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ATOMIC STRUCTURE AND RADIOACTIVITY (Atomic structure (mass number = number…
ATOMIC STRUCTURE AND RADIOACTIVITY
Atomic structure
mass number = number of protons and neutrons
atomic number = number of protons
number of neutrons = mass number - atomic number
Isotopes = atoms of the same element, that have the same number of neutrons and different number of protons
Ions = atoms that lose or gain electrons and have a charge
Radioactivity
Some isotopes have an unstable nucleus , and radioactive decay is the process in which a nucleus gives off radiation to become stable
Activity = rate at which unstable nucleus decays, measured using Geiger-muller tube
Radiation:
Alpha particles - 2 protons and 2 neutrons
Beta particles - an electron
Gamma radiation - electromagnetic radiation
Alpha scattering and nuclear model
Plum pudding model = a ball of positive charge with electrons scattered inside it
alpha scattering experiment =fired positive alpha particles into gold foil and saw most pass but some deflected so they found that atoms were mostly empty space and the centre is positive
Properties
Alpha - can be stopped by a piece of paper, can travel 5cm, strongly ionising
Beta - stopped by aluminium, travels 15cm, quite ionising
Gamma - can be stopped by lead, travels several metres, weakly ionising
Nuclear equations
Alpha decay:
Particle represented by helium atom
Atomic number decreases by 2
Mass number decreases by 4
Beta decay:
Neutron changes to proton and electron
Atomic number increases by 1
Mass number doesn't change
Half life
Time taken for the number of nuclei to halve in the process of radioactive decay
Irradiation and contamination
Irradiation - exposing an object to radiation, but not making the object radioactive
Contamination - unwanted radiation on other materials, which can be dangerous
Level of hazard depends on radiation:
Alpha - very dangerous but easily stopped
Beta - can easily penetrate into the skin
Gamma - less hazardous
Background radiation
Radiation that is around us
Natural sources: radioactive rock and cosmic rays
Man-made sources: nuclear weapon testing and nuclear accidents
Nuclear radiation in medicine
Used in medicine to explore organs and control/destroy unwanted tissues
Tracer must emit radiation that can pass out the body, not be strongly ionising, must not decay and must have a short half life
