Photon Count calculation
In this example, photon counts calculation for a single radioactive particle that emits gamma-ray has been performed. We perform the calculations for a set of given positions inside a cylindrical tank using a Monte-Carlo technique. The Monte-Carlo calculation generates the estimated counts with respect to a detector for each particle’s position inside the vessel. The geometry of the vessel and the detector is illustrated below:
In the subsection “rpt parameters”, we define a set of positions inside the reactor. Using “particle positions file” option we specify the file’s name that Lethe uses as input to determine the particle’s positions. In this example we use 106 iterations for the Monte-Carlo simulation. “Monte-Carlo iteration” option defines the number of traced gamma-rays from each particle position to the detector within the defined solid angle. If the user is interested in exporting the photon count number in the format of a .csv file, the “export counts” option should be set to true.
set particle positions file = positions1.particle
set export counts = true
set monte carlo iteration = 1000000
set random number seed = auto
set reactor radius = 0.1
set peak-to-total ratio = 0.4
set sampling time = 1
end
In the subsection “parameter tuning”, and in order to calculate the photon counts for a given mesh, the user must set the “tuning” option to false in order to avoid the parameter tunning process. Parameters related to the detector such as dead time, and attenuation coefficients must be specified in this section. Moreover, the tracer particle activity also should be defined here.
set tuning = false
set dead time = 2.7e-6
set activity = 9.5e6
set gamma-rays emitted = 2
set attenuation coefficient reactor = 7.1
set attenuation coefficient detector = 21.477
end
In the subsection “detector parameters”, we specify the file that contains the position of the detector face canter and the position of a point inside the detector on its axis. In this example, the detector face center position is [0.15, 0, 0.08] and [0.17, 0, 0.08] is another point on the detector’s axis.
set detector positions file = positions1.detector
set radius = 0.0381
set length = 0.0762
end
The plots below visualize the received photon counts by the detector from different positions inside the cylinder. The algorithm of RPT works based on a precise phenomenological model which relates the spatial coordinate of the radioactive particle and the number of photon counts received by the detector. The following plots are the top view (x-y plane) and front view (x-z plane) of the vessel. As it is shown, if the particle is placed in an area closer to the detector, the detector senses a higher amount of gamma-rays intensity compared to the areas further from the detector’s face.
