Emission current from hot cathode in an X-ray sourse

[proudtobeaj]

Part of an experiment involved measuring the intensity of an X-ray beam through a piece of aluminium as a function of emission current of the X-ray source. I originally fitted a linear fit to my data (although it does start to level off at high emission currents). The marker however said that it was not a linear fit, and said it was heading towards "saturation", but I am not quite sure what he meant. The detector is definitely NOT at saturation as the measured intensities are well below the saturation level (measured earlier)

Why does the intensity of the beam level off at high emission currents? Is it because there can only be so many electrons "boiled off" from the cathode, so it can only produce so many X-rays in collisions with the target?

 

[gneill]

Why does the intensity of the beam level off at high emission currents? Is it because there can only be so many electrons "boiled off" from the cathode, so it can only produce so many X-rays in collisions with the target?

Was the saturation intensity measured with the same aluminum block interposed? Could the intensity on the source side of the block be higher than on the detector side?

 

[proudtobeaj]

Was the saturation intensity measured with the same aluminum block interposed? Could the intensity on the source side of the block be higher than on the detector side?

The saturation intensity was measured with no aluminium in the path of the beam. the count rate (with the block in place) begins to level off at higher emission currents with only about half of the count rate of the beam whose path was unimpeded.

 

[gleem]

At some point as you heat the filament the electrons emitted from the filament begin to shield the filament with a cloud of electrons that have not been pulled out of the vicinity of the filament. Unless you increase the anode voltage and extract these electrons more quickly the flow will stop increasing. See "space charge effect"

 

[rwisz]

The intensity of the X-ray beam does indeed level off at high emission currents because of the limitations of the hot cathode in the X-ray source. As you mentioned, there is a limit to the number of electrons that can be "boiled off" from the cathode. This is known as the saturation level. Once this level is reached, the cathode can no longer produce any more electrons, and therefore, the intensity of the X-ray beam cannot increase any further.

Additionally, as the emission current increases, the electrons being produced by the cathode may not have enough energy to effectively collide with the target material and produce X-rays. This can also contribute to the leveling off of the intensity.

It is important to note that the detector may not be at saturation, but the cathode in the X-ray source is. The detector is simply measuring the intensity of the X-ray beam that is being produced by the cathode, and if the cathode is at its saturation level, the intensity will not increase any further.

In conclusion, the leveling off of the intensity at high emission currents is a result of the limitations of the hot cathode in the X-ray source, and it is important to consider this when analyzing the data from your experiment.