QL40-SGR Spectral Gamma CeBr Probe ImageQL40-SGR-2G Spectral Gamma BGO Probe Image


The QL40-SGR-2G is a new generation of borehole logging Spectral Gamma Tool. This new logging probe consists of a completely redesigned and ruggedized mechanical assembly, electronics and gamma module. It implements also the latest telemetry developments to enhance tool performance on long single and multi-conductor wirelines.

The QL40-SGR-2G probe measures the total gamma counts in API as well as the full energy spectrum of the gamma radiation emitted naturally from within the formations crossed by a borehole. A Full Spectrum Analysis (FSA) is performed on the recorded energy spectra. The FSA derives in real time the concentration of the three main radioisotopes 40K, 238U, 212Th, and thus provides insight into the mineral composition of the formations. The spectral gamma ray log is widely used in the mining and environmental industries for the identification of lithology, correlation between boreholes, and clay content analyses.

The QL40-SGR-2G spectral gamma well logging tool includes a modular platform that can be equipped with a BGO (Bismuth Germanium Oxide) scintillation crystal or with a CeBr3 (Cerium Bromide) scintillation crystal.

The BGO crystal is characterized by a very high scintillation efficiency, good energy resolution, and is mechanically strong. It makes the tool ideal for a wide range of applications.

The QL40-SGR-2G implementing the CeBr3 crystal is characterized by a very good spectral resolution and high sensitivity. The short dead time value of the system (less than 1 μs) combined with the latest design of the measurement electronics allows a perfect linearity of the total gamma counts even in a high radiation context. It makes the tool ideal for ore grade analysis when a fine spectral resolution is required to identify radioisotopes with narrow energy bands.

The QL40-SGR-2G spectral gamma probe is supplied as an inline sub. It can be combined with other logging tools of the QL product line or can be operated as a standalone tool. It is compatible with all of the current ALT/MSI acquisition systems.


  • Mineral Detection
  • Sedimentology- Facies changes and depositional environment
  • Lithology Studies
  • Identify and Classify Clay Types
  • Recognition of Radioactive material
  • Contamination Research
  • Well to well correlation
  • Additional CeBr3 Applications:
    • Mineral composition
    • Uranium exploration
    • Ore grade analysis

Operating Conditions

Borehole Fluid
[X] Water
[X] Mud
[X] Dry

[X] Uncased
[X] PVC Borehole
[X] Steel

[_] Required
[X] Non-Necessary

LoggerSuite Real Time Spectrum-22Na Isotope

Features & Benefits

  • Cutting edge Full Spectrum Analysis (FSA) of data in WellCAD and LoggerSuite
  • Versatile, ubiquitous probe which functions with a wide range of applications and borehole conditions.
  • WellCAD Spectral processing is fast and easy in real time with Medusa calibration
  • Mount Sopris manufactures more natural gamma and spectral tools than any other slim tool manufacturer in the world today.

Specifications – Metric/English

Specification Metric Imperial
Diameter 40 mm 1.6 in.
Length 1.01 m 39.4 in.
Weight 6 Kg 13 lbs
Max. Temp. 70ºC 158ºF
Max. Pressure 200 bar 2900 psi


Specifications – Sensor BGO Crystal

  • Scintillation crystal : BGO (Bismuth Germanium Oxide)
  • Dimensions : 25.4  x 100 mm (1.0 x 4.0 in.)
  • Sensitivity (compared to NaI crystal) : x 3
  • Spectral Resolution @ Cs (%) : 13.6
  • Dead Time (μs) : 4.8

Specifications – Sensor CeBr3 Crystal

  • Scintillation crystal : CeBr3 (Cerium Bromide)
  • Dimensions : 20 x 96 mm (0.79 x 3.78 in.)
  • Sensitivity (compared to NaI crystal) : x 1.9
  • Spectral Resolution @ Cs (%) : 6.2
  • Dead Time (μs) : 0.8

Measurement Range: Up to 3000 keV

CeBr3 vs BGO crystal – Spectral resolution comparison (137Cs isotope)

QL Stack Possibilities

Full Spectrum Analysis (FSA)

The latest releases of WellCAD and LoggerSuite contain an implementation of the Full Spectrum Analysis (FSA) method developed by Medusa Explorations BV in collaboration with the Nuclear Physics Institute of the University of Groningen (Netherlands). FSA comprises the mathematically most efficient method to derive nuclide concentrations from gamma ray spectra.

Gamma ray analysis is performed in two steps. First spectrum stabilization will be performed: Each multichannel spectrum in the data set will be converted to a spectrum having all count peaks at the corresponding energy position. This process implies a close comparison with reference spectra obtained during the calibration process of the spectral gamma tool at the Medusa calibration facility. In a second step the now stabilized spectrum will be convoluted into concentrations of (naturally occurring) radionuclides (40K, 238U, 232Th, or other man-made nuclides like 137Cs or 60Co). Corrections taking borehole diameter, rock density, casing type and thickness, tool position and borehole fluid conditions into account can be applied.

QL40-SGR Field Isotopes and Stabilized Spectrum

Field record – Radioisotope concentrations and stabilized spectrum

WellCAD provides an easy to use interface to load the source log containing the raw spectrum data, select the Medusa calibration file and enter the parameters from which the borehole condition corrections will be computed and applied. The process will compute and output in WellCAD the nuclide concentrations and corresponding uncertainties, the stabilized spectra, and the applied stabilization factor. The following image shows the comparison of the raw spectrum showing a considerable spectrum drift due to temperature variations and the resulting stabilized spectrum which will be used as base for the nuclide concentration computation.

Gamma Spectrum with Cs peak drifting and after stabilization

For more information on this new approach to spectral data analysis, please see the research papers and discussions on the Medusa website.


QL40-SGR-2G BGO Spectral Gamma Probe Brochure
QL40-SGR-2G CeBr Spectral Gamma Probe Brochure
Please Contact Us for the User Guide

Print Friendly, PDF & Email