FIGSal: 
Counting Suspensions in 
Liquid Scintillators 
CouNTING SUSPENSIONS of solid sam- 
ples in a liquid scintillator makes many 
compounds accessible to liquid scintil- 
lation counting for the first time. 
Additional advantages are ease of 
sample recovery through filtration and 
absence of conventional quenching 
problems. Problems present here, but 
not in solution counting, are self- 
absorption and light scattering. How- 
ever, small particle size minimizes self- 
absorption and stabilizes the suspension 
at the same time. 
We surveyed the potentialities and 
limitations of suspension counting for 
several materials and the radioisotopes 
H3, Cl4, $35 and Ca‘®. The only 
chemical requirements were that the 
samples be solids insoluble in toluene. 
Sample preparation is discussed on 
p. 50. 
* Work done under the auspices of the 
U. S. Atomic Energy Commission. 
t In early phases of the study we used 
a 90-ml Pyrex bottle; some of the results 
given here were obtained that way. How- 
ever, experience proved the smaller bottle 
better. 
Now materials insoluble in liquid scintil- 
lators can be counted with high efficiency. 
Sample preparation is rapid and counting 
techniques are straightforward. Settling 
Liquid scintillation counter showing sample 
bottles and the nonrefrigerated lead shield with light 
lock permitting insertion of sample without turning off 
high voltage 
Counting Procedures 
Here are the procedures and materi- 
als we used to count suspensions. 
Counting bottles. Kimble Opti- 
clear 10-dram vials, 29 mm in diameter 
and 85 mm high (including poly- 
ethylene cap), were used (Fig. 1). 
Maximum useful volume was about 
35 ml.f 
Stock solution. The 
scintillator 
= 
9 
@ 
fo) 
.6— 
Fraction of Original Rate 
C —) 
N“ 
bee] = ie! “a : ‘ 
ae 60 120 
of the suspension, self-absorption, and 
light absorption are solvable problems 
By F. NEWTON HAYES, BETTY S. ROGERS, and 
WRIGHT H. LANGHAM 
Los Alamos Scientific Laboratory * 
University of California 
Los Alamos, New Mexico 
liquid scintillator in common _ use 
for solution counting also was 
used in this study. It was 4 gm/l 
2,5-diphenyloxazole (PPO) and 0.05 
gm/1 1,4-di-(2-(5-phenyloxazolyl)]-ben- 
zene (POPOP) in toluene. It repre- 
sents an excellent compromise among 
pulse height, economy, and ability to 
remain homogeneous. Since an inert 
suspension does not act to precipitate a 
dissolved solute, the latter criterion 
§ of i 1a eae ae 
180 240 “300. 
Elapsed Time {sec) 
FIG. 2. Effect of settling rate on scintillation counting of a suspension of 20 mg 
Cat®C20,4 
1 
