Analytical Challenges of Pre

Analytical Challenges of Pre

Ra Measurements in Brin

Zoltan Szabo

U.S. Geological Survey
NORM in Produced Waters: Process-based studi

need precise enough characterization of radionucneed precise enough characterization of radionuc

that mechanisms of mobility and progressive chacan be determined 

• Characterizing U, Ra, other isotope ratios and mixture

the produced waters. What level of precision and detecapability is needed? 

• To determine solely whether activity level is too high 

acceptable likely does not need high precision or detecapacity, at least at a “screening” level?

• For isotopic forensics for studying wasteproducts 

generation during the fracturing process, analyses reqhigh precision and accuracy to study progressive chan

• Analytical challenges need to be overcome• Build an Approach:

– E

v u e d oub es oo e s g y c e ods al

uat

e an

d troub

les

hoot 

exi

stin

g anal

yti

cal m

ethods

– Identify matrix interferences and how they can be removed– Refine or modify analytical methods as needed
Notes of concern for using 

“indicators

” for NORM in for NORM in

produced waters

• Isotopic forensics required for 

comprehensive characterization of the wastes

• O h f h i i h b h 

Once t

he nature o

f t

he 

isotope m

ixtures 

has 

been c

hara

direct analyses, the more generalized gross gamma and activit

y yg measurements ma

y be enou

gh (with care!) for 

purposes to indicate those drilling and waste products o

• Characterize and monitor radionuclides in other wastes

sludges salts For workers or residents might there be sludges, salts. For workers or residents, might there be 

exposure concerns? (Likely Yes). Gamma spectroscoptechniques ought to provide enough sensitivity for dete

concentrations in these waste products of concern.
Detection of gross alpha is extremely limited in 

with increasing TDS (or SC) as illustrated below with increasing TDS (or SC) as illustrated below 

drinking water samples. Co-precipitation methodilution and/or some ion-exchan

ge clean-u

p nee
NORM in produced waters: Isotope characterization is a 

Gross alpha varies considerably with time of measuremensampl ll i b i f i f h le collect

ion on 

bas

is o

f m

ix o

f s

hort-li d i 

live

d

isotopes. 

occurrence is common, here see effect in drinking-water 
Analyses for Ra with High Precision, Low M

(Process based studies or precise verification 

• Radioactivit

y g Countin

g

• -Radon emanation (Rn-em): Ra-226• -Alpha spectrometry, direct or of progeny (AS): Ra-22

224, Ra-223 

• -Gamma spectrometry (GS): All• -D l d C i id ti (DCC) All tl f 

D

e

laye

d

C

o

incidence counting (DCC): All, mostly 

fo

Ra-224

• Atom 

() g Mass

) Countin

g

• -Thermal Ionization Mass Spectrometry (TIMS): Ra-2• -Multiple Ion Counting Plasma Mass Spectrometry (M

MS): Ra-226, possibly Ra-228
Precision Background Precision, Background

Activity Activity = (Net (= Total-Background Background) counts

) counts

(Yield)(Volume)(Detector Efficiency)(Branc

Maximize total counts relative to background, yield, 

For efficient laboratory operations: minimize time, 

Minimize background plus matrix interferen

Critical level (instrument response) is defined for a m

on a distribution of blank samples and a probability of on a distribution of blank samples and a probability of 

(false detection).

Clean-up y /Extraction necessary to remove interfere

maintaining high yield is necessary. These need to b

independently of “blank” samples.
Precision or Uncertainty

( ) ( ) ( ) ( ) ( ) 6 V u u V Vt

N

t

N

t t V

N t N t

u c 2

2

2

2

2 2

B

B

S

S

2 2 2

B

2

S

2

B S

2

2 S B

c ⎥⎦⎤ ⎢⎣⎡ + ε ε × ε × ⎟⎟⎠⎞ ⎜⎜⎝⎛ − + × × ε × × − × α =

Precision or Uncertainty

Net combined uncertainty becomes the square root o

for the already considered terms; that is of Net Cou

Total-Background count rates) of Background count rates), of Yield, Volume an

Volume, an

Efficiency.

Atomic counting minimizes, relative to activity countin

in total counts by avoiding random radioactivity cou

relative to background yield efficiency relative to background, yield, efficiency

Still need to minimize variances in background and ef

necessary g 

 to remove interferences and to maintaining 
Barium ( ) lead, strontium) sulfate co-p p reci it

• Used typically with all counting techniques except • Poor yield with high Ca Sr waters (problem all Poor yield with high Ca, Sr waters (problem, all

techniques): needs ion-exchange and/or EDTA addsupernatant

• Uneven crystal size and heterogeneous planchet 

distribution (problem, especially AS): seeding soluslow precipitation Empore disk as precipitation surslow precipitation, Empore disk as precipitation sur

• Thorium interference (problem, especially GS): ani

exchange pretreatment 

• For atomic counting, extraction is more difficult, us

requiring a carbonate matrix precipitation and anioncation-exchange resin purifications exchange resin purifications
Manganese Dioxide or Other Resin Extrac

(usually completed directly in the field)

• Mostly used for DCC, but has been tested with suc

all counting techniques 

• Yi ld f i d b i l i 

Yi

eld o

ften est

imate

d

by compar

ing re

lat

ive concen

on successive resin cartridges

• Spiking directly of cartridges with Ra, Th isotope s

Spiking directly of cartridges with Ra, Th isotope s

added to cartridge with slow drip 

• Acidic and reducing waters (deep brines?) are limit

th i f h id O i d lk 

he propert

ies o

f t

he manganese oxide; 

O

x

ic an

d alk

waters are optimal 

• Isotope specific resins being developed are more ex

Isotope specific resins being developed are more ex

–yields from brines would still need to be demonstr
Yield Monitoring

• Ba-133 for any sulfate salt co-precipitate counted b

Gamma-spectroscopy

-D d i ld i h hi h C S l di 

Decreased yield with high Ca, Sr waters; also diverge

Ra yield in such waters 

• Ra-228 and Th 228 and Th-229 tracers for Ra 229 tracers for Ra-226 and Th 226 and Th-228 

228 

atom counting (TIMS, MC-ICP-MS)

-Ba interference: no easy fix -organic compounds could be especially a problem for 

brines; needs additional periods of thermal degassinTIMS