A novel instrument and method for real time directional neutron spectrometry
File(s)
Author(s)
Reed, Nick
Type
Thesis
Abstract
In the modern workplace, radiation dosimetry is necessary to quantify the risk to human health from ionising radiation. The most accurate metric for radiation dose, effective dose, cannot currently be measured in real-time, only estimated in offline analysis. This thesis details the development of nFacet 3D, a novel radiation dosimeter sensitive to both energy and direction of the incident radiation field and as such capable of estimating effective dose in real time.
nFacet 3D is a segmented scintillation detector sensitive to neutrons, gammas, and muons. A detailed technical overview of the detector is given, including a simulation study performed to optimise the detector design for a future iteration. The sensitivity of this instrument to the energy and direction of incident radiation is demonstrated, and a thorough series of calibration measurements and techniques are outlined in order to develop the necessary precision for a dose measurement.
The distribution of neutron capture events in the detector encodes the energy of the incident radiation field. This was exploited to discriminate between different source energies, and the simulated response of the detector to different radionuclide sources was used to train an artificial neural network to reconstruct the incident radiation fluence. The ambient dose equivalent can be subsequently determined through application of fluence-to-dose conversion coefficients. The performance of this method was validated in lab and workplace environments, showing potential but also highlighting key areas for improvement.
Finally, a proof-of-concept study was performed to investigate using this instrument to perform a directional decomposition of neutron fields into six different directions of incidence and determine the energy spectrum in each of these directions. This decomposition was used to produce a first estimate of effective dose. Initial results showed potential and further development of this method is well-motivated to better characterise neutron fields and estimate effective dose.
nFacet 3D is a segmented scintillation detector sensitive to neutrons, gammas, and muons. A detailed technical overview of the detector is given, including a simulation study performed to optimise the detector design for a future iteration. The sensitivity of this instrument to the energy and direction of incident radiation is demonstrated, and a thorough series of calibration measurements and techniques are outlined in order to develop the necessary precision for a dose measurement.
The distribution of neutron capture events in the detector encodes the energy of the incident radiation field. This was exploited to discriminate between different source energies, and the simulated response of the detector to different radionuclide sources was used to train an artificial neural network to reconstruct the incident radiation fluence. The ambient dose equivalent can be subsequently determined through application of fluence-to-dose conversion coefficients. The performance of this method was validated in lab and workplace environments, showing potential but also highlighting key areas for improvement.
Finally, a proof-of-concept study was performed to investigate using this instrument to perform a directional decomposition of neutron fields into six different directions of incidence and determine the energy spectrum in each of these directions. This decomposition was used to produce a first estimate of effective dose. Initial results showed potential and further development of this method is well-motivated to better characterise neutron fields and estimate effective dose.
Version
Open Access
Date Issued
2023-11-10
Date Awarded
01/04/2024
License URL
Advisor
Vacheret, Antonin
Taylor, Graeme
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)