Detector

In 2002, Soreq NRC embarked on an internally-funded development of high spatial resolution (sub-mm) fast-neutron detector, based on scintillating fibers. In parallel, PTB developed the principles of the Time-Resolved Integrative Optical Neutron detector (TRION). In 2004, Soreq and PTB started a collaborative project on development of an improved version of TRION (1st generation). Fig. 1 shows an engineering drawing of this detector.

Fig. 1 drawing of the TRION-detector

In this design neutrons from a nanosecond pulsed, broad energy neutron beam arrive at the detector after their energy dependent Time-of-Flight (TOF). The neutrons interact in a scintillating fiber array screen and produce a light image. Optics (mirror and lens) transfer this image to a gated image intensifier, which acts as an electronic shutter. This gate is opened for a well defined period at a pre-selected neutron TOF, thus allowing only neutrons in a well selected energy range (out of the broad neutron spectrum) to contribute to the image formation. A CCD camera views the image created at the phosphor of the gated intensifier. A typical pulsed fast-neutron burst duration is 1.5-2 ns and the burst repetition rate is of the order of 2 MHz. Within the time window of ~500 ns, depending on the neutron-source/detector and the width of the relevant energy bin, the detector integrates neutrons into an image in a well-defined TOF-bin relative to the beam pulse. By varying the gate delay time TOF, transmission images at any selected neutron energy can be taken.

In this project we shall develop a detector capable of capturing simultaneously several (up to 8) images at different pre-selected energies. This is achieved by a speciall camera system as shown schematically in Fig. 2. The optical image behind the scintillating fibre plate, which reflects the energy- and spatial distribution of the neutron field is amplified by a special image intensifier which preserves the fast timing capability of the converter screen. The image is then split by a patented image splitter into 9 identical, geometrically separated images. These focused onto a single 8-fold segmented image intensifier, shown in Fig. 3. 8 of the 9 segments are independently gated, enabling up to 8 distinct, pre-selectable TOF-bins to be defined within each beam burst. This segmented intensifier can be read, in turn, by a single, high resolution CCD camera. In this fashion, the camera can take up to 8 different images at pre-selected neutron energies. Good statistics and high quality images are accumulated over many beam bursts. The development of this camera and its evaluation are the key tasks in this project.

Fig. 2 TRION-detector with the segmented image intensifier Fig. 3 the 8-fold segmented image intensifier

The successful development of such a camera would provide a very compact neutron imaging system capable of capturing multiple neutron images at different energies simultaneously.