鈥淭here are many applications for ultracold neutrons in fundamental physics,鈥� Oliver Zimmer tells 麻豆淫院Org.com. 鈥淎nd we will find even more applications with a stronger source of ultracold neutrons.鈥� Zimmer, a scientist at the Institut Laue Langevin in Grenoble, France, thinks that he and his colleagues may have found a way to tap a better source for ultracold neutrons by extracting them from superfluid helium.

鈥淩ight now,鈥� Zimmer explains, 鈥渢he best source provides not more than 50 neutrons per cubic centimeter. When we extract them from superfluid helium, we could get a factor 100 more.鈥�

Zimmer led a team of scientists from the physics faculty of the Technical University Munich in Germany, the Laboratory of Nuclear Problems in Russia, the ILL in Grenoble, the Munich research reactor FRM II and the Paul Scherrer Institut in Switzerland in creating a prototype that shows how neutron extraction from superfluid helium works. Their findings are published in 麻豆淫院ical Review Letters in a piece titled, 鈥淪uperfluid-Helium Converter for Accumulation and Extraction of Ultracold Neutrons.鈥�

鈥淓xtracting the neutrons from the superfluid is particularly important for a neutron lifetime measurement because when left in the helium, it can be absorbed by impurities, or get additional energy by scattering, even at a low temperature,鈥� Zimmer says. He explains that extraction solves these problems, and it makes the use of ultracold neutrons also more versatile. 鈥淢ore possibilities for broader application of these neutrons open up when you don鈥檛 have to do experiments in the superfluid helium.鈥�

The international team is building on an idea that was first suggested 30 years ago. However, a first attempt 20 years ago to extract ultracold neutrons accumulated in helium didn鈥檛 work because the scientists involved were using 鈥渨indows鈥� to try and extract the neutrons horizontally.

Instead, Zimmer and his colleagues switched the direction. 鈥淲ith the windows,鈥� he explains, 鈥渢he neutrons had to pass through a series of foils to get out. We use a vertical extraction, so the neutrons don鈥檛 have to pass through any material. In the earlier experiments, the neutrons were probably being eaten away by absorption in the foil material and by leakage through gaps in the neutron guide.鈥�

Most of the present uses for ultracold neutrons are to do with fundamental physics. Zimmer points out that even though everyday applications with ultracold neutrons are a long way off, experiments with this neutral particle advance the understanding in many areas, including 鈥渢he synthesis of chemical elements in the early universe during the first minutes after the big bang, or the question why there is so much matter found in the universe but practically no anti-matter. Experiments on the neutron lifetime and the search for the electric dipole moment of the neutron are crucial for this.鈥� He continues, expounding via email: 鈥淎nd when we have a stronger source for these neutrons, we will probably find more applications for ultracold neutrons because their present low number is severely limiting the counting statistical accuracy in any experiment.鈥�

Zimmer insists that this ultracold neutron extraction method adds the missing piece to creating a source for experimental purposes: 鈥淔irst, scientists discovered that this high rate of production in ultracold neutrons is possible. Next, they found that these neutrons can accumulate for a long time, allowing you to get a higher density of them.鈥� He emphasizes: 鈥淭hese things have been done in helium. The last missing part is to get the neutrons out of the helium, and our prototype has shown we can do this.鈥�

How close are ultracold neutrons to being extracted from superfluid helium for cutting edge experimental purposes? According to Zimmer, not far off. 鈥淥ur second apparatus currently being constructed will already serve as a facility for this. As a first application, I think within the next two years, we will carry out a compelling neutron lifetime experiment.鈥�

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