Radiation absorbed dose microcalorimetry is a direct technique for energy deposition measurements in low power benchmark mixed neutron and gamma-ray radiation fields. MkII adiabatic microcalorimeters, developed at Imperial College, are described. The results of recent electrical calibration and ⁶⁰Co gamma-ray field measurements are presented for graphite and iron microcalorimeters.

In order to assess sources of error, a finite-difference conduction-heat-transfer computer code has been employed to model the microcalorimeter performance. Model predictions are in good agreement with experimental results.

As a result of the error assessment, a redesigned MkV graphite microcalorimeter has been constructed, and results for electrical calibration and ⁶⁰Co gamma-ray measurements are presented. Systematic errors are reduced by a factor of about 10 for electrical calibration. for the ⁶⁰Co measurements, the discrepancy between the graphite MkV microcalorimeter and calibrated ionization chambers is less than 2%.