Electronic structure

• Protons have a charge of +1 and a mass of 1

• Neutrons have a charge of 0 and a mass of 1

• Electrons have a charge of -1 and a mass of 0

• Some elements have more neutrons than they are meant to have. This means that are an isotope, and some isotopes are radioactive.

• Changing the amount of electrons in an atom to make it balanced is making it an ion, but the element remains the same.

• Changing the number of neutrons doesn’t change the element or produce an ion. It produces an isotope.

• An unstable isotope will decay by emitting radiation to form a more stable isotope.

• Atomic number is the number of protons/electrons in an atom.

• The mass number is that added amount of protons and neutrons.

• An isotope is each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element. Isotopes aren’t always radioactive.

Types of Radiation

• There are three main types of radiation- Gamma, Beta and Alpha.

• Alpha radiation is the most ionising and least penetrating- it only takes a few centimetres of air or paper to stop alpha particles. It is the nucleus of a helium particle and travels at a very high speed. An atom decays into a new atom by and emits alpha particle

• Alpha radiation has 2 neutrons and 2 protons, has a charge of +2 and has a penetrating power of being stopped by paper or a few centimetres of air as well as the effect of a magnetic/electric field is weakly deflected

• When an alpha particle is emitted from a nucleus the nucleus loses two protons and two neutron. This means the atomic mass number decreases by four and the atomic number decreases by 2.

• Alpha particles don’t travel that fast- this is because they have such as large mass. This means that they tend to collide with plenty of other atoms. Therefore, they cause a lot of ionisation by pulling electrons off the atoms.

• Alpha radiation is not highly penetrating, so it can be stopped by a piece of paper or a few centimetres of air.

• Beta radiation is a fast moving high energy electron, and is called a beta particle. An atom decays into a new atom by changing a neutron into a proton and an electron.

• Beta decay occurs when in a nucleus with too many protons or neutrons, one of the protons or neutrons gets transformed into the other. The atomic number increases by +1.

• They are moderately ionising

• Beta radiation is a high energy electron with an electric charge of -1, a relative atomic mass of 1/1860 and a penetrating power of being stopped by a few millimetres (5mm) of aluminium, as well as the effect of a magnetic/electric field is strongly deflected. Their range in air is a few metres.

• Gamma radiation is part of the EM spectrum; a wave with a very high frequency and a very short wavelength. When alpha or beta decays surplus energy is usually emitted. The atom itself remains unchanged.

• Gamma radiation is a high energy electromagnetic radiation with an electric charge of 0 and a relative atomic mass of 0. It’s penetrating power is that it can be stopped by several centimetres of lead or several metres of concrete. As well as this, the effect of a magnetic/electric field is not deflected.

• They have a high range in air and are low ionising.

• There is also neutron radiation, and the formula subtracts 1 from the previous element (the one at the beginning of the arrow.)

History of an Atom

• The model of the atoms started of with the plum pudding model which was a spherical cloud of positive charge with electrons. It soon changed to the nuclear model at the founding of testing where high speed alpha particles were shot at a piece of gold foil. Some penetrated it but others bounced of or changed direction.

Radioactive Formula

• For alpha decay, it decreases the charge an the mass of the nucleus. When the helium particle leaves the atom, the atomic number is reduced by 2 and the atomic mass is reduced by 4.

• For beta decay, the atomic number increases by one when the electron is removed due to a neutron turning into a proton.

• Gamma rays don’t change the charge or mass of the nucleus, and are a way of getting rid of excess energy.

Developing the model of the atom

• Bohr refined Rutherford’s idea of the Nuclear model of the atom.

• Bohr said that electrons orbited the nucleus in energy levels, as his theoretical calculations agreed with experimental data.

• Further research made it discovered that the nucleus is made up of a group of particles (protons) which have the same positive charge which add up to equal the overall charge of the nucleus.

• James Chadwick later on discovered the neutron.

Contamination

• Radioactive contamination is the unwanted presence of materials containing radioactive atoms on other materials.

• When an object is exposed to ionising radiation it is said to become irradiated but it doesn’t become radioactive.

• It is more dangerous to eat food contaminated with an alpha source as it is more ionising.

• It is more dangerous to go into a place with gamma radiation as it is more penetrating.

Formulas

• To work out wave speed= frequency x wavelength.

Measuring Radiation

• The instrument used to detect the effects of radiation is called the Geiger-Muller tube (can detect and measure radiation).

• Activity is the rate at which a source or unstable nuclei decays.

• Activity is measured in becquerel (Bq)

• Count rate is the number of decays actually recorded per second by detector (ex: Geiger-Muller Tube). The count rate is proportional to the activity as long as the distance between the detector and the source doesn’t change.

• Half-life- the time it takes for half the nuclei to decay.

• Radioactive decay is the process by which an unstable atomic nucleus loses energy by radiation. (in other terms, the nucleus decays).

• Radioactive decay- becoming stable. This is a random process so we know when the nuclei will decay but we don’t know which nucleus will decay next.

• Safety precautions needed to be taken when in a distance of radioactive substance is to keep exposure times as low as possible, store radioactive sources in shielded containers and wear protective clothing.

Background Radiation

• Everyone is exposed to a certain amount of nuclear radiation everyday, this is known as background radiation.

• Some examples of waves could be microwaves, ultra-violet rays, infrared rays and finally gamma rays.

• Background radiation percentages- 10% cosmic, 11.5% food and drink, 14% ground, 14% medical, 50% air (radon), 0.2% nuclear weapons, 0.2% air travel, 0.1% nuclear reactors.

Terms

• Irradiated- when an object has been exposed to ionising radiation/ radiation.

• Ionisation- Atoms that have become charged by their electrons being knocked of by radiation.

• Peer review- data published and checked by other scientists.

• Count rate- the number of counts per second on a geiger counter.

• Half-life- How long it takes for half the nuclei to decay.

• Becquerel- Unit of activity which is 1 decay per sec.

Uses of radiation

• Alpha radiation is used in fire alarms due to its low penetration, meaning that it can be stopped by smoke and also a few centimetres of air. This means when there is smoke, the smoke absorbs the ions created by the source, and the alarm sounds when the current (created by the air particles going through the gap in the fire alarm) stops.

• In gauging thickness, beta radiation is used. If too much radiation is going through the paper when beta is fired, this means the paper is too thin meaning that the computer tells the rollers to move apart. If not enough radiation is going through, the paper is too thick so the computer tells the roller to move more closer.

• Radioactive tracers are used to detect polyps, cancerous mutations and others. An example could be a gamma camera. An isotope is attached to molecules which the body would normally use. The isotope in the emits gamma rays that are detected by the gamma camera. This method is good to detected blood leaks, etc.

• Internal radiotherapy is when a radioactive source, usually a beta source such as iodine 131 is placed within a tumour to help kill the cancer. This method is usually dangerous though as it is harmful, and is not used often.

• External radiotherapy is when several different lower strength radioactive beams are shot at the tumour from different directions. As well as this, it can also be a strong singular beam. This method of radiotherapy is more common.

• Pallative care is when you treat something incurable/terminal.

• Gamma rays are used to sterilise syringes because gamma rays are penetrating but as well as this gamma rays kill viruses and bacteria.

Half Life

• Radioactivity is a totally random process.

• Radiation can be counted with a geiger-muller tube and counter, which records the count rate.

• Radioactive decay is completely random so you can’t exactly pinpointed which nucleus in a sample will decay or when any one of them will decay.

• You can find how long it takes for half the nuclei to decay, and this is called half life.

Decrease of radioactivity over a period of time

• The radioactivity of a source decreases over a period of time to become a stable nucleus.

• For some isotopes it takes a few hours for all the unstable nuclei to have decayed, whilst others last for millions of years.

• The half life is the time taken for the number of radioactive nuclei in an isotope to halve.

• A short half life means that the activity falls quickly, because the nuclei are highly unstable and decay rapidly. Sources with a short half life can be dangerous because of the high amount of radiation they emit at the start, but become safe very quickly.

• A long half life means the activity falls more slowly because most of the nuclei don’t decay for a long time- the source just sits there releasing small amounts of radiation for a long time. This can be dangerous as nearby areas are exposed to radiation for millions of years.

How to read half life of a graph

• First read a value such as 80 for the activity in becquerels. Then find half of that which would be 40, and find how long it takes for one half life to occur. For example, it could be 2 hours.

Nuclear fission and fusion

• Nuclear Fission: The process in which a heavy nucleus splits into two or more lighter nuclei, releasing a large amount of energy. This process is utilized in nuclear power plants and nuclear weapons.

• Nuclear Fusion: The process in which two light nuclei combine to form a heavier nucleus, releasing even more energy than fission. Fusion is the process that powers the sun and other stars, but it has yet to be efficiently replicated for energy production on Earth.