Modern topics in nuclear physics. Nuclear decay

There are 80 elements which have at least one stable isotope, and 250 such stable isotopes. However, there are thousands more well-characterized isotopes which are unstable. These radioisotopes may be unstable and decay in all timescales ranging from fractions of a second to weeks, years, or many billions of years.

For example, if a nucleus has too few or too many neutrons it may be unstable, and will decay after some period of time. For example, in a process called beta decay a nitrogen-16 atom (7 protons, 9 neutrons) is converted to an oxygen-16 atom (8 protons, 8 neutrons) within a few seconds of being created. In this decay a neutron in the nitrogen nucleus is turned into a proton and an electron and antineutrino, by the weak nuclear force. The element is transmuted to another element in the process, because while it previously had seven protons (which makes it nitrogen) it now has eight (which makes it oxygen).

In alpha decay the radioactive element decays by emitting a helium nucleus (2 protons and 2 neutrons), giving another element, plus helium-4. In many cases this process continues through several steps of this kind, including other types of decays, until a stable element is formed.

In gamma decay, a nucleus decays from an excited state into a lower state by emitting a gamma ray. The element is not changed in the process.

Other, more exotic decays are possible. For example, in internal conversion decay, the energy from an excited nucleus may be used to eject one of the inner orbital electrons from the atom, in a process which produces high speed electrons, but is not beta decay, and (unlike beta decay) does not transmute one element to another.

I. Reading exercises:

Exercise1. Read and memorize using the dictionary:

liquid-drop model, surface tension, electrical repulsion, binding energy, nuclear fission, superimpose on, quantum-mechanical effects, shell model, interacting boson model, high spin, excitation energy, artificially induced fusion, accelerator, phase transition, quark-gluon plasma, segregate in triplets, multiple isotopes

Exercise 2. Answer the questions:

1. How many nucleons can a heavy nucleus contain?

2. What is the liquid-drop model able to reproduce?

3. Why are nuclei with certain numbers of neutrons and protons particularly stable?

4. What does much of current research in nuclear physics relate to?

Exercise 3. Match the left part with the right:

1. A heavy nucleus can contain hundreds of nucleons which means	a. it may be unstable and will decay after some period of time.
2. Nuclei with certain numbers of neutrons and protons	b. or extreme neutron-to-proton ratios.
3. Nuclei may also have extreme shapes (similar to that of American football)	c. are particularly stable, because their shells are filled.
4. If a nucleus has too few or too many neutrons	d. that with some approximation it can be treated as a classical system rather than a quantum mechanical one.

Exercise 4. Open brackets using the right words:

Experimenters can (use/create) such nuclei using artificially induced (fusion/fission) or nucleon transfer reactions, employing ion beams from an accelerator. If a nucleus has too few or too many neutrons it may be (unstable/stable), and will (change/decay) after some period of time.

The Speaking Module

II. Speaking exercises:

Exercise 1. Describe nucleon; quantum-mechanics; repulsion; nuclear binding energy; nuclear fission using the suggested words and expressions as in the example:

nucleon for a proton or a neutron; a collective name; the main constituents; these particles are; of atomic nuclei; the same mass; have approximately; have spin of ½; through the process of beta decay; and can transform into each other example: Nucleon – a collective name for a proton or a neutron, these particles are the main constituents of atomic nuclei; have approximately the same mass, have a spin of ½, and transform into each other through the process of beta decay

quantum-mechanics of matter; the modern theory; of electromagnetic radiation; and of the interaction; between matter and radiation; which it generalizes and supersedes; it differs from classical physics; mainly in the realm of atomic; also known as quantum theory; and subatomic

repulsion to increase the distance; a force which tends; between the two bodies; electric charges or the force; having like; between atoms or molecules; at very short distances; which keeps them apart; also known as a repulsive force

nuclear binding energy to separate an atom; the energy required; into its constituent protons; and electrons; neutrons

nuclear fission into parts of comparable; the division of an atomic nucleus; of comparable mass; to heavier nuclei; usually restricted; such as isotopes or uranium; plutonium and thorium

Exercise 2. Ask questions to the given answers:

1. Question: ____________________________________ ?

Answer: Nuclei may also have extreme shapes.

2. Question: ____________________________________ ?

Answer: Beams with even higher energies can be used to create nuclei at very high temperatures.

3. Question: ____________________________________ ?

Answer: The element is transformed to another element in the process.

The Writing Module

III. Writing exercises:

Exercise 1. Complete the sentences with the suggested words: beta decay; within; many; after; converted; unstable:

If a nucleus has too few or too ______ neutrons it may be______ , and will decay ______ some period of time. For example, in a process called ______ a nitrogen-16 atom (7 protons, 9 neutrons) is ______ to an oxygen-16 atom (8 protons, 8 neutrons) ______ a few seconds of being created.

Exercise 2. Fill in the table with words from the text. Group the synonyms:

heavy	strength
tension	modern
feature	little
picture	suggest
use	couple
large	especially
particularly	complex
complicated	painting
propose	hard
pair	to apply
current	voltage
few	function
force	big

Exercise 3. Compose a story on one of the topics (up to 100 words):

“Liquid-drop model”

“Shell model”

“Nuclear decay”

Lesson 4

The Reading Module