  We use the ISOPHOT 60 micron image of Tuffs et al. (1996) to study the 60
micron light distribution and its correlation with radio continuum within the
disk of spiral galaxy NGC6946, and to resolve the long-standing IRAS
controversy as to whether the infrared-to-radio continuum ratio, Q, decreases
radially out in galaxy disks. Our main results are: (1) The disk at 60 microns
also appears to follow an exponential fall-off. Its e-folding scale-length lies
between 1'.3 and an upper limit of 1'.9, obtained from the mean radial profile
between 1'.5 and 4' in radius. This scale length is smaller than that derived
from the radio continuum data at either 20cm or 6cm, with or without the
thermal component removed, at a significance level of >~ 2 sigma. From 1'.5 to
4' in radius, the 60 micron -to-radio continuum surface brightness ratio, Q,
decreases by a factor of 1.5 to 1.7 on average. These quantitative results
agree with that of Marsh & Helou (1995) using IRAS HiRes data, but not with
that of Fitt et al. (1992) based on IRAS CPC data. Our results also fit into
the picture of the radio disk as a ``smeared'' version of the infrared disk,
but are not consistent with the picture in which the variation of Q is a result
of the thermal and non-thermal radio components having two distinct, constant
values of the infrared-to-radio ratio.
