| While the knowledge about the spectral information from high energy x-ray machines is fundamental in some applications, like megavoltage photon therapy, how to get the information presents a daunting task. The difficulty lies in the fact that the detector is always inundated with billions of particles, and will be saturated instantly. In addition, the detecting efficiency falls off drastically at high energy. To remedy this situation, the scattering method is proposed and has been tried on several occasions. The scattering method can effectively reduce the high intensity and the energy spectrum is shifted to a suitable range. However, in applying this method to a practical situation, attention should be paid to some complicating factors.; In this research project, a complete formulation for the incoherent scattering method is given; the scattering method is then applied to a cobalt-60 radiation therapy machine, and the scattered spectrum is measured and then transformed back to the primary spectrum. When the Monte Carlo technique (MCNP) is used to simulate the scattered spectrum, good agreement is observed. The broadening effect inherent to the scattering method is introduced and demonstrated quantitatively for the first time. The broadening effect is the cause of energy resolution loss when the measured scattered spectrum is transformed back to the incident spectrum. Also, the effect of the collimator is observed experimentally and Monte Carlo (MCNP) simulation confirms the observation. Methods are proposed to minimize this unwanted complication based on the radiological properties of materials and the physical design of the collimator.; The incoherent scattering method has been applied to medical electron accelerators using the Monte Carlo (MCNP) technique. The primary and the scattered spectra are obtained under ideal experimental conditions. The MCNP simulated scattered spectrum is transformed back to primary spectrum and good agreement is observed. |
