Determination of 

Radium-228 in 

Natural Waters

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1696-G
Determination of 

Radium-228 in 

Natural Waters

By JESSE O. JOHNSON

RADIOCHEMICAL ANALYSIS OF WATER 

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1696-G

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1971
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

Library of Congress catalog-card No. 72-610150

For sale by the Superintendent of Documents, U.S. Government Printing Office' 

Washington, D.C. 2O4O2 Price 25 cents (paper cover)
CONTENTS

	Page

Abstract ____________-______-_----------------------------------- Gl

Introduction _______________---__-_------------------------------ 1

Review of radium-228 methods and studies -------------------- 5

Collection of water samples for radium-228 analysis ------------ 9

Development of the radium-228 method ---------------------------- 10

Natural radioactive nuclide interference ----------------------- 10

Radium-228 standard preparation ---------------------------- 13

Standards from "old" thorium nitrate ------------------------ 14

Standards from "old" thorium or thorium oxide _____-._-_-_---- 15

Standards from recently processed thorium reagents ----------- 15

Discussion of the method __.__-_---_-.__-_-__-------------------- 16

Apparatus ___._..__._______________.____-_-__------------------- 18

Reagents __________________---____--___---__-----_-------------- 18

Procedure for analysis of radium-228 ----------------------------- 20

Calculation of results ___-_--__---_--___-----_-----_-------------- 22

Errors and precision _______--_-_______-_-_-_-_--_---------------- 24

References ___.__.________________________________-__----------- 25

ILLUSTRATIONS

Page

FIGURE 1. Chart of the natural radioactive decay series ------------ G3

2. Graph of decay of airborne radioactivity trapped by

membrane filters -______-_-----__--_-___--_------.-_- 12

TABLES

Page

TABLE 1. Radioactive element content of Colorado Front Range

streams ____________________________________________ G8

2. Chemical analyses and radioactive element content of

selected ground waters _______________________________ 8

3. Calculation factors for radium-228 determination -------- 22

ni

RADIOCHEMICAL ANALYSIS OF WATER

DETERMINATION OF RADIUM-228 IN 

NATURAL WATERS

By JESSE 0. JOHNSON

ABSTRACT

Radium isotopes are important radioactive constituents of most natural 

waters, although they are present in extremely minute quantities. This paper 

describes a method for determining the beta-active isotope radium-228; extensions of the method for determining the alpha-emitting radium isotopes 

are discussed.

Radium-228 is determined by coprecipitating the radium isotopes with 

barium and lead sulfates. The sulfate precipitates are then dissolved in 

alkaline ethylenedinitrilotetraacetic (EDTA) acid after washing with concentrated nitric acid. Barium and radium sufates are precipitated by pH 

adjustment, redissolved, then reprecipitated using strontium and yttrium as 

"holdback" carriers.

The barium sulfate precipitate is again dissolved in alkaline EDTA. 

Lead and yttrium carriers are added to the solution, which is aged for 36 

hours or longer. Ammonium sulfide is then added to the solution to precipitate 

lead sulfide, and after the lead sulfide is removed, excess sodium hydroxide is 

added to precipitate yttrium hydroxide.

Radium-228 is determined by beta counting the yttrium hydroxide precipitate, which contains the actinium-228, daughter of radium-228.

INTRODUCTION

Radium isotopes from mass No. 219 and 230 are known, but only 

the naturally occurring radium isotopes are usually of concern in 

natural waters. The naturally occurring radium isotopes include 

radium-226 of the uranium series, radium-224 and radium-228 of 

the thorium series, and radium-223 of the actinium series. All are 

alpha emitters with the exception of radium-228, which is a 

very weak beta emitter ft max = 0.055 Mev (million electron

Gl
G2 RADIOCHEMICAL ANALYSIS OF WATER

volts). The only reactor produced radium isotopes that have half 

lives long enough to be detected in natural waters are radium-225 

(14.8 day £-) and radium-227 (41 minute /?-). These isotopes could 

enter a water supply by accidental discharge of process waste from 

a nuclear installation.

The following table gives the half lives and decay information of 

these radium isotopes:

Radium isotope Mode of decay Half life Source

223; (AcX) a 11.4 days ------------ Natural (U 285 ).

224; (ThX) a 3.64 days ------------ Natural (Th 282 ).

225 ft- 14.8 days ------------ Daughter (Th 229 ).

226; (Ra) a 1,620 years ---------- Natural (U 288 ).

227 ft- 41 minutes ----------- Ra^fa,?).

228; MsThi 0- 6.7 years *________-__ Natural (Th 2M ).

1 Holden, N. E., and Walker, P. W., 1968, in the Chart of the Nuclides Rev. list the half 

life of radium-228 as 5.75 years.

Figure 1 shows the main members of the natural radioactive 

series and the location of the radium isotopes in the decay schemes. 

A more complete chart showing minor branch decays will be found 

in radiochemistry texts such as Friendlander, Kennedy, and 

Miller (1964).

The determination of the alpha-emitting radium isotopes, particularly radium-226, in various materials has been the object of 

many studies; and a large number of procedures are available for 

special studies. Kirby and Salutsky (1964) gave an excellent review on the radiochemistry of radium, and 43 procedures were 

described in detail for determining radium in a variety of materials. Most are concerned with the determination of radium-226 

in miscellaneous substances. A few of the procedures describe 

the determination of radium-228 in natural waters.

Radium-226 has the lowest maximum permissible concentration 

(MFC) of any radioactive nuclide in food and domestic water. The 

U.S. Public Health Service (1962) listed this MFC for radium-226 

at 3 pCi/1 (picocuries per liter). The U.S. Public Health Service 

does not cover the other radium isotopes specifically; but the National Committee on Radiation Protection and the International 

Commission on Radiological Protection (1959) gave the MPC for 

radium-228 at 9 pCi/1, radium-223 at 210 pCi/1, and radium-224 

at 600 pCi/1. Radium-228 has the lowest MPC of any beta-emitting 

nuclide and is known to be present in food and water and biological 

materials in small but significant amounts; therefore, some knowledge of its concentration in those materials is desirable. The data 

on radium-228 concentrations in various materials are limited 

compared to the data on concentrations of radium-226, mainly because of the difficulty of measuring the weak beta radiation from
URANIUM SERIES ACTINIUM SERIE

URANIUM; 92U 

PROTACTINIUM; 91Pa 

THORIUM; 90 Th 

ACTINIUM; 89Ac 

RADIUM; ggRa 

FRANCIUM; 87Fr 

RADON; 86Rn

POLONIUM; 

BISMUTH; ^Bi 

LEAD; ggPb 

THALLIUM; 81T1

238 

4.51X109 

yr

234 

24.1 

days

234 

1.17 - 

min

/

234 

2.47 X105

yr

^

235 

7.1X108 

yr

230 

7.8X10 4

yr

226 

1600

yr

222 

3.820 

days

218 

3.05 

min

231 

25.5 

hr

Beta particle / 

Alpha particle

214 210 

1.64 XKT4 138.4 

sec days

214 ^ 210 S 

19.7 ^ 5.01 ' 

min , days

214 

26.8 

min

y 22\° / 206 

' 22 

235 

stable

7.1X10* 

yr

231 

32,400

yr

231 

25.5 

hr

210 

138.4 

days

/

206 

stable

/

227 

18.7 

days

227 oSi£xC 

21.8 &* 

yr

0)

..a

223 

11.4 

days

223 ./" 

22 ^

min

219 

3.96 

sec

215 

1.78 XKT3 

sec

211 

36.1 

min

1. The nataral radioactive deeay MrtM. lOnnr daeay Mhaaet not rixmn. NacUd

(1968). Half lives are rounded to 3 significant figures when known to 
G4 RADIOCHEMICAL ANALYSIS OF WATER

radium-228 at very low concentration levels. However, Eisenbud, 

Petrow, Drew, Roser, Kegel, and Cullen (1964) analyzed a variety 

of materials including food, water, and biological materials for 

radium-228.

The U.S. Geological Survey is interested in radium-228 concentration at this level as part of its general studies regarding the 

occurrence and distribution of radioelements in natural waters.

Barker and Scott (1958), and Scott and Barker (1959, 1962) 

measured the radium and uranium concentrations of various natural waters in the United States. They established correlations 

between uranium and radium concentrations and the major geologic provinces. No radium-228 determinations were made in these 

studies as it did not seem that equipment and methods at that 

time were sufficiently sensitive for finding the expected concentrations. The presence of radium-228 was indicated, as some samples 

showed detectable concentrations (unpublished) of radium-224. 

The concentration of radium-228 in the hydrosphere is of interest 

both because of its geochemical reactions and because radium-228 

is an undesirable contaminant of certain domestic water supplies. 

It is probable that when the hydrosphere as a whole is considered, 

the total dissolved radium-228 and radium-226 (in terms of radioactive disintegrations per unit time) would be approximately 

equal. This is inferred from the parent abundance ratio Th232 / 

U238 of about 3 in the earth's mantle and the inverse specific radioactivity ratio of about one-third.

Studies are in progress by the U.S. Geological Survey to determine radium-228 and thorium in some of the streams and waters 

from various aquifers that were previously analyzed for radium226 and uranium.

The radium-226 content in many phases of man's environment 

has been studied intensively for many years. Radium-226 has been 

measured in water, food, minerals, plants, and soils. The various 

organs of the human body have also been assayed for radium. 

From these studies and others, an increased cancer incidence of 

individuals having unusually high radium content was established 

(Looney and others, 1955). Maximum permissible concentrations 

for radium-226 in water, food, and the body itself have been 

assigned.

Radium-228 studies are few compared with radium-226 studies, 

although the content and distribution of radium-228 in nature 

should be similar to that of radium-226. The MFC of radium-228 

is one of the lowest of all radionuclides, and radium-228 content 

in food and drinking water is of concern from a public health as-
DETERMINATION OF RADIUM-228 IN NATURAL WATERS G5

pect. The main reason that more studies have not been made regarding the content and distribution of radium-228 in environmental samples is that most of the published radium-228 methods 

are for a particular type of sample and are not applicable to general use. The U.S. Geological Survey has developed a method suitable for the determination of radium-228 in natural waters. Before 

describing this method, a brief review of methods and studies of 

others is presented.

REVIEW OF RADIUM-228 METHODS AND STUDIES

An environmental study of importance was made by Krause 

(1959), who measured the radium-228 content of water samples 

from public water supply wells in the States of Iowa, Illinois, Wisconsin, and Missouri. The waters had been previously analyzed 

for radium-226 by Lucas and Ilcewitz (1958), and many of the 

wells had radium-226 concentrations in excess of 4 pCi/1. The total 

population consuming water having a radium-226 content in excess of 4 pCi/1 was estimated at 480,000. The waters having the 

highest radium-226 concentrations were from deep sandstone 

formations of Ordovician to Precambrian age.

The radium-228 content of many of the shallow wells was also 

high, most had concentrations above 1 pCi/1. The waters from the 

deeper formations, such as the Galesville Sandstone of Cambrian 

age and older Precambrian rocks, had a radium-228 content as 

high as 9.1 pCi/1. The average radium-228 to radium-226 ratio 

was approximately unity for waters from the deep sandstone 

formations.

Petrow, Cover, Schiessle, and Parsons (1964) developed a procedure for the determination of radium-228 and thorium-228 in 

biological materials. The method is sensitive to 1 pCi of radium228 and 0.02 pCi of thorium-228. Analyses were made on a variety 

of biological materials, including fruits and vegetables from both 

the United States and Brazil. The materials from Brazil were from 

a thorium-rich area, and the amount of radium-228, as expected, 

was considerably greater in the Brazilian samples than in the 

United States samples. The average concentration of radium-228 

in the Brazilian foods was about 10 times that of radium-228 in 

the American foods. The Ra22S/Th228 in biological materials was always greater than unity, showing that the uptake of radium by 

plants is greater than the uptake of thorium.

Petrow and Alien (1961) published a method for determining 

the radium isotopes in uranium mill effluents. They used leadcarrier precipitations to obtain radium free of other radioactive
G6 RADIOCHEMICAL ANALYSIS OF WATER

contaminants. Radium-223, radium-224, and radium-228 are 

determined from radioassay of their respective daughters, lead211, lead-212, and actinium-228. Actinium-228 is separated from 

radium isotopes by extraction into Di (2-ethylhexyl) phosphoric 

acid (EHPA). Actinium-228 is then extracted from the EHPA 

with dilute hydrobromic acid. Lead and bismuth interferences are 

removed by extraction into Aliquat-336 (a high-molecular-weight 

quaternary amine). Radium-228 is determined from the beta 

activity of actinium-228.

Henry, Loveridge, and Weaver (1963) cited a method for the 

assay of radium-228 in reactor effluents. They used a lead-barium 

sulfate precipitation to isolate radium from solution; an ethylenedinitrilotetracetic acid (EDTA) separation was used to remove lead 

carrier; ion-exchange resins were used to separate actinium from 

radium and the rare-earth activities. The method was stated to 

have decontamination factors of greater than 10* for bariumlanthanum-140 and greater than 105 for rare-earth activities. High 

decontamination factors from those isotopes is of especial importance in analyzing reactor effluents for radium-228.

A method suitable for the determination of actinium-227 and 

radium-228 in uranium mill effluents and natural waters was discussed by Barrata and Feldman (1961). Actinium is coprecipitated 

with lanthanum carrier. Decontamination is achieved by the use 

of ion-exchange resins and (or) solvent extraction separations. 

After purification, lanthanum and actinium are precipitated as the 

oxalate and then transferred to a counting planchet. Actinium-227 

and actinium-228 (radium-228) are determined by beta assay of 

the precipitate. When both actinium isotopes are present, actinium228 is first determined by masking the beta radiation of 

actinium-227 with a thin absorber. After actinium-228 has decayed, actinium-227 may be determined by beta counting of the 

precipitate or by storing for several days for buildup of alphaemitting daughters, and then using alpha-counting techniques.

The process history of thorium becomes important when the 

metal or its alloys are to be fabricated, as about 100 microcuries of 

radium-228 will be present in a kilogram of old thorium which 

has been chemically undisturbed for 60 years or longer. This 

amount of radium-228 only weighs about 0.4 /xg (microgram), and 

its concentration in small volumes of chemical and metallurgical 

process solutions is to be expected. It is therefore important that 

thorium process wastes be analyzed for radium-228 to assure that 

any release to the hydrologic environment is within safe limits.

Radium-228 might also be concentrated in an inhomogeneous
DETERMINATION OF RADIUM-228 IN NATURAL WATERS G7

manner in thorium or its compounds. In this case the possibility 

of airborne contamination of radium-228 would be increased 

during fabrication processes.

In any event the amount of gamma radiation from thorium is 

dependent to a large extent on the radium-228 concentration and, 

if not already at its maximum concentration, will increase with 

time. Fresco, Jetter, and Harley (1952) presented a graphical 

solution to the Bateman equations describing the alpha and beta 

activities of the members of the thorium series under various 

conditions of radioactive disequilibrium. The graphs in conjunction with an alpha and (or) beta analysis enables one to estimate 

the concentration of radium-228 and other members of the series.

Allison, Moore, Richardson, Peterson, and Voight (1954) published a procedure for measuring radium-228 in thorium and 

thorium nitrate. Lead and lanthanum carriers are added to the 

thorium solution, and thorium is extracted into theonyltrifluoroacetone (TTA) at pH 2. The pH is then raised to 6 and lead, 

actinium, and lanthanum are extracted. Lead interference is removed by precipitation as the sulfide, and lanthanum and actinium-228 are precipitated as the oxalate. Radium-228 is measured 

by the activity of actinium-228.

Volkova and Ziv (1961) presented a different method that may 

be used to determine the radium-228 content of thorium. In this 

procedure, thorium hydroxide is precipitated by the addition of 

carbon dioxide free ammonia. The supernatant liquid, which contains barium "holdback" carrier and the radium, is evaporated to 

dryness and calcined to remove ammonium salts. The barium-radium residue is leached with 0.1 N HBr. After aging the solution 

for iy% months, barium and radium bromides are precipitated 

by the addition of 5 volumes of ether. After allowing for ingrowth 

of actinium-228, that isotope is extracted by washing the precipitate with a very small volume of a 2:1 ether-ethanol mixture.

The U.S. Geological Survey is studying radium-228 concentrations in various surface and ground waters. Some of the preliminary results of radium-228 from surface waters are given in table 

1. The samples analyzed are from major streams draining the 

Front Range of Colorado. The radium-228 activity for most of the 

streams is several times that of radium-226. The higher radium228 concentration could be caused, in part, by the fact that the 

average thorium concentration of rocks in the Front Range is over 

twice that of the average continental rocks (Phair and Gottfried, 

1964). More study would be necessary to confirm this. Table 2 

gives the radium-228 concentrations of several ground waters,
G8 RADIOCHEMICAL ANALYSIS OF WATER

TABLE 1. Radioactive element content of Front Range streams

Stream and location

South Platte River at Waterton,

Bear Creek at Morrison, Colo.

Clear Creek at roadside park 

9 miles above canyon mouth __ 

South Boulder Creek at Eldorado

Boulder Creek at highway bridge,

Left Hand Creek at gaging 

station near canyon mouth .. 

South St. Vrain River at Lyons,

Cache La Poudre River at U.S. 287 

bridge, Ft. Collins, Colo

Plum Creek at Colorado state highTurkey Creek at junction of 

U.S. 285 and road to 

Tiny Town, Colo __________

Coal Creek, 3 miles above canyon

Thompson River at Estes Park, 

Colo., U.S. 287 bridge _______

Date

sampled

11-08-67

11-09-67

11-08-67 

11-09-67

11-09-67

11-09-67 

11-13-67

11-13-67

11-08-67

11-09-67

11-09-67

11-13-67

Gross 3 

activity 

(pCi/1)

5.6

3.0

9.1 

2.7

2.2

9.0 

3.6

5.9

6.6

4.6

2.5

2.8

Gross a 1 

activity Ra226 

(MB/1) (pCi/1)

18. <0.1

3.9 <.l

3.4 .2 

2.2 <.l

1.5 <.l

23. .2 

3.3 <.l

27. .1

24. .3

5.6 <.l

1.1 <.l

4.3 .1

Ra228 

(pCi/1)

1.0

.3

1.1 

1.4

1.3 

.8

1.1

.8

1.2

1.7

1.2

U

2.3

1.1

2.3

1.0

1.4

14. 

1.3

7.9

3.9

1.0

1.0

.8

1 Gross alpha activity is in units of equivalent natural uranium.

mostly from the Dawson Arkose, which is a major aquifer in the 

Denver area. These radium-226 ratios are closer to unity than the 

radium-228 ratios of the Front Range streams.

TABLE 2. Chemical analyses and radioactive

[Well data and analytical information mostly from Scott and

Curie

Well,

Water-bearing unit

Spring, Precambrian granite _ _ _

801 ft Dawson Arkose . .___-

Location

NEi,4 sec.29, T.2 N., R.71 W,

Boulder County.

NE1^ sec.3, T.7 S., R.67 W,

Douglas County.

R S"2s

w

34

a ^ s bt 

'-3O-5

O

384

39

S

'5 ?

S»1

I

54.

2.9

Well, 1,795 ft Dawson Arkose ---_.____ __________ do ------------ 7 36 1.0

Well, 165 ft Dawson Arkose -_..____ NW1^ sec.20, T.10 S., R.66 W, 34 19 .5

Douglas County.

Well, 715 ft Dawson Arkose and SE1^ sec.33, T.6 S., R.68 W, 14 42 2.9 

Arapahoe Formation ______________ Douglas County

Well, 110 ft Dawson Arkose _________ SW^ sec.31, T.10 S, R.66 W, 33 24 2.9

Douglas County. 

Well, Dawson Arkose ________________ NW1^ sec.30, T.10S., R.66W,

Douglas County. 

Spring, Dawson Arkose _____________ SEi/iNE1^ sec.22, T.10 S.,

R.66 W, Douglas County.
DETERMINATION OF RADIUM-228 IN NATURAL WATERS G9 

COLLECTION OF WATER SAMPLES FOR RADIUM-228 ANALYSIS

The collection and preservation of water samples for radium-228 

analysis generally involves the same problems that are encountered 

in other radionuclide or trace-element studies. The sample should 

be as representative as possible of the water unit being sampled, 

within the reasonable limits of economics.

The problems associated with water sampling are discussed in 

detail by Barker and Robinson (1963), Rainwater and Thatcher 

(1960), and Hem (1959) and will be reviewed very briefly here. 

The preferred method of sampling lakes and large sluggish streams 

is to obtain a depth integrated sample across a section of the water 

body. If the radioelement discharge of a stream is being studied, a 

time-integrated and discharge-integrated sample is most desirable. 

Sometimes continuous samplers are used to obtain a composite 

sample. Wells should be pumped before sampling to remove 

stagnant water. Springs should be sampled by inserting a tube 

into the orifice and drawing the water into an evacuated flash.

Pyrex, polyethylene, and teflon bottles have been found generally 

satisfactory for sample collection. New bottles should be washed 

thoroughly, filled with dilute nitric acid, and allowed to stand for 

several days to dissolve any leachable trace elements that might 

be present. The sample bottle should be rinsed with the water 

to be sampled before being used for collection.

element content of selected ground waters

Vogeli (1961). Constituents given in milligrams per liter]

SM Remarks

'&£<*- 

m

500

15

24

J*~

32.

4.2

4.0

Na+K=12.

32 5.

Na+K= 10.

3

921.

156.

154.

76

160.

44

O

75.

2.0

2.0

2.0

1.0

8.5

£5 Q

0.0 2,940

2.4 220

.0 168

3.2 114

1.7 248

44. 161

5 V UC"^"3

ffl

230

21

14

6

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10

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17. 6.5

19. .9

1.3 .9

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1.7 1.3

1.2 2.2

.9 2.0

r

7.0

1.1

.2

.3

2.3

<.l

Radium-224 17 pCi/1.

Radium-228 sample

from tank

by wells.

Do.

No chemical

supplied

analysis.
G10 RADIOCHEMICAL ANALYSIS OF WATER

If the water sample is clear and free from suspended material, 

the sample is acidified and sealed with an airtight stopper. The 

U.S. Geological Survey has used acetic acid-chloroform mixture, 

nitric acid, or hydrochloric acid as fixing agents for trace elements 

and radioelements. At present, hydrochloric acid is used more than 

nitric acid because nitric acid interferes with the uranium analysis. Two milliliters of concentrated nitric or hydrochloric acid added to 1 liter of distilled water produces a pH of 1.5. This amount of 

acid will prevent the precipitation of ferric hydroxide, calcium 

sulfate, and calcium carbonate in almost any natural water. Precipitation of these compounds will remove several trace elements, 

including radium, from solution.

A complicated analytical decision arises when the water sample 

contains suspended material such as, clay, sand, silt, organic 

debris, oils, or greasy materials. The problem is to accurately separate the solute and suspended phases so that the radium content 

of each may be independently determined. This separation is impractical (if not impossible) to do on an absolute basis because of 

the difficulty of separating colloidal and fine suspended matter 

from true solute in a practical field procedure. It is necessary to 

treat each sample in exactly the same way so that relative comparison of values is possible. This is achieved by allowing a filter 

medium to define solute and suspended phases. Porosity of the 

filter medium is specified, and the designated filter is used each 

time in exactly the same way in the same filter apparatus.

A field apparatus for filtering large volumes of samples, designated for use in the Water Resources Division, is described by 

Skougstad and Scarbro (1968). It has a reservoir of 1.5-2.5 liters, 

and the water is filtered under pressure of an ordinary tire pump 

through a 0.45 micron cellulose ester filter. The use of this filter 

is a reasonable compromise between complete removal of colloidal 

material and filtration speed. The filter removes most of the clay 

particles, and only the finest clay particles and colloidal particles 

remain.

The filtered water sample is acidified with nitric acid for fixation 

of the radium.

DEVELOPMENT OF THE RADIUM-228 METHOD 

NATURAL RADIOACTIVE NUCLIDE INTERFERENCE

Two radioactive nuclide contamination problems were encountered in the development of the radium-228 method. Yttrium 

and lanthanum compounds were found to contain considerable
DETERMINATION OF RADIUM-228 IN NATURAL WATERS Gil

amounts of radioactive impurities. An unexpected source of contamination was found from radioactive atmospheric aerosols which 

were attracted to the filters.

A small amount of reagent contamination in some of the reagents was anticipated, but the amount of contamination of lanthanum and yttrium carriers by nuclides of the uranium-235 

series, mostly actinium-227 and daughters, exceeded expectations. 

A source of yttrium oxide was obtained which was free of detectable radioactive impurities (American Potash and Chemical Co., 

West Chicago, 111.), and a yttrium-carrier solution was prepared 

from this compound. However, after collecting yttrium and actinium hydroxides on a cellulose ester-membrane filter, radioactivities 

other than the 6.13-hour half life of actinium-228 were observed. 

The radioactive impurities consisted of a long-lived activity ( several days or longer) and a short-lived activity (approximately 30 

minutes). A study was made to determine if the short-lived activity could be a combination of lead-214 (26.8 minutes) and bismuth214 (19.6 minutes). It was thought that these activities were trapped during the filtration process.

Figure 2 shows the decay of radioactive aerosols collected on a 

membrane filter. The aerosols were collected by passing air through 

the filter for a period of 80 minutes using a water-aspirator suction. The decay data for the first 2 hours approximates the expected decay of short-lived daughters of radon-222. The presence 

of longer-lived activities is indicated after about 120 minutes, as 

the points no longer follow the theoretical decay (Curve 2). Later 

studies showed that the longer-lived activities consisted of radioactive aerosols from the thorium series (Pb212-Bi212 ) and probably, 

(Pb210-Bi210-Po210 ). If the filtration process were the only method 

by which radioactive aerosols could be trapped on the filter, filtrations could be done in an inert atmosphere. However, later experiments showed that the electrostatic attraction between the 

filters and the atmospheric aerosols is sufficient to contaminate the 

filters. The filters are stated by the manufacturer to have a highnegative electrostatic charge; it is well known that radon-daughter 

ions are predominantly positively charged and attach themselves to 

atmospheric aerosols (Wilkering, 1964).

The attractive force between membrane filters (0.22/0 and 

radioactive aerosols was tested by simply exposing the filter to 

the atmosphere for a period of 10 minutes. The net beta and alpha 

activities immediately after exposure were found to be 20 and 5 

cpm (counts per minute) respectively. These activities indicate 

that cellulose ester membrane filters, when exposed to the atmos-
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i i i i

i i i i

seta activities trappe 

2 micron, 47 mm, wh 

air pulled through fil 

aresents beta activit 

-214 after sudden re 

s the beta activity o 

tioned conditions. ( 

allowing polonium-2^ 

cal functions for cur 

t time zero, are: 

tivity of lead-214 

29e-0.02586t_012g4e - 

tivity of bismuth-214 

!352<rO-2273t+4.258eeta activity = A! + A2 I 

7e -0.02586t_ 3.279e-C 

minutes after remov

xx

. \

i i i i

i 

d by 

te) 

er fo

y of 

mov

lead

ilurve 

8 plu

ves 1 

0.227

(curv

0.025

curve 

.0351

al of 

\

\

i 

50 100 150 20d 

TIME, IN MINUTES AFTER EXPOSURE

Fioon f Decay of airbora* radioactivity trapped by membrane filters. 

(Bateman equations) assumes decay products to be in secular equilibr

exposure.
DETERMINATION OF RADIUM-228 IN NATURAL WATERS G13

phere, attract the radioactive lead, bismuth, and polonium aerosols 

from the atmosphere to a degree that seriously limits their usefulness for low-level radioactivity determinations. Membrane 

filters of different composition from other manufacturers were 

tested for aerosol attraction and all showed detectable radioactivity 

when exposed to the atmosphere for several minutes or longer. 

Treatment with antistatic compounds reduced the attraction effect 

but did not eliminate it. Very fine porosity filter paper (Whatman 

42) was found to have a detectable radioactive (^0.5 cpm beta 

and zz 0.1 cpm alpha) initial activity after a short exposure to 

the atmosphere. The attraction exhibited by various membrane 

filters for radioactive atmospheric aerosols is unfortunate because 

the filters offer a very convenient method of preparing precipitates 

for assay of radioactivity.

Stainless steel planchets were tested for attraction of atmospheric aerosols. After a 200-minute exposure to the atmosphere, no 

detectable radioactivity was observed. This test indicated that the 

yttrium-actinium hydroxide precipitate would have to be transferred directly to a planchet, at least until aerosol contamination 

of membrane filters could be eliminated.

Direct transfer of precipitates to planchets is tedious, and it 

is difficult to obtain uniform distribution of the precipitate. A 

glove box was constructed to determine the improvement obtained 

by carrying out filtration and sample mounting in an inert atmosphere. These studies have not yet been completed, and therefore, 

the analytical results are from the direct-transfer technique.

RADIUM-228 STANDARD PREPARATION

A problem was encountered in obtaining an accurately standardized radium-228 solution. Radium-228 standard solutions obtained 

commercially were found to vary considerably from the stated 

activity. Yttrium-91 made a useful substitute standard for this 

procedure until a suitable radium-228 standard solution was obtained. The isotope is available in accurately standardized solutions 

and the isotope's chemical behavior is similar to actinium-228, the 

isotope actually counted in this procedure. The detection efficiencies are quite comparable; for our equipment they are: 0.71 cpm 

per pCi for yttrium-91 and 0.61 cpm per pCi for actinium-228.

The best sources for obtaining radium-228 of accurately known 

concentrations are "old" thorium or thorium compounds. ("Old" 

throughout this discussion means the preparation was processed 

at least 40 years ago.) Thorium preparations that old contain an 

amount of radium-228 with a disintegration rate of at least 99 

percent of that of thorium-232. Radium-228 standards of less precise calibration can be directly prepared from thorium prepara-
G14 RADIOCHEMICAL ANALYSIS OF WATER

tions that are only 20 years old. These standards may be satisfactory for some purposes. A 20-year-old preparation would 

contain 87-100 percent of the equilibrium radium-228 concentration. The lower value assumes complete removal of radium-228 on 

the date at which the thorium was processed.

If "old" thorium reagents are not available for the preparation 

of radium-228 standards, satisfactory standards can be prepared 

by removing radium-228 from a thorium reagent and allowing 

the thorium to age for a specified period. Usually the thorium must 

be aged for a period of several months so that a reasonable amount 

of radium-228 will be formed. Methods for obtaining suitable 

radium-228 standard solutions from both "recent" and old thorium 

compounds will be discussed.

The laboratory was fortunate in having a moderate quantity 

of thorium nitrate (45 years old) on hand; some thorium oxide 

which was at least 60 years old was obtained later. Both reagents 

were used to obtain satisfactory radium-228 and thorium-232 

standards. Practically any "old" thorium compound, with the 

probable exception of the sulfate, can be used as a source for the 

direct preparation of radium-228 standard solution. In this method 

of radium-228 standard preparation, the radium-228 remains 

in solution with its parent, thorium-232. This state is preferable 

for this procedure, but not for other procedures; for them, the 

radium-228 would have to be removed by a series of multiple 

barium sulfate precipitations or by other techniques.

The following procedures describe the preparation of combined 

thorium-232 : radium-228 standard solution from old thorium and 

its compounds, the nitrate and the oxide. Thorium chloride may 

also be used, but should first be converted to the nitrate by using 

several evaporations with concentrated nitric acid. Thorium metal 

and the oxide require special dissolution techniques.

STANDARDS FROM "OLD" THORIUM NITRATE

Make up the thorium nitrate to the desired concentration in 

1 N nitric acid. A little barium nitrate solution containing 5-15 j«,g 

of Ba++ should be added before the solution is made up to volume. 

A thorium concentration of about 10 mg/ml is convenient for a 

stock solution.

Transfer several aliquots of the thorium solution containing 

50 mg or more thorium to tared platinum crucibles. Reduce the 

volume of solution by evaporating under an infrared lamp. After 

the solutions have become viscous, place the crucibles in a muffle 

furnace with the door open. Carefully raise the temperature until 

nitrogen oxide fumes are no longer evolved. Close the door and
DETERMINATION OF RADIUM-228 IN NATURAL WATERS G15

very slowly increase the temperature to 950 °C. Maintain this 

temperature for at least 1 hour, then cool gradually to about 

100°C. Transfer to a dessicator and cool to room temperature. The 

exact thorium concentration is determined by weighing as Th02. 

The radium-228 activity calculated from the equation 

Ra228 (dpm/ml) = 246 W(l - e-°M34t), 

where

t = years since thorium reagent was processed and

W = thorium concentration in milligrams per milliliter.

STANDARDS FROM "OLD" THORIUM OR THORIUM OXIDE

Thorium metal and thorium dioxide are not readily soluble 

in the common laboratory acids. Dilute hydrofluoric, nitric, sulfuric, and concentrated perchloric acids attack thorium metal 

slowly. The metal is attacked vigorously by hydrochloric acid, but 

a black residue of uncertain composition remains. Thorium oxide 

is even more difficult to dissolve than the metal. Hot concentrated 

sulfuric acid converts the oxide to the moderately soluble sulfate.

Schuler, Steahly, and Stoughton (1952) described methods for 

dissolving thorium and thorium oxide using mixtures of nitric 

acid and hydrofluoric acid.

The following describes a method for preparing accurately 

standardized thorium-232 and radium-228 from "old" reagent 

Th02 :

1. Weigh out a 1.0000 g sample of thorium dioxide to the nearest 

0.1 mg.

2. Transfer the sample to a 250 ml erlenmeyer flask containing 

20 ml of acid mixture (15.7 N HN03 - 0.05 N HF). Carefully heat and stir the mixture until the Th02 dissolves. 

Transfer the solution to a 200 ml volumetric flask and add a 

little barium nitrate solution containing 5-15 /tg of barium. 

Make up to volume with 1 N nitric acid. The solution should 

contain 4.3928 mg/ml (W) thorium. The Ra228 (dpm/ml) = 

246 W (1 - e-o.io34*) = 1>080 (Within 1 percent if * > 40 

years).

STANDARDS FROM RECENTLY PROCESSED THORIUM REAGENTS

Henry, Loveridge, and Weaver (1963) described a method for 

preparing standardized radium-228 from thorium nitrate of recent 

or unknown age. Their method is as follows:

Dissolve 12 g of thorium nitrate tetrahydrate in 500 ml of water 

and add 60 ml of 9 M sulfuric acid. Add 2 ml of barium carrier 

solution (5 mg Ba++/ml) to the mechanically stirred solution at 

room temperature. The solution is stirred for 15 minutes and then 

filtered. This process is repeated four times with separate additions
G16 RADIOCHEMICAL ANALYSIS OF WATER

of barium solution; the solution is chilled to 5°C before addition 

of barium. This step insures that the thorium solution will not 

become supersaturated with respect to barium sulfate at room 

temperature. A longer aging period before filtration is advisable 

to be certain that the last traces of barium sulfate crystals have 

formed. The thorium concentration of the solution is then determined as follows:

Pipet a 10 ml sample of the thorium solution into a 250 ml 

beaker; add 10 ml of concentrated HC1. Evaporate cautiously until 

moist solids remain, then add 100 ml of 0.15 M hydrochloric acid 

and heat to incipient boiling. Add 21 ml of 10 percent oxalic acid 

and digest the precipitate at 90-95 °C for about 1 hour. Filter the 

solution through an ashless filter paper and wash the filter with 

50 ml of a 2.5 percent oxalic acid solution containing 3.5 ml of 

concentrated HC1. Transfer the precipitate and filter to a tared 

platinum crucible and dry under an infrared lamp. Ignite to 

1,100°C to constant weight. Weigh as ThO2 . Two more analyses 

of the solution plus two blanks should be made. The radium-228 

content of the thorium solution is determined on the basis of the 

number of days (T) since the final barium sulfate precipitation 

and the weight of thorium in mg/ml (W). Ra228 (dpm/ml) = 246

J/P (1 g-0.693772,447 \

DISCUSSION OF THE METHOD

The U.S. Geological Survey requires a radium-228 method for 

water that is capable of measuring concentrations as low as 0.3 

pCi/1 for a 1 liter sample and 0.1-0.2 pCi/1 for larger samples. 

These concentrations and lower ones are easily obtained for radium-226 when using the radon method (Rushing, 1967). This 

method has been modified by the U.S. Geological Survey and is 

used for the determination of radium-226 in water and solid materials with excellent results. Most natural surface-water samples 

contain only small amounts of radium-226, often 0.1 pCi/1 or less, 

and presumably these samples contain about the same amount 

of radium-228.

A method for determining the alpha-emitting isotopes of radium 

was described by Goldin (1961). This method was found suitable 

for obtaining a radium solution sufficiently free from interferences that, with several extensions, radium-228 could also be 

determined.

The modified method for determining radium-228 is outlined as 

follows. Lead and barium carriers together with yttrium "holdback" carriers are added to the sample; and lead, barium, and
DETERMINATION OF RADIUM-228 IN NATURAL WATERS G17

radium sulfate are coprecipitated, while yttrium and other rareearth contaminants remain in solution. The precipitates are 

washed with concentrated nitric acid, then dissolved in alkaline 

EDTA. Barium and radium sulfates are precipitated by lowering 

the pH.

The barium-radium sulfates are further purified by additional 

reprecipitation steps using small amounts of strontium and yttrium "holdback" carriers. After the reprecipitations, the bariumradium sulfate is dissolved in alkaline EDTA solution for the last 

time, and yttrium and lead carriers are added to the solution. The 

solution is aged for a period of 36 hours or longer in order for 

actinium-228 to approach its equilibrium concentration with radium-228.

After the aging period, ammonium sulfide is added to the solution, and lead sulfide is precipitated. The lead sulfide precipitate 

is separated from the solution, and a large excess of sodium hydroxide is added to precipitate yttrium and actinium hydroxides.

Several steps of the procedure serve to give high decontamination factors from most radiochemical impurities, especially the 

naturally occurring radioactive elements.

Goldin (1961) showed that the initial nitric acid wash greatly 

improved the decontamination factors for polonium. Presumably 

this step would also be effective in minimizing interferences from 

thorium and nuclides such as cesium-137 and sodium-24.

The EDTA separations serve to separate the radium from thorium, uranium, and radioactive descendents such as lead-210 of the 

natural activities, including thorium and lead. Strontium and 

yttrium carriers were added to improve the decontamination factors for such nuclides as strontium-90, yttrium-90, and rare-earth 

activities.

The aging process (36 hours or more) for actinium-228 buildup 

in the purified radium solution results in a buildup of radioactive 

lead and bismuth nuclides from the alpha-emitting radium isotopes. The bismuth isotopes would be carried on the final yttrium 

hydroxide precipitate, and a lead sulfide precipitation is made 

immediately before to remove bismuth interference. The lead 

sulfide precipitation was shown to be effective in removing bismuth from solution. Equilibrium thorium solution containing 

1,455 pCi of each descendent was analyzed repetitively for radium228, and only actinium-228 was detected in the final yttrium 

hydroxide precipitate. This fact indicates high decontamination 

factors for lead and bismuth daughters of alpha-active radium isotopes.
G18 RADIOCHEMICAL ANALYSIS OF 'WATER

Minimum decontamination factors found for other beta emitters are

Uranium (beta descendants, Th 23*-Pa 234 ) __________-__-_-_.-- 500

Lead-210; bismuth-210 (equilibrium) ________-_._---_------- 500

Strontium-90; yttrium-90 (equilibrium) ______._--___---__-_ 600

Cesium-137 ...___._.......__...._.__.__._-..__-..-- ---. 600

A possible interference could occur in analyzing a solution containing the fission product (Ba140-La140 ). The barium-140 would 

not interfere, but lanthanum-140 would grow into partial equilibrium with its parent during the aging process. The lanthanum140 would be carried on the yttrium precipitate. This interference 

would not normally be encountered in natural waters not contaminated by nuclear wastes. The amount of interference from lanthanum-140 can be determined by resolving the decay curve of 

actinium-228 and lanthanum-140.

APPARATUS

Most of the equipment used in the analysis of radium-228 is of 

the type available in most radiochemical laboratories. Special 

equipment may include some of the following: 

Heavy-walled graduated centrifuge tubes. 

2-inch stainless steel planchets (preferably concentric ring

type).

6-inch teflon stirring rods. This item is very desirable in preventing damage to centrifuge tubes.

Low-background beta counter having a beta background 

count of less than 2 cpm. Manual low-background counters 

are generally satisfactory for the method and are much less 

expensive than the automatic counters. Two or three manual units may be purchased for the price of one automatic 

unit, and a greater production volume can be achieved.

REAGENTS

All reagents are reagent-grade unless otherwise specified. 

1. Barium-carrier solution (16 mg/ml): Dissolve 28.460 g of 

barium chloride di-hydrate in water, add 2 ml of concentrated nitric acid and dilute to 1 liter.

2a. Lead-carrier solution (15 mg/ml): Dissolve 23.97 g of lead 

nitrate in water, add 2 ml of concentrated nitric acid and 

dilute to 1 liter.

2b. Lead-carrier solution (1.5 mg/ml): Dilute 100 ml of leadcarrier solution (15 mg/ml) to 1 liter.
DETERMINATION OF RADIUM-228 IN NATURAL WATERS G19

3. Yttrium-carrier solution (18 mg/ml): Add 22.85 g of yttrium oxide (Y2 03 ) to a 250 ml erlynmeyer flask containing 20 ml of water, swirl, then place on a hotplate and heat 

to boiling. Carefully add small additions of concentrated 

nitric acid while stirring. Usually about 30 ml of concentrated nitric acid is necessary to dissolve the yttrium oxide. 

Small additions of water may be required to replace that 

lost by evaporation. The dissolution is accomplished more 

easily if a magnetic stirring hotplate is available. After the 

yttrium oxide has dissolved, add 70 ml of concentrated 

nitric acid and then dilute to 1 liter.

NOTE. Yttrium oxide, sufficiently free of radioactive contaminants for use 

as a carrier, was obtained from American Potash and Chemical Co., West 

Chicago, 111. (Code No. 1117, Lot No. LWO 811). All carriers should be 

tested for radioactivity before using. This is especially true for yttrium.

4. Strontium-yttrium carrier (0.9 mg/ml Sr+2 and » 0.9 mg/ 

ml Y+3 ): Dilute 10 ml of yttrium-carrier solution (18 mg/ 

ml) to 100 ml (solution A). Dissolve 434.8 mg of strontium nitrate in water, dilute to 100 ml (solution B). 

Combine solutions A and B.

5. Citric acid (1M): Dissolve 210.1 g of citric acid monohydrate in water and dilute to 1 liter.

6. Sulfuric acid (18 N): Add 465 ml of concentrated sulfuric 

acid (36 N) to 535 ml of water while stirring.

7. Ammonium sulfate solution (200 mg/ml): Dissolve 200 g 

of ammonium sulfate in a minimum of water and dilute 

to 1 liter.

8. EDTA reagent (0.25 M disodium ethylendinitrilotetraacetate dihydrate containing 20 mg/ml NaOH): Dissolve 

20 g of sodium hydroxide in about 750 ml of water, heat, 

then slowly add 93 g of disodium ethylenedinitriloacetate 

dihydrate while stirring. After the sodium salt of EDTA 

has dissolved, dilute to 1 liter.

9. Ammonium sulfide solution (2 percent (NH4 ) 2 S): Dilute 

10 ml of ammonium sulfide (20-24 percent (NH4 ) 2 S) to 

100 ml.

10. Sodium hydroxide (10 N): Carefully dissolve 400 g of NaOH 

pellets in a minimum amount of water; dilute to 1 liter. 

Store in a polyethylene or teflon bottle.

11. Binder solution: Dissolve 1 ml of "Duco" cement (E.I. 

DuPont de Nemours and Co., Wilmington, Del.) in 100 

ml of acetone.
G20 RADIOCHEMICAL ANALYSIS OF WATER

PROCEDURE FOR ANALYSIS OF RADIUM-228

1. The sample selected for radium-228 analysis is filtered 

through a 0.45 micron molecular-membrane filter, preferably at the time of collection, and 2 ml of concentrated 

nitric acid is added for each liter of filtrate. The material 

on the filter is retained if an analysis is to be performed 

on the suspended material.

2. In the laboratory add 5 ml of citric acid for each liter of 

sample and a few drops of methyl-orange indicator. If 

the solution is yellow, add concentrated nitric acid until 

the red color is obtained.

3. Add 10 ml of lead-carrier solution (15 mg/ml), 2 ml of 

barium-carrier solution (16 mg/ml), and 1 ml of yttriumcarrier solution (18 mg/ml). Heat to incipient boiling 

and maintain at this temperature for about 30 minutes.

4. Add concentrated ammonium hydroxide until the yellow color 

of methyl orange is obtained, then add a few drops excess. 

Precipitate lead and barium sulfates by adding 18 N 

sulfuric acid until the red color reappears, then add 0.25 

ml excess. Add 5 ml of 200 mg/ml of ammonium sulfate 

for each liter of solution. Keep the sample at a temperature 

of about 90 °C for 30 minutes and stir the sample frequently. Remove the sample from the hotplate and allow it 

to settle for at least 2 hours, then siphon or decant most of 

the supernatant liquid and discard.

5. Transfer the precipitate to a 40 ml centrifuge tube. Centrifuge 

and discard the supernatant liquid.

6. Wash the precipitate twice with concentrated nitric acid using 

centrifugation wash techniques. Add 25 ml of EDTA reagent. Heat in a hot water bath and stir intermittently, 

add a little additional 10 M NaOH if the precipitate does 

not dissolve readily.

7. Add 1 ml of strontium-yttrium carrier solution. Stir thoroughly. Add a few drops of 10 N NaOH if any precipitate 

forms.

8. Add 1 ml of ammonium sulfate solution (220 mg/ml) and 

stir thoroughly, then add glacial acetic acid dropwise until 

barium sulfate precipitates and then add 2 ml excess. 

Allow the precipitate to digest in a hot water bath until 

the precipitate has largely settled. Centrifuge, then discard the supernatant liquid.
DETERMINATION OF RADIUM-228 IN NATURAL WATERS G21

9. Add 20 ml of EDTA reagent, heat, and stir until the barium 

sulfate precipitate dissolves. Repeat steps 7 and 8. (Note 

the time of the last barium sulfate precipitation.)

10. Dissolve the barium sulfate precipitate in 20 ml of "EDTA 

reagent," then add 1 ml of yttrium-carrier solution (18 

mg/ml) and 1 ml of lead-carrier solution (1.5 mg/ml 

Pb++ ). If any precipitate forms, it can be dissolved by 

adding a few drops of 10 AT NaOH. Transfer the solution 

to a teflon or polyethylene container and age it for 36 

hours or longer. The sample should be covered to prevent 

evaporation.

11. Transfer the aged solution to a centrifuge tube; add 0.3 ml 

of ammonium sulfide solution. Add 10 N NaOH dropwise 

while stirring vigorously until the lead sulfide precipitates, 

then add about 10 drops excess. Stir intermittently over a 

period of about 10 minutes.

12. Centrifuge the solution and transfer the supernatant liquid 

to a clean centrifuge tube.

13. Place the centrifuge tube in a hot water bath and slowly add 

10 AT sodium hydroxide to the supernatant liquid while 

stirring until yttrium hydroxide precipitates. Add 1 ml 

excess and stir intermittently for several minutes. Note 

the time of the precipitation. Centrifuge as soon as the 

yttrium hydroxide has largely settled. Transfer the supernatant liquid to a clean centrifuge tube and save if the 

alpha-emitting radium isotopes are to be determined.

NOTE. The alpha-emitting isotopes may be conveniently determined at this 

stage by reprecipitating barium and radium sulfate by the addition of glacial 

acetic acid. The radium isotopes can then be measured by one of several 

methods, for example, by Goldin's method (1961).

14. Wash the precipitate thoroughly with 5 ml of water containing about 10 drops of 10 N NaOH; centrifuge and 

discard the wash solution.

15. Transfer the precipitate to a 2-inch counting planchet using 

small volumes of distilled water while drying under an 

infrared-light lamp. The last washing should contain 1 

ml of binder solution.

16. Count the sample in a low-background beta counter for a 

sufficient length of time to obtain the best counting statistics. For most natural waters, a counting period of 

about 300-500 minutes is desirable because of the low 

concentration of radium-228.
G22 RADIOCHEMICAL ANALYSIS OF WATER 

CALCULATION OF RESULTS

The following formula is used to calculate the radium-228 concentration in a water sample:

Ra« (pCi1) - ' > x

where

Ra - gross counting rate of sample,

Rb = count rate of blank, including instrument background,

£1 = elapsed time from yttrium hydroxide precipitation to

the beginning of the counting period in minutes, 

t2 = length of the counting period in minutes, 

£3 = time of ingrowth for Ac228 in minutes measured from

end of step 9 to yttrium hydroxide precipitation.

(See Note 1.)

Va = volume of sample in milliliters, 

A = decay constant of Ac228 (0.001885 min-1 ), 

E = efficiency of detector for Ac228 in counts per minute per

picocurie (cpm/pCi).

NOTE 1. The factor n - e-^ \ may be neglected if ts is greater than 

2,200 minutes.

NOTE 2. e~xti and -73 * xt . may be obtained directly from table 3. \.i e 3)

TABLE 3. Calculation factors for radium-228 determination 

[X = 0.001885 min -1]

. (min)

1 ____--.

2 _______

3 _______

4 --__-__

5 _______

6 --___._.

7 ---____

8 _______

9 ----.__

10 _--_--.

20 _______

30 _______

40 --__-__

50 _______

60 _______

70 _______

80 ________

90 ________

100 ________

110 ______

\t

- 0.001885

.003770

_ .005655

_ .007540

.009425

_ .011310

.013195

.015080

.016965

- .018850

- .03770

.05655

.07540

.09425

.1131

.1320

. .1508

. .1697

.1885

.2074

e -x«

0.998117

.996237

.994361

.992488

.990619

.988754

.986892

.985033

.983178

.981327

.9630

.9450

.9274

.9101

.8931

.8763

.8600

.8440

9999

.8127

(1 - e-xt )

0.001883

.003763

.005639

.007512

.009381

.011246

.013108

.014967

.016822

.018673

.0370

.0550

.0726

.0899

.1069

.1237

.1400

.1560

1 71 ft

.1873

\t

(1 - e-x ')

1.0011

1.0018

1.0028

1.0037

1.0047

1.0057

1.0066

1.0075

1.0085

1.0095

1.019

1.028

1.038

1.048

1.058

1.067

1.077

1 099

1 097

1.107
DETERMINATION OF RADIUM-228 IN NATURAL WATERS G23

TABLE 3. Calculation factors for radium-228 determination Continued

t (min)

120 ---___.-

130 _--_.__-

140 _-___-_.

150 _---____

160 _--__.__

170 __-_-__.

180 _-___-.-

190 ________

200 ________

210 ________

220 ________

230 ________

240

250 ________

260 ________

270 _______

280 ________

290 ________

300 ________

310 ________

320 ________

330 ________

340 ________

350 ________

360 ________

370 . ______

380 ________

390 ________

400 ________

410 ________

420 ________

430 ________

440 ________

450 ________

460 ________

470 ________

480 ________

490 ________

500 ________

510 ________

520 _____

530 ________

540 ________

550 ______

560 _______

570 ________

580 ________

590 ________

600 ________

610 ______

620 ________

630 ________

640 _____ __

650 ________

660 ________

670 ______ _

680 ________

690 ________

700 ________

\t

0.2262

.2451

.2639

.2828

.3016

.3204

.3393

.3582

.3770

.3958

.4147

.4336

.4524

.4712

.4901

.5090

.5278

.5466

.5655

.5844

.6032

.6220

.6409

.6598

.6786

.6974

.7163

.7352

.7540

.7728

.7917

.8106

.8294

.8482

.8671

.8860

.9048

.9236

.9425

.9614

.9802

.9990

1.0179

1.0368

1.0556

1.0774

1.0933

1.1122

1.1310

1.1498

1.1687

1.1876

1.2064

1.2252

1.2441

1.2630

1.2818

1.3006

1.3195

e~x '

0.7976

.7827

.7681

.7537

.7396

.7258

.7123

.6990

.6859

.6731

.6605

.6482

.6361

.6242

.6126

.6011

.5899

.5789

.5680

.5574

.5471

.5369

.5268

.5170

.5073

.4979

.4886

.4794

.4705

.4617

.4531

.4446

.4363

.4281

.4202

.4123

.4046

.3971

.3897

.3824

.3752

.3682

.3614

.3546

.3480

.3405

.3351

.3288

.3227

.3167

.3108

.3050

.2993

.2937

.2882

.2828

.2775

.2724

.2673

(1 - e-xt )

0.2024

.2173

.2319

.2463

.2604

.2742

.2877

.3010

.3141

.3269

.3395

.3518

.3639

.3758

.3874

.3989

.4101

.4211

.4320

.4426

.4529

.4631

.4732

.4830

.4927

.5021

.5114

.5206

.5295

.5383

.5469

.5554

.5637

.5719

.5798

.5877

.5954

.6029

.6103

.6176

.6248

.6318

.6386

.6454

.6510

.6595

.6649

.6712

.6773

.6833

.6892

.6950

.7007

.7063

.7118

.7172

.7225

.7276

.7327

\t

(1 -e-x ')

1.117

1.127

1.138

1.148

1.158

1.168

1.179

1.190

1.200

1.211

1.221

1.232

1.243

1.253

1.265

1.276

1.287

1.298

1.309

1.320

1.332

1.343

1.354

1.366

1.377

1.389

1,401

1.412

1.424

1.436

1.448

1.459

1.471

1.483

1.496

1.508

1.520

1.532

1.544

1.557

1.569

1.581

1.594

1.606

1.622

1.634

1.644

1.657

1.670

1.683

1.696

1.709

1.722

1.735

1.748

1.761

1.774

1.788

1.801
G24 RADIOCHEMICAL ANALYSIS OF WATER

Example of a sample calculation

Blank count rate (Rt) = 1.52 cpm.

Sample count rate = 900 counts in 500 minutes.

= 1.80 cpm.

Volume of sample Vs = 3,000ml. 

E from efficiency studies using actinium-228:

Ac228 = 0.61cpm/pCi. 

ti = 120 minutes. 

tz = 500 minutes. 

e-^i from table = 0.7976.

x* 

2 _ = 1.544.

Ra« X (1'80 ~ L52)

3,000 x 0.61 x 0.7976 

= 0.3 pCi/1

ERRORS AND PRECISION

The assignment of a precision index to a radium-228 determination involves errors common to both gravimetric-chemical analyses and low-level radiochemical analyses. Barium and radium 

were assumed to behave identically in the chemical separations, 

at least to the final barium sulfate precipitation. Barium-carrier 

recovery was measured by weighing the final barium sulfate precipitate and was found to be nearly quantitative. Recovery of 

added radium-228 was measured by measuring the activity of 

actinium-228 in the final yttrium hydroxide precipitate. Recoveries 

were usually greater than 85 percent above the 5 pCi level.

A radium-228 method suitable for the analyses of most natural 

water samples should be able to detect concentrations of that 

isotope of less than 1 pCi/1. The practical minimum detection 

limit of this method is about 0.3 pCi/1 when using a 3-liter sample, 

although counting statistics alone indicate a lower limit of about 

0.15 pCi/1. The calculation of a radium-228 concentration near 

the minimum detection limit was shown as the example of a 

sample calculation. The sample was counted for about 8 hours 

on a low-background beta counter which had a very stable background (1.52 ±0.10 at the 95 percent confidence limit for the 

counting period).

Two methods for lowering the detection limit are available: 

the use of large samples (10 liters or larger) and counting the 

sample in a counter having a lower background.

Detection systems with beta backgrounds between 0.1 and 0.5
DETERMINATION OF RADIUM-228 IN NATURAL WATERS G25

cpm are commercially available. Some problems in sample preparation would be encountered in using the lowest background 

detectors because of their small detection area.

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G26 RADIOCHEMICAL ANALYSIS OF WATER

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U.S. GOVERNMENT PRINTING OFFICE: 1971 0 411-001