Geiger counter and low-energy x-rays

[Plat]

I have a geiger counter, the specifications say it is sensitive to x-rays down to 30kev. I wonder where that number comes from? Am I correct in thinking that any x-ray photon that enters the geiger tube will register a count, regardless of it's energy? Perhaps the 30kev minimum is there to ensure that the amount of radiation being detected is accurate? What do you think? There is a large attenuation loss due to the glass walls of the geiger tube at lower energies.

I ask because I wonder if the meter would be suitable as a qualitative test for danger from my experiment, which could be producing x-rays from 20-30kev. Thanks for your thoughts.

 

[rootone]

It sounds to me the spec is saying that below 30kevs the instrument sensitivity will start to drop off and so accuracy isn't guaranteed in that range.

 

[Plat]

Just what I was thinking. I wish I had an xray source of known energy to test it with. But from a physics standpoint, there is no reason to believe that a 20kev photon will not ionize the gas in the geiger tube, assuming it penetrates the wall?

The voltage I am using may well be over 30kev, and therefore make photons that the meter is designed to detect. It is pulsed DC from an automotive ignition coil, and arcs more than 3.2cm in air. Some info I am finding online says this should exceed 30kv judgeing by the arc length.