Measurements can be performed in a vacuum or helium atmosphere.

测量可在真空或氦气氛中进行。

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In general, the heavier atoms in the atmosphere sink and the light ones remain at the surface, which is why some white dwarfs, for example, have mostly pure hydrogen or helium atmospheres.

总体来说，较重的原子在大气圈中沉积，而较轻的原子则存在于大气圈表面，这也是一些白矮星具有较纯净的氢和氦大气圈的原因。

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The particles are generally protons , electrons and helium nuclei and when they collide with nuclei in the Earth's upper atmosphere they can produce shower s of daughter particles.

这些粒子主要是质子、电子和氦原子核，并且当他们与地球高层大气中的原子核碰撞，就能产生次级粒子簇射。

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When the apes made calls while in an atmosphere rich in helium, the team analysed the calls' frequencies.

BBC: Helium-huffing gibbons 'sing with soprano technique'

The authors go to great lengths to describe how rogue thinkers at Intellectual Ventures hope to build a hose into the sky (suspended by large helium balloons) that spews sulphur dioxide constantly into the atmosphere.

ECONOMIST: The controversy over SuperFreakonomics