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 of plastic organic scintillators. POLIMI uses electron equivalent light output (MeVee) for simulating  detector responses. I assumed the detectors have a neutron energy deposition threshold of 0.2 MeV, giving an equivalent light output threshold of 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.
-Neutron energy deposition from collisions with both hydrogen and carbon are converted to electron equivalent light output (MeVee). All neutron collisions that occur within the pulse collection time window of 10 ns of one another are summed together. 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.
+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.
-=Statistics=
+=Simulation source=
-n-n correlation was not simulated, as source particles were emitted isotropically, one by one. Nonetheless, given a fission rate and neutron multiplicity, a theoretical n-n coincidence rate can be estimated to provide a quantity that can be compared against the simulated crosstalk rate. This rate can be described as the rate of n-n events if the fission neutrons were emitted together uncorrelated and isotropic. This rate is estimated from the simulation as follows:
+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>R_{nn}=f*\nu(\nu-1)*N(N-1)*P_{d}^{2}</math>
+[[File:POLIMI Correlation.png|750px]]
-:<math>f</math> is the fission rate,
-:<math>\nu</math> mean neutron multiplicity,
-:<math>N</math> in the number of detectors,  and
-:<math>P_{d}</math> is the probability that a single neutron registers a hit in a single given detector. This value can be calculated directly from the simulation: <math>P_{d}=\frac{\text{total number of single hits}}{N*(\text{total number of src neutrons})}</math>
+=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.
-The crosstalk rate, <math>R_{X}</math>, simply scales proportionally with neutron multiplicity, fission rate, and the number of detectors. The estimated crosstalk rate is given by:
+[[File:CrosstalkVScoincidence.png|750px]]
-<math>\displaystyle R_{X}=f*\nu*N*P_{X}</math>
+=MCNP POLIMI input deck=
+[[File:POLIMICrossTalkSimulation2017.txt]]
-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{R_{nn}}{R_X}=\frac{(\nu-1)*(N-1)*P_{d}^{2}}{P_{X}}</math>
-I'm uncertain about the exact value for neutron multiplicity, so I will assume it's equal to 2, since this value is reasonable and serves as a worst case scenario.
-=Result=
-Out of <math>10^8</math> source particles there were <math>3.236572\times10^6</math> singles and <math>5.074 \times10^3</math> crosstalk events. This gives a signal-to-noise-ratio (defined above) of 8.6.
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Difference between revisions of "CrossTalk"