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 SPD-1
Submergible Photon Detector
- Compact size (~37-in. long and 12-in. diameter)
- Weight ~100 lbs
- Totally waterproof, submergible
- LN2 refillable without opening the shroud cover
- Split-ring lead shield for shielding and negative buoyancy
- HPGe coaxial detector
- Preamp, H.V. filter, LN2 level probe, and H.V. cutoff protection included
- 30-foot operating depth
- Stainless steel shroud for easy cleaning and decontamination
- Thin (30 mil) side window in shroud to enable low energy photon (³50
keV) spectroscopy
The ORTEC Submergible Photon Detector (SPD-1) is designed for nuclear
fuel element scanning in storage pools. The SPD-1 is useful in other simular applications
that require a totally waterproof, submergible photon detector for shallow depth pools. In
the fuel element scanning application, high-resolution spectroscopy is desired, dictating
the use of a High-Purity Germanium (HPGe) Photon Detector. As with all germanium
detectors, liquid nitrogen (LN2) cooling is required for operation. A special compact LN2
dewar (thermos vessel) supplies 20 liters of LN2 during operation. The dewar can be
refilled at the surface of the pool without removing the waterproof shroud cover.
Operating time of the SPD-1, before LN2 refilling is required, is approximately 12 to 14
days. An LN2 low level alarm and high-voltage (H.V.) cutoff circuitry monitor and protect
the system.
 The compact (approximately 37-in long x 12-in. diameter) stainless steel
shroud contains the HPGe detector element, cryogenic package, 20-liter LN2 dewar, LN2
level probe, preamplifier, H.V. filter, and lead shield. The split-ring lead shield is
provided behind the detector element to shield from contaminated water in the pool and
also to provide negative buoyancy to the system. The stainless steel package has three
lifting eyes and can be easily cleaned or decontaminated. The particular system shown was
designed for pool depths up to 30 feet. Polyvinyl chloride tubing is used to carry the
electrical cables to and from the detector package and to vent the LN2 to the pool
surface. A thin (30 mil) side window is provided in the stainless steel shroud to enable
low energy photons (down to 50 keV) to enter the detector package.
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