Page 296 - Radiochemistry and nuclear chemistry

280 Radiochemistry atut Nuclear Chemistry

of the cyclone, since the HTO concentration in the normal atmosphere is different from that
of surface ocean water due to isotopic effects.
Radioactive tracers like T20, 24Na+, 82Br- (/~-y tt h 1.471 d) and 51Cr-EDTA (EC-y tv2
27.704 d), are used in hydrology to determine the volume of natural water reserves (even
underground) and to map the movement of ground and surface water as well as effluent
pathways, Figure 9.17. Also the consumption of water and water flow in industries are
readily determined, and leaking dams and pipes checked by radiotracers.
In order to avoid hazardous pollution it is important to discharge communal and industrial
waste (silts, liquids, gases) so that the wastes are properly dispersed. The mapping of
different dispersal sites is conveniently and commonly carried out by injecting a radioactive
tracer at a testing spot, and then following its distribution at various depths, heights, and
directions. In such a test it was found that sludge emptied into the River Thames at one
point traveled upstream, which led to a repositioning of the sludge pipe exit. The simple
technique of identifying hidden pipe leaks is illustrated in Figure 9.17 left. This technique
is used not only for liquids, but also for checking the seal of underground electric cable
hoses in which case gas tracers like 85Kr (/T'y t~ 10.72 y) or 133Xe (B-3~ ttA 5.24 d) are
used.
Westermark and co-workers have developed a unique method of revealing environmental
history of natural rivers during the last 100 - 200 years. It is based on the freshwater pearl
mussel Margaritana margaritifera living in these fiver. The mussel adds a new outer layer
to its shell each year, incorporating into it trace metals (and also to some extent organics)
dissolved in the water. The shell is cut and sectioned into small pieces, which are analyzed
by cz-track autoradiography, INAA and/~-PIXE. The latter is a "microprobe"-PIXE, i.e.
the proton beam is focused by lenses to a resolution of a few microns. To get sufficient
information the shell sample usually covers 3 - 15 years. With these techniques
concentrations of some 30 elements have been determined retrospectively for > 100 years
in a number of Swedish rivers. Several unexplained trends have been observed, e.g.
decreases in Ag, Au, Fe and Co. This is believed to be related to increasing air
concentrations of SO 2. The observation of an increase in Br beginning in the 1940's is
believed to be due to Br-additions to gasoline fuel. The technique has great potentials for
increasing our knowledge on environmental changes of trace elements in nature. It could
also be used as a long term biochemical control system at environmentally strategic places.

9.8. Exercises

9.1. The blood volume of a patient is to be determined by means of 32p. For this purpose 15.0 ml of blood is
withdrawn from the patient and mixed with a very small volume of Na2H32po4 of high specific activity. In 1 h
the erythrocytes (red blood cells) take up all the 32p; 1 ml is found to have an activity of 216 000 cpm in the
detector system used. Exactly 5.00 ml of this tagged sample is reinjected into the patient, and 30 min later a new
sample is withdrawn; 10 ml of this gives 2300 cpm. Calculate the blood volume.
9.2. A mixture of amino acids is to be assayed for cysteine. A 1.0 ml sample (density 1 g ml "z) is withdrawn,
and 2.61 nag of 35S labeled cysteine of specific activity 0.862/~Ci nag "l is added. From this mixture pure cysteine
is isolated by liquid-partition chromatography; 30.6 nag is isolated and measured to give 169 000 cpm in 27 %
detection efficiency. What is the percentage of cysteine in the original mixture?
9.3. In order to determine the lead content of a color pigment, 8.9871 g was dissolved in cone. HNO 3, and 5.00
ml 21~ solution added. After excess acid had been removed through evaporation, excess 1 M NaCI was added,
the solution heated and filtered. ARer cooling and crystallization, the PbCI 2 was washed and recrystallized, 0.3276