Radiation for SQA Higher Physics
This page covers the following topics:
1. Nuclear equations
2. Background radiation
3. Inverse square law
Nuclear equations describe what happens when a nucleus changes into another element by alpha or beta decay. In alpha decay, 2 protons and 2 neutrons are released from the nucleus to release an alpha particle, thus the atomic number decreases by 2 and the mass number decreases by 4. In beta decay, a neutron changes into a proton and releases an electron, thus the mass number stays the same and the atomic number increases by 1.
Background radiation is radiation that exists around us at all times. This can be from both naturally occuring or artificial sources. Some natural sources of background radiation are radon gas from radioactive emitting rocks and soil in the ground, cosmic rays that reach the Earth from space and living things, as plants absorb radioactive materials from the soil they grow in and pass them up through the food chain. Some artificial sources of background radiation are medical procedures and nuclear power and weapons. When conducting experiments involving radiation, the background radiation must first be calculated and deducted from all results so as not to interfere with them.
A source of gamma radiation emits gamma rays equally in all directions. This means that for a distance r from the source, the gamma rays are spread over the surface of a sphere with radius r and surface area 4πr². The intensity of the source is defined as the energy per unit time per unit area and can be calculated using I = E/4πr², where E = energy of the gamma rays and r = radius of sphere. As the distance from the source increases, the intensity of the gamma rays decreases, since they will be spread over a greater area. According to the formula for intensity, gamma radiation follows an inverse square law, meaning that the intensity of the source is directly proportional to the inverse of the square of the distance from the source.
A potassium nucleus ⁴²₁₉K emits a beta particle. Write the nuclear equation for this beta decay.
⁴²₁₉K → ⁴²₂₀Ca + ⁰₋₁β
Write the nuclear equation for a lithium nucleus ⁷₃Li emitting an alpha particle.
⁷₃Li → ³₁H + ⁴₂a
Fill in the gaps of the given nuclear equation.
²¹⁰₈₄Po → ⁴ₐHe + ᵇₑPb
a = 2, b = 206, e = 82.
Explain what happens to a nucleus that undergoes alpha decay.
When a nucleus undergoes alpha decay, it loses two protons and two neutrons, which are emitted as an alpha particle. The mass number of the nucleus decreases by 4 and the atomic number decreases by 2.
Give the symbol of the nucleus ¹⁴₆C changes into after it releases a beta particle.
The mass number will remain the same and the atomic number will increase by 1. The element with atomic number 7 is nitrogen, so it changes into ¹⁴₇N.
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