| 研究実績の概要 |
In earlier our finding, the event intensity of neutron detections increased remarkably as a function of operating temperature using a superconducting Nb-meanderline detector with a boron-10 conversion layer [1]. As a target of this project, we achieved the improvement of the detection efficiency at 1 meV from 0.7 % to 3 % by increasing temperature from 4K to 8.2K and increased from 0.9 % to 2.7% when increased thickness of Boron layer from 70nm to 220 nm at an operating temperature of 7.9K.
This fiscal year, we demonstrated that our detector can be used to investigate the Bragg-edge studies of materials even for a very narrow sample area [2] and observations of nuclear resonance dips were conducted even at epi-thermal neutron energies [3]. We attempted to build a new cryostat with a concaved window to be used for measurements, where test samples at room temperature can be placed at a close distance from a cryogenic detector. This was successful in measuring transmission imaging with room-temperature test samples, and could be used for various measurements in the next fiscal year.
1. T. D. Vu, et al., Kinetic inductance neutron detector operated at near critical temperature, Journal of Physics: Conference Series 1590 (2020) 012036.
2. T D. Vu, et al., Narrow-area Bragg-edge transmission of iron samples using superconducting neutron sensor, Journal of Physics: Conference Series, in press.
3. H. Shishido, T. D. Vu (2/15), et al., Neutron imaging toward epithermal regime using a delay line current-biased kinetic-inductance detector, Journal of Physics: Conference Series, in press.
|
| 今後の研究の推進方策 |
The event position in the meanderline is determined by identifying a signal-source segment, but it takes 200 ps for an electromagnetic-wave signal to transverse through a single segment. We plan to improve a temporal resolution of the readout circuit (named as the Kalliope-DC circuit) to 30 ps, which is much better than a current temporal resolution of 1 ns. Therefore, it would further improve a spatial resolution of our superconducting imaging sensor.
It is a primitive idea that the detection efficiency is mainly specified by the spatial covering fraction of the superconducting Nb meanderlines in the sensitive area because it has a space between superconducting segments. It is necessary to know how large a size of hot spot is in the meanderlines. The hot-spot size is determined by a superconducting property as well as local heat conduction, and is dependent on an operating temperature. A detection efficiency can be improved when a hot spot size is larger than a period of the superconducting segments. A detection efficiency as a function of operating temperature would be a clue to understand the operating principle of our superconducting neutron detector.
Our device is fabricated using a superconductive foundry of National Institute of Advanced Industrial Science and Technology (AIST). We plan to optimize a fabrication process to minimize possible defects in meanderlines because defects of neutron detector may give artifact patterns in the neutron transmission images due to scattering of transmission signals in superconducting delay lines.
|
| 次年度使用額が生じた理由 |
We are going to buy a new PC for new Kalliope with Ubuntu os, a Function Generator for testing kalliope system.
Cost for fabricating new neutron detector and upgrade Kalliope board; Buy some electronics parts (connectors, HDDs, cables, etc).
Travel fee (Osaka=Tokai) for preparing samples and discussing with colleagues; ISS2022 Conference fee; ASC 2022 6 days, USA; publication fees
|
