Source-detector Configuration Research Articles

Solid-state detection of energetic neutrons based on mercuric iodide crystals

The usefulness of mercuric iodide (HgI 2) crystals for measuring pulses of fast neutrons was investigated. The dominant mechanisms determining the sensitivity of HgI 2 to energetic (1–15 MeV) neutrons are inelastic neutron scattering from the iodine and mercury atoms within the HgI 2 crystal and the absorption of gamma rays associated with neutron-to-gamma conversion in the shielding material. The relative role of these two mechanisms depends on the thickness of the HgI 2 crystal and the amount and type of shielding material selected for the detector assembly. Both types of excitation events create a large number of free charge carriers per scattered neutron. Under the influence of an applied bias, this free charge is collected and appears as a current pulse which is proportional to the flux in the incident neutron pulse. Calculations of the energy deposited for our source-detector configuration are also reported.

The factors affecting in vivo x-ray fluorescence measurements of lead in bone

The factors affecting the sensitivity of X-ray fluorescence determination of lead in bone phantoms using 57Co are investigated with the object of applying the technique to in vivo measurements in tibia. An analysis of the components of the measured pulse height spectrum in a hyperpure Ge detector is presented and the implications for the optimisation of the source-detector configuration discussed. Finally, some preliminary investigations using a 109Cd source are outlined.

In-line D 2O analysis

A technique has been developed for in-line monitoring of D 2O concentration in process streams. Commercially available neutron counters are used to detect neutrons from deuterium in water irradiated with 2.62 MeV gamma rays [ 1 2D(γ,n) 1 1H]. Using this technique, deuterium concentrations from 0.015% to 0.13% D 2O in water were measured in laboratory tests with an accuracy of 1% in 30 min. A source-detector configuration was developed and the proposed system successfully tested in the laboratory. The technique was not applied in the existing heavy water plant because of a shortage of funds, and because justification for modification of existing towers was insufficient. Use of the technique for new plants, where towers could be designed initially to include such an instrument, should be much more economically advantageous.

Source Size as a Theoretical Limitation on the Determination of Wave Vectors by Detector Arrays

An important class of infrasonic waves in the atmosphere and seismic waves in the earth's crust are generated by ocean waves in marine storms. The determination of wave vectors from such large sources by detector arrays is limited by the systematic errors introduced by the large sources, as well as by the resolving power and ambiguities associated with any given array configuration. The apparent phase lag and coherency between two detectors, each receiving signals from the multitude of mutually incoherent oscillators comprising a large source, is discussed as a function of source size and source-detector configuration. It is found that the apparent phase lags between two detectors may deviate from the phase lag of a ray from the source center. As a result, the apparent phase lags among the detectors in an array may lead to an apparent wave vector discrepant with the wave vector from the source center. Empirical results are presented to confirm the validity of this approach in the case of microbarom generation by ocean waves.

Magnetic Steering Device for Electron Coincidence Experiments

The highly convergent fringing field produced by a 100 kVA C-magnet has been used to guide electrons emitted at a source around a 90° arc to a Si(Li) detector. This source-detector configuration is often desirable because it enables the electron detector to be effectively shielded from other radiations emitted at the source. The electron motion in this device consists of a superposition of a trochoidal motion and a vertical oscillation through the magnet symmetry plane. The high detection efficiency of the system (∼5%) makes it particularly well suited for applications in electron coincidence experiments. Utilization of the device in a study of internal conversion in coincidence with fission is described, and several other applications are suggested.