Rapid technique for liquid scintillation counting of carbon-14-labelled barium carbonat

Allred, J. B.

English

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RAPID TECHNIQUE FOR L I Q U I D  SCINTILLATION 
COUNTING OF CARBON- 14-LABELLED 
BARIUM CARBONATE 
John B. A l l r e d ,  Oklahoma C i t y  U n i v e r s i t y ,  
Oklahoma C i t y ,  Oklahoma 
Liquid s c i n t i l l a t i o n  coun t ing  has  become the  
hethod of  cho ice  f o r  t he  measurement of low-energy 
? - a c t i v i t y  a l though some d i f f i c u l t y  i s  s t i l l  encountered  
uhen t h e  r a d i o a c t i v e  sample i s  i n s o l u b l e  i n  t h e  coun t ing  
s o l u t i o n .  For  s o l i d  samples ,  one method has  been t o  
suspend the  f i n e l y  ground material  i n  the  coun t ing  so lu -  
t i o n  and by some means c o r r e c t  f o r  t he  f a c t  t h a t  the  
suspended m a t e r i a l  w i l l  s e t t l e  o u t ,  reducing  c o u n t i n g  
e f f i c i e n c y  . Another method t h a t  has  been used i s  t o  1 
reduce the  r a t e  of s e t t l i n g  of suspens ions  w i t h  g e l s  2 * 3  ,
Although t h e  a d d i t i o n  of g e l s  t o  t h e  coun t ing  s o l u t i o n  
'Oe WaOd AZIliavd 
- 1  reduces  c o u n t i n g  e f f i c i e n c y ,  r ang ing  from a r e l a t i v e l y  
2 
minor dec rease3  t o  major e f f e c t s  , t he  major  d i sadvantage  
t o  bo th  of  t h e s e  methods i s  t h e  e x t e n s i v e  t i m e  r e q u i r e d  
f o r  sample p r e p a r a t i o n .  The method r e p o r t e d  he re  u t i l i z e s  
4 
s o n i c a t i o n  t o  r a p i d l y  reduce p a r t i c l e  s i z e ,  t h u s  d e c r e a s i n g  
L 
1 
. 
https://ntrs.nasa.gov/search.jsp?R=19670007287 2020-03-16T18:40:06+00:00Z
p r e p a r a t i o n  t i m e  and s e t t l i n g  r a t e ,  and e l i m i n a t i n g  the  
need t o  a g i t a t e  t h e  sample between s u c c e s s i v e  coun t s  o r  
c o r r e c t  f o r  t he  s e t t l i n g  rate.  
Experimental  
Reagents ~ Barium ca rbona te  of low s p e c i f i c  a c t i v i t y  
was prepared  by adding a c i d  t o  BaC 14 03 commercially a v a i l -  
a b l e  and t r a p p i n g  evolved C1402 i n  1 .0  N sodium hydroxide 
which con ta ined  c a r r i e r  sodium c a r b o n a t e .  
w a s  then  p r e c i p i t a t e d  from t h i s  s o l u t i o n .  
t h i s  barium ca rbona te  was assayed commercially (New England 
Barium ca rbona te  
A sample of 
Nuclear  Assay Corpora t ion ,  Boston, Mass.)  t o  determine 
s p e c i f i c  a c t i v i t y .  The coun t ing  s o l u t i o n ,  shown by 
p r e l i m i n a r y  exper iments  t o  g ive  the  h i g h e s t  count ing  
e f f i c i e n c y  and minimal s e t t l i n g  ra te ,  w a s  based upon a 
dioxane-napthalene system4 and con ta ined  15 grams of 
r e a g e n t  grade  naphtha lene  , 1.05  grams of 2 ,5-diphenyloxazole  
(Packard Ins t rumen t  Co. , Downer's Grove, Illv), 0,045 
grams of 4-bis-2-(5-phenyloxazolyl)-benzene (Packard 
Ins t rument  Co. ,  Downer's Grove, 111.) d i s s o l v e d  i n  15 ml 
of a b s o l u t e  e t h a n o l  and 150 m l  of p-dioxane ( S p e c t o q u a l i t y  
Reagent,  Matheson, Coleman and B e l l ,  East Ru the r fo rd ,  
N L ) *  
. 2  
Procedure.  BaC 14 0 was weighed i n t o  g l a s s  coun t ing  
3 
v i a l s ,  i n  amounts from 10 t o  40 m g  and 10 m l  of coun t ing  
s o l u t i o n  was added. Each sample w a s  sub jec t ed  t o  son ica -  
t i o n  f o r  20 t o  30 seconds u s i n g  a Branson S o n i f i e r  
(Branson I n s t r u m e n t s ,  I n c . ,  Stamford, Conno) tuned t o  maxi- 
mum ove r tones .  The probe of t h e  s o n i f i e r  was then r i n s e d  
w i t h  an a d d i t i o n a l  5 m l  of coun t ing  s o l u t i o n .  A f t e r  
c o o l i n g  t o  2 " C ,  each  v i a l  was v igo rous ly  a g i t a t e d  j u s t  
p r i o r  t o  coun t ing .  Each sample was counted f o r  3 minutes  
t h r e e  success ive  t imes wi thou t  a g i t a t i o n  between coun t s  
u s i n g  a Paekard Tr i -Carb  Liquid S c i n t i l l a t i o n  Counter  
(Peckard Ins t rument  Co. , Downer's Grove, 1 1 1 , ) .  I n  
s t u d i e s  on s e t t l i n g  r a t e s ,  c o u n t s  were recorded  f o r  each  
3-minute i n t e r v a l  f o r  a pe r iod  up t o  30 minu tes ,  w i t h  n0 
a g i t a t i o n  between coun t s .  
R e s u l t s  and Discuss ion  
A s  shown i n  Table I ,  t h i s  method gave r ep roduc ib le  
r e s u l t s  w i t h  h igh  coun t ing  e f f i c i e n c y .  The r a t e  of s e t t l i n g  
was very slow i n i t i a l l y  (Table 11)  so  t h a t  c o r r e c t i o n s  
f o r  t he  dec rease  i n  e f f i c i e n c y  over  t he  9-minute coun t ing  
pe r iod  was unnecessary.  I f  a longer  coun t ing  time was 
3 
needed because of l o w  l e v e l  of a c t i v i t y ,  the  sample could  
be resuspended by a g i t a t i o n  and the  normal coun t ing  
procedure r e p e a t e d .  Once s o n i c a t e d ,  samples could be 
resuspended f o r  coun t ing  a t  any subsequent  time up t o  
s e v e r a l  months. 
The most impor tan t  a s p e c t  of t h i s  m o d i f i c a t i o n  of 
p rev ious  methods i s  the  reduced t i m e  needed f o r  sample 
p r e p a r a t i o n .  The s o n i c a t i o n  procedure r e q u i r e s  less than 
1 minute compared t o  t h e  3 t o  5 minutes  needed t o  g r i n d  
each  sample f o r  suspension coun t ing ,  and avo ids  q u a n t i t a -  
t i v e  t r a n s f e r s  of s o l i d  from g r i n d i n g  v e s s e l  t o  coun t ing  
v i a l  .. 1 
L i t e r a t u r e  C i t e d  
1, F.  €4, Hayes ,  B. S .  Rogers and W .  H ,  Langham, 
1 
Nucleonics ,  _. 14,CNo. 3), 48 (1956).  
2 .  C .  G. White and S. Helf , I b i d .  , -3 14 - (No. 10 1) 46 
(1956) 
3 .  D. G .  O t t ,  C .  R. Richmond, T. T .  T r u j i l l o  and H ,  
Foreman, I b i d .  , 1 7 ,  (No. 9), 106 (1959) -
H. Werbin, I. L. Chaikoff  and M. Ro Imada, Proc ,  
I 
4 '  
SOC. Expt.  Biol. and Med 102,  8 (1959) .  - - - - ' I -  
4 
This  i n v e s t i g a t i o n  was suppor ted  i n  p a r t  by NASA 
&ant  N s G  300 nd Pub l i c  Heal th  Se rv ice  Research Grant 3. 
> AM 06673 f romCIns t i t u t e  of  A r t h r i t i s  and Metabol ic  Diseases  
Table Io 
of va r ious  s ized  samples of son ica t ed  BaCI4O3 
Observed s p e c i f i c  a c t i v i t y  and count ing  e f f i c i e n c y  
,Sample weight  Spec if ic  Ac t iv i ty*  
15.0 943 f 6 
20.0  941 f 7 
25.0 
30.0 
937 f 11 
933 1 
40.0 914 2 3 
E f f i c i ene  y* 
66 ,7  2 0,1 
66.5 9 0.2  
66 ,2  2 0,1 
64.8 2 0 , l  
*values  a r e  g iven  w i t h  s t anda rd  d e v i a t i o n .  
c 
c 
Table 11. Counting e f f i c i e n c y  a t  v a r i o u s  t i m e  i n t e r v a l s  
a f t e r  a g i t a t i o n  r e l a t i v e  t o  the i n i t i a l  t h r e e  minute 
coun t ing  p e r i o d .  
Time I n t e r v a l  R e l a t i v e  E f f i c i e n c y  
(min) 10 mg sample 20 mg sample 
0-3 1.000 1.000 
9- 1 2  0 . 9 9 9  0 . 9 9 2  
18-21 0.985 0 . 9 7 0  
27-30 0 . 9 7 0  0 . 9 1 2  
6 


Rapid Technique for Liquid Scintillation Counting of Carbon-14-labelled Barium Carbonate

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