  We investigate the type III radio bursts and X-ray signatures of accelerated
electrons in a well observed solar flare in order to find the spatial
properties of the acceleration region. Combining simultaneous RHESSI hard X-ray
flare data and radio data from Phoenix-2 and the Nan\c{c}ay radioheliograph,
the outward transport of flare accelerated electrons is analyzed. The
observations show that the starting frequencies of type III bursts are
anti-correlated with the HXR spectral index of solar flare accelerated
electrons. We demonstrate both analytically and numerically that the type III
burst starting location is dependent upon the accelerated electron spectral
index and the spatial acceleration region size, but weakly dependent on the
density of energetic electrons for relatively intense electron beams. Using
this relationship and the observed anti-correlation, we estimate the height and
vertical extent of the acceleration region, giving values of around 50 Mm and
10 Mm respectively. The inferred acceleration height and size suggests that
electrons are accelerated well above the soft X-ray loop-top, which could be
consistent with the electron acceleration between 40 Mm and 60 Mm above the
flaring loop.
