Simulation models to obtain X-ray spectra using the Compton scattering technique

Abstract

Quality control of X-ray tubes for medical radiodiagnostic services is very important. Therefore, it is convenient 10 develop new procedures to characterise the X-ray primary beam, obtaining an accurate assessment of the actual photon spectrum. The Compton scattering technique is very useful to determine X-ray spectra, avoiding the pile-up effect in the detector, as usually a large room is not available to apply other techniques. The Compton scattering procedure has been simulated using the Monte Carlo method. Several simplified models have been developed for the scattering assernbly, considering the X-ray focus as a point source.1. Introduction The development of new procedures to characterise the primary photon beam from medical X-ray tubes under normal work conditions is very important for quality control of those devices.In X-ray spectra measurements, the number of photons per time unit that reaches the detectcr shall he limited since detectors cease to work properly at high count rates. At high fluence rate a 'pile-up' effect can be observed. In the pile-up, an accumulation of pulses produces a distortion of the X-ray spectrum measured. To obtain appropriate count rates for X-ray tubes with high fluence rate avoiding the pile up effect, a collimator with.small diameter and long tube-detector distance should be used. Nevertheless, this equipment assembly is hard 10 use in a laboratory or X-ray room a cause of the small space available. Therefore, a Compton scdttering technique is proposed in order to avoid the pulse pile-up [I J. Computer simulation is always a useful tool that permit?, to check various dispositions and components of an cxperimental technique in order to improve it. In this work, the Compton scattering technique is simulated using the MCNP 4C code [Z], based on the Monte Carlo method. Different models are dcveloped in order to compare the effect on the obtained spectrum of each cumponent of the Compton scattering equipment. 0-7803-7939-X/03/$17.00 0 2003 IEEE 228The MCNP code is a well established computer code, very useful to simulate the calibration of a HPGe detector [3]. It was validated for monoenergetic sources [4], but it can be also applied when an energy spectrum is provided. In particular, it has been used to obtain pulse height distributions from gamma sources [SI. Compton spectrometerThe Compton spectrometer includes a shielding chamber, a scattering chamber containing the scattering material (PMMA or lucite) and a spectrometer tube with lead collimators [6]. The assembly can be seen in figure 1. Shielding and scattering chambersThe main purpose of those chambers is to line up the primary beam coming from the X-ray tube and also to direct the 90" scattered beam towards the spectrometer tube. Moreover, this, assembly avoids the undesired scattered photons to reach the spectrometer tube. Collimators A, B and C define the direction of the primary beam. Furthermore, collimator C reduces the backscattering effect produced by photons that pass across the scattering chamber without being...

Monte Carlo simulation of the Compton scattering technique applied to characterize diagnostic x‐ray spectra

“…Some variations on the MCNP simulation were analyzed in an earlier study. 13 A simplified model including only the scattering rod, the spectrometer tube without collimators and the detector has been selected ͑Model 1͒. Results obtained with MCNP for this model are represented in Fig.…”

Utilization of High-Power Leds as Non-Invasive KV Meter Detectors in Collimation of Lighting

“…Furthermore, x-ray machines of both radiography and fluoroscopy are also often used to determine the condition of human body. To use this machine, two parameters are commonly used for the settings [5] [6]. The first parameter is the KV value, while the second parameter is the mA value.…”

“…The full mare model gives not-so-good results, which can further attribute to the fact that the more complicated models, the less it will work well with the small solid angles used for the point source model. Therefore, it is necessary to carry out several experimental measurements to validate the model developed [6], [17]- [20].…”