P8: Atomic physics

The nuclear atom

The nucleus of an atom is made up of protons and neutrons
Protons are particles with a charge of positive 1
Neutrons and particles with a charge of negative 1
Nucleons are the particles in the nucleus (meaning that they are the protons and neutrons in the atom)
The symbol for the proton number is Z
The symbol of a nucleon (protons or neutrons) number is A
An isotope is an atom that has different amounts of neutrons from the regular number. Isotopes different in masses and physical properties, but not chemical ones
Nuclide notation shows the mass number and atomic number of the isotope. The number on the top left will be the mass number, and the number on the bottom left of the symbol will be the atomic number

Radioactivity

Radiation is where unstable atoms break down and release high energy particles
The nature of radiation emission is random, which means that it is impossible to predict the exact behaviour of a nucleus in its emission of radiation
When radiation passes close to an atom, it ionises the atom and causes electrons to move
Alpha particles, beta particles, and gamma rays are the three main types of radiation

Alpha particles are particles of 2 protons and neutrons, which is a type of radiation normally found from nuclei that are too large
It can be stopped by paper and has a little range in air. The ionsiation by the radiation is high
Beta particles are particles that are electrons with a lot of energy. This type of radiation happens in the case where a nucleus has too many neutrons
It can be stopped by thin aluminium and has a few tens of centimeters of range in air. The ionsiation by the radiation is medium
Gamma rays are the emissions of electromagnetic waves of a large amount of energy. They are often found from nuclei that have an excess amount of energy
The range of gamma waves in air is infinite and can be lowered by a thin sheet of lead. The ionisation by the radiation is low

When a radioactive particle are close to other atoms, electrons will be pushed out and the atom will be ionised
Alpha and beta (charged) particles can be deflected in electric fields and magnetic fields
Alpha particles deflect towards the negative side, beta particles deflect towards the positive
Beta is deflected more than alpha since it has less mass
Gamma rays have no charge and don't deflect

Ionising radiation

Ionising radiation can be used to describe the radioactive emissions of particles
Alpha is the most ionising type of radiation

Alpha particles affect basically every atom around them
They quickly lose energy and affect atoms only closely around them
Therefore, because alpha particles only affect particles nearby, they can be harmless when controlled properly, but could be dangerous when alpha particles affect the body

Beta particles ionise less atoms than the alpha particles, and have a longer range
Due to their ability to travel for long distances, beta particles could penetrate the skin and cause significant damage

Gamma rays can a greater range and can penetrate easier, which makes it more dangerous when it is in great quantities
Gamma rays are less ioning and affect less ions

Applications of Radioactivity

Radioactivity can be used in several different ways
Beta particles is to control thickness in the manufacture of thin materials (eg. paper)

When materials are on top of a source of beta radiation, particles can move through the material
These particles are monitored by a detector
The thicker the material, the more particles will be absorbed. This will also mean that less particles will pass through the material
Depending on how many beta particles the detector receives, they send a signal to the manufacturing devices to increase or decrease the force on the material to make it thinner or thicker

Some radioactive isotopes can monitor the flow of fluids. These isotopes are called tracers. Gamma radiation is used for this.

Tracers can be used to check blood flow and clots
They can also monitor oil to check for any leakage
Tracers are used in little amounts to make sure that people are not exposed to too much radiation as it is dangerous
Isotopes that are used often last short times to complete the task of monitors, but not expose people to too much radiation
Gamma radiation ionises less (and therefore will affect people less) and penetrates well (meaning that detection is easier)

Radioactivity is used to treat cancer through killing living cells. This radiation is especially dangerous to bacteria and cancer cells
Gamma rays penetrate the body to attack the cancerous cells
The rays need to be moved around to prevent too much exposure and harm to healthy tissue

Sterilisation is the use of radioactivity to kill bacteria and destroy viruses on medical instruments

Gamma rays are extremely effective in killing bacteria as they can kill bacteria in the instruments thoroughly which hot water and chemical treatment would be less effective in
This ensures that medical instruments would be safe for use

Background radiation

50% comes from radon gas
13% comes from medical uses (such as x-rays)
11% comes from food
10% comes from cosmic rays (high energy protons and atomic nuclei sourcing from the surface of the sun and other sources in the universe)

Background radiation is mostly natural, even though a small amount coming from sources such as medical applications are articifical
The amount of background radiation can be different depending on the environment

Radiation detectors

Radiation detectors detect the presence or chemical changes of particles that have been ionised by radiation
Radiation iones atoms by knocking out their electrons

Radioactive decay

Because of the instability of isotopes (which is often caused by the large size of the nucleus and the unbalanced numbers of neutrons and protons), isotopes will emit radiation and decay to become more stable and become smaller
When isotopes decay and emit radiation, protons and neutrons are lost, meaning that the isotopes will change into a different element
In nuclide notation, we can represent the loss of protons and neutrons

Half-life

Isotopes will lose a number of neutrons and protons, meaning that the isotope will slowly become less active
The half-life is the duration it takes for an isotope to reach half of their initial activity levels
For example, a half-life will be complete when the activity falls from 1/2 to 1/4, and 1/4 to 1/8 of initial activity
Half-lives vary in many isotopes
Even though the activity of an isotopes will continue to halve, it will never reach 0
With information, we can work out the half-life of an isotope by seeing the amount of time it takes for the activity of an isotopes to halve

Safety precautions

As radiation is dangerous and can ionise atoms, they can also cause changes in living cells
Therefore, to prevent the risks of radiation, certain measures and safety precautions are put in place

Radiation sources are kept away from people to prevent exposure to radiation, and are kept in boxes coated with lead
The amount of time and interaction with sources of radiation is reduced as much as possible to avoid exposure