Neutron imaging has been recognized as one of the most powerful tools for conducting nondestructive inspection of a wide range of materials. We first proposed the idea of a superconducting neutron detector called a current-biased kinetic inductance detector (CB-KID) [1] and reported systematic investigations of the CB-KID characteristics to optimize the operating conditions in recent years [2,3]. A delay-line technique of the four-terminal CB-KID was successful in achieving neutron imaging with a spatial resolution of 16 µm [4]. We revealed that neutron transmission images of practical test samples (various different sized Gd islands) with CB-KID were in good accordance with SEM images [5]. It is a particular advantage of CB-KID to be able to choose a tunable pixel size for analyses. Since neutrons behave as waves, they provide information of the wave-length sensitive properties of materials. In this paper, we intend to examine the CB-KID performance for investigating Bragg-edge spectra from restricted areas of neuron transmission of materials. As a typical test sample, we employed iron samples of the size 3×3×1.5 mm3. We can observe the most visible edges with a single sample area of 450×450 µm2, with a minimum time bin of 50 µs in ToF spectrum or a wave-length resolution of 0.0014 nm of each neutron pulse at beam line BL10 of J-PARC center. Our next interest is to determine how narrow we can choose a test area to investigate the Bragg edges. Because of the limitation of available beam time at the facility, we instead utilize the Ergodic theorem to obtain a visible transmission spectrum. In other words, we assumed that a long time average of a transmission spectrum can be evaluated by space average of independently-chosen area spectra with the same ensemble size. A Bragg edge spectrum as a sum of random 1000 ensembles (with an ensemble size 9×9 μm2) thus obtained has a good signal-to-noise ratio and can be fitted well with RITS (Rietveld Imaging of Transmission Spectra) program with Miller indices [6]. We consider that our CB-KID system is in principle able to analyze the Bragg edge of a sample as small as 9×9 μm2.
This work is partially supported by Grant-in-Aid for Scientific Research (Nos. JP16H02450, JP21H04666, JP21K14566) from JSPS
References
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[2] Vu T D, Iizawa Y, Nishimura K, Shishido H, Kojima K M, Oikawa K, Harada M, Miyajima S, Hidaka M,Oku T, Soyama K, Aizawa K, Koyama T and Ishida T 2019 J. Phys.: Conf. Ser. 1293 012051.
[3] Vu T D, Nishimura K, Shishido H, Harada M, Oikawa K, Miyajima S, Hidaka M, Oku T, Soyama K, Aizawa K, Kojima K M, Koyama T, Malins A, Machida M and Ishida T 2019 J. Phys.: Conf. Ser. 1293 012051
[4] Iizawa Y, Shishido H, Nishimura K, Vu T D, Kojima K M, Koyama T, Oikawa K, Harada M, Miyajima S, Hidaka M, Oku T, Soyama K, Aizawa K, Suzuki S Y and Ishida T 2019 Supercond. Sci. Technol. 32 12500
[5] Vu T D, Shishido H, Aizawa K, Kojima K, Koyam T, Oikawa K, Harada M, Oku T, Soyama K, Miyajima S, Hidaka M, Suzuki S Y, Tanaka M M, Malins A, Machida M, Kawamata S, Ishida T 2021 Nucl. Instrum. Meth. Phys. Res. A 1006 165411
[6] Sato H 2018 J. Imaging 4 7
Keywords: Superconducting neutron detector, CB-KID, Bragg-edge, Neutron image