586
Anal. Chem. 1980, 52,
II 3
.I@-
. .
II
-
12-
74116
.
IC2
586-587
quency to counter 0 is 2 MHz, and the values in this look-up table are actually a factor of 2 greater than the decimal value requested. Because of this minimum count restriction, t h e total dynamic range of clock periods will be 2 x lo4 to (216 - 1) x 104 p s (-655 s i . T h e additional versatility of this design should be further commented upon with regard t o its use as a more universal real time clock. In this regard, the addition of a n appropriate ill permit use of this same basic output latch and gating logic w circuit as a n elapsed time clock. I n such a n application, appropriate software would be used t o read t h e contents of counter, 1,operating with a range of 216 times the base period set into counter 0. In a n additional potential application as a n event counter, the accumulated counts into the third counter can be used as a scaler, which would be gated for a total timing period as preset by t h e basic clock consisting of counters 0 and 1 described in this paper. Although this design is presented for the micro NOVA computer system, extensions t o other micro- a n d minicomputers should be fairly straightforward. LITERATURE CITED
74123
SET DONE
IC 312
I
Figure 1. The 74174 is a positive-edge-triggered hex latch with clear: the 741 16 is an &bit latch with clear; the 74123 is a dual retriggerable monostable; and the 8253 is the Intel programmable interval timer
count carried from t h e FORTRAN call, whereas counter 0 is loaded from a simple look-up table indexed according to the value of the exponent (0-4) requested in the call. As the 8253 will not operate for counts of less than 2, the primary fre-
(1) Hahn, B. K.; Enke, C. G. Anal. Chem., 1973, 4 5 . 651A. (2) Danielson, J. D. S.;Brown. S.D.; Appellof, C. J.; Kowalski, B. R . Chem., Biomed: Environ. lnstrum. 1979, 9 , 29. ( 3 ) Titus, J. A.; Titus, C. A.; Larsen, D. G.; Rony, P. R. Am. Lab. 1979 (3), 111. (4) Larsen. D. G.; DeJong, M. 1.; Rony, P. R.: Titus, J. A,: Titus, C. A. Am. Lab. 1978 (2), 150.
RECEIVED for review August 9, 1979. Accepted November 29, 1979. Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society and to the Cottrell Research Grants Program of Research Corporation for partial support of this work.
Nonvolatile Liquid Scintillator Takahisa Kato” Isotope Center, School of Medicine, Mie University, Tsu, Mie, Japan
Toshifumi Hatagami Magnetic Disk Section, Fujitsu Limited, Nakahara, Kawasaki, Kanaga wa, Japan
Liquid scintillation counting is suitable for determination of low energy 0-emitters. Characteristics are high sensitivity and ability to analyze many kinds of nuclide nuclear spectra. Previous papers ( I , 2 ) reported that for measurement by liquid scintillation counting of air contaminated with radioactive gases, sampling of the gases was required. Sampling was with a nonvolatile liquid adsorbent which was counted by mixing in a volatile liquid scintillator. Most common scintillators are organic nonpolar liquids, e.g., toluene, dioxane, or xylene (3, 4 ) , each having volatile properties. If the sample itself, which adsorbs the radioactive gases, is a liquid scintillator, the measuring process in the case of monitoring radioactive gases in air can be shortened. In this paper, a silicone oil-based liquid scintillator in which wave length shifters P P O and P O P O P are compounded is made and tested with low energy @-raysources, tritium and carbon-14. EXPERIMENTAL Method a n d Materials. Reagents are prepared from the 0003-2700/80/0352-0586$01 OO/O
following: 1,5diphenyloxazole (PPO), 2,2’-phenylenebis(5phenyloxazole) (POPOP), and silicone oil HIVAC F4 from Nakarai Chemicals, Ltd. An Intertechnique Liquid Scintillation Spectrometer Model SL-30 was used for counting with 20-mL low-potassium glass vials, (Wheaton Glass Co.). Radioactive materials were: [ m e t h ~ l - ~thymidine H] aqueous solution and L- [U-14C]leucineaqueous solution containing 2 70 ethanol. The composition of the silicone oil scintillator was as follows: silicone oil, 100 mL; PPO, 0.7 g/100 mL: and POPOP, 0.02 g/100 mL. Determination a n d Spectral Analysis. 3H-thymidine and 14C-leucine are dissolved in 1-mL aliquots of ethanol. Then 0.02-0.2 mL of each solution is added separately to the silicone oil scintillator, to toluene (toluene 0.7 L, ethanol 0.3 L, PPO 4.0 g/L, POPOP 0.1 g/L) and to dioxane ( 3 ) ,and measured by liquid scintillation counting. The y r a y spectrum of the silicone scintillator is measured with a 13:Cs external standard source ( 5 ) ,and the results are plotted. Decays per minute (DPM) corrections for toluene and dioxane scintillators are calculated and a similar C 1980 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 52, NO. 3. MARCH 1980 Table I .
587
Counting and Decaying Rates and Ratios D-rays carbon-14 upper win tlow lower -_______
,-ray, cesium-137 ~-________
tritium
6.50 1.70
6.00
5.90
1.00
4.74 4.88 __________.
silicone scintillator
22245 (23382) = 0.95
1134 (Issa)=o.60
2 8 2_ 21 _
toluene scintillator
25904
=0,51
1263 = 0.37 3380
8.80
92865 -~
...
. . .
CPMa
DPhlb 28264
71136 30632 __ ... . . . __ ____-._______ ~~
silicone scintillator
=
= 0.91
J-= 0.55 (29666)
dioxane scin ti llat or
3763 - =0.95 39S6
19068 44916 = u . 4 2
(3010)
2L!xo ...
109604
15784 ... _
10 5 0 62 ____ . . .~ . ~ .__-
....
(:PM
DPM
a
~
_
_
Counts per minute.
~--
~
Decays per minute. ______
I
, Log€
(E
Energy
of
correction for the silicone scintillator is applied by substituting the toluene quenching standard correction curve for the silicone curve. Such correction is, however, an approximation. The counting values and results are shown in Table I. In Table I, counts per minute (CPM),DPM, and the ratios for the respective windows are indicated. DPM for the silicone scintillator is shown in parentheses because of the quench approximation used. From the results, the silicone scintillator functions as well a5 the toluene. T o compare the $-ray spectrum of the silicone scintillator with that of toluene, the same amount of I4C-leucine sample is mixed with the silicone and with the toluene scintillator. In each case, the I4C spectrum is analyzed with a pulse height analyzer. The spectra are shown in Figures 1 and 2. Figure 1 shows the spectrum curve of an unquenched standard and Figure 2 shows two curves for the quenched spectra. The dotted curve with open circles represents the silicone scintillator and that with solid circles the toluene scintillator. The silicone spectrum curve shows less quenching than the toluene.
DISCUSSION As shown in Table I, t h e counting function of t h e authors' silicone scintillator approximates that of toluene and dioxane. T h i s silicone solution acts as a n excellent adsorber for ra-
~
. .~
1
-
2
Log E
beta-rays)
Figure 1. Carbon- 14 &-ray liquid scintillation unquenched standard spectrum
. I.
.o -~
0
3 (E
4
5
6"
7
Energy of beta-rays)
Flgure 2. Two curves show carbon-14 d-ray quenched spectra. The dotted curve with open circles represents the silicone scintillator and the solid circles, the toluene scintillator. 'The silicone spectrum curve is less quenched than the toluene dioactive gases in air and also can be used as scintillator. As seen from the spectrum shift in Figure 2, the silicone solution exhibits less quenching effect t h a n a toluene solution. Tsang and Street (6) recently reported t h e photoluminescence decay of glow-discharge-deposited amorphous silicon. I t may be considered that t h e silicone has some conjugated structure responsible for this scintillation.
ACKNOWLEDGMENT I wish to thank David. B. Izard for his help with the English corrections.
LITERATURE CITED (1) (2) (3) (4) (5) (6)
Kato, T. Nucl. Instrum. Methods 1979, 163, 463-465. Kato, T. Int. J . Appl. Radiat. Isot. 1979, 30, 349-351.
Bray, G. A . Anal. Biochem. 1960, I , 279-285. Butler, F. E. Anal. Chem. 1961, 33, 409-414. Horrocks, D. L. Nature (London) 1964, 202, 78-79. Tsang. C.; Street, R. A,, Philos. Mag. B , 1979, 3 7 ( 5 ) ,601-608.
RECEIVED for review August 21, 1979. Accepted October 15, 1979.
