Far Field Gamma Monitor for drums and small objects, G3620-340

This figure shows the most basic configuration of the Far Field Gamma Monitor. This configuration does not include automatic drum loading or movement of the drum rotation platform. It does not include the facility to move the detector closer to or father away from the drum. Also omitted from this system are gamma ray filters that would reduce the dose rate seen by the detector and a detector specific collimator. In this basic configuration the detector collimation is provided by recessing the detector into the cylindrical lead shield.

The ANTECH Model G3620-340 Far Field Gamma Monitor is the basic assay system for drums and small objects using far field gamma ray measurement geometry.

It is based on the generic ANTECH Model G3601 Far Field Gamma Assay Instrument and is designed specifically for drums and small objects. The system consists of:

  • Shielded and collimated high purity germanium detector
  • Automated gamma ray filters (as required)
  • Digital gamma ray spectrometer
  • Drum rotation platform
  • Drum weigh scale
  • Detector cooling, either by liquid nitrogen or by electro-mechanical coolers, such as the X-Cooler 3




FFGM Datasheet


The detector is shielded with a stainless steel clad lead shield. This shield contains a graded internal liner of tin and copper to suppress lead x-rays generated in the lead shield. The front section of the shield usually serves as cylindrical collimator. The degree of collimation (and hence the detector field of view) can be adjusted by moving the cylindrical HPGe detector along the axis of the shield. The detector field of view is reduced as the front face of the detector is withdrawn into the shield.

The Model G3620-340 is applicable to measurements of both low activity and high activity, especially for objects where the density distribution is relatively uniform. For measuring drums and small objects where the activity is neither very low nor very high, the segmented gamma scanning measurement technique provides more accurate results, especially where there is a variation of density over the object being measured.

Features & Benefits


  • Collimated detector field of view includes the entire waste drum or object
  • HPGe detector may use either liquid nitrogen (LN) or electro-mechanical cooling
  • Object being measured or assayed is rotated during the measurement
  • Distance between the collimated and shielded detector and the waste drum or object can be adjusted (depending upon the configuration)
  • Average density correction based on measurement of the weight of the object
  • Background may be reduced by the use of a shadow shield placed behind the drum or object
  • Filters or separation may be used to reduce the count rate (dose-rate) at the detector


  • Measures wide range of sample activity from very low level waste (VLLW) where the density is uniform to high activity remote handled (RH) waste
  • Automatic or manual filters can be used to reduce detector dead time for measurement of drums and objects with a high surface dose rate
  • Detector count rate and dead-time can be adjusted (for example for RH measurements) by adjusting detector-sample separation distance
  • Counting time is reduced and counting efficiency is increased as the entire drum or sample object is within the detector field of view
  • Detector field of view (collimation) can be adjusted to reduce background
Detector High Purity Germanium (HPGe)
Drum rotation Drum or sample is rotated during the measurement
Collimator Front section of detector shield usually serves as cylindrical collimator
Spectrum Front section of detector shield usually serves as cylindrical collimator. Alternatively, a separate collimator with variable thickness filters can be included for high dose rate applications.
Multi-channel analyser (MCA) DPA, DSPEC Jr2 or DSPEC 50
Power requirements 115/240 VAC
Options Roller conveyor drum loading or drum rotation platform movement using slide rails.
Different collimator options and automated gamma ray attenuating filters.
Slide rail movement of the detector to adjust detector drum separation distance.
Comprehensive factory calibration available for a wide range of drums and objects.