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Heat loss mechanisms in a measurement of specific heat capacity of graphite.

Shipley, D R; Duane, S (1996) Heat loss mechanisms in a measurement of specific heat capacity of graphite. NPL Report. CIRA(EXT)003

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Abstract

Absorbed dose to graphite in electron beams with nominal energies in the range 3-20 MeV is determined by measuring the temperature rise in the core of a primary standard graphite calorimeter. This temperature rise is related to absorbed dose by a separate measurement of the specific heat capacity of the graphite core. There is, however, a small but significant amount of heat lost from the sample in the determination of specific heat capacity and correlations for these losses are required. This report discusses the sources of heat loss in the measurements and, where possible, provides estimates for the magnitude of these losses. For those mechanisms which are significant, a more realistic model of the measurement system is anlalysed and corrections for the losses are provided.
Radiation from the sample to the surrounding environment was found to be the major source of heat loss in the measurement of specific heat capacity. The rate of heat loss by this process was at least one hundred times greater than the rate by any other process. A more realistic model of the measurement system (in which radiation was the only form of heat loss) indicated that, with a linear fit applied to the post-heating sample data, the extrapolated temperature rise requires a correction of 1.0003:± 0.0001 (95% C.L.) to obtain the expected temperature rise of the sample. A correction of 0.9999:±: 0.0001 (95% C.L.) is required when a quadratic fit is used. The model and actual measurement system were found to agree to within a factor of two.

Item Type: Report/Guide (NPL Report)
NPL Report No.: CIRA(EXT)003
Subjects: Ionising Radiation
Ionising Radiation > Dosimetry
Last Modified: 02 Feb 2018 13:19
URI: http://eprintspublications.npl.co.uk/id/eprint/418

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