Page 279 - Radiochemistry and nuclear chemistry

Uses of Radioactive Tracers 263

AKUFVF UNIT LISOL UNIT
main liquid flow small withdrawal
signal
scintillation cocktail
pure phase
acid

_1
w
0 t liquid
CENTRIFUGE PMT waste
,.z, 9 1{3
.,.,,
~i
(n
IK
pure ~ aqueous phase I I COUNTING AND
~ signal DATA TREATMENT

FIG. 9.10. The AKUFVE-LISOL system used in investigating the system in Fig. 9.9.

also Nd 3+) may hydrolyse. Also, the very low D-values obtained (1 to 10 -5) are difficult
to measure exactly with conventional technique. Therefore advanced techniques were
developed, see Figure 9.10: (a), AKUFVE, which is a closed flow system, where the two
liquid phases are mixed continuously and separated in a special flow-through centrifuge,
and, after passing detection devices, returned to the mixing chamber. (b), LISOL, an
"on-line" liquid-scintillation detection technique, in which a tiny fraction of the circulating
phases is withdrawn, mixed (i) with acid to suppress sorption and hydrolysis, and (ii) with
a liquid scintillator, and (iii) pumped to the PMT-detector. The LISOL avoids detector
memory effects occurring in conventional on-line detectors and also allows measurements
of pure c~- and ~-emitters (of. w
As a second example we choose a chemically more complicated system, which, however,
in practice is simpler than the one above, and therefore of more common use. The
complexation of 23 I1 4+ by HSO 4 in 0.1 M NaCIO 4 was studied by SX using the system
Np
aqueous solution/CHCl 3 containing the organic extractant thenoyltrifluoroacetone (HTTA).
In this case the relation

DNp/DOp = [;/3xtHSO4-] x (9.23.b)

can be derived, where DNp is the distribution ratio of Np in the presence, and D~ in the
absence, of HSO4-; in this case pH and [HTTA] must be constant during the experiment,
any change requiring correction. From the data in Figure 9.11 the formation constants #x
for Np(IV) sulphate complexes were determined.
The solvent extraction technique has been used extensively for studying complexation of
metals for which it may not be possible or desirable to use macroscopic amounts, as e.g.
for the heavy actinides or transactinides (Ch. 16).