Introduction to the World of Nuclear Physics. Lidiya Strautman

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      Beta particles are electrons or positrons (electrons with positive electric charge, or antielectrons). Beta decay occurs when, in a nucleus with too many protons or too many neutrons, one of the protons or neutrons is transformed into the other. In beta minus decay, a neutron decays into a proton, an electron, and an antineutrino. In beta plus decay, a proton decays into a neutron, a positron, and a neutrino. Both reactions occur because in different regions of the Chart of the Nuclides, one or the other will move the product closer to the region of stability. These particular reactions take place because conservation laws are obeyed. Electric charge conservation requires that if an electrically neutral neutron becomes a positively charged proton, an electrically negative particle (in this case, an ele ctron) must also be produced. Similarly, conservation of lepton number requires that if a neutron (lepton number = 0) decays into a proton (lepton number = 0) and an electron (lepton number = 1), a particle with a lepton number of -1 (in this case an antineutrino) must also be produced. The leptons emitted in beta decay did not exist in the nucleus before the decay – they are created at the instant of the decay. To the best of our knowledge, an isolated proton, a hydrogen nucleus with or without an electron, does not decay. However within a nucleus, the beta decay process can change a proton to a neutron. An isolated neutron is unstable and will decay with a half-life of 10.5 minutes. A neutron in a nucleus will decay if a more stable nucleus results; the half-life of the decay depends on the isotope. If it leads to a more stable nucleus, a proton in a nucleus may capture an electron from the atom (electron capture), and change into a neutron and a neutrino. Proton decay, neutron decay, and electron capture are three ways in which protons can be changed into neutrons or vice-versa; in each decay there is a change in the atomic number, so that the parent and daughter atoms are different elements. In all three processes, the number A of nucleons remains the same, while both proton number, Z, and neutron number, N, increase or decrease by 1. In beta decay the change in the binding energy appears as the mass energy and kinetic energy of the beta particle, the energy of the neutrino, and the kinetic energy of the recoiling daughter nucleus. The energy of an emitted beta particle from a particular decay can take on a range of values because the energy can be shared in many ways among the three particles while still obeying energy and momentum conservation.

      Ex. 1. Make the following sentences negative.

      1. In beta decay the change in the binding energy appears as the mass energy. 2. Many nuclei more massive than lead decay by this method. 3. Because of its smaller mass, most of the kinetic energy goes to the alpha particle. 4. The energy of an emitted beta particle from a particular decay can take on a range of values. 5. A neutron in a nucleus will decay if a more stable nucleus results, the half-life of the decay depends on the isotope.

      Ex. 2 Make up questions to which the following sentences are the answers.

      1. In beta decay the change in binding energy appears as the mass energy and 24 kinetic energy of the beta particle, the energy of the neutrino, and the kinetic energy of the recoiling daughter nucleus. 2. Beta decay occurs when, in a nucleus with too many protons or too many neutrons, one of the protons or neutrons is transformed into the other. 3. Proton decay, neutron decay, and electron capture are three ways in which protons can be changed into neutrons. 4. Alpha radiation reduces the ratio of protons to neutrons in the parent nucleus, bringing it to a more stable configuration.

      Ex. 3 Translate the following sentences into Russian.

      1. For scientific development to be of benefit for man, scientists must occupy themselves with problems that have direct bearing on our lives. 2. Molecular biologists are known to borrow their techniques from other sciences, mainly from physics. 3. How the application of his discovery will affect man is sometimes rather hard for the scientist to foresee. 4. The author devoted a special chapter of his book to what may be expected to dominate the science scene in the near future. 5. The method of inductive reasoning known to be established by Bacon leads from observation to general laws. 6. His idea was fruitful enough for others to take it up and develop it further. 7. For an original idea to be a product of one man's genius is quite natural. But for an idea to be transformed into a product, many people's effort is required.

      Ex. 4. Translate the following sentences into English.

      1. Мне трудно об этом спорить. 2. Им важно подкрепить теорию дополни-тельными экспериментальными данными. 3. Физикам важно поддерживать контакт, с биологами. 4. Ребенку необходимо учиться на собственном опыте. 5. Нам часто трудо угадать, каким будет будущее. 6. Естественно, что на такой анализ затрачивается около года. 7. Необходимо, чтобы реакция была ускорена. 8. Чтобы две молекулы вступили в реакцию, они должны столкнуться.

      Ex. 5 Fill in the blanks with the appropriate words from the list given below.

      1. Mankind is known to be most intimately … nature. 2. Is it difficult to … one state of matter … another? 3. Atoms can be neutral and positively or negatively … 4. If an atom … one or more electrons, a negative ion is formed. 5. Antimatter is composed of antiatoms made of negative … at their centers and positive electrons, moving around them. 6. Because protons … each other the nuclei should fly apart, but they do not. 7. The most characteristic thing about meteorites is that they possess compounds of carbon with metals, which are … carbides. 8. If the earth's … were entirely iron, its total quantity within the whole earth would be at least 35 per cent. 9. Let us … that these angles are equal. 10. Living things are not always easy to … from non-living ones, and we should therefore know the characteristics which indicate that a thing is alive.

      a) charged, b) assume; c) tell from, d) nuclei, e) additional, f) distinguish, g) gains, h) called, i) associated with, j) core, k) repel