Structure and characteristics of proton

Date: 2015-10-07; view: 462.

FREE-READING PASSAGE

It is advisable that you read the following passage about one of the basic constituents of matter. You can pick up some new vocabulary items. Try to do some practice on translation.

The proton is 1,836 times as heavy as the electron. For an atom of hydrogen, which contains one electron and one proton, the proton provides 99.95 percent of the mass. The neutron weighs a little more than the proton. Elements heavier than hydrogen usually contain about the same number of protons and neutrons in their nuclei, so the atomic mass, or the mass of one atom, is usually about twice the atomic number. Protons are affected by all four of the fundamental forces that govern all interactions between particles and energy in the universe. The electromagnetic force arises from matter carrying an electrical charge. It causes positively charged protons to attract negatively charged electrons and holds them in orbit around the nucleus of the atom. This force also makes the closely packed protons within the atomic nucleus repel each other with a force that is 100 million times stronger than the electrical attraction that binds the electrons. This repulsion is overcome, however, by the strong nuclear force, which binds the protons and neutrons together into a compact nucleus. The other two fundamental forces, gravitation and the weak nuclear force, also affect the proton. Gravitation is a force that attracts anything with mass (such as the proton) to every other thing in the universe that has mass. It is weak when the masses are small, but can become very large when the masses are great. The weak nuclear force is a feeble force that occurs between certain types of elementary particles, including the proton, and governs how some elementary particles break up into other particles.

The proton was long thought to be a pointlike, indivisible particle, like the electron. In the 1950s, however, scientists used beams of electrons to probe the proton and found that it has a definite shape and size. These experiments showed that, rather than being an indivisible point, the proton has an outer diameter of about 10-13 cm, with a cloudlike shell surrounding dense center.

Beginning in 1947, physicists discovered more and more elementary particles in addition o the proton, neutron, and electron. These particles appeared to be related to protons and neutrons and to each other. Two different elementary particles had one property, such as an electric charge, that was identical, while another two particles were related by having the exact opposite property. These relationships suggested that protons and other elementary articles might be made up of smaller building blocks, which scientists called quarks. In 1967 physicists used high-powered electron beams to probe deep inside the proton and discovered evidence that quarks exist. Three quarks join together to form a proton. The strong nuclear force is actually a force that attracts quarks to each other to make a proton or neutron. The quarks of a neutron or proton will also attract the quarks of another neutron or proton, thus holding a nucleus together. Protons originally formed about a thousandth of a second after the Big Bang, the explosion that scientists believe occurred at the beginning of the universe (see Big Bang theory). In that short time, the temperature of the early universe dropped sufficiently for energetic quarks to join together. It is possible that protons may break up again, but this type f event, called proton decay, would be extremely rare. Experiments have shown that the average lifetime of the proton is at least 1035 years (the number 1035 means a 1 followed by 5 zeros). This may appear to be an odd answer, since the age of the universe is only about 15 x 09 years. Some protons live for a much shorter time than the average value, however, and scientists are constructing large experiments with thousands of tons of material, hoping to see a proton decay.

(From http://encarta.com)