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gsce physics > radioactivity and particles 7 > Flashcards

radioactivity and particles 7 Flashcards

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1
Q

what does the nucleus of an atom contain?

A

protons and neutrons
making up mass of atom

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2
Q

what makes up the atomic number of an atom?

A

number of protons

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3
Q

why are atoms neutral?

A

number of protons = number of electrons

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4
Q

what is an isotope?

A

atoms with the same number of protons but different numbers of neutrons

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5
Q

what does it mean a nucleus is unstable?

A

isotopes tend to be radioactive and the nucleus is unstable so it decays and emits radiation

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6
Q

is radioactive decay predictable or random?

A

RANDOM

the nuclei of an unstable isotope break down randomly
unaffected by physical conditions like temperature or chemical bonding
when the nucleus decays it spits out one type of radiation (alpha, beta, gamma, neutrons)
nucleus often changes into a new element

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7
Q

examples of background radiation nuclear sources:

A

earth - air, food, building materials etc
space
the sun
living things - radioactive material in all living things
radiation due to human activities - fallout from nuclear radiation, nuclear waste

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8
Q

how does nuclear radiation cause ionising radiation?

A

causes ionisation by bashing into atoms and knocking electrons off them
the atoms have no overall charge are turned into ions which are charged hence the term ionisation

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9
Q

types of ionising radiation
structure of alpha:

A

alpha particles are helium nuclei
4
He
2
alpha particles are made up of two protons and two neutrons, they are big, heavy and slow moving

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10
Q

types of ionising radiation
penetration of alpha:

A

don’t penetrate far into materials

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11
Q

types of ionising radiation
ionisation of alpha:

A

strongly ionising due to their size, therefore bashing into a lot of atoms and knocking their electrons off

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12
Q

types of ionising radiation
charge of alpha:

A

they are electrically charged (with a positive charge) alpha particles are deflected (their direction changes) by electric and magnetic fields

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13
Q

types of ionising radiation
how does alpha affect atomic number and mass number:

A

decreases atomic number by 2
decreases mass number by 4

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14
Q

types of ionising radiation
structure of beta:

A

beta particles are electrons
beta particles are electrons which have been emitted from the nucleus of an atom when a neutron turns into a proton and an electron
0
e-
-1
fast, quite small

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15
Q

types of ionising radiation
how does beta affect atomic number and mass number:

A

number of protons in nucleus increases by 1
therefore the atomic number increases by 1 but the mass number stays the same

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16
Q

types of ionising radiation
penetration and ionisation of beta:

A

penetrate moderately before colliding
moderately ionising too

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17
Q

types of ionising radiation
charge of beta:

A

they are charged negatively, beta particles are deflected by electric and magnetic fields

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18
Q

types of ionising radiation
structure of gamma waves:

A

gamma waves are very short-wavelength em waves
gamma waves are the opposite of alpha particles
they have no mass, just energy

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19
Q

types of ionising radiation
penetration of gamma:

A

penetrate a long way into materials without being stopped

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20
Q

types of ionising radiation
ionisation of gamma:

A

weakly ionising as they tend to pass through rather than collide with atoms, but eventually they hit something and cause damage

21
Q

types of ionising radiation
charge of gamma:

A

they have no charge so they are not deflected by electric or magnetic fields

22
Q

types of ionising radiation
when does gamma radiation occur:

A

after beta or alpha decay
you NEVER get just gamma rays emitted

23
Q

types of ionising radiation
how does gamma affect atomic number and mass number:

A

has no effect
if nucleus has excess energy, it loses this energy by emitting a gamma ray

24
Q

what are alpha particles blocked by?

A

blocked by paper, skin, a few cm of air

25
Q

what are beta particles blocked by?

A

thin metal

26
Q

what are gamma waves blocked by?

A

thick lead or very thick concrete

27
Q

practical
the penetration of radiation:

A
  • you can detect ionising radiation with a Geiger-müller detector
  • set up the equipment (radioactive source and geiger-müller detector) so that when nothing is placed between the source and sector the counter records a high count rate
  • remove the source to measure the background count over a time period
    divide your count by the time period to get a background count rate, do this 3 times to get a mean, and subtract this from all your results
  • replace the source and measure the count rate (minus the background count rate) with no material present 3 times to get a mean
  • then insert different materials between the source and detector, record the count rate for each material 3 times to find a mean
  • if the count rate stays the same when the material is inserted then the radiation can penetrate the material
  • if it drops by a large amount the radiation is absorbed by the material and blacked
  • repeat the experiment with different sources to investigate the penetration of different kinds of radiation
28
Q

what do you use to detect ionising radiation?

A

gieger-müller detector
- gives a count rate, the number of radioactive particles reaching it per second

29
Q

how do you safely store radioactive sources?

A
  • keep in lead-lined box when not in use
  • only be picked up by using long-handled tongs or forceps
  • don’t point them at anyone and keep safe distance
30
Q

neutron emission:

A

1
n
0

31
Q

radioactivity of a sample always decreases over time:

A

each time decay happens and an alpha or beta particle or gamma ray is given out it means one more radioactive nucleus has disappeared
as the unstable nuclei all disappear the activity will decrease so the older the sample becomes the less radiation it will emit

32
Q

definition of half-life:

A

half-life is the time taken for half of the radioactive atoms now present to decay

the time taken for activity or count rate to fall by half

33
Q

a short half-life means…

A

activity falls more slowly as lots of the nuclei decay quickly

34
Q

a long half-life means…

A

the activity falls more slowly because most of the nuclei don’t decay for a long time, they just sit there basically unstable

35
Q

what’s on the y and x axis of a half-life graph:

A

x - time seconds
y - activity becquerel

36
Q

how are beta and gamma suitable as medical tracers?

A

they penetrate the skin and other body tissues
- can be detected externally
- can check whether organs of the body are working properly
- the radioactive source should have a SHORT HALF-LIFE so the initial levels are high enough to detect by the radioactivity inside the patient quickly disappears

37
Q

why would alpha source as a medical tracer be useless and damaging?

A

useless - as it would be stopped by body tissue, could never detect it externally
damaging - its strong ionising power makes alpha radiation really harmful if it gets inside of you

38
Q

radiation used to treat cancer:

A

ionising radiation can kill or damage cells or tissues, which can cause cancer but also treat it
radiotherapy kills the cancer cells by using high doses of gamma rays

39
Q

ionising radiation can damage cells and tissues:

A

beta and gamma can penetrate the skin and soft tissues to reach delicate organs in the body, which makes them more hazardous than alpha while outside the body, if they get inside their radiation mostly passes straight out without doing much damage

alpha radiation can’t penetrate the skin but is very dangerous if it gets inside the body

collide with the molecules in your cells and cause ionisation which damages or destroys molecules

40
Q

what effect do lower doses of radiation have?

A

causes minor damage without killing the cell, causing mutations and uncontrollable division - cancer

41
Q

what effect do higher doses of radiation have?

A

kills cells completely causing radiation sickness

42
Q

what is irradiation?

A

when objects are exposed to radiation
doesn’t make something radioactive

43
Q

what is contamination?

A

when radioactive atoms touch or get into an object therefore becoming contaminated
theses contaminating atoms might decay releasing radiation which could cause harm

44
Q

how do you dispose of low-level radiation?

A

burying it in secure landfill sites

45
Q

how do you dispose of high-level radiation?

A

sealed into glass blocks, which are then sealed in metal canisters, then buried deep in the ground

has to be a geologically stable place, if it gets into the groundwater could cause contamination of soil and get into our drinking water

46
Q

what is nuclear fission?

A

its the splitting of an atom which releases energy, can be spontaneous but in a reactor it is made to happen

47
Q

how do power stations use nuclear fission chain reactions?

A

uranium 235
- a slow-moving neutron is absorbed by a uranium 235 nucleus and the nucleus splits
- each time this happens it spits out a small number of neurons, these can then hit another uranium 235 atom and so on and so on causing a CHAIN REACTION
when uranium splits is causes two daughter nuclei to be formed both lighter elements these nuclei are radioactive (radioactive waste)
each splitting releases a huge amount of energy
in a reactor the energy is transferred to thermal energy stores to produce steam to drive a turbine

48
Q

how nuclear reactors work safely:

A

neutrons released by fission have a lot of energy therefore moving very fast, however for a chain reaction to occur the nuetron needs to slow down
the MODERATOR using graphite or water slows down nuetrons
CONTROL RODS made of boron limit the rate of fission by absorbing excess neutrons
high energy neurins and gamma waves are highly generating ionising radiation therefore SHIELDING is used to absorb the radiation, THICK CONCRETE, LEAD

49
Q

what is nuclear fusion?

A

two light nuclei collide at high speeds and join to create a larger, heavier nucleus
heavier nucleus doesn’t have as much mass so some of the mass is converted into energy and then this energy is released via radiation

can only occur at REALLY HIGH TEMPERATURES AND PRESSURES this is because positively charged nuclei have to get very close to fuse so they need to be moving fast to overcome strong force due to the electrostatic repulsion

gsce physics (9 decks)

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