Nuclear Physics Definitions

Question 1

Define activity

Answer 1

The rate of decay of the radioactive nuclei in a given isotope. It is proportional to the total number of nuclei in the sample and is measured in Becquerels.

Question 2

Define alpha decay

Answer 2

The emission of an alpha particle (2 protons and 2 neutrons) from an unstable nucleus (usually one with too much mass) to make it more stable. Alpha radiation is strongly ionising and is stopped by a few centimetres of air or a sheet of paper

Question 3

Define atomic mass unit

Answer 3

A unit mass to express atomic masses. One AMU is equal to the one twelfth of the mass of a carbon atom.

Question 4

Define background radiation

Answer 4

Radiation that is found in small quantities all around us. It originates from natural sources such as rocks and cosmic rays as well as man-made sources such as nuclear accidents and medical sources.

Question 5

Define beta decay

Answer 5

The emission of a beta particle when a proton turns into a neutron (or vice versa) in an unstable nucleus. Beta minus radiation is weakly ionising. Bet plus radiation is immediately annihilated by electrons.

Question 6

Define binding energy

Answer 6

The amount of energy required to split a nucleus into all its separate consistent nucleons. It is equivalent to the mass defect.

Question 7

Define chain reaction

Answer 7

The process of the neutrons released by a fission reaction inducing further fissile nuclei to undergo fission

Question 8

Define closest approach

Answer 8

A method of estimating a nuclear radius by firing an alpha particle at it. It involves calculating the distance at which all the alpha particle’s kinetic energy is converted to electric potential energy

Question 9

Define contamination

Answer 9

The introduction of radioactive material to another object. The object is consequently radioactive

Question 10

Define control rods

Answer 10

Rods found in nuclear reactors to absorb neutron and control the rate of reaction. They can be raised or lowered depending on the rate required.

Question 11

Define coolant

Answer 11

A substance that passes through nuclear reactors and is responsible for removing heat from the core. This heat is then used to generate energy.

Question 12

Define critical mass

Answer 12

The smallest mass of fissile material required in a fission reactor for a chain reaction to be sustained.

Question 13

Define electron capture

Answer 13

A process that occurs in proton-heavy nuclei, in which an electron is drawn into the nucleus, causing a proton to transition into a neutron. An electron neutrino is also produced.

Question 14

Define fission

Answer 14

The splitting an nucleus, to form two smaller daughter nuclei, neutrons and energy

Question 15

Define fusion

Answer 15

The joining of two smaller nuclei to form a larger nucleus and to release energy

Question 16

Define gamma decay

Answer 16

The emission of gamma rays from an unstable nucleus that has too much energy. Gamma radiation is only very weakly ionising but requires several centimetres of lead to be stopped.

Question 17

Define half-life

Answer 17

The average time it takes for the number of radioactive nuclei in a sample to halve

Question 18

Definitely the inverse square law

Answer 18

A law that governs the intensity of gamma radiation. It means that the intensity of radiation at any point is inversely proportional to the square of the distance from its source

Question 19

Define irradiation

Answer 19

The exposure of an object to radiation. The exposed object does not become radioactive

Question 20

Define mass defect

Answer 20

The difference in mass between a nucleus and the sum of the masses of its constituent nucleons

Question 21

Define moderator

Answer 21

A material in nuclear reactors that absorbs energy from fast moving neutrons, to slow them down to speeds that can be absorbed by fissile neutrons to induce fission

Question 22

Define radioactive dating

Answer 22

The use of radioactive isotopes with known half-lives to date objects. The isotope that is usually used is carbon-14

Question 23

Define radioactive waste

Answer 23

The waste produced from the products of fission reactions. Since the waste is unstable and radioactive, it must be stored and handled carefully.

Question 24

Define random nature of radioactive decay

Answer 24

Radioactive decay is random - you can’t predict when a nucleus will decay or which nucleus will decay next.

Question 25

Define Rutherford scattering

Answer 25

An experiment involving firing alpha particles at a thin gold foil and observing their deflections. It showed the existence and nature of the nucleus