# Stationary Target X-Ray Tubes - Energy

1. Aug 23, 2016

### ChrisJ

1. The problem statement, all variables and given/known data
An x-ray tube with a stationary target is operated with a constant voltage and current of 100kV and 50mA for 0.2s . Approximately how much energy will be deposited as heat in the target and how much emitted as x-rays?

2. Relevant equations
$P=IV$ ?

3. The attempt at a solution
This is not coursework but preparation for an exam, it is is a past paper question.

I'm just a bit confused really as I cant find any reference to how to calculate the ammount as heat/x-rays etc.

But the Energy in 1/5s would just be
$P=IV=(50 \times 10^{-3})(1 \times 10^5)=5000$ W
So therefore in 1/5s of a second the energy would be 1000J.

But how do I work out how much of that is heat or x-rays? Is that even correct as it? The only reference to anything at all relating to this in the lecture notes/slides says that usually only around 1% is x-rays, so I dont know if the question just wants me to say that and therefore say ~10J as x-rays and 990J as heat?

2. Aug 23, 2016

### drvrm

i think the quoted estimate of 1% of energy being emitted as X-rays is an operational figure and the details of the estimate can not be done with the available data.
There are formulae for estimating the continuous X-ray intensity and it is proportional to Z the atomic number, tube current and square of the Potential difference applied.about one percent of the KE of electrons are used up in producing X-rays.