A liquid ionisation chamber for neutron dosimetry

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Abstract
Theories of ionisation in liquid and the use of liquid ionisation chambers in mixed neutron field dosimetry have been studied. Theoretical models developed by G. Jaffe (J. Physique, vol.5, p.262, 1906; Ann. Phys., Lpz., vol.42, p.303, 1913) and by L. Onsager (Phys. Rev., vol.54, p.554, 1938) were used for comparison with the experimental measurements. The Jaffe method predicts a higher collecting efficiency than does the Onsager model. Gamma and neutron sensitivities of a liquid chamber can be calculated by the Bragg-Gray principle and Onsager's theory. The calculation is subject to relatively large uncertainties, mainly due to insufficient knowledge of the ion distribution in ionisation tracks and of W/e values for iso-octane. The chamber constructed for clinical use should work best for mixed neutron fields with gamma-neutron ratios of 10-20%; however, it would be difficult to use a liquid ionisation chamber to detect small neutron variations in mixed fields with large gamma components.