Research opportunities with compact accelerator-driven neutron sources

A neutron imaging facility, PKUNIFTY, based on a radio frequency quadrupole (RFQ) accelerator-driven compact neutron source, presently under construction at the Peking University, is described. It consists of a deuteron linear accelerator, a neutron target–moderator–reflector assembly, and a thermal neutron imaging system. Neutrons are generated via the deuteron–beryllium reaction with an expected fast-neutron yield of 3×10 12  n/s. The thermal neutron flux on the imaging plane is 5×10 5  n/cm 2 /s at a nominal L/D ratio of 50, and the L / D ratio can be selectable over a range of 25–200. The corresponding n/γ ratio is close to or higher than 1×10 10  n/cm 2 /Sv. The field of view is 20 cm×20 cm at 2 m downstream of the collimator entrance aperture where the thermal neutron flux uniformity is better than 7%. The effective Cd ratio can be tuned by using a light chopper and neutron time-of-flight technique without excessive sacrifice of the thermal neutron flux.

PKUNIFTY: A neutron imaging facility based on an RFQ accelerator

Neutron imaging has been recognized to be very useful to investigate inside of materials and products that cannot be seen by X-ray. New imaging methods using the pulsed structure of neutron sources based on accelerators has been developed also at compact accelerator-driven neutron sources and opened new application fields in neutron imaging. The world’s first dedicated imaging instrument at pulsed neutron sources was constructed at J-PARC in Japan owing to the development of such new methods. Then, usefulness of the compact accelerator-driven neutron sources in neutron science was recognized and such facilities were newly constructed in Japan. Now, existing and new sources have been used for neutron imaging. Traditional imaging and newly developed pulsed neutron imaging such as Bragg edge transmission have been applied to various fields by using compact and large neutron facilities. Here, compact accelerator-driven neutron sources used for imaging in Japan are introduced and some of their activities are presented.

https://www.mdpi.com/2313-433X/4/4/55/pdf

Neutron Imaging at Compact Accelerator-Driven Neutron Sources in Japan

Multi-objective particle swarm optimization algorithms (MOPS) are used successfully to solve real-life optimization problems. The multi-objective algorithms based on particle swarm optimization (PSO) have seen various adaptations to improve convergence to the true Pareto-optimal front and well-diverse non-dominated solution. In some cases, the values of the MOPS control parameters need to be fine-tuned while solving a specific multi-objective optimization problem. It is challenge to correctly fine-tune the value of the PSO control parameters when the true non-dominated solutions are not known as in case of a real-life optimization problem. To address this challenge, a multi-objective particle swarm optimization algorithm that uses constant PSO control parameters was developed. The new algorithm called NF-MOPSO is capable of solving different multi-objective optimization problems without the need of fine-tuning the value of the PSO control parameters. The NF-MOPSO enhances the convergence to the true Pareto-optimal front and improves the diversity of Pareto-optimal using the same fixed values for all the PSO control parameters. The NF-MOPSO uses constant values of the PSO control parameters such as acceleration coefficients $$c_{1}$$
 and $$c_{2}$$
 , and inertia weight $$\omega$$
 . A Gaussian mutation is applied to the position of particles to increase diversity while a penalty function is used as constraint mechanism. The algorithm has been tested on 45 well-known benchmark test functions using four performance metrics. The test results demonstrate the capability of the NF-MOPSO to solve different multi-objective optimization problems using the same value of the PSO control parameters. The capability of the NF-MOPSO was demonstrated in real-life optimization problem by solving a multi-objective optimization problem of a neutron radiography collimator. The results of collimator optimization showed that the optimizer was able to provide a set of Pareto optimal solutions from which the geometrical design parameters of a collimator could be retrieved for given application.

A multi-objective particle swarm for constraint and unconstrained problems

Neutrons have been used in a wide field of applications by using various neutron sources. Material science is one of the widest research fields. The activity is supported by nuclear research reactors and high-intensity spallation neutron sources based on a high-intensity proton accelerator. However, it is desired to perform a measurement when researchers want to do and to perform adventuresome experiments that have not yet confirmed its importance. Furthermore, trial and error measurements are necessary to improve a measurement method. Compact accelerator-driven neutron sources are suitable for such usage and in some cases can complement the measurement at a large facility. The use of the compact neutron source has sometimes led to new methods. Other than material science, a new application of soft error acceleration test has been performed at the compact accelerator-driven neutron sources. Another neutron application is radiation therapy called as boron neutron capture therapy. In this field, nuclear reactor neutron sources have been used but many of them shut down. It was desired to construct the BNCT facility near a hospital. Therefore, BNCT facilities based on the compact accelerator have been constructed in the world. Here, the neutron sources and new methods and applications developing at compact accelerator-driven neutron sources are introduced.

/pdf/neutron-applications-developing-at-compact-accelerator-i39p504u5x.pdf

Neutron applications developing at compact accelerator-driven neutron sources

The Peking University Neutron Imaging Facility (PKUNIFTY) is a Radio Frequency Quadruple (RFQ) accelerator based system. The fast neutrons are produced by 2 MeV deuterons bombarding beryllium target. The moderator, reflector, shielding and collimator have been optimized with Monte–Carlo simulation to improve the neutron beam quality. The neutrons are thermalized in water cylinder of Φ 26×26 cm 2 with a polyethylene disk in front of Be target. The size of deuteron beam spot is optimized considering both the thermal neutron distribution and the demand of target cooling. The shielding is a combination of 8 cm thick lead and 42 cm thick boron doped polyethylene. The thermal neutrons are extracted through a rectangular inner collimator and a divergent outer collimator. The thermal neutron beam axis is perpendicular to the D + beam line in order to reduce the fast neutron and the γ ray components in the imaging beam. When the neutron yield is 3×10 12  n/s and the L / D is 50, the thermal neutron flux is 5×10 5  n/cm 2 /s at the imaging plane, the Cd ratio is 1.63 and the n/γ ratio is 1.6×10 10  n/cm 2 /Sv.

Neutronic design and simulated performance of Peking University Neutron Imaging Facility (PKUNIFTY)

Progress of PKUNIFTY – a RFQ Accelerator based Neutron Imaging Facility at Peking University

Neutron radiography with compact accelerator at Peking University: Problems and solutions☆

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PKUNIFTY: A neutron imaging facility based on an RFQ accelerator

Neutronic design and simulated performance of Peking University Neutron Imaging Facility (PKUNIFTY)

Progress of PKUNIFTY – a RFQ Accelerator based Neutron Imaging Facility at Peking University

Neutron radiography with compact accelerator at Peking University: Problems and solutions☆