1
Q
How does sterilisation of food and surgical instruments work?
A
- food exposed to a high dose of gamma ways to kill microbes
- medical instruments too
- doest involve high temperates so they won’t be damaged
- food is not reactive afterwards
- strong gamma emitter and reasonably long half-life
2
Q
What are unstable isotopes?
A
- radioactive
- they decay into other elements and give out radiation
3
Q
What are masses and charges of protons, neutrons and electrons
A
YOU KNOW THIS
4
Q
What happens when a nucleus emits an alpha particle?
A
- mass number decreases by 4, because it loses two protons and neutrons
- atomic number decreases by two, because it has two less protons
- forms a new element
5
Q
What is half life?
A
- the average time it takes for the number of nuclei in a radioactive isotope sample to halve
6
Q
Explain the life cycle of stars
A
- stars initially form form clouds of dust and gas. the force of gravity makes the gas and dust spiral in together to form a protostar
- gravitation energy is converted into heat, so temperature rises. when temp is high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei and give out massive amounts of heat and light. a star is born. smaller masses of gas and dust may pull together to form planets that orbit the star
- star enters a long stable period, where heat created by nuclear fusion provides and outward pressure to balance the force of gravity pulling everything inwards. star maintains its energy out for millions of years. this stable period is main sequence star and last several billion years
- eventually hydrogen runs out. heavier elements such as iron are made by nuclear fusion of helium. star sells into a red giant if its a small star or a red super giant if its a big star. it becomes red because the surface cools
- a small to medium sized star like sun then becomes unstable and ejects its outer later of dust and gas as a planetary nebula
- this leaves behind a hot, dense solid core, the white dwarf, which cools to a black dwarf and eventually disappears
- big stars start to glow brightly again and undergo more fusion and expand and contract several times, forming elements as heavy as iron. eventually they explode in a supernova, and ejecting elements heavier than iron to form new planets and stars
- the exploding supernova throw the outer layers of dust and gas into space, leaving a very dense core called a neutron star. if the star is big enough it becomes a black hole.
7
Q
What happens when a nucleus emits a beta particle?
A
- mass number doesn’t change because it loses a neutron but gains a proton
- atomic number increases by 1 because it has one more proton
- new element formed
8
Q
How does radiotherapy work?
A
- high doses of gamma rays will kill all living cells
- used to treat cancers
- have to be directed carefully and at just th right dosage without damaging too many normal cells
9
Q
What blocks alpha radiation?
A
- paper
10
Q
What are gamma rays?
A
- very short wavelength EM waves, with not mass or charge
- penetrate far into materials, pass straight through air
- weakly ionising because they tend to pass through rather than collide
- it doesn’t change the element of the nucleus since its just energy
11
Q
What are electrons
A
- whizz around the outside of nucleus
- gives the atom its overall size
12
Q
What sources of radiation are most dangerous outside the body?
A
- beta and gamma because they re more penetrative and can get inside organs
- alpha isn’t penetrative
13
Q
What is nucleus fission?
A
- the splitting up of big atomic nuclei
- nucleus power stations generate electricity using nuclear reactors
- a controlled chain reacrtion takes place so that nuclei split up and release energy as heat
- then used to heat water to make steam,
14
Q
What is ionisation?
A
- alpha, beta, gamma radiation enter living cells and collide with molecules
- damages or destroys the molecules
- lower doses cause minor damage without killing the cell
- this can give a rise to mutant cells, which divide uncontrollable and cause cancer
- higher doses kill cells completely
15
Q
What is radioactivity?
A
- radioactive substances give out radiation from the nuclei of their atoms, no matter what is done to them
- random process
- unaffected by temperature or chemical bonding
- spit out three types of radiation: alpha, beta, gamma
16
Q
Describe chain reactions
A
- for nuclear fission to happen, a slow moving neutron must be absorbed into uranium or plutonium nucleus
- addition of this neutron makes the nucleus unstable, causing it to split
- each time a uranium or plutonium nucleus splits, it spits out two or three electrons, one of which might hit other nucleus causing it to split also, keeping chain reaction
- when a large atom splits, it will form two smaller nuclei
- they are usually radioactive because they have the worn number of neutrons in them
- nuclear fission gives out a lot of energy
- releases much more energy than chemical processes
17
Q
How do tracers in medicine work?
A
- always use short half-life beta or gamma emitters
- certain radioactive isotopes can be injected or swollowed
- using an external detector, computer converts reading
- must be gamma or beta so that radiation passes out of the body and last a few hours so that radioactivity inside the patient disappears quickly
18
Q
Describe beta particles
A
- it is a fast-moving electron that comes from a nucleus
- move quite fast and quite small
- penetrate moderately into material before colliding
- long range about 1m an moderately ionising
- for every beets particle emitted, neutron turns into a proto in the nucleus
19
Q
Describe nuclear fusion
A
- two nuclei can join to create a larger nucleus
- fusion releases a lot of energy
- requires really high temperatures ( at least 10,000,000 ˚C) and pressures
20
Q
What is a nucleus?
A
- tiny but makes up most of the mass of an atom
- contains protons and neutrons
21
Q
How were natural elements produced?
A
- by nuclear fusion
- high temps and pressures causes different nuclei tp fuse
- early universe contained only hydrogen
- a lot of helium created after the big bang
- other elements formed as storms go through different life cycles
- other heavier elements formed when pressure an temperatures got high enough
- distributed during supernovae
22
Q
What happens when alpha and beta travel through a magnetic or electric field?
A
- particles will be deflected
- alpha particles have a positive charge and beta a negative
- deflected in opposite direction because of opposite charge
- alpha have a larger charge, so feel a greater force but alpha deflected less because they have a greater mass
- gamma doest get deflected
23
Q
What blocks beta?
A
- think aluminium, any metal
24
Q
What sources are most dangerous inside the body?
A
- alpha because it is the most ionising
25
What is background radiation?
- radiation present at all times from:
- natural sources such as unstable isotopes found in rocks and radiation from space (cosmic rays)
- man-made sources such as nuclear weapon test, accidents
26
Descrive alpha particles
- it is a helium nucleus with a mass of 4 and a charge of +2
- made up of two protons and two neutrons
- when a nucleus emits an alpha particle, it forms a new element
- relatively big and heavy and slow moving
- don't penetrate very far and stopped quickly
- range of about 5cm in air
- due to size they are strongly ionising and bash into a lot of atoms and knocks electrons off
27
What blocks gamma?
- thick lead, thick concrete
28
How do smoke detectors used alpha radiation?
- weak source of alpha placed in detector, between two electrodes
- source causes ionisation and current flows between electrodes
- smoke in fire will disrupt the current, causing alarm to sound
IGCSE Physics
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