 212Po for the 232Th 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% (232Th); ~60% (238U)

Cuts on energyand on pulse-shapegive excellentidentification oftrue - coincidences

Data from Assay RDA3E

nerg

y of

Pul

se-s

hape

of

True coincidences plotted against time (hrs)

True - coincidences shown in green.

Fit

ted

to d

ecay

cha

in