Radioactivity & Nuclear Energy

Plants and animals also absorb radioactive material that is present in the atmosphere. These plants and animals are part of the food chain. We constantly receive cosmic radiation from space. Exposure to low levels of radioactivity is part of everyday living.

A dose of radiation that exceeds normal levels can be dangerous. Radiation can affect the way in which the cells in bodies operate and can cause them to become cancerous.

Radiation, however, when used in a careful controlled way can be beneficial. Radiation can be used in medicine. It can be used to kill cancerous body cells.

Radioactive sources can also be used to find out if different organs in our bodies are working properly. The radioactive substance is carried by the blood to the organ. The radiation coming from the organ is measured. The measurements can be processed so that an image of the organ is displayed. This helps to diagnose what is wrong with the organ.

Types of radiation

An atom is made up of a small nucleus surrounded by orbiting electrons. The nucleus of the atom contains particles called protons and neutrons.

The nuclei of the atoms in some elements are unstable and emit radiation. The radiation can be of three types - alpha radiation, beta radiation and gamma radiation.

Alpha α radiation is slow moving helium nucleiBeta β radiation is fast moving electronsGamma γ radiation is high-energy electromagnetic waves.The three radiations transfer energy from the nucleus when they are emitted.

Type of Radiation Alpha particle Beta particle Gamma ray

Symbol or  or   or 

Mass (atomic mass units) 4 1/2000 0

Charge +2 -1 0

Speed slow fast very fast (speed of light)

Ionising ability high medium 0

Penetrating power low medium high

Stopped by: paper aluminium lead

Absorption of radiation

Ionisation

The radiation on passing through the material causes electrons to be stripped from some of the atoms in the absorbing material. The process is called ionisation. As a result the atoms become positive ions.

Energy is transferred to the absorber during the ionisation process. Negative ions occur when electrons are added to atoms which doesn’t happen in

nuclear radiation

Activity of a radioactive source

The activity of a radioactive source is the number of ionising radiations it emits per second. Activity is measured in becquerels. The symbol for becquerel is Bq. One becquerel is one ionising radiation emitted per second. The activity of a radioactive source decreases with time.

Safety and radiation dose

Safety precautions are necessary when working with radioactive sources. Radioactive sources should be kept away from the body and never brought close to the eyes.

The radiation dose received by body tissue depends on the type of radiation absorbed by the tissue. The radiation dose received also depends on the energy of the radiation.

A way of expressing the radiation dose received from different sources is in terms of a quantity called equivalent dose. Equivalent dose is measured in sieverts (Sv). A dose of one sievert from an alpha radiation source, for example, is equivalent to a dose of one sievert from a beta radiation source or any other source of radiation.

Nuclear power stations

Nuclear power stations use fuel containing uranium or plutonium.

These are the steps by which electricity is generated by nuclear power:

1. Uranium atoms split releasing energy so fuel becomes hot. This heats the water turning it into steam.

2. The steam turns the turbine.3. The turbine turns a generator and electricity is produced.4. The electricity goes to the transformers to produce the correct voltage.The fuel used eventually becomes solid nuclear waste. This waste is radioactive and emits ionising radiation.

Nuclear power

Nuclear power is created from the release of energy from nuclear reactions. These reactions usually use uranium or plutonium.

Advantages of nuclear power:

1. Only small amounts of fuel needed to produce lots of energy compared to fossil fuels2. Low carbon emissions3. Tends to be supported by large companies and governments4. Once up and running it is cheap to produce electricity5. There has been a lot of investment in making sure it is as safe as possible

Disadvantages of nuclear power:

1. Nuclear waste is highly radioactive2. Accidents and leaks can be deadly and last for a long time3. Storing nuclear waste is very expensive4. Decommissioning nuclear power stations is very expensive5. Uranium and plutonium are not renewable so will run out

Nuclear reactors use a type of nuclear reaction called nuclear fission. Another type of nuclear reaction - nuclear fusion - happens in the Sun and other stars.

Nuclear fission

Nuclear power reactors use a reaction called nuclear fission. Two isotopes in

common use as nuclear fuels are uranium-235 and plutonium-239.

Fission is another word for splitting of a nucleus. Uranium or plutonium isotopes

are normally used as the fuel in nuclear reactors, because their atoms have

relatively large nuclei that are easy to split, especially when hit by neutrons.

When a uranium-235 or plutonium-239 nucleus is hit by a neutron, the following

happen:

1. The nucleus splits into two smaller nuclei, which are radioactive

2. Two or three more neutrons are released

3. Energy is released

The additional neutrons released may also hit other uranium or plutonium nuclei

and cause them to split. Even more neutrons are then released, which in turn can

split more nuclei. This is called a chain reaction. The chain reaction in nuclear

reactors is controlled to stop it going too fast.

Nuclear fusion

Nuclear fusion involves two atomic nuclei

joining to make a large nucleus. Energy is

released when this happens.

The Sun and other stars use nuclear fusion

to release energy. The sequence of nuclear

fusion reactions in a star is complex, but

overall hydrogen nuclei join to form helium

nuclei. Here is one nuclear fusion reaction that takes place:

Hydrogen-1 nuclei fuse with Hydrogen-2 nuclei to make Helium-3 nuclei

Water In

Steam Out Inside a nuclear reactor

Marie became fascinated by rays that were discovered by scientists. She began to do experiments and examined pitchblende. She expected there to be few rays from uranium, but instead found a lot of rays. She realized that there must be an undiscovered element in pitchblende. 

Marie spent hours in their lab investigating it. She had discovered two new elements! 

Marie named the elements polonium and other radium. The Curies came up with the term "radioactivity" to describe elements that emitted strong rays. 

In 1903, the Nobel Prize in Physics was awarded to Marie and Pierre Curie as well as Henri Becquerel for their work in radiation.

In 1911 Marie won the Nobel Prize in Chemistry for discovering two elements. Scientists came from around the world to study radioactivity with Marie.