ISSN: 0090-3973
Page Count: 7

Experimental Evaluation of a Laboratory Twin-Probe Nuclear Gage for Specimen Density Measurement
Fwa, TF
Senior Lecturer, National University of Singapore,

Tan, SA
Senior Lecturer, National University of Singapore,

(Received 27 June 1990; accepted 8 May 1991)

Abstract

This paper describes a series of tests conducted to establish the operating requirements of a laboratory twin-probe nuclear gage for density measurement of cylindrical specimens of homogeneous materials. The nuclear device is an adaptation of a direct transmission field gage for laboratory density measurement. It is shown in this evaluation program that three forms of analysis are required for the setting up of such an apparatus: calibration analysis, precision evaluation, and accuracy assessment. Three specimen diameters (75, 100, and 150 mm), three materials with densities from 0.8 to 2.7 g/cm³, and nuclear gage source-to-detector spacings ranging from 250 to 450 mm were included in the evaluation program.

It was found that density calibration based on radiation attenuation theory is valid, and that a diameter-count rate relationship can be established experimentally so that only a single set of density calibration using one specimen diameter is needed for routine testing. In the accuracy assessment, it was found that there exists a narrow range of source-to-detector spacings for unbiased density estimation. A spacing of 280 mm is recommended for the device studied. At this spacing, the density measurement precision at 95% confidence level, using four 1-min counts per test, is found to vary from 0.010 g/cm³ for 150-mm-diameter specimens to 0.017 g/cm³ for 75-mm-diameter specimens.

Keywords:
nuclear density gage, cylindrical specimens, gage calibration, precision analysis, accuracy assessment, source-to-detector spacing

Paper ID: JTE11897J
DOI: 10.1520/JTE11897J
ASTM International is a member of CrossRef.