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Atomic structure (Developing the model of the atom (1804- John Dalton…
Atomic structure
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Nuclear equations
Nuclear equations used to show radioactive decay by using element symbols. Written as:
Atom before decay :arrow_right: Atom after decay :arrow_right: Radiation emitted
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When atom emits alpha particle, atomic number reduces by 2 and mass number by 4. Proton is positive and neutron is neutral so charge decreases.
When beta decay occurs, a neutron in nucleus turns to proton and releases fast-moving electron. No. of protons in nucleus increases by 1- increases positive charge of nucleus (atomic number). Loses neutron and gains proton so mass of nucleus doesn't change.
Gamma rays get rid of excess energy from nucleus, so no change in atomic mass or number of atom.
Half-life
Radioactive substances give out radiations from nuclei of atom- no matter what. Radiation can be measured with a Geiger-Muller tube and counter; records count-rate-number of radiation counts reaching it per second. Radioactive decay is random, so can't predict exactly which nucleus in sample will decay next or when they will decay.
But can find out half-life-- time taken for the number of radioactive nuclei in an isotope to halve. Can be used to make predictions about radioactive sources, even though decay is random.
Half-life can be used to find rate at which a source decays- activity (measured in Becquerel, Bq, when 1 Bq is 1 decay per second).
Each time radioactive nucleus decays to become stable, activity as a whole will decrease (older sources emit less radiation). Time varies for unstable nuclei to decay, for different isotopes. This means activity never reaches 0 so half-life is used.
Find half-life as a percentage:
1) Find activity after each half-life.
2) Divide final activity by initial activity, x 100
Half-life using graphs:
1) Half activity and find time by going across graph.