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Science

What is radioactivity?

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Nuclear radiation - Higher tier

You need to be able to write nuclear equations to show single alpha and beta decay.

Symbols

The nucleus of an atom can be represented as:

Shows X representing the chemical symbol. In front of X, A (at the top) represents atomic mass and Z (at the bottom) represents atomic number

In this symbol:

  • A is the atomic mass (number of protons + neutrons)
  • Z is the atomic number (number of protons)
  • X is chemical symbol (as shown on the periodic table)

Alpha decay

Two protons and two neutrons are lost from a nucleus when it emits an alpha particle:

  • The atomic mass number decreases by 4
  • The atomic number decreases by 2

A new element is formed that is two places lower in the periodic table than the original element.

For example, radon decays into polonium when it emits an alpha particle. Here is the equation for that radioactive decay:

[219/86]Rn -> [215/84]Po + [4/2]a

Beta decay

In beta decay a neutron changes into a proton plus an electron. The proton stays in the nucleus. The electron leaves the atom with high energy as a beta particle.

The nucleus has one more proton and one less neutron when it emits a beta particle:

  • The atomic mass number stays the same
  • The atomic number increases by one

A new element is formed that is one place higher in the periodic table than the original element. For example, carbon-14 is a radioactive isotope of carbon. Here is the equation for the beta decay of carbon-14 into nitrogen:

[14/6]C -> [14/7]N + [0/-1]b

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