物理學家對氦核進行了迄今為止最精確的測量

物理學家對氦核進行了迄今為止最精確的測量

Helium is a very important element, much more than just a way to make balloons float or increase the pitch of our voices. It is the second most abundant element in the universe and the lightest of the noble gases. Physicists have now announced a breakthrough in our understanding of this element: The most precise measurement of its nucleus yet.

氦是一個非常重要的元素，不僅僅是一種讓氣球浮起來或提高我們聲音的方法。它是宇宙中第二豐富的元素，也是稀有氣體中最輕的。物理學家們現(xiàn)在宣布我們對這種元素的理解有了突破:對其原子核的最精確的測量。

An international team of researchers has established that the radius of the helium nucleus is 1.67824 femtometers – or 1.67824×10-15 meters (5.506×10-15 feet). To give you a comparison, if the nucleus was the size of your thumbnail, your actual thumbnail would then be the size of the Earth’s orbit. This new measurement is 4.8 times more precise than previous estimates. The findings are reported in Nature.

一個國際研究團隊已經確定氦原子核的半徑為1.67824毫米，即1.67824×10-15米(5.506×10-15英尺)。給你一個比較，如果原子核是你的縮略圖的大小，那么你實際的縮略圖就是地球軌道的大小。新的測量方法比以前估計的精確4.8倍。研究結果發(fā)表在《自然》雜志上。

The helium atom, in its most abundant form, is made of a nucleus comprised of two protons and two neutrons surrounded by two electrons. The electrons have a negative electric charge, while the protons are positive. Neutrons have no electric charge but are key to keep the protons from repelling each other. Protons and neutrons are made of quarks, and quarks interact via the strong nuclear force.

最豐富的氦原子是由兩個質子和兩個中子組成的原子核組成的，原子核被兩個電子包圍著。電子帶負電荷，而質子帶正電荷。中子不帶電荷，但它是阻止質子相互排斥的關鍵。質子和中子是由夸克組成的，夸克通過強核力相互作用。

Dr Alfredo Carpineti

This will tell you that the particles in the nucleus are not just staying still, and the nucleus hasn’t got a well-defined boundary. Its radius is estimated by working out the interaction between the nucleus and negatively charged particles.

這將告訴你，原子核中的粒子不僅僅是靜止的，原子核也沒有一個明確的邊界。它的半徑是通過計算原子核和帶負電荷的粒子之間的相互作用來估計的。

In this latest experiment, researchers tweaked the helium by switching electrons with muons. Muons have the same electric charge as the electron but they are 200 times more massive. This difference allowed researchers to make more precise measurements.

在最新的實驗中，研究人員通過交換電子和介子來調整氦。介子和電子的電荷是一樣的，但是它們的質量是電子的200倍。這種差異使研究人員能夠進行更精確的測量。

"We don't work with normal atoms, but with exotic atoms in which both electrons have been replaced by a single muon. So with muonic helium, we can draw conclusions about the structure of the atomic nucleus and measure its properties," senior author Aldo Antognini, from the Paul Scherrer Institute, said in a statement.

“我們研究的不是普通原子，而是兩個電子都被一個μ子所取代的奇異原子。因此，有了介子氦，我們就可以得出有關原子核結構的結論，并測量其性質，”保羅·謝勒研究所的資深作者奧爾多·安托格尼尼在一份聲明中說。

This same approach with muon was used a few years back to obtain a more precise measurement of the proton. This led to a bit of contradiction in the size of the proton. Researchers thought that this was just an experimental error in older measurements, but they were open to the idea that maybe it was a hint of more complex physics.

幾年前，人們用同樣的方法研究質子，以獲得對質子的更精確的測量。這導致了質子大小的矛盾。研究人員認為這只是以前測量的一個實驗誤差，但他們也認為這可能是更復雜物理的一個暗示。

There is no disagreement in the measurement of the helium – the latest number is a clear and simple improvement on previous estimates. This strengthens the proton results, making it unlikely to be a product of unknown physics.

在氦的測量上沒有分歧——最新的數(shù)字是對以前估計的一個明確而簡單的改進。這增強了質子的結果，使得它不太可能是未知物理的產物。

"Our measurement can be used in different ways," says Julian Krauth, first author of the study. "The radius of the helium nucleus is an important touchstone for nuclear physics."

“我們的測量方法可以用在不同的方面，”該研究的第一作者朱利安·克勞斯說。氦核的半徑是核物理學的重要試金石。

This work is a perfect testbed for several physical theories, from theoretical models of nuclear structure to refining our understanding of the strong nuclear force in fundamental physics.

這項工作為多種物理理論提供了一個完美的實驗平臺，從核結構的理論模型到基礎物理中增強我們對強核力的理解。