Biodegradable mems. Vocabbox. A lot of machines made by physicists are used in medicine now, страница 8

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Reading

Read the text. Divide into logical parts. What is the purpose of each part?

The ability of physicists to trap and cool atomic gases with a combination of lasers and magnetic fields has revolutionized atomic physics in recent years. Now a team of physicists from the US, Germany and France has turned its attention to more elementary particles, and succeeded in storing neutrons in a 3-D magnetic trap. The development should lead to a more accurate measurement of the neutron lifetime, and a detailed understanding of the weak nuclear force that governs radioactive beta decay and nucleosynthesis in stars.

The neutron lifetime has previously been measured with an accuracy better than 1 % using ultracold neutrons stored in a quartz ”bottle”. However, this level of uncertainty dominates recent theoretical predictions of the abundance of helium-4 created in the big bang — an important yardstick in cosmology. The sensitivity of previous experiments was largely limited by neutrons interacting with the walls of the bottle and fluctuations in the initial number of neutrons used. But by trapping the neutrons with magnetic fields, the research team has avoided these problems.

Magnetic traps are routinely used to confine neutral atomic gases by exploiting  the magnetic moments of the atoms. However, it is more difficult to trap neutrons because their intrinsic magnetic moments are much weaker. Moreover, the laser-cooling techniques that are usually used to slow down atomic gases before trapping cannot be used to cool neutrons.

The researchers passed a beam of cold neutrons at 11 K from a reactor into a trapping vessel surrounded by a series of magnets and filled with superfluid helium-4. They found that a small fraction of the neutrons lost almost all their energy through collisions with the helium, while the rest were absorbed by the walls surrounding the trap. This enabled the researchers to trap and cool neutrons at temperatures below 1 mK. The liquid helium also doubled as a scintillator, producing pulses of light when a neutron decayed into a proton, electron and neutrino.

Although the uncertainty of its first measurement of the neutron lifetime was relatively large, the team expects to improve the precision to a few parts in 10⁵ by using a deeper magnetic trap and a more intense source of cold neutrons.

Comprehension check

Answer the following questions:

1.  What has revolutionized atomic physics in recent years?

2.  What have physicists turn their attention to now?

3.  How have the physicists avoided their problems?

4.  Why is it more difficult to trap neutrons than to confine neutral atomic gases?

5.  What enables the researchers to trap and cool neutrons at temperatures below 1 mK?

6.  How do the researchers expect to improve the precision of the measurement of the neutron lifetime?

Give a summary of the text.

UNIT 10

SILICON  GERMANIUM  MAKES  ITS  MARK

Vocabbox

noun collocations

§  the overriding factor

§  a number of inherent properties of silicon

§  relentless exponential growth

§  silicon field effect transistors

§  the conduction and valence bands

§  greater flexibility for designing devices

§  global positional systems (GPS)

verb collocations

§  drive down the cost per transistor

§  rely heavily on

§  reach the phenomenal yields of silicon chips

§  be predicted to grow enormously

§  be grown onto silicon wafers

§  give the opportunity to study

Pre-reading task

Before you read name the main problems that you think are discussed in this text.

Reading

Read the text and explain the title of it.