SOME REFINEMENTS IN MEASUREMENT OF SURFACE DENSITY BY GAMMA RAY ABSORPTION

Abstract

THE AASHO ROAD TEST SYSTEM OF NUCLEAR DENSITY DETERMINATION IS DESCRIBED, WITH EMPHASIS ON THE SOURCE OF ERROR THAT HAS BEEN ISOLATED AND IN SOME CASES ELIMINATED. SOME OF THE IMPORTANT CONSIDERATIONS IN THE DESIGN OF NUCLEAR SURFACE GAGES ARE DISCUSSED, AS WELL AS CALIBRATION TECHNIQUES, LICENSING, HEALTH PRECAUTIONS, AND COST. THE PRINCIPLES INVOLVED IN NUCLEAR DETERMINATION OF DENSITY ARE PRESENTED IN AN APPENDIX. CONCLUSIONS OF THE SURVEY ARE THAT: (1) THE NUCLEAR SURFACE DENSITY GAGE CAN BE USED FOR CONSTRUCTION COMPACTION CONTROL TESTING, (2) MOISTURE CONTENT MUST BE CONSIDERED WHERE PRECISE ESTIMATE OF DENSITY IS DESIRED, (3) IF THE MATERIAL BEING CHECKED EXISTS IN A THIN LAYER THE DENSITY OF THE UNDERLYING MATERIAL MUST BE TAKEN INTO ACCOUNT, AND (4) OPTIMUM SURFACE GAGE DESIGN DIMENSIONS VARY WITH THE DENSITY OF THE MATERIAL UNDER TEST, SO PROVISION SHOULD BE MADE FOR CHANGING THE SOURCE-TO-TUBE DISTANCE IN THE FIELD.