| 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 (WC) 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.
We are happy to report that this primary goal has been accomplished during FY2015.
Since October 2014 the 200-ton EGADS detector has been full of water. Stepwise gadolinium loading began in November of 2014, and was completed - meaning that the target goal of 0.2% gadolinium sulfate by mass had been dissolved in the water - by the end of April 2015. At this point EGADS became the world's first (and most advanced) Gd-loaded water Cherenkov supernova neutrino detector.
The detector has been carefully calibrated and data taking now takes place 24 hours a day without interruption. The remainder of FY2015 was therefore primarily devoted to stable operations of the 200-ton EGADS detector, where EGADS now stands for Employing Gadolinium to Autonomously Detect Supernovas.
|
| 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 have successfully built and now continuously operate the world's most advanced WC-based supernova neutrino detector, a significant accomplishment.
Currently we are making excellent, steady progress toward our ultimate supernova detection goal: fully automated, immediate notification of the world's astronomers following detection of a burst of neutrinos from a Milky Way core collapse supernova explosion.
EGADS's all-important selective water filtration system, which keeps the water in the detector clean but does not remove the dissolved gadolinium, has been continually improved and upgraded during the past few years. 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.
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 have achieved. 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.
Indeed, in June of 2015, based primarily upon these outstanding EGADS results, the Super-Kamiokande Collaboration officially approved the gadolinium loading of Super-K itself.
|
| 今後の研究の推進方策 |
Now that the detector itself is 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.
|
