DGA-C Focused Gamma Tool

DGA-C

Directional Gamma Tool

DGAThe DGA-C, Directional Gamma Tool, is a Tungsten-collimated version of the NGT-T gamma tool.  These tools are sometimes referred to as “focused” or “shielded” gamma tools.  In this design a 67° “window” is machined along the length of the Tungsten shield that surrounds the crystal/phototube detector.  Only gamma ray entering from the formation through this window can be detected and counted.  When aligned with the tool face or other physical reference, the DGA-C indicates the direction from which gamma ray energies originate.

The DGA-C is interchangeable with the standard NGT-T gamma tool.  It is same overall length and diameter.  Because of the required thickness of the Tungsten shield, the Nal(TI) scintillator crystal is of a smaller diameter.  The length is increased to 6.0” however, to deliver an equivalent volume of crystal material as in the NGT-T to provide maximum sensitivity.

DGA-C

Directional Gamma Tool

DGA

The new DGA-C is a more sensitive version of the popular DGA focused gamma tool.  It contains a larger scintillator crystal and improved eccentric tungsten-collimated shield.  These two improvements combine to offer higher count-rates and a 50% higher counts per API Sensitivity over the DGA.  In this design a 72° “window” is machined along the length of the Tungsten shield that surrounds the crystal/phototube detector.  Only gamma rays entering from the formation through this window can be detected and counted.  When aligned with the tool face or other physical reference, the DGA-C indicates the direction from which gamma ray energies originate.

The DGA-C is interchangeable with the standard DGA gamma tool.  It is same overall length and diameter. 

DGA-C Specifications

Detector Nal(TI) Scintillator Crystal0.725” Diameter  X 6.65” Length 
PhotomultiplierR3991A (Hamamatsu) 
MechanicalDiameter (OD)1.36” 
Length (make-up)13.7” 
Weight4.0 lb 
End ConnectorsMicro-D Subminiature, 15-Pin 
MaterialAluminum Alloy (chassis), Tungsten (shield) 
PerformanceSensitivity0.52* CPS/API (decreased due to Tungsten shield) 
Accuracy+/- 5% to 300°F
+/- 10% to 350°F
 
Thin-Bed Resolution (8” hole Diameter)8.8” 
Operating Temperature0°F to 350°F 
Survival Temperature-40°F to 400°F 
Vibration (3 axis) 50-1000Hz, Random20G RMS 
EnvironmentalHeat/Cool Rate, Max. 5°F per minute 
Shock (3 axis)1000G, 0.5ms, half-sine 
Power RequirementsDC Input Voltage17-48 VDC, 50VDC Max. 
Tool Current8-11 mA 
Output SignalNegative Pulse+5V to GND, 5 uSec width 

* Counts are collected with gamma tool mounted within standard BeCu pressure barrel, (OD 1.875″, ID 1.500″).  API Calibration performed with AEA Technology, QSA Inc., KUTh Field Verifier #188074, S/N 255 Radionuclides: K-40(11.7%), U-238(90 ppm), Th-232(40 ppm).

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