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Introduction to Photon Detectors ORTEC offers a complete line of semiconductor photon
detectors for the nuclear spectroscopist working in the energy range from <1 keV to
above 10 MeV (see Photon Detector Selection Guide). To lower the
leakage current and enhance the "noise," ORTEC photon detectors are designed to
operate at near-liquid-nitrogen temperature. A photon detector (Fig.
10) consists of:
(a) A detector element mounted, in most systems, inside the
vacuum enclosure of its PopTop capsule. The detector element is either a Si(Li) or a
Germanium (HPGe)
device (planar or coaxial).(b) A charge-sensitive preamplifier and a HV filter, with
accompanying cable pack. The first stage of the preamplifier is also mounted inside the
vacuum enclosure to ensure proper cooling for optimum noise and reliability. The second
stage of the preamplifier and the HV filter are part of the PopTop assembly but reside
outside the vacuum enclosure to which they are connected by vacuum feedthroughs.
(c) A dipstick cryostat and a 30-liter LN2 dewar,
or a combination cryostat-dewar assembly, or a cryostat that is
electrically cooled.Some Key Dimensional Data for PopTop Capsules
- Thickness of endcap walls: 1.3-mm Al for 70-mm endcap diameters; 1-mm Al for 82.5-, 95-
and 108-mm diameters
- Thickness of front window by endcap diameter: Al: 1.3-mm for 70-mm, 1-mm for 82.5- and
95-mm; 1.5-mm for 108-mm Carbon Fiber: 0.76-mm nominal Be: 0.5-mm for 70- and
82.5-mm; 0.76-mm for 95-mm
- Thickness of detector element mount cup walls: 0.5-mm Al
- Thickness of the small section of the mounting cup where the screws that hold the
detector in the cup are located (not shown in the drawing): 1.5-mm Al
- Thickness of mounting cup front window (GAMMA-X, GLP, SLP, or LO-AX): 0.13-mm aluminized
Mylar
- Distance between the front window of the endcap and the front contact of the detector:
3- to 4-mm nominal for coaxial and LO-AX detectors, 7-mm nominal for planar detectors
- Largest possible diameter detector that can be accommodated in the 70-mm outer-diameter
(OD) endcap: 59 mm
- Largest possible diameter detector that can be accommodated in the 82.5-mm OD endcap: 70
mm
- Largest possible diameter detector that can be accommodated in the 95-mm OD endcap: 82
mm
- Largest possible diameter detector that can be accommodated in the 108-mm OD endcap: 94
mm
As shown in Fig. 11, the
flexibility of the PopTop concept allows you to switch a "capsule" from one
cooling assembly to another without pumps, heater tapes, or other equipment.
The PopTop Advantage
With the exception of certain special detectors, ORTEC’s
photon detectors are mounted in a PopTop capsule, offering unique flexibility and
reliability. In particular, the LN2-free X-COOLER
II
may be used and the PopTop
easily exchanged for service. |
