In Reply to: X - Ray generation posted by Shariq on 09/22/03 at 2:19 AM:
I will try to answer your questions to the best of my knowledge, but if you want more detail you could find some very good articles by searching on the Web.
1. The energy distribution emitted by an X-ray tube is mainly dependent on a three factors: The target material type (usually Tungsten in medical and dental tubes), the magnitude of the high voltage (max photon energy = KVpeak), and the filtration material (usually Aluminum in medical and dental tube heads). The energy distribution contains both "characteristic" and "Bremstrahlung" radiation.
2. As mentioned above, the max photon energy can not be greater than the max high voltage. The Kilovoltage level determines the "hardness" or penetrating ability of the X-ray beam. The tube current (mA) determines the "intensity" (flux density) of the X-ray beam.
3. Altering the kilovoltage will alter the "shape" of the energy distribution and will affect one or more peaks of the characteristic lines (especially at the higher energy end of the spectrum). Altering the current (mA) will affect the overall magnitude of the entire spectrum.
More info: X-ray machine manufacturers always place additional material in the path of the X-ray beam as the beam exits the tube head. This is known as "added filtration". It is needed because the "raw" beam has a lot of energy at the lower region of the spectrum which serves no radiological purpose because it is non-penetrating. In fact, it can cause skin burns resulting in cancer. The added filtration serves to greatly attenuate the lower portion of the radiated spectrum.
Mike Gray, President
Amery X-ray, Inc.