Trace Elements by Instrumental Neutron Activation Analysis for

9 Trace Elements by Instrumental Neutron Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 3, 2018 | https://pubs.acs.org Publication Date: September 1, 1975 | doi: 10.1021/ba-1975-0141.ch009

Activation Analysis for Pollution Monitoring DEAN W. SHEIBLEY Lewis Research Center, National Aeronautics and Space Administration, Cleveland, Ohio 44135

Methods and technology were developed to analyze 1000 samples/yr of coal and other pollution-related samples. The complete trace element analysis of 20-24 samples/wk averaged 3-3.5 man-hours/sample. The computerized data reduction scheme could identify and report data on as many as 56 elements. In addition to coal, samples of fly ash, bottom ash, crude oil, fuel oil, residual oil, gasoline, jet fuel, kerosene,filteredair particulates, ore, stack scrubber water, clam tissue, crab shells, river sediment and water, and corn were analyzed. Precision of the method was ±25% based on all elements reported in coal and other sample matrices. Overall accuracy was estimated at 50%.

' T ' h e c o m b u s t i o n of fuels, p a r t i c u l a r l y c o a l , is a major source of trace A

element p a r t i c u l a t e s e m i t t e d i n t o the atmosphere.

I n 1970 alone, over

0.5 b i l l i o n tons of c o a l , over 100 b i l l i o n gallons of m o t o r f u e l , a n d n e a r l y 60 b i l l i o n gallons of f u e l o i l w e r e b u r n e d i n the U n i t e d States ( 1 ).

Trace

levels of elements that are present i n these fuels represent a p o t e n t i a l l y l a r g e c o n t r i b u t i o n to the e n v i r o n m e n t a l b u r d e n , e v e n i f o n l y a p o r t i o n is i n j e c t e d i n t o air. Methods and technology

were developed

a n d u s e d at the

NASA

P l u m B r o o k R e a c t o r ( P B R ) to a n a l y z e trace elements i n p o l l u t i o n - r e l a t e d samples b y i n s t r u m e n t a l n e u t r o n a c t i v a t i o n analysis ( I N A A ). T h i s w o r k is significant b e c a u s e i t demonstrates that I N A A is a u s e f u l a n a l y t i c t o o l f o r m o n i t o r i n g trace elements i n a v a r i e t y of s a m p l e m a t r i c e s r e l a t e d to environmental protection.

I n a d d i t i o n to c o a l , other samples

analyzed

f o r trace elements i n c l u d e d fly ash, b o t t o m ash, c r u d e o i l , f u e l o i l , r e s i d u a l o i l , gasoline, jet f u e l , kerosene, filtered a i r p a r t i c u l a t e s , v a r i o u s ores, stack 98 Babu; Trace Elements in Fuel Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

9.

SHEiBLEY

Instrumental

Neutron

Activation

99

Analysis

s c r u b b e r w a t e r , c l a m tissue, c r a b shells, r i v e r s e d i m e n t a n d w a t e r , cement, limestone, a n d c o r n . F o u r goals w e r e established for t h e I N A A p r o g r a m at P B R .

These

goals w e r e t o :

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 3, 2018 | https://pubs.acs.org Publication Date: September 1, 1975 | doi: 10.1021/ba-1975-0141.ch009

1. D e v e l o p t h e t e c h n o l o g y a n d m e t h o d s to a n a l y z e a l a r g e n u m b e r of samples p e r y e a r e n c o m p a s s i n g a v a r i e t y of s a m p l e matrices. 2.

D e t e r m i n e a n d r e p o r t o n as m a n y elements as possible

3.

E s t a b l i s h a n d m a i n t a i n a h i g h degree of a c c u r a c y a n d p r e c i s i o n

4. P e r f o r m t h e w o r k w i t h m i n i m u m m a n p o w e r a n d e q u i p m e n t , b a s i c a l l y as a p a r t - t i m e effort. T o a c h i e v e these goals, t h e analysis scheme w h i c h i n v o l v e d s a m p l e preparation, irradiation, sample counting, a n d data reduction was opti m i z e d to achieve m a x i m u m s a m p l e o u t p u t w i t h m i n i m u m

manpower

expended. Procedure and System

Description

Capability Development.

T h e w o r k of D a m s et al. ( 2 ) a n d Z o l l e r

a n d G o r d o n ( 3 ) w a s the basis f o r b u i l d i n g t h e I N A A c a p a b i l i t y . T h e I N A A p r o c e d u r e t h e y u s e d i n v o l v e d t h e f o l l o w i n g steps. T h e s a m p l e a l i q u o t s w e r e e n c a p s u l a t e d i n p o l y e t h y l e n e vials f o r t h e i r r a d i a t i o n p e r i o d . T w o aliquots of the s a m p l e p l u s t w o standards w e r e i r r a d i a t e d i n a p n e u m a t i c transfer i r r a d i a t i o n system, o n e set ( s a m p l e p l u s standards ) f o r a l o n g t i m e p e r i o d ( 1 2 - 2 4 hrs ) a n d t h e other for a short t i m e p e r i o d ( 5 m i n ) . A f t e r i r r a d i a t i o n the samples w e r e i m m e d i a t e l y r e m o v e d f r o m t h e v i a l s . T h e short-time s a m p l e w a s c o u n t e d after d e c a y intervals of 3 m i n , 30 m i n , a n d 24 hrs. T h e l o n g - t i m e s a m p l e w a s c o u n t e d after a d e c a y i n t e r v a l o f 3 w k s ; sometimes the d e c a y i n t e r v a l s w e r e 7 - 1 0 days. T h e t y p i c a l n e u t r o n flux w a s 1 0 neutrons/cm /sec. C o u n t i n g d a t a w e r e processed t h r o u g h c o m p u t e r i z e d d a t a r e d u c t i o n codes. T w e n t y t o t h i r t y elements w e r e r e p o r t e d . 1 3

Several major

differences

existed b e t w e e n

2

this scheme

a n d one

compatible w i t h the P B R facilities. T h e P B R d i d not have an operating p n e u m a t i c transfer i r r a d i a t i o n f a c i l i t y , n o r w a s there a s o p h i s t i c a t e d γ-ray s p e c t r u m analysis a n d d a t a r e d u c t i o n c o m p u t e r p r o g r a m a v a i l a b l e . I r r a d i a t i o n f a c i l i t i e s at P B R w e r e h y d r a u l i c . A l u m i n u m capsules

(rabbits)

w e r e u s e d to c o n t a i n a n d transfer samples to a n d f r o m t h e core. T h e use o f a l u m i n u m r a b b i t s m e a n t that d a t a o n t h e s h o r t - l i v e d elements o b t a i n e d f r o m t h e 5 - m i n d e c a y c o u n t w o u l d b e lost. S i g n i f i c a n t p e r s o n n e l r a d i a t i o n exposures w e r e o b t a i n e d f r o m h a n d l i n g the a l u m i n u m r a b b i t (•—50 g ) d i r e c t l y f r o m t h e reactor core b e c a u s e of the 1780 k e V g a m m a of 2 . 2 - m i n

2 8

A l a n d a remote m e t h o d u s e d to o p e n the r a b b i t t o o k

too m u c h t i m e ( i n excess of 20 m i n ). H i g h d e n s i t y p o l y e t h y l e n e p r o v e d to b e a n a c c e p t a b l e r a b b i t m a t e rial.

W i t h a 2 . 5 - m m t h i c k w a l l , i t a d e q u a t e l y w i t h s t o o d t h e 1.1 Χ 1 0

Babu; Trace Elements in Fuel Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

6

100

TRACE

newton/m

ELEMENTS

IN FUEL

( 160 l b / i n . ) h y d r a u l i c pressure of the P B R i r r a d i a t i o n t r a n s

2

2

fer system. T h e m a t e r i a l d i d not s i g n i f i c a n t l y d e g r a d e i n the P B R c o r e for p e r i o d s u p to 1 h r . T h e i m p u r i t y l e v e l of the p o l y e t h y l e n e w a s l o w . A s a result, r a d i a t i o n levels r e s u l t i n g f r o m a c t i v a t i o n of the i m p u r i t i e s was s l i g h t , a n d these r a b i b t s c o u l d b e o p e n e d m a n u a l l y w h e n r e t u r n e d f r o m the reactor core. Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 3, 2018 | https://pubs.acs.org Publication Date: September 1, 1975 | doi: 10.1021/ba-1975-0141.ch009

W e n o w h a d a c c e p t a b l e r a b b i t s for the s h o r t - t e r m and long-term (aluminum)

(polyethylene)

i r r a d i a t i o n s . S i n c e the i n t e r n a l v o l u m e

this r a b b i t d e s i g n w a s c o o l e d b y p r i m a r y c o o l i n g w a t e r

flowing

of

through

the r a b b i t , samples w e r e p r o t e c t e d b y e n c a p s u l a t i o n i n p o l y e t h y l e n e a n d q u a r t z vials for the short- a n d l o n g - t e r m i r r a d i a t i o n s , r e s p e c t i v e l y . D e c a y t i m e w a s c r i t i c a l to the d e t e r m i n a t i o n of elements f r o m the 5- a n d 3 0 - m i n d e c a y counts, so w e d e c i d e d to use t h e r a b b i t i r r a d i a t i o n facilities w i t h the h i g h e s t t h e r m a l n e u t r o n flux ( 1 0 u p the specific a c t i v i t y of s h o r t - l i v e d isotopes.

14

n / c m / s e c ) to b u i l d 2

T h e h i g h e r flux also p r o

v i d e d a greater sensitivity. Evaluation of P B R Capability. T o evaluate o u r o v e r a l l c a p a b i l i t y at this p o i n t , 10 p a r t i c u l a t e samples c o l l e c t e d o n W h a t m a n - 4 1 filter p a p e r were

encapsulated,

irradiated, and counted.

Results o n

16

elements

w e r e m a n u a l l y c a l c u l a t e d . T h e average t i m e e x p e n d e d p e r s a m p l e w a s 10 hrs. T h e entire process was t h e n e x a m i n e d to i d e n t i f y those parts w h i c h could be improved.

T h i s r e s u l t e d i n significant m a n p o w e r savings a n d

m o r e elements r e p o r t e d . T h e analysis scheme for the 10 e v a l u a t i o n samples u s e d t w o a l i q u o t s (.—

25 c m

2

polyethylene

of filter p a p e r / a l i q u o t ) .

O n e aliquot was encapsulated i n

a n d i r r a d i a t e d i n a p o l y e t h y l e n e r a b b i t for 5 m i n i n a

t h e r m a l n e u t r o n flux of a p p r o x i m a t e l y 1 0

1 4

n/cm /sec.

T h i s sample was

2

c o u n t e d at d e c a y times of 5 m i n , 30 m i n , a n d 24 hrs. T h e other a l i q u o t was e n c a p s u l a t e d i n h i g h p u r i t y s y n t h e t i c q u a r t z a n d i r r a d i a t e d i n a n a l u m i n u m r a b b i t 1 2 - 2 4 hrs.

T h e s e samples w e r e c o u n t e d t w i c e , after

d e c a y p e r i o d s of 10 days a n d 3 w k s . S a m p l e c o u n t i n g e q u i p m e n t i n c l u d e d one 4 0 9 6 - c h a n n e l γ-ray spectrometer a n d a G e ( L i )

detector.

T h e c r y s t a l of the G e ( L i ) detector was 35 m m i n d i a m e t e r a n d 27 m m l o n g . It h a d a n o m i n a l a c t i v e v o l u m e of 20 c m

3

a n d resolutions of

t h e 1332.5 k e V photons of 2.18 ( f u l l w i d t h — h a l f m a x i m u m ) a n d 4.09 k e V (full width—0.1 maximum). about

C o u n t i n g losses at 2 0 %

dead time were

6%.

T h e d a t a i n the m e m o r y of the γ-ray spectrometer was p u n c h e d o n 8 - c h a n n e l p a p e r tape, c o n v e r t e d to p u n c h e d cards, a n d processed t h r o u g h a rather primitive computer program w h i c h provided both a count per c h a n n e l o u t p u t p l u s a not too r e l i a b l e r o u t i n e for p e a k finding a n d i n t e g r a t i n g net area. A l l results w e r e h a n d c a l c u l a t e d f r o m net p e a k areas a n d


9.

SHEiBLEY

Instrumental

Neutron

Activation

Analysis

101

t h e o r e t i c a l n u c l e a r d a t a parameters. Standards w e r e not u s e d since they i n c r e a s e d the n u m b e r of items to b e i r r a d i a t e d a n d c o u n t e d .

Sixteen

elements w e r e r e p o r t e d . Manpower

Analysis.

E x a m i n a t i o n of

the

10

man-hours/sample

s h o w e d the f o l l o w i n g b r e a k d o w n :


1. O n e - h a l f h o u r was r e q u i r e d to cut filter a l i q u o t s , l o a d into vials, seal, a n d c h e c k the vials for leaks. 2. O n e h o u r was n e e d e d for the 5 - m i n i r r a d i a t i o n a n d c o u n t i n g after d e c a y intervals of 5 a n d 30 m i n . 3. O n e - q u a r t e r h o u r w a s necessary i n t e r v a l s of 24 hrs, 10 days, a n d 3 w k s .

for

4. T h e l o n g - t e r m i r r a d i a t i o n o p e r a t i o n o n e - q u a r t e r h o u r for seven samples.

each

count

procedure

after

decay

required

only

5. E i g h t hrs w e r e r e q u i r e d to h a n d c a l c u l a t e the d a t a o n 16 elements f r o m c o m p u t e r - c a l c u l a t e d net areas. T h e h a n d calculations w e r e p e r f o r m e d o n p r o g r a m m a b l e electronic calculators. E v i d e n t s h o r t c o m i n g s of the process w e r e that the n u m b e r of shortt e r m i r r a d i a t i o n s p e r w e e k w a s a p p a r e n t l y l i m i t e d b y the a v a i l a b l e a n a l y z e r c o u n t i n g t i m e a n d the m a n p o w e r n e e d e d for d a t a r e d u c t i o n . T h e s e t w o parts of t h e s c h e m e w e r e s t u d i e d to i m p r o v e efficiency b y i n c r e a s i n g the n u m b e r of s h o r t - t e r m i r r a d i a t i o n s a n d c o u n t i n g i n a n 8-hr shift as w e l l as significantly r e d u c i n g the m a n - h o u r s for d a t a r e d u c t i o n . T h e s o l u t i o n to i n c r e a s i n g the n u m b e r of s h o r t - t e r m i r r a d i a t i o n s w a s s i m p l e a n d also i m p r o v e d a n a l y z e r use efficiency.

B y irradiating

two

samples i n the same r a b b i t , w e c o u l d take a d v a n t a g e of the h i g h e r specific a c t i v i t y d u r i n g l o n g e r d e c a y times. T h e first s a m p l e w a s c o u n t e d

after

5 m i n d e c a y a n d the s e c o n d s a m p l e was c o u n t e d i m m e d i a t e l y after the first at 10—12 m i n decay.

T h e 3 0 - m i n d e c a y counts w e r e p e r f o r m e d after

a d e c a y t i m e of 2 2 - 2 5 m i n o n the first s a m p l e a n d 4 0 - 4 5 m i n o n the s e c o n d s a m p l e . T h u s , s h o r t - t e r m i r r a d i a t i o n s a m p l e o u t p u t was

doubled

w h i l e a d d i n g o n l y a p p r o x i m a t e l y 0.25 h r to the o r i g i n a l t i m e i n t e r v a l of 1 h r / s a m p l e . A l l c o u n t i n g was p e r f o r m e d o n the same a n a l y z e r . Data

Reduction The

data reduction

problem

required a reliable computer

data

r e d u c t i o n p r o g r a m c o m p a t i b l e w i t h a n existing I B M m o d e l 67 c o m p u t e r facility.

T h e l i t e r a t u r e i d e n t i f i e d various c o d e s : I N V E N b y D a m s a n d

Robbins ( 4 ) , G A M A N A L b y G u n n i c k and N i d a y (5, 6 ) , and S P E C T R A b y B o r c h a r d t et al. ( 7 ) .

I N V E N c o u l d not b e o b t a i n e d i n c o m p l e t e f o r m .

G A M A N A L was w r i t t e n for the C D C 6600 c o m p u t e r a n d w o u l d r e q u i r e a n extensive r e w r i t e for the I B M 360. S P E C T R A , a l t h o u g h not too sophist i c a t e d , w a s q u i t e a d e q u a t e for this w o r k . T h e p e a k find, p e a k i n t e g r a t i o n , a n d p e a k i d e n t i f i c a t i o n properties w e r e u s e d as w r i t t e n . W e i n s e r t e d


102

TRACE

ELEMENTS

IN F U E L

SAMPLE ENCAPSULATION ALIQUOT IN ALIQUOT IN (A) (B) POLYETHYLENE QUARTZ

(0 ..RRADIATION 12 HR;

(D)

IRRADIATION, 5 MINUTES; FLUX 1 . 5 x l 0 1 4 N/CM 2 -SEC

(F)

COUNTING: 5 M l Ν - 1 0 M l Ν DECAY 20 - 40 MIN DECAY

FLUX, 1 . 5 x l O l 4 N / C M 2 - S E C


(E)

COUNTING: 18 - 25 DAYS DECAY

(G)

(H)

COUNTING: 24 HOURS DECAY

PAPER TAPE TO MAGTAPE CONVERSION ADD PREDATA INFO

(I) LOAD MAG TAPE INTO IBM-360

(1) (I)

(I)

EXECUTE "SPECTRA" ANALYSIS IBM-360 (RESULTS)

X-Y PLOTS OF γ - R A Y SPECTRUM

Figure 1.

ONLY

STORE RESULTS IN IBM-360

PROGRAM LISTING

CHECK INPUT; VERIFY RESULT

(K)

RESULTS

PREPARE FOR ERO DATA EDIT

TRANSMIT DATA TO EPA AND OTHERS

(J)

EDIT STORED DATA

(J)

FILE EDITED DATA FOR FUTURE DATA ANALYSIS BY ERO

Flow chart showing scheme for irradiation, and data reduction of various samples

counting,

the e q u a t i o n s f o r h a n d c a l c u l a t i o n s , since t h e c o d e c a l c u l a t e d results b a s e d o n c o m p a r i s o n s w i t h standards.

O u r equations also p e r m i t t e d

a c c u r a t e corrections f o r d e a d t i m e losses, d e c a y d u r i n g c o u n t i n g t i m e , etc. A l i b r a r y o f s t a n d a r d s w a s a d d e d to t h e c o d e b a s e d o n elements f o u n d i n the various sample matrices. T h e standard library eventually i n c l u d e d 56 elements c a l c u l a t e d f r o m a p p r o x i m a t e l y 80 isotopes.

T h e rewrite,

p r o g r a m d e b u g g i n g , a n d i r r a d i a t i o n s o f s t a n d a r d s f o r t h e l i b r a r y took 7 m o n t h s to c o m p l e t e .


9.

Instrumental

SHEiBLEY

Neutron

Activation

103

Analysis

The Optimum Capability at P B R . T w e n t y - t w o a i r p a r t i c u l a t e s a m ples w e r e a n a l y z e d to a g a i n e v a l u a t e the analysis scheme.

T h e total time

for s a m p l e analysis a v e r a g e d 4.5 h r s / s a m p l e . T w o hrs of the t o t a l w e r e u s e d to c h e c k reported.

computer

i n p u t a n d results.

U p to 56 elements

A t this p o i n t a n i n i t i a l g o a l h a d b e e n a c h i e v e d .

We

were could

a n a l y z e 12 s a m p l e s / w k i n a p p r o x i m a t e l y 54 hrs. Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 3, 2018 | https://pubs.acs.org Publication Date: September 1, 1975 | doi: 10.1021/ba-1975-0141.ch009

W e c o n t i n u e d o u r efforts for a m o r e efficient o p e r a t i o n . interference

corrections,

A l l isotope

except for the a l u m i n u m c o r r e c t i o n o n

nesium, were computerized.

mag

T h i s saved more manpower i n data reduc

t i o n . B y u s i n g r o u t i n e s c h e d u l i n g of b o t h l o n g - a n d s h o r t - t e r m i r r a d i a t i o n s and counting, w e eventually achieved

an o p t i m u m situation on

both

manpower and counting equipment availability. This o p t i m u m situation p e r m i t t e d analysis of 2 0 - 2 4 s a m p l e s / w k w i t h a t o t a l m a n p o w e r of 3 to 3.5 h r s / s a m p l e e x p e n d e d . F i g u r e 1 shows the final s c h e m e u s e d for a l l s a m p l e types w h e n t h e p r o g r a m was t e r m i n a t e d . ( T h e P B R ceased o p e r a t i o n i n J a n . 1973. ) E a c h o p e r a t i o n is i d e n t i f i e d b y a letter i n parentheses.

Table I provides infor

m a t i o n o n the m a n p o w e r b r e a k d o w n for e a c h i d e n t i f i e d o p e r a t i o n .

Re

sults o n t h e p o l l u t i o n - r e l a t e d samples w e n t to the E n v i r o n m e n t a l P r o t e c tion Agency

( E P A ) , D i v i s i o n of A i r S u r v e i l l a n c e at R e s e a r c h T r i a n g l e

P a r k , N . C . a n d the E n v i r o n m e n t a l R e s e a r c h Office ( E R O ) , N A S A L e w i s Research Center, Cleveland, Ohio. A few comments should make F i g u r e 1 more understandable.

The

s a m p l e a l i q u o t u s e d for the 5 - m i n i r r a d i a t i o n w a s sealed i n a p o l y e t h y l e n e v i a l , tested for leaks, a n d i r r a d i a t e d 5 m i n . T h e other a l i q u o t w a s

flame

sealed i n the q u a r t z v i a l , tested for leaks, a n d i r r a d i a t e d 3 - 1 2 h r s , d e p e n d i n g o n the s a m p l e t y p e . T h e c o u n t i n g d a t a f r o m e a c h a l i q u o t w e r e

Table I.

Optimum Manpower Breakdown for 20 Samples/Wk

Operation Preparation, encapsulation Preparation, encapsulation Irradiation Irradiation Counting Counting Counting D a t a handling D a t a reduction D a t a handling D a t a handling a

Identification

a

A Β C D Ε F G H I S J 1 or Κ

Average Manhours/ Sample 0.25 0.25 0.1 0.1 0.25 0.55 0.25 0.1 0.8 S 0.8 i or 0.3 T o t a l 3.0-3.5

See Figure 1.


104

TRACE

ELEMENTS

IN

FUEL

p u n c h e d o n p a p e r t a p e w h i c h was a p e r m a n e n t r e c o r d of t h e c o u n t e d aliquot.

I n p u t d a t a , i n c l u d i n g the s a m p l e n u m b e r a n d the requestor's

i d e n t i f i c a t i o n n u m b e r , w e r e c o m p i l e d . T h e i n p u t d a t a a n d c o u n t i n g data w e r e t r a n s f e r r e d onto m a g n e t i c tape after c o n v e r s i o n to a f o r m a t p a t i b l e w i t h the I B M 360 c o m p u t e r .

T h e o u t p u t f r o m the

com

SPECTRA

c o d e consisted of a l i s t i n g of a l l i n p u t d a t a , c o u n t i n g d a t a , a n d results, Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 3, 2018 | https://pubs.acs.org Publication Date: September 1, 1975 | doi: 10.1021/ba-1975-0141.ch009

p l u s plots of the γ-ray s p e c t r u m of e a c h s a m p l e count. E P A d a t a listings c o n t a i n e d a s u m m a r y sheet of i n p u t d a t a a n d results for d a t a t r a n s m i t t a l . U s i n g a c o m p u t e r t e r m i n a l t h e E R O results w e r e s t o r e d i n d a t a sets i n the I B M - 3 6 0 m e m o r y , w h e r e they w e r e e d i t e d for errors a n d r e f i l e d i n m e m o r y for use i n other E R O d a t a r e d u c t i o n c o m p u t e r p r o g r a m s .

The

56 elements r e p o r t e d are s h o w n i n T a b l e I I . T h e y are g r o u p e d a c c o r d i n g to t h e d e c a y t i m e g r o u p i n w h i c h t h e y w e r e d e t e r m i n e d . Alternatives to Optimum Sample Processing.

The 20-24

samples/

w k w e r e c o n s i d e r e d the o p t i m u m because that n u m b e r of samples c o u l d b e c o m p l e t e l y a n a l y z e d i n 5 days, w o r k i n g one 8^-hr s h i f t / d a y . A n o t h e r i r r a d i a t i o n scheme u s e d to r e d u c e s a m p l e b a c k l o g s r e q u i r e d performing 30-36 short-term irradiations d u r i n g 1 w k , w i t h the number of l o n g - t e r m i r r a d i a t i o n s p e r w k i n c r e a s e d a n d h e l d for c o u n t i n g 3 w k s later. T h i s a p p r o a c h i n v o l v e d l o n g e r r a n g e s c h e d u l i n g , w a s less r o u t i n e , a n d w a s less efficient w h e n u n e x p e c t e d reactor s h u t d o w n s o c c u r r e d . Problems Some

Encountered problems

developed

i n sample preparation and

irradiation

b e c a u s e of the v a r i e t y of s a m p l e m a t r i c e s s u b m i t t e d for I N A A .

Some

samples w e r e p a r t i c u l a t e s ( c o a l , fly ash, b o t t o m ash, o r e ) , some w e r e v o l a t i l e h y d r o c a r b o n s (gasoline, jet f u e l , etc.), s o m e w e r e solids.

some w e r e aqueous, a n d

O u r m e t h o d s of s a m p l e p r e p a r a t i o n w e r e r e f i n e d to

p r o v i d e a l l samples i n sealed q u a r t z a n d p o l y e t h y l e n e v i a l s for i r r a d i a t i o n (see

F i g u r e 1 ) . D e p e n d i n g o n the contents of the q u a r t z v i a l s , t h e l e n g t h

of i r r a d i a t i o n was v a r i e d f r o m 3 - 1 2 hrs to m i n i m i z e v i a l b r e a k a g e f r o m

Table II.

Elements Listed in D a t a Summary According to Decay G r o u p

< 15 min Al Rh S Ti V

>15 min < 100 min Ba Ca CI Dy Ge I In

Mg Mn Na Sr Te U

>100 min < 5000 min As Au Br Cd Cu Eu Ga

Gd Ir Κ La Mo Pt Re

Sm W

> 5000 min Ag Ce Co Cr Cs Fe Hf

Hg Lu Nd Ni Rb Sb Sc

Se Sn Ta Tb Th Yb


Zn Zr

9.

SHEIBLEY

Instrumental

Table III.


Element

Neutron

Activation

105

Analysis

Impurity Level of Whatman-41 Filter Paper μρ 125.8

Ag Al Ba Ca Ce Cl Co Cr Cu Dy

Element

cm

2

0.0088 1.03 0.049 3.5 0.026 3.23 0.0022 0.051 0.08 0.00009

μη 125.8

Fe Hg Mn Na Sb Sc Ti U Zn

pressure b u i l d u p c a u s e d b y r a d i o l y s i s of the samples.

cm

2

1.57 0.0046 0.018 3.38 0.0046 0.0016 0.15 0.00067 0.601

M i n i m u m break

age o c c u r r e d (less t h a n 5 s a m p l e s / 1 0 0 i r r a d i a t e d ) w h e n v o l a t i l e h y d r o carbons (gasoline, kerosene, jet f u e l ) w e r e i r r a d i a t e d for 3 hrs or less. L e s s v o l a t i l e h y d r o c a r b o n s a n d aqueous samples w e r e i r r a d i a t e d 6 hrs. S o l i d samples w e r e i r r a d i a t e d 12 hrs. A n o t h e r p r o b l e m e n c o u n t e r e d was the i m p u r i t y content of the

filter

p a p e r u s e d i n the h i g h v o l u m e samplers to collect the p a r t i c u l a t e samples. T h e c o n v e n t i o n a l filter m a t e r i a l u s e d b y E P A w a s glass fiber filter m e d i a . H o w e v e r , this was not c o m p a t i b l e w i t h I N A A because of its h i g h a n d v a r i e d i m p u r i t y content.

D i s c u s s i o n s w i t h K . R a h n of the F o r d R e a c t o r

at the U n i v e r s i t y of M i c h i g a n r e v e a l e d that W h a t m a n - 4 1 filter p a p e r was the most d e s i r a b l e m e d i u m for use w i t h I N A A ( see Ref. 2 ). O u r analyses s h o w e d W h a t m a n - 4 1 to be v e r y l o w i n i m p u r i t i e s w i t h consistent i m p u r i t y levels f r o m b a t c h to b a t c h . A v e r a g e i m p u r i t y levels, b a s e d o n 12 b a t c h analyses, are s h o w n i n T a b l e I I I . A l t h o u g h the levels for c a l c i u m , c h l o rine, sodium, a l u m i n u m , a n d iron appear large, they rarely

affected

e l e m e n t a l levels f o u n d i n filtered p a r t i c u l a t e s . I m p u r i t y levels d i d not v a r y m o r e t h a n 2 5 % f r o m the m e a n . I m p u r i t y levels w e r e also i m p o r t a n t i n the q u a r t z a n d p o l y e t h y l e n e vials. D u r i n g the l o n g i r r a d i a t i o n t i m e i n q u a r t z , the samples d e c o m p o s e d so m u c h that i t w a s i m p o s s i b l e to c o m p l e t e l y r e m o v e the s a m p l e f r o m the v i a l for c o u n t i n g . T h e samples h a d to b e c o u n t e d i n the vials.

We

e v e n t u a l l y d e t e r m i n e d t h a t S u p r a s i l ( S u p r a s i l T - 2 0 , 6 - m m i . d . , 8 - m m o.d.; s u p p l i e r , A m e r s i l , Inc., H i l l s i d e , N . J . ), a s y n t h e t i c q u a r t z , best s e r v e d o u r needs for a l o w i m p u r i t y v i a l m a t e r i a l . I n T a b l e I V , w e i g h t s of i m p u r i t i e s are expressed i n m i c r o g r a m s b a s e d o n a v i a l 5 c m l o n g , w i t h a 6 - m m i . d . , 8 - m m o.d., a n d w e i g h i n g 2.77 g.

F o r some elements the l e v e l v a r i e d

significantly f r o m one b a t c h to another. most s i g n i f i c a n t l y was a n t i m o n y .

T h e element w h i c h

changed

T h e i r r a d i a t i o n of v o l a t i l e fuels

for

E P A r e q u i r e d t h a t w e also d e t e r m i n e the i m p u r i t y l e v e l of p o l y e t h y l e n e b e c a u s e l i q u i d samples w e r e c o u n t e d i n the i r r a d i a t i o n vials. W e f o u n d


106

TRACE

ELEMENTS

IN F U E L

that i m p u r i t y levels v a r i e d s o m e w h a t f r o m b a t c h to b a t c h of p o l y e t h y l e n e . T a b l e V presents a v e r a g e results o n i m p u r i t y levels of 16 p o l y e t h y l e n e vials. V i a l s w e r e 5 c m l o n g , w i t h 6 - m m i . d . , a n d 9 - m m o.d. T h e average w e i g h t of t h e s e a l e d v i a l w a s 2.00 g. H i g h d e n s i t y p o l y e t h y l e n e was u s e d because of its better r a d i a t i o n resistance. T h e h i g h i m p u r i t y levels i n these v i a l s f o r S, N a , C l , K , A l , a n d C a severely l i m i t e d the Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 3, 2018 | https://pubs.acs.org Publication Date: September 1, 1975 | doi: 10.1021/ba-1975-0141.ch009

s e n s i t i v i t y to these elements i n gasoline a n d other v o l a t i l e m a t e r i a l s w h i c h h a d to b e c o u n t e d i n the vials. P o l y e t h y l e n e w a s also s u s c e p t i b l e t o p i c k i n g u p r a d i o n u c l i d e s f r o m t h e p r i m a r y coolant.

T h i s interference w a s e l i m i n a t e d b y s e a l i n g t h e

s e a l e d p o l y e t h y l e n e v i a l s i n t o h e a t - s h r i n k a b l e t u b i n g w h i c h w a s easily r e m o v e d after s a m p l e i r r a d i a t i o n . T h e p r o b l e m of f l a m e - s e a l i n g gasoline a n d other v o l a t i l e m a t e r i a l s into quartz for the long irradiation was solved b y using a cold

finger

condenser i n l i q u i d n i t r o g e n . T h e q u a r t z t u b e ( a b o u t o n e - h a l f f u l l , 0.8 cm ) 3

w a s p o s i t i o n e d i n a n a l u m i n u m r o d w h i c h h a d b e e n b o r e d o u t to

a c c o m m o d a t e the l e n g t h of t h e t u b e f r o m its b o t t o m to a b o v e t h e l i q u i d l e v e l . T h i s r o d w a s t h e n l o w e r e d into a D e w a r c o n t a i n i n g l i q u i d n i t r o g e n a n d a l l o w e d to s t a n d u n t i l t h e g a s o l i n e b e c a m e s l u s h y a n d / o r a r i n g of frost a p p e a r e d just a b o v e t h e t o p of t h e a l u m i n u m . T h e n t h e t u b e w a s sealed using a n oxygen-acetylene

flame.

T h i s process

took less t h a n

5 min.

Table I V .

T y p i c a l Impurity Levels of a 2.77-g Suprasil V i a l

Element

μς

Element

μρ

Au Ce Cr Co Fe

0.00035 0.003 0.0144 0.0012 0.52

Hg Sb Sc Ta Zn

0.00059 0.01 0.0014 0.00017 0.092

Table V .

Impurity Levels in a 2.00-g Polyethylene V i a l

Element Al Au Ba Br Ca CI Cu I

Element 3.6 0.009 0.48 0.25 4.5 9.0 0.27 0.062

In Κ La Mn Na S Ti V

0.0003 9.4 0.037 0.046 8.1 162. 0.95 0.016


9.

SHEiBLEY

Instrumental

Neutron

Activation

107

Analysis

Spectra Code T h e computer program S P E C T R A (7) find,

contained an adequate peak

p e a k i n t e g r a t i o n , a n d p e a k m a t c h i n g r o u t i n e . T h e c o d e also d i s

t i n g u i s h e d t w o types of peaks b a s e d o n the statistical significance of the γ-ray c o u n t d a t a . T h e c o d e r e s o l v e d d o u b l e t s a n d t r i p l e t s u s i n g a m i n i Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 3, 2018 | https://pubs.acs.org Publication Date: September 1, 1975 | doi: 10.1021/ba-1975-0141.ch009

m u m p e a k area of five channels ( 5 k e V ) . T h i s degree of r e s o l u t i o n w a s a d e q u a t e for a l m o s t a l l peaks used. S P E C T R A also c o n t a i n e d a n o p t i o n c a l l e d G - s e a r c h . T h e G - s e a r c h r o u t i n e was u s e d to estimate the c o n c e n t r a t i o n of elements i n c l u d e d as s t a n d a r d s , b u t not f o u n d d u r i n g the p e a k find

a n d m a t c h i n g r o u t i n e . T h e c o d e t h e n e x a m i n e d the energy r e g i o n

w h e r e γ-ray peaks s h o u l d b e l o c a t e d a n d p r o v i d e d three estimates of the element c o n c e n t r a t i o n . T h e s e features w e r e left intact. W e d i d w r i t e i n t o the c o d e a l i b r a r y of standards w h i c h was u s e d i n l i e u of i r r a d i a t i n g a n d c o u n t i n g standards a l o n g w i t h t h e samples.

T o establish o u r w o r k i n g standards, w e

used

s p e c t r a of t y p i c a l s a m p l e matrices. E l e m e n t concentrations w e r e c a l c u l a t e d f r o m n u c l e a r d a t a . W e s u b s t a n t i a t e d the e l e m e n t a l values of these m a t r i x standards b y c o m p a r i s o n w i t h N B S a n d other standards.

Where

d i s c r e p a n c i e s of greater t h a n 2 0 % existed, the d a t a w e r e e x a m i n e d , t h e p r o b l e m i d e n t i f i e d , a n d c o r r e c t i v e a c t i o n t a k e n . F r o m this w e c o n c l u d e d that for these s a m p l e types no significant m a t r i x effects w e r e present.

We

r e t a i n e d the o r i g i n a l standards d a t a tapes a n d o c c a s i o n a l l y r e r a n t h e m to c h e c k

for

error i n the a u t o m a t i c d a t a p r o c e s s i n g

equipment

and

software. E l e m e n t standards w e r e g r o u p e d i n t o f o u r s t a n d a r d l i b r a r i e s , cor r e s p o n d i n g to t h e f o u r d e c a y c o u n t i n g times.

D e c a y time boundaries

for e a c h s t a n d a r d l i b r a r y are s h o w n i n T a b l e I I . I n e a c h l i b r a r y , at least t w o elements w e r e c a l c u l a t e d f r o m different standards. T h e s e t w o s t a n d ards r e p r e s e n t e d

different

concentrations,

counting

geometries,

dead

times, d e c a y times, a n d s a m p l e matrices. V i s u a l i n s p e c t i o n of the c o m p u t e r l i s t i n g p r o v i d e d a r a p i d spot c h e c k for c o m p u t e r p r o g r a m m a l functions. A n o t h e r a c c u r a c y p r o b l e m area i n v o l v e d the l i n e a r i t y of the γ-ray spectrometer

(analyzer)

detector

system.

SPECTRA

control

integers

w e r e a d j u s t e d to a l l o w o n l y a t h r e e - c h a n n e l v a r i a t i o n i n γ-ray p e a k e n e r g y to ensure p r o p e r p e a k m a t c h i n g w i t h s t a n d a r d p e a k energies. e a r i t y of the analyzer—detector system w a s c h e c k e d d a i l y w i t h 6 0

C o sources.

C s and

T h e a c t i v i t y of these sources p r o d u c e d d e a d times i n the

a n a l y z e r - d e t e c t o r system of less t h a n 1 0 % . occur.

The lin 1 3 7

H o w e v e r , linearity drift d i d

G a i n shifts i n l i n e a r i t y also o c c u r r e d w h e n s a m p l e activities w e r e

too h i g h .

W h e n the l i n e a r i t y s h i f t e d m o r e t h a n three channels, peaks

d i d not m a t c h w i t h standards o r p o s s i b l y c o u l d b e i m p r o p e r l y m a t c h e d .


108

TRACE

Table V I . Element/ isotope (X) 6 4

Cu


6 5 1 4 1

2 4 75

Zn Ce

82

B

4e

59

M g (g)» 203JJgc

Na Se Sc F

e

"Mo Al(g) Yb, Se

r

IN FUEL

Interference Corrections for Various Isotopes

Interfering isotope (Z)

203JJg

ELEMENTS

1 7 5

7 6

Correction

Required"

N A ( 5 1 1 k e V X) — 0 . 0 8 8 6 ( N A 1369 k e V Z) N A ( 2 7 9 . 1 k e V X) — 0 . 3 8 6 6 ( N A 264.4 k e V Z) N A ( 1 1 1 5 . 4 k e V X) — 0 . 7 7 6 7 ( N A 889 k e V Z) N A Î 1 4 5 . 4 k e V X) — 0 . 3 6 ( N A 1292 k e V Z) N A ( 7 7 6 . 5 k e V X) — 0 . 3 4 ( N A 740 k e V Z) g of M g c a l c u l a t e d — 0.057 (g of A l ) See t e x t

° Ν A refers to n e t area of p e a k . T h i s correction was d e t e r m i n e d e m p i r i c a l l y b u t n o t p r o g r a m e d into S P E C T R A ; a l l others were. C o r r e c t i o n coefficients used were d e t e r m i n e d f r o m a t w o - l e v e l factorial design. 6

c

A s u b r o u t i n e f o r l i n e a r i t y adjustment w a s a d d e d to S P E C T R A to correct f o r n o n l i n e a r i t y or d r i f t i n g of the a n a l y z e r system. T h e s u b r o u t i n e p r o v i d e d i n f o r m a t i o n o n the t r u e e n e r g y l o c a t i o n of six peaks w h i c h c o u l d reasonably be expected i n a given decay time group.

T h e search area

for e a c h p e a k w a s r e s t r i c t e d to a g i v e n n u m b e r of channels.

Coefficients

for a l i n e a r e q u a t i o n w e r e d e r i v e d f r o m a least-squares fit of t h e differ ence b e t w e e n t r u e e n e r g y l o c a t i o n a n d a c t u a l e n e r g y l o c a t i o n of at least f o u r peaks. T h e a c t u a l p e a k locations w e r e t h e n m a t h e m a t i c a l l y r e l o c a t e d closer to the t r u e energy l o c a t i o n before the p e a k m a t c h i n g r o u t i n e w i t h the standards w a s p e r f o r m e d . T h i s s u b r o u t i n e v i r t u a l l y e l i m i n a t e d m i s s e d peaks or i m p r o p e r p e a k matches.

T h i s saved considerable

man-hours

since peaks n o t m a t c h e d w i t h standards h a d to b e m a n u a l l y i d e n t i f i e d and hand calculated. S o m e elements w e r e c a l c u l a t e d f r o m t h e same isotope i n different d e c a y groups. A n d other elements w e r e c a l c u l a t e d f r o m different isotopes i n t h e same o r different d e c a y groups.

This duplication was used to

improve accuracy. Interference Corrections. I n c e r t a i n cases, the γ-rays of one element isotope are close to t h e γ-ray energy of a n isotope u s e d to d e t e r m i n e a n o t h e r element. interference.

I n these cases, it w a s necessary to correct for this

S u b r o u t i n e s f o r interference

corrections

were

added

to

S P E C T R A to e l i m i n a t e p e r f o r m i n g s u c h corrections m a n u a l l y . T h e c o r r e c t i o n factors u s e d w e r e n o r m a l l y d e r i v e d f r o m n u c l e a r d a t a i n f o r m a t i o n . B u t w e d i d c h e c k these corrections b y i r r a d i a t i n g m i x t u r e s of these ele ments i n v a r i o u s concentrations.

T h e i n t e r f e r e n c e corrections u s e d are

s h o w n i n T a b l e V I . T h e c o r r e c t i o n for

2 8

A 1 on

2 7

M g was determined

e m p i r i c a l l y b e c a u s e i t w a s specific to the i r r a d i a t i o n l o c a t i o n i n t h e P B R . T h e d e t e r m i n a t i o n of m e r c u r y i n c o a l p r o d u c e d a n interference cor rection p r o b l e m w h i c h was quite complex.

W e f o u n d that c o u n t i n g a n


9.

Instrumental

SHEiBLEY

Neutron

Activation

109

Analysis

i r r a d i a t i o n c o a l s a m p l e at 5—6-wks d e c a y t i m e p r o d u c e d a smaller m e r c u r y v a l u e t h a n t h e v a l u e c a l c u l a t e d f r o m t h e c o u n t at 3-wks decay. c o r r e c t i o n for

7 5

S e was b e i n g m a d e o n

2 0 3

H g , b u t the l o w e r

A

mercury

results ( f r o m 0.5 to 0.1 times s m a l l e r ) at 6-wks d e c a y c o u l d n o t

be

explained. A search of the N u c l e a r D a t a T a b l e s ( 8 ) Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 3, 2018 | https://pubs.acs.org Publication Date: September 1, 1975 | doi: 10.1021/ba-1975-0141.ch009

ference: 4.2-day with

2 0 3

Yb.

1 7 5

H g , b u t also the 4 0 0 . 7 - k e V p e a k of

K e V p e a k area of

1 7 5

p r o d u c e d another i n t e r

N o t o n l y d i d the 2 8 2 - k e V p e a k of 7 5

1 7 5

Y b interfere

S e i n t e r f e r e d w i t h the 396-

Y b , w h i c h was u s e d for the Y b c o r r e c t i o n o n

I n a d d i t i o n , another y t t e r b i u m isotope, 3 2 - d a y 2 6 4 - k e V p e a k area of area at 279 k e V ) .

75

1 6 9

2 0 3

Hg.

Y b i n t e r f e r e d w i t h the

S e , w h i c h is u s e d i n the c o r r e c t i o n o n

2 0 3

H g (peak

T h e s e discrepancies w e r e not e l i m i n a t e d b y u s i n g

t h e o r e t i c a l corrections. F i n a l l y , the p r o b l e m w a s r e s o l v e d b y i r r a d i a t i n g standards a n d m i x tures of standards i n a f a c t o r i a l e x p e r i m e n t . T h e e x p e r i m e n t d e s i g n w a s a f u l l f a c t o r i a l e x p e r i m e n t w i t h three v a r i a b l e s , m e r c u r y , s e l e n i u m , a n d y t t e r b i u m , at t w o levels w i t h r e p l i c a t i o n a n d w i t h a center p o i n t a d d e d to test h i g h e r order effects.

T h e p e r t i n e n t i n f o r m a t i o n o n treatments a n d

levels of v a r i a b l e s are s h o w n i n T a b l e V I I . R e g r e s s i o n analysis o n the d a t a was u s e d to estimate t h e coefficients in a predictive model equation.

T h e d e p e n d e n t v a r i a b l e w a s chosen as

t h e difference b e t w e e n the c o m p u t e r - c a l c u l a t e d v a l u e f o r m e r c u r y

(or

s e l e n i u m or y t t e r b i u m ) a n d the true v a l u e . I n d e p e n d e n t v a r i a b l e s w e r e the elements p l u s p l a u s i b l e interactions (e.g., the i n t e r a c t i o n of s e l e n i u m Table VII. Factorial Design Treatments for Y b and Se Interferences on H g Coded Level of

a

(

Variable"

Treatment

Se

Hg

Yb

1 2 3 4 5 6 7 8 Replicates 4 7 8 Center point

-1 + 1 -1 -1 + 1 - 1 + 1 + 1

-1 -1 + 1 -1 + 1 + 1 + 1 -1

-1 -1 -1 + 1 -1 + 1 + 1 + 1

-1 + 1 + 1 CP

-1 + 1 -1 CP

+ 1 + 1 + 1 CP

(-1)

indicates low level, 10 μg.

( + 1) indicates h i g h level, 100

μg.

CP

h i g h level + low level \

2

)


indicates

110

TRACE


NBS

Sb Ce Co Eu Au La Th Sc Ag

610

PBR

— — (390) — (25) — — — (254)

IN

FUEL

Comparison of N B S Standard

Table VIII. Element

ELEMENTS

NBS

PBR

612

— —

(39) (35) (36) (5) (36) 37.6±0.1

37±2 31±1 26±1 5±1 35±15 31±1

180±80

22.0±0.8

31±7

135±14

— 20±2

° N B S values in parentheses are interim values. Others are certified values. and ytterbium on mercury).

T h e coefficients d e r i v e d f o r the p r e d i c t i v e

e q u a t i o n s s e r v e d as the basis for t h e e m p i r i c a l c o r r e c t i o n of y t t e r b i u m and selenium on mercury. F o r c o m p a r i s o n , the t h e o r e t i c a l a n d e m p i r i c a l corrections

are

as

follows: 1. T h e o r e t i c a l corrections for s e l e n i u m a n d y t t e r b i u m interferences on mercury A B D

c c c

= = =

A B D

u u u

-

0.0369 X 0.118 A 0.959 B c

c

0.387

A

c

2. E m p i r i c a l f o r m of s e l e n i u m a n d y t t e r b i u m c o r r e c t i o n factors interference o n m e r c u r y Table IX.

for

Comparison of P B R Mean Values Coal

Element As Co Cr Cu Hg Mn Ni Rb Se Sr Fe Th U V Zn a

NBS* 5.9±0.4 — 22 ± 2 18 ± 2 0.11 47 ± 3 — — 2.8±0.2 — — 3 1.4±0.1 35 ± 4 37 ± 4

PBR 5.9

±0.5 — 19.0 ± 0 . 8 14.1 ± 0 . 9 0.95±0.09 38 ±3 — — 3.8 ± 0 . 5 — — 3.1 ± 0 . 2 0.98±0.08 36 ±4 —

Data taken from: "Characterization of Standard Reference Materials For the File Number 0168-4 (May 1, 1973).

0158(D),


9.

Instrumental Neutron Activation

SHEiBLEY

Reference Materials with P B R Results ( p p m ) NBS

PBR

614


(1.06)

1.1

NBS

0.59±0.1 1.1 ± 0 . 6 1.0 ± 0 . 8

Trace Elements by Instrumental Neutron Activation Analysis for

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