Measurement of Lead Equivalence
There are various standards which explain how to measure Lead Equivalence such as EN IEC 61331-1:2002, ASTM 2547-06F and DIN 6857. All these methods compare the protection provided by pure lead sheet against that provided by the protective sheeting.
Lead equivalence can be measured at various kilo voltages starting from 40kV to 150kV. Current and time is set according to different voltages.
Following equipment is needed to measure the lead equivalence.
1. Calibrated high voltage multi frequency X-ray machine
2. Calibrated pure Lead reference with known lead thickness
3. Density measurement tool
4. X-ray film processor
5. Test sample of size minimum 1 square inch.
- Cut the protective sheeting required to be tested which is at least 1 square inch in size. Prepare the x-ray cassette by inserting a film and place the cassette below the x-ray tube with tube side up.
- Place the calibrated pure lead reference strip on one side of the cassette. Place the samples to be tested on the cassette. Set the x-ray machine to the voltage at which lead equivalence of the sample is to be tested. Expose to x-ray and process the film. Now we measure the optical density of the reference pure lead and test sample.
How to get the test result?
- Measure the density with densitometer.
- Note down the density readings for the calibrated lead step wedge
- Plot the lead equivalent values in X-axis (scale e.g. 10 mm = 0.01 mm Pb) and Density on the Y-axis (scale e.g. 10 mm = 0.1 D) on the graph paper.
- Join all the points and draw a straight line.
- Measure the density of the image at three points starting at the centre of the test sample.
- Draw a line parallel to X-axis and intercept the line drawn for reference.
- From the point of interception, draw a line parallel to Y-axis and connect X-axis.
- The point at which the line joins X-axis is the Lead equivalence for the test sample.