Advanced Information
A Beta particle is the same as an electron.It has a charge of -1, and a mass of around 1/2000th of a proton.
But wait a minute! If a nucleus contains protons and neutrons, what's an electron doing coming out of a nucleus?
To answer this, we need to know more about protons and neutrons:
Protons & neutrons are made of combinations of even smaller particles, called "quarks". Under certain conditions, a neutron can decay, to produce a proton plus an electron. The proton stays in the nucleus, whilst the electron flies off at high speed.
This means that when a nucleus emits a b-particle,
- the atomic mass is unchanged,
- the atomic number increases by 1.This is because a neutron has changed into a proton (almost the same mass - we can ignore the tiny mass of the electron) and thus the number of protons has gone up.
Example: Strontium-90 undergoes b decay and forms Yttrium-90.
This isn't the whole story - an almost massless particle called an "anti-neutrino" is also emitted. Furthermore, we are only considering "beta-minus" emission (negatively-charged electrons).
There is another type of beta decay, called "beta-plus", where a positively-charged electron (called a "positron") is emitted, along with a neutrino.
Don't worry about this right now, this is way beyond what's required for GCSE, and takes us into 'A' level physics concepts such as antimatter.
Beta decay occurs in very "neutron-rich" elements, for example, Strontium-90 and Iodine-130. These elements are typically created in nuclear reactors.
These elements have too few protons and too many neutrons to be stable. They can thus become more stable by emitting a beta particle.
Beta particles have a charge of -1, and weigh only a tiny fraction of a neutron or proton. As a result, b particles interact less readily with other atoms than alpha particles.
Thus beta particles cause less ionisation than alphas, and have a longer range, typically a few metres in air.
Remember, in Beta decay :-
- atomic number increases by one
- atomic mass unchanged.
This site is designed to be viewed at 800 x 600 resolution, with level 4 browsers or better.
Created by Andy Darvill, www.darvill.clara.net,Science teacher at Broadoak Community School, Weston-super-Mare, England
