By Kiera Gambon Unit 20 Medical Physics
Task 1 (a)
The structure of an atom is quite simple(a). Within the nucleus there are two types of particles: protons and neutrons. (Protons and neutrons can be split even further but I will discuss this later) (c). a
Both have a similar mass of one, However, neutrons have no charge whereas protons are positively charged to counteract electrons.
Electrons are negatively charged particles outside the nucleus situated on shells and have a relative mass of around 1/2000. Electrons have a specific way that they spin within their shells. For example, in simple terms, the first shell which can hold two electrons: one electron would be spinning up and the other down. I have presented a few diagrams to briefly explain how this works(d) (e) (f). S spins can hold up to 2, p spins can hold 6 and d spins can hold 10 electrons.b
The number of electrons must be the same as the number of protons or the atom becomes charged. You can tell the number of electrons and protons in a neutral atom by looking at the proton (atomic) number of an atom. Similarly, you can tell the number of neutrons in an atom by taking the proton number away from the mass number, which shows how many neutrons and protons combined are within an atom.
An isotope is two or more atoms of the same element with the same number of protons but a different number of neutrons, as seen in the diagram(b) c
As previously mentioned, the nucleus is made up of protons and neutrons which are made up by three quarks; quarks are fundamental particles, meaning they cannot be split. There are two main types: up and down quarks. although there are many types, these two are the only ones that are stable. Up and down refers to their spin. For their calculations to work, they need to have a fractional charge. The up quark has a charge of +2/3 of the charge of an electron and the down quarks have a charge of -1/3.
Task 1 (c)
TASK 1 (B)
2 protons, 2 neutrons
Positive electron (positron)
Behaviour in an electric field
Left toward negative as alpha is a helium nucleus which is positive
Right toward positive as it is a negative electron
Left toward negative as it is a positron
Is not affected, carries straight on/ no reaction to an electric field
Ability to ionise substances
One alpha particle can ionise 10,000 atoms, therefore a high ionising ability. It has a charge of 2+ which means it has more to gain than beta.
Beta- minus, as it is a high-speed electron, has medium level of ionisation of atoms as it knocks one electron out of an energy level.
Beta-plus, as a positron, has a medium level of ionisation as it annihilates an electron in an energy level of an atom due to its opposing charge.
As Gamma rays are a wave of energy, within the E-M spectrum, they are poor ionisers.