IMPORTANCE OF PULSE-HEIGHT ANALYSIS IN THE GAMMA-RAY ATTENUATION TECHNIQUE FOR MEASUREMENT OF SOIL MOISTURE

EXPERIEMTS UTILIZING THE GAMMA-RAY ATTENUATION METHOD OF MEASURING SOIL MOISTURE CONTENT WERE RUN TO DETERMINE WHETHER A PULSE-HEIGHT ANALYZER IS NECESSARY IN THE COUNTING SYSTEM. THE GAMMA SOURCE WAS CESIUM-137 HELD IN A CYLINDRICAL CAVITY DRILLED CENTRALLY IN A LEAD CYLINDER; THE CAVITY WAS CLOSED WITH A LEAD PLUG HAVING A CENTRAL RECTANGULAR SLIT. THE DETECTOR WAS PLACED IN A SIMILAR SHIELD, AND ITS FRONT WAS SHIELDED WITH A SLOTTED LEAD PLATE. THE TWO SLITS WERE HORIZONTALLY ALIGNED. A CELL WAS CONSTRUCTED TO TEST FOR A LINEAR RELATIONSHIP BETWEEN 1N I (OF THE GAMMA RAY BEAM) AND THE ABSORBING LENGTH OF WATER BY USING A METHOD FOR OBTAINING VARIABLE WATER THICKNESSES. THREE OPERATING MODES WERE TESTED: THE ANALYZER SET TO ACCEPT TWO DIFFERENT ENERGY RANGES, AND THE DETECTOR CONNECTED DIRECTLY TO THE SCALER. A SECOND EXPERIMENT EMPLOYED QUARTZ SAND SATURATED WITH WATER AND ALLOWED TO DRAIN. MOISTURE CONTENT WAS CALCULATED BY AN EQUATION FOR 1N I FOR THE TWO ENERGY RANGES OF THE FIRST EXPERIMENT. THE DIFFERENCE IN MOISTURE CONTENT VALUES FOR THE TWO METHODS DID NOT EXCEED TWO SIGMAS, I.E., BOTH WERE EQUALLY PRECISE. IT IS CONCLUDED FROM BOTH EXPERIMENTS THAT THE PULSE-HEIGHT ANALYZER HAD LITTLE OR NO EFFECT ON THE RESULTS. THE SLIT IN FRONT OF THE DETECTOR EFFECTIVELY ELIMINATED MOST OF THE SCATTERED PHOTONS, A CONCLUSION STRENGTHENED BY TWO ADDITIONAL TESTS RUN TO CONFIRM ITS IMPORTANCE IN OBVIATING THE PULSE-HEIGHT ANALYZER.

  • Supplemental Notes:
    • Vol 110, No 4, PP 283-286, 3 FIG, 1 TAB, 6 REF
  • Authors:
    • Saxena, G S
    • Franklin, R E
    • Taylor, G S
  • Publication Date: 1970-10

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Filing Info

  • Accession Number: 00237926
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Dec 2 1970 12:00AM