Reply To: Fusion Oil

[jamesr]

vansig wrote: Would a wide band gap semiconductor do, for this purpose? such as
Aluminium gallium indium nitride (AlGaInN) ?

I just checked up the various methods for normal diagnostic X-ray detectors, such as in X-Ray Data Booklet. They use different materials are used for different energy ranges an fluxes. We are operating in a completely different regeme to these detectors, as the flux of x-rays will be much larger (and harder). Although the premise is the same – to produce a current from the energy deposited by the x-rays as efficiently as possible. It is just that in our case the total current should be substantial.

A rough calculation of 15kJ of X-rays at average of 50keV emitted over 50ns onto a 50cm radius sphere puts the flux at ~10^21 photons/cm^2/s. Which is many orders of magnitude greater than a normal detector would saturate at.

Googling for recent papers I found one using a different wide band gap semiconductor (Fast High-Flux Response of CdZnTe X-Ray Detectors by Optical Manipulation of Deep Level Defect Occupations), quoted as high flux levels a figure of 10^9photons/cm^2/s on a 2mm thick slice.

So unlike detectors which are built to be as sensitive as possible and absorb as many x-ray photons in a small volume as they can. We need a material that as it saturates the rest of the photons pass through to the next layer & so on. Rather than one which absorbs more than it can cope with, and the excess ending up wasted as heat.

So if we have a flux of 10^21photons/cm^2/s and an onion with 1000 layers, (ignoring the fact that the outer layers have a larger area), then each layer has to cope with absorbing 10^18 photons/cm^2/s – still 9 orders of magnitude higher that their wide band-gap semiconductor can cope with.

Of course this assumes the materials don’t exhibit some weird non-linear response at such high fluxes & short pulse duration. I guess the only way to really find out is by experiment (or very detailed modeling).