Practical low dose limits for passive personal dosemeters and the implications for uncertainties close to the limit of detection.

Recent years have seen the increasing use of passive dosemeters that have high sensitivities and, in laboratory conditions, detection limits of <10 µSv. However, in real operational use the detection limits will be markedly higher, because a large fraction of the accrued dose will be due to natural background, and this must be subtracted in order to obtain the desired occupational dose. No matter how well known the natural background is, the measurement uncertainty on doses of a few tens of microsieverts will be large. Individual monitoring services need to recognise this and manage the expectations of their clients by providing sufficient information.

Introduction of the InLight monitoring service.

A new external monitoring service has been developed combining the excellent features of optically stimulated luminescence (OSL) with the convenience of Panasonic readers. This article briefly reviews OSL, and describes the InLight personal dosimetry system and its introduction into the European market.

A scintillation spectrometer for direct comparison of neutron energy spectra at high and low rates.

The energy spectrum of the HB11 beam at HFR, Petten, has previously been measured by proton and alpha recoil in hydrogen and helium gas proportional counters at power levels of a few kW. There is some doubt whether the spectrum remains the same at the much higher power of 45 MW required for therapeutic fluxes. In order to test this point, a scintillation detector has been developed at the Paul Scherrer Institute, Villingen, Switzerland. While the device is again based on the proton recoil reaction, a combination of mm-sized plastic scintillators and fast electronics will allow it to operate at both a few kW and 45 MW, permitting direct comparison of energy spectra at these very different power levels. Results of preliminary tests at LFR, Petten, are presented.

A review of boron neutron capture therapy (BNCT) and the design and dosimetry of a high-intensity, 24 keV, neutron beam for BNCT research.

This paper reviews the development of boron neutron capture therapy (BNCT) and describes the design and dosimetry of an intermediate energy neutron beam, developed at the Harwell Laboratory, principally for BNCT research. Boron neutron capture therapy is a technique for the treatment of gliomas (a fatal form of brain tumour). The technique involves preferentially attaching 10B atoms to tumour cells and irradiating them with thermal neutrons. The thermal neutron capture products of 10B are short range and highly damaging, so they kill the tumour cells, but healthy tissue is relatively undamaged. Early trials required extensive neurosurgery to exposure the tumour to the thermal neutrons used and were unsuccessful. It is thought that intermediate-energy neutrons will overcome many of the problems encountered in the early trials, because they have greater penetration prior to thermalization, so that surgery will not be required. An intermediate-energy neutron beam has been developed at the Harwell Laboratory for research into BNCT. Neutrons from the core of a high-flux nuclear reactor are filtered with a combination of iron, aluminium and sulphur. Dosimetry measurements have been made to determine the neutron and gamma-ray characteristics of this beam, and to monitor them throughout the four cycles used for BNCT research. The beam is of high intensity (approximately 2 x 10(7) neutrons cm-2 s-1, equivalent to a neutron kerma rate in water of 205 mGy h-1) and nearly monoenergetic (93% of the neutrons have energies approximately 24 keV, corresponding to 79% of the neutron kerma rate).