  The presence of dusty debris around main sequence stars denotes the existence
of planetary systems. Such debris disks are often identified by the presence of
excess continuum emission at infrared and (sub-)millimetre wavelengths, with
measurements at longer wavelengths tracing larger and cooler dust grains. The
exponent of the slope of the disk emission at sub-millimetre wavelengths, `q',
defines the size distribution of dust grains in the disk. This size
distribution is a function of the rigid strength of the dust producing parent
planetesimals. As part of the survey `PLAnetesimals around TYpical Pre-main
seqUence Stars' (PLATYPUS) we observed six debris disks at 9-mm using the
Australian Telescope Compact Array. We obtain marginal (~3-\sigma) detections
of three targets: HD 105, HD 61005, and HD 131835. Upper limits for the three
remaining disks, HD20807, HD109573, and HD109085, provide further constraint of
the (sub-)millimetre slope of their spectral energy distributions. The values
of q (or their limits) derived from our observations are all smaller than the
oft-assumed steady state collisional cascade model (q = 3.5), but lie well
within the theoretically expected range for debris disks q ~ 3 to 4. The
measured q values for our targets are all < 3.3, consistent with both
collisional modelling results and theoretical predictions for parent
planetesimal bodies being `rubble piles' held together loosely by their
self-gravity.
