Page 297 - Radiochemistry and nuclear chemistry

Uses of Radioactive Tracers 281

g of the crystals was measured in a scintillation counter, giving 185 160 counts in 5 min. 1.000 ml of the original
2t~ solution gave 57 000 cpm. The background was 362 cpm. Calculate the lead content (%) of the pigment.
9.4. What is the smallest amount of indium which can be determined in a 100 mg aluminum sample using NAA
with a neutron flux of 10 t6 n m "2 s'l? Consider the neutron capture in both 27A1 and ll5In: 27Al(n,3 , o 0.230 b)2SAl
t,/i 2.25 min; ttsIn(n, T o 45 b)tt61n t,/i 14 s. The lowest detectable activity for lt6In is assumed to be 10 Bq, and
the interference from 2SAI not more than 20%.
9.5. In order to determine the amount of gallium in meteorite iron, 373.5 nag meteorite iron (A) and 10.32 nag
gallium oxinate (B) were irradiated in a reactor under similar conditions in 30 min. After a short cooling, A was
dissolved in concentrated HCI and 4.53 mg inactive Ga 3+ was added. After a number of chemical separation steps,
which were not quantitative, a precipitate of 25.13 nag pure gallium oxinate was isolated (C). Sample B was also
dissolved and diluted to 50 ml; 0.50 ml was removed, 4 mg inactive Ga 3+ added, and gallium oxinate precipitated
(D). The radioactive decay curves gave two straight lines: log R c = 3.401 - 0.0213 t, and log R D = 3.445 -
0.0213 t. What was the gallium content in sample A?
9.6. A 10.0 g sample of iodobenzene is shaken with 100 ml of 1 M KI solution containing 2500 cpm 131I. The
activity of the iodobenzene at the end of 2 h is 250 cpm. What percent of the iodine atoms in the iodobenzene have
exchanged with the iodide solution?
9.7. A sodium iodide solution contains some radioactive t3tl. An ethanol solution was prepared containing 0.135
M of this sodium iodide and 0.910 M inactive C2H51. In the exchange reaction

kf
C2H51 + t29 I- r 6 C2H5t29I + I"
kr

the reaction rate constant is assumed to be the same in both directions: kf = kr. One part (A) of the solution was
removed and heated to high temperature so that equilibrium was rapidly reached. Another part (B) was kept in a
thermostated bath at 30~ After 50 min ethyl iodide was separated from both solutions. The concentration of
radioactive iodine in C2H51 in B was found to be only 64.7% of that in A. Calculate k (k r = k a b in w
9.8. With Figure 9.9 one can estimate the stability constants (Bl - B3) for the lutetium acetylacetonate complexes.
Make this estimation using Figure 9.9. A simplified approach to estimate B,~ is the use of the approximate relations
kn = Bn/Bn-t = l/[AaI~fn-o.5 and rl = z - d(logD)/d(log[Aa]); for Lu 3+ n < 4, but z = 3.
9.9. Calculate B4 and the distribution constant using (9.23a) and Figure 9.9.
9.10. One wants to determine the residual liquid volume of a closed sedimentation tank (nominal volume 80 m3),
which has been in use for many years, and in which CaSO 4 precipitates. 0.50 ml 24Na2SO4 (specific activity
3.2 • l0 s cpm ml "l) is added to the tank, and 10 ml withdrawn after 2 h of settling; measurements yield a net value
(background subtracted) of 500 counts in 10 rain. Calculate the free liquid volume in the tank.
9.11. Calculate the critical deposition potential (E- E ~ for 10 .22 M 2t~ on a gold cathode (no over-voltage)
from the Nernst equation (9.4), where the chemical activity of the reduced state (Bi ~ is set to unity.
9.12. A mineral ore contains cobalt and small amounts of nickel. In order to determine the nickel concentration
it must be separated from cobalt. Solvent extraction using 0.01 M 8-hydroxyquinoline in CHCI 3 is chosen. Which
metal should be extracted from the other, and at what pH? Consider Figure 9.3 and connected text.
9.13. In a solvent extraction system consisting of uranium and lanthanum in 1 M HNO 3 and 100% TBP, D U =
20 and DLa = 0.07. If a phase ratio 0 = Vorg/Vaq = 0.5 is chosen, how much uranium is removed from the
aqueous phase in three repeated extractions? How much of the lanthanum is co-extracted? The fraction extracted
with n fresh organic volumes (Vorg) from one aqueous volume (Vaq) is:
E n = 1 - (1 + D e) -n (9.26)

9.9. Literature

A. C. WAHL and N. A. BONNER (Eds.), Radioactivity Applied to Chemistry, Wiley, 1951 (still useful).
T. BRAUN and J. T6LGYESSY, Radiometric 7itrations, Pergamon Press, Oxford, 1967.
J. RUZlOCA and I. STARY, Substoichiometry in Radiochemical Analysis, Pergamon Press, Oxford, 1968.
J. F. DUNCAN and G. B. COOK, Isotopes in Chemistry, Clarendon Press, 1968.
A. K. DE, S. M. KHOPKAR and R. A. CHALMERS, Solvent Extraction of Metals, van Nostrand Reinhold, 1970.