Nath R, Schulz R J
Med Phys. 1976 May-Jun;3(3):133-41. doi: 10.1118/1.594217.
The determination of high-energy x-ray spectra has required scintillation spectrometers with massive shielding, neutron time-of-flight spectrometers, or the tedious counting of electron tracks in nuclear emulsions. A new approach has been developed which takes advantage of the energy dependence of photoactivation cross sections. Radioactivity is produced in a small packet of C, Cu, Co, Y, Zr, and Au foils by approximately 5000 rad (tissue). Since the amount of radioactivity produced in each foil is given by the integral of the product of photonuclear cross section and differential photon fluence, a numerical method for unfolding the spectrum is required, and the orthonormal expansion has been employed for this purpose. The photoactivation method has been used to determine the x-ray spectra produced by 30-MeV electrons incident upon thin and thick tungsten targets, and filtered by equivalent amounts of lead and aluminum. These spectra have been compared to calculated thin-target spectra as well as to those determined by a neutron time-of-flight spectrometer. The central-axis and off-axis x-ray spectra produced by a 33-MeV betatron have also been determined.
高能X射线光谱的测定需要配备大量屏蔽装置的闪烁光谱仪、中子飞行时间光谱仪，或者在核乳胶中繁琐地计数电子径迹。现已开发出一种新方法，该方法利用了光致激活截面的能量依赖性。通过约5000拉德（组织）的辐射，在一小包由碳、铜、钴、钇、锆和金制成的箔片中产生放射性。由于每个箔片中产生的放射性量由光核截面与微分光子注量乘积的积分给出，因此需要一种展开光谱的数值方法，为此采用了正交归一展开。光致激活法已用于测定30兆电子伏电子入射到薄和厚钨靶上并经等量铅和铝过滤后产生的X射线光谱。这些光谱已与计算出的薄靶光谱以及由中子飞行时间光谱仪测定的光谱进行了比较。还测定了33兆电子伏电子感应加速器产生的中心轴和离轴X射线光谱。
