Latest revision as of 21:58, 22 February 2017

Old simulations

crosstalk_simulation_2016

Simulation geometry

An array of 6 detectors are placed radially at a distance of 1 meter from a correlated CF-252 source. The image below shows a top down view of the simulation geometry. The detector setups have a vertical extent of 30".

Simulation detector physics

The detector physics used in the simulation are MCNP-POLIMI's default treatment for plastic organic scintillators. POLIMI uses electron equivalent light output (MeVee) for simulating detector response. I assumed the detectors have a neutron energy deposition threshold of 0.2 MeV, giving an equivalent light output threshold of 0.03 MeVee.

Neutron energy deposition from collisions with both hydrogen and carbon are converted to electron equivalent light output (MeVee). All neutron collisions that occur within a pulse collection time window of 10 ns of each other are converted to MeVee and summed. If the cumulative light output of a pulse exceeds the 0.03 MeVee threshold, then a detection is registered. The value 0.03 MeVee was chosen because it corresponds to a mean neutron energy deposit of 0.2 MeV. The detectors in the simulation had a 55% efficiency for detecting CF-252 neutrons.

Simulation source

POLIMI is used to simulate a correlated CF-252 SF source. The source neutrons are correlated by angle, energy, and multiplicity. The mean multiplicity of the source is 2.7 neutrons/fission. A correlated n-n opening angle distribution (shown below) is produced by dividing the opening angle distribution of neutrons selected from single fissions, by the opening angle distribution of neutrons selected from separate fissions.

Simulation results

The number of n-n coincidences was a factor of 36 times greater than the number of n-crosstalk coincidences. n-n coincidence is defined as an event as two or more neutrons from the same fission registering a hit in two different detectors. If two neutrons are detected in coincidence, then that makes one n-n opening angle, three coincident neutrons makes three n-n opening angles, four neutrons makes six opening angles, and so on. An n-crosstalk coincidence event is defined as a singe source neutron (or any secondaries it produces) registering a hit in two different detectors.

MCNP POLIMI input deck

File:POLIMICrossTalkSimulation2017.txt

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-=Geometry=
+=Old simulations=
-An array of 6 detectors are placed radially at a distance of 1 meter from an uncorrelated 252-CF source.  The image below shows a top down view of the simulation geometry. The detector setups have a vertical extent of 30".
+[[crosstalk_simulation_2016]]
+=Simulation geometry=
+An array of 6 detectors are placed radially at a distance of 1 meter from a correlated CF-252 source.  The image below shows a top down view of the simulation geometry. The detector setups have a vertical extent of 30".
-[[File:GeomEdited.png|750 px]]
+[[File:Crosstalkgeom2017.png|750 px]]
-=Detector physics=
+=Simulation detector physics=
-The detector physics used in the simulation is MCNP-POLIMI's default treatment for plastic organic scintillators. POLIMI uses electron equivalent light output (MeVee) for simulating  detector response. Assuming the detectors have a energy deposition threshold of 0.2 MeV, the corresponding threshold, in electron equivalent light output, becomes 0.03 MeVee.
+The detector physics used in the simulation are MCNP-POLIMI's default treatment for plastic organic scintillators. POLIMI uses electron equivalent light output (MeVee) for simulating detector response. I assumed the detectors have a neutron energy deposition threshold of 0.2 MeV, giving an equivalent light output threshold of 0.03 MeVee.
-==Summary==
+Neutron energy deposition from collisions with both hydrogen and carbon are converted to electron equivalent light output (MeVee). All neutron collisions that occur within a pulse collection time window of 10 ns of each other are converted to MeVee and summed. If the cumulative light output of a pulse exceeds the 0.03 MeVee threshold, then a detection is registered. The value 0.03 MeVee was chosen because it corresponds to a mean neutron energy deposit of 0.2 MeV. The detectors in the simulation had a 55% efficiency for detecting CF-252 neutrons.
-Neutron energy deposition from collisions with hydrogen and carbon are converted to electron equivalent light output (MeVee) by MCNP-POLIMI. Neutron collisions that all occur within a pulse collection time of 10 ns of each other are converted to MeVee and cumulated. If the cumulative light output exceeds 0.03 MeVee then it is considered a detection.  The value 0.03 MeVee was chosen because it corresponds to a mean neutron energy deposit of 0.2 MeV.
-==Detector response==
+=Simulation source=
-The electron equivalent (MeVee) conversion functions for neutrons were measured for plastic (BC 420) scintillators as a function of neutron energy deposit, <math>E_{n}</math>. For deposit on hydrogen the measurements fit the following quadratic function:
+POLIMI is used to simulate a correlated CF-252 SF source. The source neutrons are correlated by angle, energy, and multiplicity. The mean multiplicity of the source is 2.7 neutrons/fission.  A correlated n-n opening angle distribution (shown below) is produced by dividing the opening angle distribution of neutrons selected from single fissions, by the opening angle distribution of neutrons selected from separate fissions.
-<math>L=0.036E_{n}^{2}+0.125E_{n}</math>
+[[File:POLIMI Correlation.png|750px]]
-and for deposit on carbon:
+=Simulation results=
+The number of n-n coincidences was a factor of 36 times greater than the number of n-crosstalk coincidences. n-n coincidence is defined as an event as two or more neutrons from the same fission registering a hit in two different detectors. If two neutrons are detected in coincidence, then that makes one n-n opening angle, three coincident neutrons makes three n-n opening angles, four neutrons makes six  opening angles, and so on. An n-crosstalk coincidence event is defined as a singe source neutron (or any secondaries it produces) registering a hit in two different detectors.
+[[File:CrosstalkVScoincidence.png|750px]]
-<math>L=0.02E_{n}</math>
+=MCNP POLIMI input deck=
+[[File:POLIMICrossTalkSimulation2017.txt]]
-=Statistics=
-The correlation rate will depend on the number of detectors, <math>N</math>, the mean neutron multiplicity, <math>\nu</math>, the fission rate, <math>f</math>, and the probability that a given detector registers a hit from a single source neutron, <math>P_{d}</math>.  <math>P_{d}</math> is assumed to be the same for all detectors and is calculated from the simulation data as follows:
-<math>P_{d}=\frac{\text{total number of single hits}}{N*(\text{total number of src neutrons})}</math>
-The n-n correlation rate, <math>R_{nn}</math>, can be estimated as follows:
-<math>R_{nn}=f*\nu(\nu-1)*N(N-1)*P_{d}^{2}</math>
-The crosstalk rate, <math>R_{X}</math>, will simply scale proportionally with neutron multiplicity, fission rate, and the number of detectors. The estimated crosstalk rate is:
-<math>\displaystyle R_{X}=f*\nu*N*P_{X}</math>
-where <math>P_{X}</math> is the probability of crosstalk per source neutron, which is calculated directly from the simulation result:
-<math>P_{X}=\frac{\text{total number of cross talk events}}{\text{total number of src neutrons}}</math>
-In order to quantify the amount of crosstalk contamination, I define a 'signal-to-noise ratio' equal to the ratio between the estimated signal and crosstalk rates.
-<math>SNR=\frac{(\nu-1)*(N-1)*P_{d}^{2}}{P_{X}}</math>
-I'm uncertain about the exact value for neutron multiplicity, so I assume it's equal to 2, since this is reasonable and serves as a worst case scenario.
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Difference between revisions of "CrossTalk"