Gamma-X (GMX) N-type high-purity germanium (HPGe) coaxial radiation detector

The GAMMA-X Series detectors are designed using ORTEC-grown germanium crystals that are processed at our manufacturing facility in Oak Ridge, Tennessee. The detector is made of N-type germanium, with an inner contact of diffused Li and an outer ultra-thin contact of ion-implanted boron.

The GAMMA-X detector exhibits exceptional efficiency at both high and low energies. ORTEC offers the GMX series of HPGe detectors with relative efficiencies ranging from 10% to 100% and beyond.

ORTEC has a range of HPGe detectors. Some of these have "super specs", i.e. guaranteed energy resolution that is better than the usual guaranteed specs.

High and low energy performance of the GAMMA-X detector
The high-energy performance of the GAMMA-X detector is defined by its relative efficiency, resolution and its peak-to-scan ratio at 60Co.

The detector's low-energy performance is defined by its resolution at 5.9keV, its effective surface area and detector window thickness.

The incident contact thickness of the GAMMA-X detector is described by the area ratio of the two peaks of the readily available source. The selected peaks come from 88-keV gamma rays from 109Cd and 22.16-keV Ag K x-rays from the same source. The window attenuation rate is guaranteed to be 20.

22 keV peak/88 keV peak area
This specification quantifies the thinness of the entrance window in the GAMMA-X detector. The natural ratio of gamma rays from the 22keV and 88keV spectral lines of a 109Cd source is approximately 21:1. GAMMA-X detectors typically display >20:1 ratios.

beryllium window
GMX detectors with 70 mm (2.75 in) or 76 mm (3 in) diameter end caps (10 to ~35%) are equipped with 51 mm (2 in) diameter Be windows. GMX detectors with 83 mm (3.25 in) diameter end caps (approximately 30 to 65%) are equipped with 64 mm (2.5 in) diameter Be windows. These windows are 0.020 inches thick and have ~95% transmission coefficient at 5.9-keV. Detectors with 95 mm (3.75 in) diameter end caps (approximately 60 to 100%) are equipped with an 84 mm (3.3 in) diameter Be window that is 0.030 in thick.

High voltage inhibit and high rate indication
GAMMA-X detector has high voltage prohibition and high rate indication protection functions. If LN2 is depleted and the detector begins to warm up while the high voltage bias is applied (when using a Type 659 bias supply), the high voltage is automatically turned off to protect the FET from damage. This is achieved via a temperature sensor (located on the base behind the detector) which is used to shut down the high voltage before the molecular sieve outgasses and creates a dangerous high voltage arc. Using the high leakage current of a reheat detector to turn off the high voltage can cause damage to the FET and detector.

Resistant to neutron damage
In the GAMMA-X detector, collecting electrons is the main process. Fast neutrons will create hole-trapping centers; that is, negatively charged defects that trap holes instead of electrons.

Therefore, compared with coaxial Ge devices in which hole trapping is the main process, the GAMMA-X detector in which hole trapping is a secondary process is essentially insensitive to radiation damage. These theoretical speculations have been confirmed experimentally.

It should be noted that once severe radiation damage occurs, "maximum mileage" can be obtained by avoiding cycling the detector to room temperature. The same is true for p-type or n-type Ge detectors. However, for slightly damaged GAMMA-X detectors (~0.1 keV attenuation), rewarming cycles or even long-term storage at room temperature will not have adverse effects.

The GAMMA-X detector should be kept as close to 77 K as possible to minimize the extent of radiation damage. Therefore, the Streamline cryostat has one less thermal connection and is a better choice than the PopTop for this purpose.

Customer Neutron Damage Repairable Detector
Repair of neutron damaged GAMMA-X detectors can be performed at any of our repair facilities or by yourself in the laboratory. For more information about our customers' neutron damage repairable GAMMA-X detectors, please contact us.

Integrated cryogenic cooling system option（-ICS-E）
Integrated cryogenic cooling system (ICS) cryostats are equipped with cryogenic coolers and are not affected by regeneration cycles. Unlike the typical three days of loss with standard cryostat detectors, the ICS can be re-cooled immediately, minimizing any time lost to temporary rewarming.

SMART-1 option (-SMN)
The SMART-1 option is used to monitor and report on important system functions, as well as save verification codes and report them later. It includes high voltage, so all instruments require no external high voltage power supply. The SMART-1 is constructed of a rugged ABS molded plastic housing and is securely attached to the detector end cap via molded sealed cables. This prevents the detector from being seriously damaged by moisture leaking into the high voltage connector. The SMART-1 can be placed anywhere convenient for use without interfering with shields or other mounting hardware.

Ultra-high count rate preamplifier option（-PL）
The ultra-high count rate preamplifier (transistor reset preamplifier) can handle input count rates up to 1,000,000 counts/second at 1 MeV and has the added advantage of no feedback resistors.

Harsh environment options（-HE）
The harsh environment option is a rugged carbon fiber end cap with a sealed electronics housing and a replaceable desiccant pack to ensure the electronics remain 100% dry and indicate when the desiccant pack needs to be replaced. GMX Series detectors in 76 mm diameter or larger PopTop package designs are available with this option.

Remote preamp option（-HJ）
This option places all preamplifier and high voltage connections outside the shield and moves the preamplifier and high voltage filter out of the "line of sight" of the Ge crystal. For low background applications, this option eliminates any possibility of increased background inside the shield, originating from preamplifiers or high voltage filter components.

Low background carbon fiber end cap option(-RB, -LB-C and -XLB-C)
Low-background carbon fiber end caps are as strong as Al, Mg and Cu, produce low background, do not corrode, and can detect energies below 10 keV. This lower background material reduces the minimum detectable activity (MDA) during a specific counting time, which provides another way to increase sample throughput in low background counting applications. Carbon fiber's low Z-value provides a low-energy window without the additional background found in most alloys.

Aluminum window options（-A）
If the energies of interest exceed 20 keV, all-aluminum end caps are available.

Carbon fiber window options（-CW）
Carbon fiber windows are available for energies greater than approximately 8 keV. While this window does not pass all lower energies, carbon fiber has a lower Z than Al and does not present any hazards associated with Be.