ISSN: 1945-7553
CODEN: JTEVAB
Page Count: 7

Experimental Evaluation of a Laboratory Twin-Probe Nuclear Gage for Specimen Density Measurement

Fwa, TF
Senior Lecturer, National University of Singapore, Kent Ridge,

Tan, SA
Senior Lecturer, National University of Singapore, Kent Ridge,

(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
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