Radioactive decay
Stable nuclei
An atom's The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. The plural of nucleus is nuclei. can only be stable if it has a certain amount of Uncharged subatomic particle, with a mass of 1 relative to a proton. The relative charge of a neutron is 0. for the amount of Subatomic particle with a positive charge and a relative mass of 1. The relative charge of a proton is +1. it has.
Elements with fewer protons, such as the ones near the top of the A tabular representation of all known elements in order based on atomic number, eg all the noble gases are found on the right of the periodic table., are stable if they have the same number of neutrons and protons. For example carbon (carbon-12) is stable and has six protons and six neutrons.
However, as the number of protons increases, more neutrons are needed to keep the nucleus stable. For example lead (lead-206) has 82 protons and has 124 neutrons.
Nuclei with too many, or too few, neutrons do exist naturally but are unstable and will The process in which unstable atomic nuclei break apart or change, releasing radiation as they do so. by emitting Energy carried by particles from a radioactive substance, or spreading out from a source..
Types of radioactive decay
An unstable nucleus can decay by emitting an Subatomic particle comprising two protons and two neutrons (the same as a helium nucleus)., a A type of ionising radiation consisting of a single electron., a A type of ionising radiation that is also part of the EM spectrum. It has no mass. or in some cases a single neutron.
Alpha particles
If the nucleus has too few neutrons, it will emit a 'package' of two protons and two neutrons called an alpha particle.
An alpha particle is also a helium-4 nucleus, so it is written as \(_{2}^{4}\textrm{He}\) and is also sometimes written as \(_{2}^{4}\textrm{\alpha}\)
Alpha decay causes the The number of protons and neutrons found in the nucleus of an atom. of the nucleus to decrease by four and the The number of protons in the nucleus of an atom. Also called the proton number. of the nucleus to decrease by two.
Beta particle
If the nucleus has too many neutrons, a neutron will turn into a proton and emit a fast-moving Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons.. This electron is called a beta (尾) particle - this process is known as Radiation caused by beta particles (high-energy electrons). A beta particle is an electron ejected from a nucleus when a neutron becomes a proton..
A beta particle has a relative mass of zero, so its mass number is zero. As the beta particle is an electron, it can be written as \(_{-1}^{~0}\textrm{e}\), and sometimes as \(_{-1}^{~0}\textrm{\beta}\).
The beta particle is an electron but it has come from the nucleus, not the outside of the atom.
Electrons are not normally expected to be found in the nucleus but neutrons can split into a positive proton (same mass but positive charge) and an electron (which has a negative charge to balance the positive charge) which is then ejected at high speed and carries away a lot of energy.
Beta decay causes the atomic number of the nucleus to increase by one while the mass number remains the same.
Gamma ray
After emitting an alpha or beta particle, the nucleus will often still be too 'hot' and will lose energy in a similar way to how a hot gas cools down. A hot gas cools by emitting Electromagnetic radiation emitted from a hot object., which is an A transverse wave caused by oscillations in an electromagnetic field..
High energy particles will emit energy as they drop to lower Specific amounts of energy that electrons have when they orbit a nucleus is a particular shell. Electrons that gain energy may move to a higher energy level (a shell further from the nucleus). Electrons that lose energy may move to a lower energy level (a shell closer to the nucleus).. Since energy levels in the nucleus are much higher than those in the gas, the nucleus will cool down by emitting a more energetic electromagnetic wave called a gamma ray.
Gamma ray emission causes no change in the number of particles in the nucleus, meaning both the atomic number and mass number remain the same.
Neutron emission
Occasionally it is possible for a neutron to be emitted by The process in which unstable atomic nuclei break apart or change, releasing radiation as they do so.. This can occur naturally, ie absorption of cosmic rays high up in the atmosphere can result in neutron emission, although this is rare at the Earth's surface. Or it can occur artificially, eg firing alpha particles at beryllium results in neutrons being emitted from that.
A further example of neutron emission is in The splitting of a large nucleus to produce two smaller ones. Two or three neutrons are also released in the process. The energy from the neutrons powers a nuclear reactor., where neutrons are released from the parent nucleus as it splits.