The remnant beam contains a varied pattern of x-ray energies that reflects the different absorption rates. In discussing the interaction probability above, we implicitly assumed that (IX) the nature of the target atoms/nuclei did not change from one interaction to the next, that is, Σ remains constant as the radiation beam travels a distance x. (18), if the observed wavelengths are much smaller than the transverse size of an ion beam, the SR from the ion beam will occur primarily along the Z-axis and will cover only a tiny solid angle, which will be defined by the transverse size of the ion beam, The superradiant pulse duration depends on velocity spreads of the beam and will be defined by the function P (t, ϑ). We will consider hydrogen-like ions with a charge number of nucleus Zi ∼ 20. The radiation that leaves the tube is called primary radiation. External beam radiation for prostate cancer uses high-energy beams, such as X-rays or protons, to kill cancer cells.