Development of a high-speed camera system for neutron imaging at a pulsed neutron source

doi:10.1016/j.nima.2012.08.079

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

Volume 697, 1 January 2013, Pages 77-83

https://doi.org/10.1016/j.nima.2012.08.079 Get rights and content

Abstract

A neutron energy resolved imaging system with a time-of-flight technique has been newly developed and installed at Japan Proton Accelerator Research Complex (J-PARC) with the aim to investigate more preciously and rapidly a spatial distribution of several elements and crystals in various kinds of materials or substances. A high-speed video camera (CMOS, 1300 k frame/s) equipped system allows to obtain TOF images consecutively resolved into narrow energy ranges with a single pulsed neutrons while conventional CCD camera imaging system could obtain only one TOF image in an arbitral neutron energy region in the pulsed neutron energy region from 0.01 eV to a few keV. Qualities of the images obtained with the system, such as spatial resolution (defined by modulation transfer function, 0.8 line-pairs/mm at En∼0.01 eV), dependence of the brightness on the neutron energy and measurement errors (∼2%) of the system were examined experimentally and evaluated by comparison with those of conventional imaging system. The results obtained in the experiments show that the system can visualize the neutron energy resolved images within a small error even at high speed.

Introduction

Neutrons are well known as an effective investigative probe for non-destructive testing and inspection in broad scientific and industrial disciplines including modern material sciences, nuclear engineering, and fundamental sciences. So far, conventional neutron imaging (radiography and tomography) methods using polychromatic neutrons without selecting neutron energy are mainly performed by utilizing the differences of the attenuation lengths of elements in a sample averaged over a broad neutron energy spectrum.

In recent years sophisticated imaging methods using the energy dependence of neutron attenuation lengths have been reported. Using Bragg Edge transmission, we can obtain spatial distributions of crystal structure and crystal-line phase [1], [2], [3], texture [4], [5], and strain [6], [7] in a polycrystalline material simultaneously and quantitatively. In this analysis, neutrons should be monochromized. The well-known method of monochromization is with the use of a velocity selector [8], [9] or mono-chronometer crystals [10]. In addition, pulsed neutron beam is alternative method to obtain neutron energy structures.

Previously, at the pulsed neutron source of LANCSE in U.S, PSI in Swiss and ISIS in U.K, energy dependent images were obtained by using a gated CCD camera and time-of-flight method [11], [12], [13]. Although this method has an advantage in flexibility of the neutron energy and the energy resolution comparing to the methods mentioned above, it is still required to repeat measurements by changing the neutron energy. On the other hand, two-dimensional detectors have also been developed [14], [15], [16], [17]. They demonstrated to obtain energy dependent images simultaneously by using a two-dimensional neutron detector. It is difficult, however, to achieve a spatial resolution of less than 0.1 mm and an adjustability of field-of-view (FOV).

In this study, an energy-resolved imaging-system with a high-speed video camera was newly developed for the pulsed neutron source in J-PARC. The system could obtain consecutive TOF images of an adjustability of field-of-view (FOV) without changing the neutron energy region. At Japan Research Reactor No. 3 Modified (JRR-3M) a neutron radiography system with a high-speed video camera had been developed for void fraction distribution researches [18], [19]. This system was modified to identify the neutron flight time, namely neutron energy, for each obtained image. It was also required to develop data processing techniques for huge amount of images. The neutron intensity of pulsed neutron sources is not enough to obtain good image with few pulses even though MW-class pulsed neutron sources are realized. Therefore, images for the same neutron energy need to be accumulated. Herein, the newly developed system and its fundamental performance including the data processing techniques are described.

This paper is organized as follows: Section 2 describes the present system, named SERIAL, at J-PARC, the results are summarized in Section 3, and the conclusions are described in Section 4.

Section snippets

Experimental setup

The SERIAL system has been developed at Beam Line no.10 (NOBORU) built in J-PARC [20], [21]. The accelerator at J-PARC consists of a 180 MeV linear accelerator (linac), a 3 GeV Rapid-Cycling Proton Synchrotron (RCS), and a 50 GeV Proton Synchrotron. The linac is to be modified to accelerate up to 400 MeV in the future. These accelerators provide proton beam at a frequency of 25 Hz to a spallation neutron source, which slowed down high-energy neutrons to thermal and cold neutrons by super-critical

Evaluation of data processing

In order to evaluate the obtained images, we investigated linearity of brightness of accumulated images and whether normalization on the transmission ratio images was to smear out the position dependence owing to anisotropy of incident neutron beam and/or hardware system appropriately.

First, images without object, B_s, were obtained with Δt≈250 μs. The pixel size of the images was 512×512 pixels. Fig. 3(a) shows the brightness for B_s[x][y] images as a function of the transverse position x, where y

Conclusion

In conclusion, we have developed a neutron energy resolved imaging system using high-speed video camera, which could obtain the consecutive TOF images at specific and arbitrary ranges of neutron energies with several cm FOV size. The present system, named SERIAL, reproduced the time-of-flight spectrum consistent to that taken by a ³He neutron detector for incident pulsed neutrons produced by J-PARC. The spatial resolution of the system was evaluated by experiments for the Gd line pair sample.

Acknowledgments

The present experiments were carried out at J-PARC of JAEA with the help of many supporting staff members. The authors gratefully acknowledge the generous support and meaningful discussions for neutron beam properties from Dr. Shinohara, Dr. Oikawa and Dr. Maekawa. We thank Dr. H. Iikura for his cooperation on sample preparations and Dr. Katagiri for his supports. These experiments were performed under the approval of the Neutron Science Program Review Committee (Proposal No.2009A0081, Proposal

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Development of a high-speed camera system for neutron imaging at a pulsed neutron source

Abstract

Introduction

Section snippets

Experimental setup

Evaluation of data processing

Conclusion

Acknowledgments

Nuclear Instruments & Methods A

Physica B

Nuclear Instruments & Methods A

Nuclear Instruments & Methods A

Physica B

Nuclear Instruments & Methods A

Nuclear Instruments & Methods A

Nuclear Instruments & Methods A

Radiation Measurements

Nuclear Instruments & Methods A

Proceedings of ICANS XV 1

Journal of Physics: Conference Series