IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
IV.A.3. Matrix Effect on Laser Desorption/Ionization of
Uranyl Nitrate Solution in Laser Mass Spectromtry
Development of simple and
direct methods for
measurement of burn-up of fast
reactor fuels is an important
area. The direct determination
of burn-up based on the
method based on measurement
of intensity ratio (i.e. ratio of
ion intensity corresponding to a
burn-up monitor element to
that corresponding to U)
requires the determination of U
in uranyl nitrate solution. If only
one of the ionic species UO2 + ,
UO + , U + were to be present in
the laser-vaporized plume, the
burn-up measurement could be
subject to error, since the single
species signal may get
saturated. (For 10 at % fission,
the number of atoms of heavy
elements present in a spent fuel
would be a few hundred times
more than that of 143Nd atoms
produced). However, if the U
bearing species U + , UO + and
UO2 + are all present, then the
saturation problem may not
exist. Furthermore, if the ion
intensity of one of the above
species were to become
comparable to that of 143 Nd
bearing species, then
determination of the ratio of
Nd/U will be easier and more
reliable. With these aspects in
mind, a study of the effect of
different matrices such as Tributyl
dissolved in 1 ml of the medium
phosphate (TBP), was loaded on the Al sample
Nicotinic acid and Polyethylene holder (see Fig.1), dried under
oxide (PEO) of molecular IR lamp and transferred to the
weight 2000, on the laser
desorption and ionization of
uranyl nitrate solution was
taken up. The experiments were
carried out using a laser mass
spectrometry system comprising
sample chamber. The samples
contained typically about 10 19
atoms of U. Under low intensity
laser beam, the spread in
kinetic energy of the ions
produced will be low, and thus
of an in-house developed resolution in the mass spectrum
reflectron time-of-flight mass
+
will also be better. Only UO 2
spectrometer. A schematic of and UO + were observed on
the experimental facility is
shown in Fig.1. Methanol was
laser desorption/ionization of
uranyl nitrate solution without
used as the medium for PEO any matrix (Fig. 2a). On
and TBP matrices and water addition of a matrix, keeping
was used for nicotinic acid all other experimental
matrix. The matrix to sample
ratio was maintained about
100:1. About 10µL of the
conditions same, the signal
intensity increased in all the
three cases. With nicotinic acid
sample and the matrix mixture as the matrix, UO + was the
Fig.1 Laser TOF-MASS Spectrometry - Schematic
FUEL CYCLE 85