Question

(a) In an x-ray tube, if the energy of the electrons striking the target is increased, do you expect the wavelength of the characteristic x-rays to increase, decrease or be unchanged? Justify your answer. (b) Both CT and PET scanners use a ring of detectors around the patient. Explain how the two techniques differ.

Answer 1

(a) X-rays are produced by bombarding a target material with high energy electrons. If the incident electron interacts or collides with an atom in the target then it will lose some of its kinetic energy. This energy can be emitted as an x-ray. The broad range of x-ray wavelengths is the bremstrahlung (“braking radiation”). It arises from the sudden decelerations of the electrons as they strike the target.Since wavelenght is inversely proportional to Energy and X-ray Energy depends upon electron energy(in another words X-ray Energy is proportional to electron energy),Hence on incresing electron energy characteristic X-rays wavelenght decreased.

(b)in CT scanners uses X-rays for imaging and in PET scanners uses Radioactive tracers that emit positrons are used. The positrons are tracked by the system to generate a 3D image over time