composition, and possibly b y addition of carrier. Absorption of Radiation by t h e Solution. Inorganic solutes i n u p t o 1M concentrations do n o t absorb enough radiation from a n y of t h e isotopes studied t o affect the counting rate. For example, if care is taken t o avoid foaming a n d sorption problems, Cs13’ gives the same efficiency in 131 HCI, 0.02M HCl, and l X NaCl. Tritium, which rvould be the most likely isotope to shm- a n eff’ect, likewise gives the same efficiencies in 0.01N 0.1, 0.3, or 1 . O X HCl, 0.01.Y HC1 NaC1, O . O O l X HC1 0 . l N NaCl, and 0.09X XaOH. This insensitivity to solute concentration is one of the greatcqt advantages of this method of counting. and stems from the fact that the solute contributes but a small fraction of the totnl electrons in the solution. Tor inore concentrated solutions or for .elutes of high atomic number of course, would not be true. I C extent to which water, the most impoi tant radiation-absorbing material prescnt, affects the counting rate was determined by rcmoving the water from the swtmi. The ratios R1 and RIR of T:ible 111 should equal 1 and 5, respectively, if no radiation is absorbed by nntcr and if the isotope remains intimately associated with the anthracene during the drying procedure. The large values obtained r i t h H3 show t h a t absorption by n a t e r is a major factor in decreasing the efficiency with which this isotope is counted. T i t h the this does not possible exception of appear t o b r true for the other isotopes. T h e low ~ a l u e of s these ratios for Cs137 and of Ra (which should equal 5 ) for all isotopes except S35 indicates that some of the isotope is lost from the anthrnccne during drying. Ancillary experiments have shown that this material is on the wall of the counting vial. Because of this difficulty, drying, nhile it increases the counting rate of nonvolatile H3 samples, cannot be recommended as a routine analytical procedure without further development. With isotopes other than H3, drying appears to offer no advantages. Effects of Nonaqueous Solvents. Admixture of methanol, ethanol, acetone, or acetic acid in amounts u p to 75% b y volume with Verona1 buffer solutions of Ca45 had essentially no effect on the counting of 3-ml. samples. Efficiencies, relative to water, ranged from 0.90 to 1.07. Since these results were obtained under extreme conditions i t seems almost certain that small amounts of these substances would have very little effect.
+
Table 111.
Isotope H3
ss
Cs’n
SrgO-YgO Po210
+
ACKNOWLEDGMENT
Effect of Water on Counting Rate
Ri Composition 12.3 Thymidine in 0.01N HC1 Thymidjne 0.01N HC1 0.1N NaC1 8.4 Thymjd!ne 0.01N HCl 0.3N NaCl 6.4 Thymidine 0.01N HCl 1.ON NaCl 4.4 Thymidine 0.001N HC1 0.1N NaCl 6.5 Thymidine 0.09N NaOH 7.3 1.1 0.1N HC1 0.9 1N HC1 0.9 0.01X KaOH (foamy) 1 0 1N HCl 1 .o 0.02N HC1 1 .o H,O CU+* Counts in dry 0.6-ml. sample R1 = Counts in wet 0.6-m1. sample Counts in dry 3.0-ml. sample R2R Counts in wet 0.6-ml. sample Counts in dry 3.0-ml. sample R3 = Counts in dry 0.6-ml. sample
++ + ++
+ + + +
+
Urist. The authors gratefully acknowledge his valuable suggestions and continued interest and encouraerment. They also express their appreciation to Henry Talifer for terhnical assistance. LITERATURE CITED
(1) Davisson, C. JI., Evans, R . D.j Revs. Modern Phys. 24, 79-107 (19.52).
(2) Hevesy, G., Paneth, F. A.,“.4 Manual of Radioactivity,” PP. 164-5, 2nd e d . ~ Oxford University Press, London, 1938. (3) Hodgson, T. s.3 Gordon, B. E., Ackerman, ill. E., JVuc2eonics 16,No. 7 , 89 (1958). (4) Hopkins, J. I., Reo. Xci. Inst?. 22, 29-33 (1951). ( 5 ) Kettelle, B. H., Boyd, G. E., J . Am. Chem SOC.69, 2800-12 (1947). (6) Moyer, H. V., ed. “Polonium,” U. S.
RzR 11.0 30.0 27.0 17.0 28.0
18.0 5.3 3.6 2.6 5.1 4.4 4.0
R3 1.o
3.8 4.4 4.0 4.4 2.9 5.0 4.0 2.7 4.8 4.6 4.9
Atomic Energy Comm. Rept. TID-5221, pp. 46-70, July 1956. (7) Roth, Louise, Phys. Rev. 75, 983 f{ iAnr n n\ I Y ] .
(8) Schubert, J., Conn, E. E., Sucleonics 4, SO. 6, 2-11 (1949). (9) Schubert, J., Lindenbaum, A., J . Am. Chem. SOC.74. 3529-32 11952). (10) Schubert, J., Russell, E. R., Rlyers, L. S.,Jr., J . Biol. Chem. 185, 387-8 (1950). (11) Schveitzer, G. K., Stein, B. R., Jackson, 77’. M., J . i l m . Cheni. Soc. 75, 793-5 (1953). (12) Steinberg, Daniel, Anal. Biochem. 1, 23-39 (1960). (13) Steinberg, Daniel, Nature 183,1253-4 (1959). RECEIVEDfor review July 26, 1961. Accepted December 27, 1961 Studies supported by Contract AT(04-1) GES-12 betm-een the U. S. Atomic Energy Commission and the University of California.
Correction Highly Accurate Continuous Recording Differential Refractometer I n this article b y F. A. Vandenheuvel and J. C. Sipos [ANAL.CHEW 33, 286 (196l)], on page 288, the circuit diagram
of the amplifier shown in the top left of Figure 1 is incorrect. The corrected diagram is shown below.
8 C A 5584
I
I
These studies were an outgrowth of a joint research program with Marshall VOL. 34, NO. 3, MARCH 1962
345
