A compact high-energy neutron spectrometer.

A compact liquid organic neutron spectrometer based on a single NE213 liquid scintillator (5 cm diameter x 5 cm) is described. The spectrometer is designed to measure neutron fluence spectra over the energy range 2-200 MeV and is suitable for use in neutron fields having any type of time structure. Neutron fluence spectra are obtained from measurements of two-parameter distributions (counts versus pulse-height and pulse shape) using the Bayesian unfolding code MAXED. Calibration and test measurements made using a pulsed neutron beam with a continuous energy spectrum are described and the application of the spectrometer to radiation dose measurements is discussed.

Determination of neutron energy spectra inside a water phantom irradiated by 64 MeV neutrons.

A NE230 deuterated liquid scintillator detector (25 mm diameter x 25 mm) has been used to investigate neutron energy spectra as a function of position in a water phantom under irradiation by a quasi-monoenergetic 64 MeV neutron beam. Neutron energy spectra are obtained from measurements of pulse height spectra by the NE230 detector using the Bayesian unfolding code MAXED. The experimentally measured energy spectra are compared with spectra calculated by Monte Carlo simulation using the code MCNPX.

The HYDAD-D antipersonnel landmine detector.

HYDAD (HYdrogen Density Anomaly Detection) systems have been developed to detect small (>200 g) antipersonnel landmines (APM) of plastic construction. The HYDAD-D detector is based on the earlier HYDAD designs HYDAD-H and HYDAD-VM. It consists of a neutron source and two identical slow neutron detectors. The difference between the responses of the two detectors is monitored as a function of position in the minefield and APM detection is based on an analysis of this difference. Laboratory tests and Monte Carlo simulations demonstrate that HYDAD-D is capable of detecting the IAEA standard dummy landmine DLM2 at burial depths up to 23 cm in dry sand and at burial depths up to 7 cm in damp sand containing 12% (by mass) water.

Increasing the capability of MNBRP for the detection of anti-personnel landmines.

Monte Carlo simulations were used to show that even very small explosives (<100g) can be detected by monoenergetic neutron backscattering with resonance penetration (MNBRP) at a depth well beyond 30 cm when time slicing is used for background suppression. At the present state of technology no other nuclear method appears to have a comparable sensitivity or penetration capability. This method has been successfully tested experimentally at a depth of 16.5 cm. A substantial simplification of the detection procedure could be achieved either by taking advantage of the time shadow rather than the geometric shadow or by applying neutron threshold detectors. Using a threshold detector could simplify the application, too.

Neutron fluence and kerma spectra of a p(66)/Be(40) clinical source.

High-resolution neutron fluence spectra have been measured in the National Accelerator Centre's p(66)/Be(40) neutron therapy beam by the pulsed-beam time-of-flight method. ICRU muscle kerma spectra have been derived from the fluence spectra. Spectral changes resulting from different irradiation conditions have been quantified in terms of the average neutron energy and the fractional low-energy (< 16 MeV) contribution. The changes observed with different thicknesses of polyethylene filtration are consistent with changes in quality parameters determined in biological and microdosimetric experiments. The dosimetry parameters (KtissueA150) N and (Wgas) N calculated for the measured spectra agree with the values recommended in the neutron dosimetry protocol. The shapes of the present fluence spectra differ from previous measurements of p(> 40)/Be spectra. In particular, they differ significantly from the spectrum measured by recoil techniques in an identical neutron therapy unit at the Clatterbridge Hospital, UK. The reasons for the difference are not known.

Detection of anti-personnel landmines by neutron scattering and attenuation.

Four methods for employing neutrons to detect abandoned small anti-personnel landmines are presented and discussed. The techniques used are based on measurements of effects due to the scattering of neutrons on the hydrogen content of the landmine.

Measurement of neutron fluence spectra up to 150 MeV using a stacked scintillator neutron spectrometer.

A stacked scintillator neutron spectrometer (S3N) consisting of three slabs of liquid organic scintillator is described. A pulsed beam providing a broad spectrum of neutron energies is used to determine the detection efficiency of the spectrometer as a function of incident neutron energy and to measure the pulse height response matrix of the system. Neutron spectra can then be determined for beams with any kind of time structure by unfolding pulse height spectra measured by the S3N. Examples of fluence spectrum measurements in the energy range 20-150 MeV are presented.

Quasi-monoenergetic neutron reference fields in the energy range from thermal to 200 MeV.

Well-characterised neutron fields are a prerequisite for the investigation of neutron detectors. Partly in collaboration with external partners, the PTB neutron metrology group makes available for other users neutron reference fields covering the full energy range from thermal to 200 MeV. The specification of the neutron fluence in these beams is traceable to primary standard cross sections.

Detection of explosive remnants of war by neutron thermalisation.

The HYDAD-D landmine detector (Brooks and Drosg, 2005) has been modified and field-tested for 17 months in a variety of soil conditions. Test objects containing about the same mass of hydrogen (20g) as small explosive remnants of war, such as antipersonnel landmines, were detected with efficiency 100% when buried at cover depths up to 10cm. The false alarm rate under the same conditions was 9%. Plots of detection efficiency versus false alarm rate are presented.