International Society for Neutron Radiology (ISNR)

Professional Certification

PhD of Enginnering, Tokyo Institute of Technology, 1985.

Career

  • Assiciate professor. Rikkyo University, -1992;
  • Professor, Rikkyo University, -2001;
  • Emeritus professor, Rikkyo University, 2001 (current).

Main activities

  • Member of Executive Committee and Domestic Program Committee of The third World Conference, Osaka, (1989).
  • Chairman of The Second International Topical Meeting on Neutron Radiography Systm Design and Characterizasion, Yokosuha and Editor of The Proceedings (1996).
  • Member of Co-Chairman of The Third International Topical Meeting on Neutron Radiography, Lucerne (1998).
  • Member of Organization Committee (Program Chairman) of The Sixth World Conference, Osaka, 1999. and Editor of "Neutron Radiography (6) Gordon and Brech (2001)".
  • Member of Organizing Committee of The Sixth International Topical Meeting on Neutron Radiography, Kobe (2008).

Main works

He started research of neutron radiography using a handmade vertical collimator installed in the TRIGA-II reactor in Rikkyo University at 1984 [1]. After the success of the preliminary experiments a new versatile irradiation facility was installed in the No.2 tangential beam port of in the reactor, which have a changeable L/D value by using various diaphragm diameters (1 cm, 2.9 cm, 5 cm and 10 cm) and L value in the 4 m long shielded irradiation room [2. 3] at 1985. The port was also able to insert arbitrary filter materials at any desired position within the collimator sleeve.

When he had joined the neutron radiography group in the Second World Conference on Neutron Radiography, Paris, only a few papers were discussed quantitatively of the neutron images. Therefore, after the conference, he had been mainly interesting the basic science side, such as to establish how to quantitatively express and analyze an image, how to evaluate an inherent spatial resolution, how to determine a quantitative characteristics on neutron beam, and so on.

His first established study was simulation analysis of system transfer function (STF) of a screen-film system using a realistic Gd converter - X-ray film and the result were confirmed by experimental observation. The used parameters in the analyses were converter thickness, emulsion thickness, coating film thickness and a converter-film separation. As the fruit, the analysis concluded that the shape of modulation transfer function (MTF) was close to the Lorentzian shape, and the theoretical inherent resolution was evaluated to be 17 μm for the Gd-Kodak (SR-5) film system [4].

Since the beam quality was tested on the TRIGA II, he had extended the performance test for many facilities in World as well as in Japan. And he had measured the L/D and effective D values of such beams using the L/D device [5] (The Kobayashi Method [6]), and characterized quality of neutron beams, effective neutron energy, with various beam set up conditions using the Beam Quality Indicator (BQI) [7, 8]. The measured effective energies of beams using the BQI were summarized on elsewhere [9, 10, 11]. Various neutron beams were inspected in worldwide and inspected 63 beams were 9 beams for non-filtered facilities, 32 non-cooled filtered beams in the 16 facilities, one cooled filtered beam, and 5 neutron guide output beams [11]. It was strongly recommended that an undefined <i>thermal</i> neutron beam is not necessarily the same thermal spectrum and give image with the same quality. One of fruits of the BQI study was that effective energies of many thermal neutron beams were frequently shifted toward lower energy side using various filters, which were originally intended to reduce gamma ray background. It is proved that some beams were turn to good sub-thermal neutron beams.

Since the beginning of his research, many new imaging devices were developed and proposed, such as a dry film, several commercially available fluorescence materials including a <i>pyrolytic boron nitrate</i> plate [12], various imaging cameras, and so on. Among those imaging studies, a cooled CCD camera was the first applied to get neutron image at 1989 [3, 13]; the first CT image using the CCD camera was also obtained in 1992 [14]. Among the several CT studies, a statistical approach of quality evaluation of CT image was theoretically analyzed. The result proved that the statistical character is well explained by the <i>log-transmittance</i> (an integrated CT values along a projection line) [15].

New imaging methods were also proposed and preliminary tested such as a stereoscopic imaging [2], a new tomography technique using imaging plate [13], scattered radiation imaging [16], and an imaging using an alpha-Al2O3:C+Gd2O3 optical stimulated luminescent material [17].

A neutron sensitive photosimulated luminescence device (IP: imaging plate) was applied to neutron radiography in 1999. The performance was analyzed in details and proved that the material should become an excellent imaging device [18]. Basic performances of IPs were published elsewhere [19, 20], and the items studied performances were covered spatial resolution, linearity, dynamic range, statistical character, repeated readout characteristics, fading effects, responses for various radiation including alpha, beta, gamma and X-rays. The IP was proved excellent static imaging device for neutrons. It is well known that the IP is essential imaging tool today.

Among his research works, he summarized some requirements and basis of design for a future neutron beam facility [21], and also important parameters of relating image quality [22].

His studies were carried out mainly using the TRIGA-II Reactor in Rikkyo University (unfortunately the reactor was not operating and becomes into the decommissioning phase), and many experiments were implemented in the KUR in Kyoto University, and the JRR-3M in Japan Atomic Energy Agency (JAEA) in Japan.

References

[1]. H. Kobayashi et al., Neutron Radiography (2), 129-136 (1987)
[2]. H. Kobayashi et al., Neutron Radiography (3), 315-324 (1990)
[3]. H. Kobayashi, First Int. Topical Meeting on Neutron Radiography System Design and Characterization, Pembroke, 189-208 (1994)
[4]. H. Kobyashi, Neutron Radiography (3), 893-902 (1990)
[5]. H. Kobyashi and H. Wakao, Neutron Radiography (3), 885-892 (1990)
[6]. J. C. Domanus ed., Practical Neutron Radiography, (Kulwer Academic Publ., 1992) 123-126
[7]. H. Kobayashi and Y. Kiyanagi, Nucl. Instr. Method, A377 52-57 (1996)
[8]. H. Kobayashi, 5th WCNR-Berlin, 313-320 (1997)
[9]. H. Kobayashi and M. Satoh, Nucl. Instr. Method, A424 1-8 (1999)
[10]. H. Kobayashi, Neutron Radiography (6), 11-21 (2001)
[11]. H. Kobayashi, Applied Rad. Isotopes 61, 443-449 (2004)
[12]. H. Kobayashi et al., Neutron Radiography (4), 771-778 (1994)
[13]. H. Kobayashi et al., Neutron Radiography (3), 421-428 (1990)
[14]. H. Kobayashi, Nucl. Instr. Methods, A377, 80-84 (1996)
[15]. H. Kobayashi et al., Nucl. Instr. Methods, A424, 221-228 (1999)
[16]. H. Kobayashi et al., IEEE Trans. Nucl. Sci. 52, No.1, 375-379 (2005)
[17]. H. Kobayashi et al., IEEE Trans. Nucl. Sci. 52, No.1, 360-363 (2005)
[18]. H. Kobayashi and M. Satoh, Nucl. Instr. Methods, A424, 1-8 (1999)
[19]. H. Kobayashi, Neutron radiography (6) 271-278 (2001)
[20]. H. Kobayashi, et al., Applied Rad. Isotopes 61, 573-578 (2004)
[21]. H. Kobayashi, Neutron radiography (6) 169-176 (2001)
[22]. H. Kobayashi, Neutron radiography (6) 11-21 (2001)

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