A simply made
made from readily available materials
created by Keith Feay
Following a trip I made to Africa in 2008 it became obvious that many hospitals had no means of measuring X-ray equipment output. As most X-ray engineers and radiographers use fluorescent screens to check if there is an output from the tube, I wondered if this could be extended to produce some measurable results.
The detector described will work best with an oscilloscope or PC soundcard oscilloscope software but it also works with a DVM or analogue voltmeter. As I live in the UK all the parts used have been found or acquired locally. I am sure that the parts required will be available in most parts of the world.
X-ray equipment can be dangerous if not used correctly. Please use radiation protection at all times. This article is intended for those technicians and engineers who have had some training in the use and safety of x-ray machines.
Fluorescent screen from an X-ray cassette.
On my trip to Africa I found several damaged cassettes in all x-ray departments. Most
were beyond repair but had good fluorescent screens.
Small Photo Voltaic cell.
A good source of these is the cheap garden lights sold in UK £1 shops.
Any small cell (up to 5cm square will do) its voltage output in daylight should be around
2.5 volts but this is not critical.
A box to put the whole assembly into.
Plastic medicine boxes are useful for this any are usually available in most hospitals.
Twin cable and suitable plugs for the oscilloscope / meter.
Screened cable is best but if not available the twist 2 thin wires together.
Test your photocell in daylight to ensure that you get an output. Mark the positive and negative poles.
Test your fluorescent screen to make sure that it glows when exposed to x-rays. Most glow blue or green and the brightness depends on their chemical composition.
The screen is placed fluorescent side against the light sensitive side of the photocell and held in place with electrical tape. The cloth Gaffer tape or Tesa tape is best but any electrical tape will do as its purpose is to keep out light.
Measure the output again in strong light the reading should be zero if all light has been successfully excluded.
Place the whole assembly in a suitable box with the lead exiting through a hole drilled in the box.
Connect the detector to a meter or scope.
Place the detector under the X-ray tube. At about 500mm from the focal spot.
The distance is not critical and may need to be closer with a low output unit.
Switch the meter / scope to the suitable voltage setting. (Try 200mV)
Set the x-ray machine to 70kV 50mA and 1 second or whatever you can on your machine.
Make an Exposure whilst watching the meter / scope.
You should get a reading of approximately 100 to 200 mV depending on the screen and the cell used.
This is not a precision instrument but will when used with an oscilloscope give you a reasonably indication of the output from an x-ray machine.
Complete solar light on the left. Cells on the right.
Completed test box on left used to check a portable x-ray unit.
Questions and remarks please directly to Keith.