RPT PARAMETERS

Radioactive particle tracking (RPT) is a non-intrusive velocimetry method which is used to study the hydrodynamics of single and multiphase systems. Launching a RPT simulation for photon count calculation in Lethe requires a solver which is rpt_3d, a parameter file, two files including detector and particle positions inside the vessel. The particle positions file includes either the experimental calibration positions or a set of generated points inside the vessel by the user. Detector positions file contains the position of detector face center and the position of a point inside the detector on its axis. In Lethe-RPT code the middle bottom of the cylinder is considered as the origin. An example of these two files can be find here. This section aims at describing the various parameters available within Lethe-RPT.

Parameters file (.prm)

In the parameter file format, the parameters are established one by one using the following syntax for instance: 'set reactor radius = 0.1' would fix the reactor radius to 0.1 m. The arguments can be either doubles, integers, or a choice between a predefined condition. In the parameter files, comments are preceded by the sharp symbol (e.g., '#comment').

The parameter file is composed of different subsections. In the following, the principal subsections of a RPT parameter template file are explained.

RPT parameters
Parameter tuning
Detector parameters
Reconstruction parameters

RPT parameters

This subsection contains the general information for photon count calculation which is described in detail in this part.

particle positions file : Filename of the text file with a set of positions inside the reactor
Options : Any text file with .particle extension with the required header : particle_positions_x particle_positions_y particle_positions_z
verbosity : Enable to show photon counts numbers results in realtime in terminal
Options : enable or quiet
export counts : Enable to export photon counts numbers in a file
Options : true or false
counts file : Filename of export counts file (.csv or .dat)
Options : Any text file with .csv or .dat extension
monte carlo iteration : Defines the number of traced gamma-rays from each particle position to the detector within the defined solid angle
Options : Any positive integer
random number seed : Seed number for the random number generator, using a particular number allows to run the same series of numbers
Options : Any positive integer
reactor radius : Radius of the cylindrical reactor vessel [m]
Options : Any positive float
reactor height : Height of the cylindrical reactor vessel [m]
Options : Any positive float

The following parameters are variables in the gamma-ray Monte-Carlo model from Beam:

peak-to-total ratio : The proportion of the events appearing in the full energy peak to the total number of events []
Options : Any positive float
sampling time : The amount of time for which the RPT hardware records the photon count at each position [s]
Options : Any positive float
dead time : Dead time of the detector per accepted pulse [s]
Options : Any positive float
activity : Radioactive source activity of the tracer [Beq]
Options : Any positive float
gamma-rays emitted : Number of gamma-rays emitted by each disintegration []
Options : Any positive float
attenuation coefficient reactor : Total linear attenuation of light coefficient of the medium, reactor wall and air []
Options : Any positive float
attenuation coefficient detector : Total linear attenuation of light coefficient of the detector []
Options : Any positive float

# --------------------------------------------------
# RPT Monte Carlo technique
#---------------------------------------------------
subsection rpt parameters
    set particle positions file          = positions.particle
    set verbosity                        = verbose
    set export counts                    = true
    set counts file                      = counts.csv
    set monte carlo iteration            = 100000
    set random number seed               = 0
    set reactor radius       		 = 0.1
    set peak-to-total ratio  		 = 0.4
    set sampling time        		 = 1
    set dead time       		 = 1e-5
    set activity  			 = 2e6
    set gamma-rays emitted        	 = 2
    set attenuation coefficient reactor  = 10
    set attenuation coefficient detector = 21.477
end

Detector parameters

This subsection contains the specific information of the detector. “Detector position file” defines the files that Lethe uses to read the detector positions. This file includes the position of detector face center and the position of a point inside the detector on its axis.

detector positions file : Filename of the text file with positions of detector(s)
Options : Any text file with .detector extension with the required header : face_positions_x face_positions_y face_positions_z middle_positions_x middle_positions_y middle_positions_z
radius : Radius of detector(s) (all detectors must have the same dimensions)
Options : Any positive float
length : Length of detector(s) (all detectors must have the same dimensions)
Options : Any positive float

#---------------------------------------------------
# Detector parameters
#---------------------------------------------------
    set detector positions file          = positions.detector
    set radius       			 = 0.0381 
    set length                           = 0.0762
end

Parameter tuning

This subsection contains information regarding the tuning parameters with NOMAD. Enable tuning parameters needs the verbosity parameter in the previous subsection to be disable thought setting it as quiet otherwise it will interract with NOMAD since it needs the cost function value only. So far there's 3 types of cost function implemented, one from the Larachi, L1 ad L2. To tune parameters, the cost function compare the calculated counts with the Monte Carlo technique and the measured counts that are provided in the .experimental file.

tuning : Enable to tuning parameters with NOMAD through showing the cost function in terminal
Options : true or false
cost function type : Type of cost function to evaluate
Options : Larachi, l1 or l2

Larachi cost function :
$f=\sum_{i=n}^{N}\left(\frac{C_i - M_i}{C_i + M_i}\right)^2$

L1 cost function :
$f=\frac{1}{N}\sum_{i=n}^{N}\left|C_i - M_i\right|$

L2 cost function :
$f=\frac{1}{N}\sum_{i=n}^{N}\left(C_i - M_i\right)^2$
experimental data file : Filename of the text file with experimental/artificial counts
Options : Any text file with .experimental extension with the required header : experimental_counts

# --------------------------------------------------
# Tuning with NOMAD
#---------------------------------------------------
subsection parameter tuning
	set tuning                           = true
	set cost function type               = larachi
	set experimental data file           = noisy_counts.experimental
end

Reconstruction parameters

refinement : Set the highest refinement level of the grid (limited by RAM capacity)
Options : Any positive integer
coarse mesh level : Set the refinement level of the coarse mesh which is the first level for research throught cells
Options : Any positive integer <= refinement
reconstruction counts file : Filename of the text file with reconstruction counts
Options : Any text file with .reconstruction extension with the required header :
detector_counts_0 detector_counts_1 ... detector_counts_n
export reconstruction positions file : Filename of the .csv or .dat file for results exportation
Options : Any filename with .csv or .data extension
analyse positions : Enable to analyse the status of final cells of reconstructed positions
Options : true or false

Depending of flags associated to the final best cell, it generates a status :

Status 0 : The final cell for the reconstructed position contains the real position
Status 1 : The final cell for the reconstructed position contains the real position but required the cost function use
Status 2 : The final cell for the reconstructed position contains the real position but is not at the refined level
Status 3 : The final cell for the reconstructed position contains the real position but required the cost function use and is not at the refined level
Status 4 : The final cell for the reconstructed position does not contain the real position
Status 5 : The final cell for the reconstructed position does not contain the real position and required the cost function use
Status 6 : The final cell for the reconstructed position does not contain the real position and is not at the refined level
Status 7 : The final cell for the reconstructed position does not contain the real position, required the cost function use and is not at the refined level

known positions file : Filename of the text file which contains the known/real positions to use analyse position
Options : Any text file with .known extension with the required header : positions_x positions_y positions_z

# --------------------------------------------------
# Particle reconstruction
#---------------------------------------------------
subsection reconstruction
    set refinement                              = 6
    set coarse mesh level                       = 1
    set reconstruction counts file              = counts.reconstruction
    set export reconstruction positions file    = reconstruction.csv
    set analyse positions                       = true
    set known positions file                    = positions.known
end

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