TM 5-6635-386-12&PSeating area requirements for the transmission modecomprise only a 2 x 6-inches wide surface under the GMtube, thus the tester can be used on very difficultsurfaces where a backscatter tester would be impossibleto use.Transmission surface roughness error is approximately1/10th that of the backscatter errors.1-18. DRILL TRANSMISSION HOLEThe transmission hole must be vertical to the smoothedsurface and must not be damaged in the process ofdrilling and retraction of the drill.Place the Cast Guideplate on the surface and use theguide to support the drill pin. Hammer the drill pin intothe ground, tap it lightly to loosen it, twist it to furtherloosen it, and pull it out of the ground.WARNINGDo not use the cast guideplate as a retractiondevice. It will damage the top of the guide hole.Figure 1-6. Transmission HoleNOTEDuring drilling and retraction, the operator’s weight on theguideplate confines the soil to prevent eruption orpuffing.The operator’s weight on the plate confines the soil indrilling and in retraction to produce a neat, undamagedhole for the readings.On heavily compacted material above 95%, cracks mayappear in the soil. These will not affect the readings ifthe tester is placed so no crack extends from the sourcedirectly back to the detector tubes.If the drill pin "walks away" as a result of striking a rock inthe soil, try another location. If repeated tries cannotproduce a satisfactory hole, then the test should beaborted.1-19. SEATING THE TESTER IN TRANSMISSIONFrom a radiation exposure standpoint, it is undesirable tohave to spend a great deal of time "playing" with thetester in seating it. Locating the hole for insertion of thesource rod in transmission is frequently a problem andCPN has made this easy for the operator.Figure 1-7. Positioning Source in Prepared HoleA small cast lip (Fig. 1-7) is on the front of the bottomcasting to provide for insertion ease.1-15
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