| 研究領域 | 重力波天体の多様な観測による宇宙物理学の新展開 |
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| 研究課題/領域番号 |
24103004
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| 研究機関 | 東京大学 |
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研究代表者 |
ヴァギンズ マーク 東京大学, カブリ数物連携宇宙研究機構, 教授 (90509902)
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| 研究分担者 |
小汐 由介 岡山大学, 自然科学研究科, 准教授 (80292960)
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| 研究期間 (年度) |
2012-06-28 – 2017-03-31
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| キーワード | 宇宙線 / 重力波 / 超新星爆発 / ニュートリノ / ガドリニウム |
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| 研究実績の概要 |
The EGADS (Evaluating Gadolinium's Action on Detector Systems) laboratory is located one km underground in the Mozumi mine in northern Gifu-ken, near the Super-Kamiokande neutrino detector. Originally designed as an R&D test bed for studying the effects of dissolving gadolinium (Gd) salts in a water Cherenkov detector (Gd makes neutrons visible, which has many potential physics benefits), the purpose of this Kakenhi is to convert EGADS into the world's most advanced supernova neutrino detector.
FY2014 was primarily devoted to the rebuilding and recovery of EGADS following an unfortunate mixup during construction in 2013. All components inside the detector must be made of high-grade stainless steel or other non-reactive materials. However, a vendor's error led to one minor component, a several meter long length of structural support wire, being made of low-grade, non-stainless iron. After installation it rapidly corroded in the liquid environment inside the detector. Since even a few parts per billion of dissolved iron will ruin water transparency, about half of the year was spent carefully cleaning the rust out the detector, repassivizing the exposed stainless surfaces, and reassembling the detector using the originally specified materials.
The recovery has been a complete success, and since October 2014 the refurbished EGADS detector has been full of water (and gadolinium), and has been operating better than ever before. The detector has been carefully calibrated and data taking now takes place 24 hours a day without interruption.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
I feel that (2) is the correct answer for where the project stands: we are making excellent, steady progress toward our supernova detection goals. This is perhaps surprising, given the six months lost due to the cleanup and recovery of EGADS following the discovery of the bad structural wire.
However, following this repair we have emerged with a detector that not only works better than before, but even better than could have been reasonably expected. Only the delay keeps us from a grade of (1).
EGADS's all-important selective water filtration system, which keeps the water in the detector clean but does not remove the dissolved gadolinium, was upgraded during the battle against the rust. Now, thanks to this improved system, we have for the first time anywhere achieved - *with* dissolved gadolinium - salted water transparency equivalent to the ultrapure water in Super-Kamiokande. This is a major breakthrough, and will allow the highest possible efficiency for detection of supernova neutrinos. Indeed, EGADS now stands for Employing Gadolinium to Autonomously Detect Supernovas.
No one expected that Gd-loaded water (there are 400 kg of gadolinium sulfate dissolved in the 200-ton EGADS tank) would ever be as transparent at Super-K's ultrapure water, but that is what we are now seeing. This has powerful implications for this new Gd-loading technology, since extremely clear water is key to the success of all large water Cherenkov detectors.
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| 今後の研究の推進方策 |
Now that the detector itself is repaired and operating at peak efficiency, it is time to make sure the DAQ and data pipeline are equally capable.
This will involve a complete upgrade of the front-end electronics. To accomplish this upgrade - which will provide the deadtime-less and zero-energy-threshold functionality needed to literally collect every possible bit of information during a once-in-a-lifetime galactic supernova explosion - new readout boards for all 240 photomultiplier tubes in EGADS have been produced. These new, custom electronics modules (known as QBEE's) will be installed this year, at which point we will unquestionably have the most advanced supernova neutrino detector in the world.
We will then install a specialized realtime computer to receive and analyze every byte of data (include all PMT dark noise and radioactively induced backgrounds) as it is collected. It will filter the data in real time, and will be capable of immediately identifying a supernova signal as genuine thanks to the dissolved gadolinium, which acts like an amplifier for these signals.
The ultimate goal of this upgraded EGADS detector is to have the capability to alert the other members of this multimessenger Kakenhi that a supernova explosion is taking place in our galaxy within one second of the first neutrino's arrival in EGADS. Therefore, in addition to keeping EGADS in good working order with the highest possible uptime fraction, continued co-ordination with the other Kakenhi members is essential, and will be vigorously pursued.
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