Neutron Detection and Imaging: Cold, Thermal, and Fast Neutrons
RMD has developed and delivered high resolution detectors for thermal neutron imaging. Primarily based on a custom scintillator coupled to a CCD or CMOS photodetector, these cameras can run in individual neutron counting mode and/or image integration mode. The detectors designed for direct in-beam use provide high spatial resolution and excellent Signal to Noise (SNR) performance. In the case of lens coupled systems, only the scintillator and a mirror is directly located within the beam, with the readout sensor placed out of the beam in an appropriate shield.
Our latest addition to our imaging detectors is the amorphous silicon flat panel detector that simultaneously provides large imaging area, high spatial resolution, and excellent dynamic range. Significant work is currently underway to make high resolution, fast neutron imagers for radiographic imaging. Some of the systems include:
A raw (uncorrected) image of a CD player and a 50 caliber BMG cartridge acquired in only a few minutes. Non-uniformity in the brightness across the imaging area is due to the beam profile. L/D: 20:1.
Custom Neutron Imagers
FPND: Amorphous Silicon Flat Panel based large area neutron detector (FPND) is the latest among the high resolution neutron imagers developed at RMD. The detector design is designed for easy scintillator change out. The detector offers 25 x 30 cm active imaging area and an intrinsic spatial resolution of 139 m. Designed specifically for radiography using laboratory sources, the detector demonstrates time efficient imaging performance even when the source strength is low, ~104 thermal neutrons/cm2/second. An image of a 50 caliber BMG cartridges and a CD drive obtained using the RMD Flat Panel Neutron Detector and a laboratory neutron source is shown above. Image acquisition time is only a few minutes. Radiographic data taken at ORNL is shown below. Notice the image quality obtained in as little as a 500 ms exposure.
• Unlike mirror/lens based designs, a FPND can be directly placed in the neutron beam. The radiation hard electronics, along with neutron and gamma shields makes it operable in high scatter environments.
• The camera can capture up to 30 frames per second and can be used for dynamic imaging using intense sources such as the reactor sources.
• Scintillator can be changed easily to optimize the performance for high resolution and/or high efficiency imaging.
• Dual mode X-ray/neutron imaging is possible.
Thermal neutron radiograph of flowers at ORNL beamline. Flowers were placed behind a 2½ inch thick lead brick, demonstrating penetrating ability of neutron in dens materials. The radiograph was acquired in 500 millisecond integration.
Lens Coupled CCD Camera
Developed for high resolution, high frame rate, low noise imaging and tomography, this detector uses a commercial EMCCD coupled to a LNI Scintillator (below). This detector offers 1K x1K pixel resolution, sub-electron noise/pixel/second, and a high thermal neutron detection efficiency in excess of 40%. The image field of view is adjustable from 2.5 x 2.5 cm2 to 10 x 10 cm2 with a corresponding intrinsic resolution of 25 m to 100 m respectively. The camera comes with a GOS, LiF/ZnS, or LNI scintillator. The detector can acquire up to 60 frames per second with full resolution and up to 600 frame per second in binned mode.
CCD based neutron imager. The scintillator screen, image resolution, and framerates are adjustable.
Developed by the Oak Ridge National Laboratory, the SiPM based Anger camera is an excellent example where a high resolution LNI scintillator can be used. The 500 m thick LNI screen, with 45% enriched 6Li and excellent microcolumnar structure provided high spatial resolution down to 350 m, a new record for resolution using Anger logic. The excellent PHD and PSD allows efficient n- discrimination. The Anger camera, the microcolumnar structure of the LNI, and the high resolution image data are shown below.
Key to the success of advanced neutron detectors is novel scintillator screens that can simultaneously provide high detection efficiency, large imaging area, and high SNR.