Topic 6 Flashcards
describe an atom
positively charged nucleus, consisting
of protons and neutrons, surrounded by negatively charged
electrons
Describe how and why the atomic model has changed over
time
plum pudding model [J.J. Thompson]
- overall charge is neutral so negative electrons cancels out with the positive pudding [protons]
Rutherford Gold foil
- most particles went straight through - so empty space
- some reflected back - nucleus is positive repelling alpha particles
- some particles deflected over 90 - nucleus contained most of the mass
what are isotopes
- same proton different number of neutrons
- atoms of same element but different mass.
Recall the relative masses and relative electric charges of
protons, neutrons, electrons and positrons
mass, charge
proton: 1,+1
neutron: 1, 0
electron: 0.0005, -1
positron: 0.0005, +1
Explain that electrons change orbit when there is absorption or
emission of electromagnetic radiation
- when electrons more to a higher orbit (further away from nucleus) the atoms absorb EM radiation
- when electrons fall to a lower orbit (closer to nucleus ) the atoms emit EM radiation
Explain how atoms may form positive ions by losing outer
electrons
when electron gain enough energy to leave the atom as an ions
how are alpha, β– (beta minus), β+ (positron), gamma rays
and neutron radiation are emitted from
unstable nuclei in a random process
Explain what is meant by background radiation
weak radiation detected from natural sources
Describe the origins of background radiation from Earth and
space
- cosmic rays
- radiation from underground rocks
Describe methods for measuring and detecting radioactivity
limited to photographic film
- film gets darker when absorbs radiation
- more darker the film for radiation
Describe methods for measuring and detecting radioactivity
limited to a Geiger–Müller tube
- a tube that can detect radiation
- each time it absorbed radiation it sends and electrical pulse tot he machine produces a clicking sound
- more clicking sound more radiation
Compare alpha, beta and gamma radiations in terms of their
abilities to penetrate and ionise
ALPHA
penetrating: weak
ionising: strong
BETA
penetrating: moderate
ionising: moderate
GAMMA
penetrating: strong
ionising: weak
Describe the process of β– decay
a neutron becomes a proton plus an electron
Describe the process of β+ decay
a proton becomes a neutron plus a positron
Explain that the half-life of a radioactive isotope
is the time taken for half the undecoyed nuclei to decay or the activity of a source to decay by half
Describe uses of radioactivity smoke alarms
- alpha particles ionise the air - allows current to flow across the gap and complete circuit
- when smoke gets in the way the current can not flow ions have slowed down
- alarm will sound
Describe uses of radioactivity tracing and gauging thicknesses
- beta radiation
- source and receiver is placed either side of the paper
- if count rate is high/low the thickness changes
Describe uses of radioactivity irradiating food
- gamma rays kill bacteria to store food for longer
Describe uses of radioactivity sterilisation of equipment
- irradiate with gamma rays
- penetrate the equipment and kill bacteria
Describe uses of radioactivity diagnosis and treatment of cancer
- a tracer moves around the body
- before a a radiographer positions a radioactive detector outside the body
- this produces picture showing where the tracer has accumilated
Explain how the dangers of ionising radiation depend on half-life and relate this to the precautions needed
- long half life may affect cells and tissues by mutating them or damaging them
=> use a shorter half life [it can decay faster]
Describe the dangers of ionising radiation in terms of tissue
damage and possible mutations
- radiation sickness
- cancer
- burns and blisters
- weak immune system
- diarrhoea
- vomiting
describe how ionising radiation can damage cells and cause mutations
- removes electrons from atoms that make up cell
- break chemical bonds
- damage tissues
- change structure of DNA
explain how people that work with radiation can ensure that they stay safe
=> increase distance from source
=> minimising time spent near source
=> wear a dosimeter to monitor he exposure
=> shielding
