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Development of a Time-resolved Neutron Imaging Detector Based on the {mu}PIC Micro-Pixel Chamber

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 Added by Joseph Parker
 Publication date 2013
  fields Physics
and research's language is English




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We have developed a prototype time-resolved neutron imaging detector employing a micro-pattern gaseous detector known as the micro-pixel chamber ({mu}PIC) coupled with a field-programmable-gate-array-based data acquisition system. Our detector system combines 100{mu}m-level spatial and sub-{mu}s time resolutions with a low gamma sensitivity of less than 10^-12 and high data rates, making it well suited for applications in neutron radiography at high-intensity, pulsed neutron sources. In the present paper, we introduce the detector system and present several test measurements performed at NOBORU (BL10), J-PARC to demonstrate the capabilities of our prototype. We also discuss future improvements to the spatial resolution and rate performance.



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We have developed a prototype time-resolved neutron imaging detector employing the micro-pixel chamber (muPIC), a micro-pattern gaseous detector, coupled with a field programmable gate array-based data acquisition system for applications in neutron radiography at high-intensity neutron sources. The prototype system, with an active area of 10cm x 10cm and operated at a gas pressure of 2 atm, measures both the energy deposition (via time-over-threshold) and 3-dimensional track of each neutron-induced event, allowing the reconstruction of the neutron interaction point with improved accuracy. Using a simple position reconstruction algorithm, a spatial resolution of 349 +/- 36 microns was achieved, with further improvement expected. The detailed tracking allows strong rejection of background gamma-rays, resulting in an effective gamma sensitivity of 10^-12 or less, coupled with stable, robust neutron identification. The detector also features a time resolution of 0.6 microseconds.
We present a detailed study of the spatial resolution of our time-resolved neutron imaging detector utilizing a new neutron position reconstruction method that improves both spatial resolution and event reconstruction efficiency. Our prototype detector system, employing a micro-pattern gaseous detector known as the micro-pixel chamber ({mu}PIC) coupled with a field-programmable-gate-array-based data acquisition system, combines 100{mu}m-level spatial and sub-{mu}s time resolutions with excellent gamma rejection and high data rates, making it well suited for applications in neutron radiography at high-intensity, pulsed neutron sources. From data taken at the Materials and Life Science Experimental Facility within the Japan Proton Accelerator Research Complex (J-PARC), the spatial resolution was found to be approximately Gaussian with a sigma of 103.48 +/- 0.77 {mu}m (after correcting for beam divergence). This is a significant improvement over that achievable with our previous reconstruction method (334 +/- 13 {mu}m), and compares well with conventional neutron imaging detectors and with other high-rate detectors currently under development. Further, a detector simulation indicates that a spatial resolution of less than 60 {mu}m may be possible with optimization of the gas characteristics and {mu}PIC structure. We also present an example of imaging combined with neutron resonance absorption spectroscopy.
A micro time-projection-chamber (micro-TPC) with a detection volume of 23*28*31 cm^3 was developed, and its fundamental performance was examined. The micro-TPC consists of a micro pixel chamber with a detection area of 31*31 cm^2 as a two-dimensional imaging device and a gas electron multiplier with an effective area of 23*28 cm^2 as a pre-gas-multiplier. The micro-TPC was operated at a gas gain of 50,000, and energy resolutions and spatial resolutions were measured.
The China Spallation Neutron Source (CSNS) operates in pulsed mode and has a high neutron flux. This provides opportunities for energy resolved neutron imaging by using the TOF (Time Of Flight) approach. An Energy resolved neutron imaging instrument (ERNI) is being built at the CSNS but significant challenges for the detector persist because it simultaneously requires a spatial resolution of less than 100 {mu}m, as well as a microsecond-scale timing resolution. This study constructs a prototype of an energy resolved neutron imaging detector based on the fast optical camera, TPX3Cam coupled with an image intensifier. To evaluate its performance, a series of proof of principle experiments were performed in the BL20 at the CSNS to measure the spatial resolution and the neutron wavelength spectrum, and perform neutron imaging with sliced wavelengths and Bragg edge imaging of the steel sample. A spatial resolution of 57 {mu}m was obtained for neutron imaging by using the centroiding algorithm, the timing resolution was on the microsecond scale and the measured wavelength spectrum was identical to that measured by a beam monitor. In addition, any wavelengths can be selected for the neutron imaging of the given object, and the detector can be used for Bragg edge imaging. The results show that our detector has good performances and can satisfy the requirements of ERNI for detectors at the CSNS
In the framework of the ATTRACT-uRANIA project, funded by the European Community, we are developing an innovative neutron imaging detector based on micro-Resistive WELL ($mu$ -RWELL) technology. The $mu$ -RWELL, based on the resistive detector concept, ensuring an efficient spark quenching mechanism, is a highly reliable device. It is composed by two main elements: a readout-PCB and a cathode. The amplification stage for this device is embedded in the readout board through a resistive layer realized by means of an industrial process with DLC (Diamond-Like Carbon). A thin layer of B$_4$C on the copper surface of the cathode allows the thermal neutrons detection through the release of $^7$Li and $alpha$ particles in the active volume. This technology has been developed to be an efficient and convenient alternative to the $^3$He shortage. The goal of the project is to prove the feasibility of such a novel neutron detector by developing and testing small planar prototypes with readout boards suitably segmented with strip or pad read out, equipped with existing electronics or readout in current mode. Preliminary results from the test with different prototypes, showing a good agreement with the simulation, will be presented together with construction details of the prototypes and the future steps of the project.
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