Nuclear Physics - Topic 7

small, dense region consisting of protons and neutrons at the centre of the atom

a particle type of nucleus that is characterized by the number of protons, neutrons, and the energy state

a proton or neutron

number of protons in nucleus

number of protons + neutrons

number of neutrons in nucleus

nuclei with same number of protons but different numbers of neutrons

1/12th the mass of a carbon-12 nucleus

mass number * unified atomic mass unit

a long range, attractive but very weak force between masses

long range, repulsive or attractive, magnetic or electrostatic forces with a relatively strong force

very short range, attractive and strongest force between any two nucleons that keeps the protons together inside the nucleus

very short range force that is involved in radioactive decay, often involves lighter particles and heavier particles

1. Low pressure gas is energized by applying a potential difference across it, causing it to heat up.

2)The hot gas emits light energy only at certain well-defined frequencies, as seen through a diffraction grating or prism.

1. Light is shone through a cool, low pressure gas

2. A diffraction grating or prism is used to determine the frequencies at which the gas passes through is absorbed

Lines characteristic of the particular element producing them.

The anti-matter version of an electron, which shares its mass but has a positive charge instead of a negative charge. It forms in beta-positive decay.

An electron

Positron

V represents an anti-neutrino particle

e represents an anti-electron particle, and v is a neutrino

y is a high energy photon

Alpha spectra - discrete

Beta spectra - continuous

Gamma spectra - discrete

As radiation passes through materials, it “knocks off” electrons from neutral atoms, thereby creating an ion pair: free electrons and a positive ion.

Allows radiation to be detected but is also dangerous since it can lead to mutations in biologically important molecules in cells, such as DNA

Particle - Helium nucleus

Penetration ability - low

Material needed to absorb it - Sheet of paper; a few cm of air

Path length in air - a few cm

Speed - about 10^7 m/s

Particle - Electron or positron

Penetration ability - low

Material needed to absorb it - 1 mm of aluminium

Path length in air - less than 1 m

Speed - About 10^8 m/s, very variable

Particle - high-energy photon

Penetration ability - high

Material needed to absorb it - 10 cm of lead

Path length of air - infinite

Speed - 3 x 10^8 m/s

Detects and counts the number of ionizations taking place

The time taken for half of the nuclides in a sample to decay

The number of radioactive disintegrations per unit time (decay rate)

The rate at which radioactive nuclei in a sample decay (the activity) is proportional to the number of radioactive nuclei present in the sample at any one time.

Difference between the mass of the nucleus and the sum of the masses of its individual nucleons

Energy requires when nucleus is separated into its individual components

E = mc^2

A nucleus is bombarded with a nucleon, an alpha particle or another small nucleus, resulting in a nuclide with a different proton number (a different element)

Two light nuclei combine to form a more massive nucleus with the release of energy

A heavy nucleus splits into two smaller nuclei of roughly equal mass with the release of energy.

When an unstable (radioactive) nucleus disintegrates spontaneously, the nucleus emits a particle of small mass and/or a photon.

Energy is usually released in the form of kinetic energy for the products.

Greater for product nuclei than for original nuclei since energy is released.

It is the fusion of hydrogen to helium. The problem with using fusion on earth is that the nuclei in fusion are positively charges and to fuse them, the need to be close enough to the point where the strong nuclear force becomes stronger than the coulomb repulsion force. This is done by colliding them at a very high speed in temperatures above 10°C.

A particle with the same rest mass but opposite charge

A particle with no internal structure that cannot be broken down further.

A virtual particle that transfers between force between interacting particles.

Process by which an electron and positron are produced.

Energy values that are continuous

Mass of the object measured in the object’s rest frame

Cannot predict when the nucleus will decay next

Quarks cannot be directly observed as free particles because the energy given to nucleons creates other particles rather than freeing quarks

The theory that describes the electromagnetic and weak interactions of quarks and leptons

The decay cannot be modified in any way

A particle that mediated one of the fundamental forces