  The ratio of pairing-energy coefficient to temperature ($a_{p}/T$) of
neutron-rich fragments produced in spallation reactions has been investigated
by adopting an isobaric yield ratio method deduced in the framework of a
modified Fisher model. A series of spallation reactions, 0.5$A$ and 1$A$ GeV
$^{208}$Pb + $p$, 1$A$ GeV $^{238}$U + $p$, 0.5$A$ GeV $^{136}$Xe + $d$,
0.2$A$, 0.5$A$ and 1$A$ GeV $^{136}$Xe + $p$, and $^{56}$Fe + $p$ with incident
energy ranging from 0.3$A$ to 1.5$A$ GeV, has been analysed. An obvious
odd-even staggering is shown in the fragments with small neutron excess
($I\equiv N - Z$), and in the relatively small-$A$ fragments which have large
$I$. The values of $a_{p}/T$ for the fragments, with $I$ from 0 to 36, have
been found to be in a range from -4 to 4, and most values of $a_{p}/T$ fall in
the range from -1 to 1. It is suggested that a small pairing-energy coefficient
should be considered in predicting the cross sections of fragments in
spallation reactions. It is also concluded that the method proposed in this
article is not good for fragments with $A/A_{s} >$ 85\% (where $A_{s}$ is the
mass number of the spallation system).
