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Physics > Radioactivity > Flashcards

Radioactivity Flashcards

1
Q

what is an isotope?

A

atoms with different numbers of neutrons

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2
Q

radioactive isotopes

A
  • usually each element only has one or two stable isotopes, like carbon-12.
  • the other isotopes tend to be RADIOACTIVE:
  • the nucleus is unstable, so it decays and emits radiation (carbon-14)
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3
Q

radioactive decay is a …

A

RANDOM PROCESS.

it’s completely unaffected by physical conditions like temp, or chemical bonding.

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4
Q

what happens when a nucleus does decay?

A

it spits out one or more types of radiation= alpha, beta, gamma or neutrons.

in the process, the nucleus often changes into a new element.

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5
Q

where does background radiation come from?

A

CBMR is around us all the time. it comes from:

  1. substances on earth
  2. radiation from space (mostly from Sun)
  3. living things (small amount of radioactive material in all living things)
  4. due to human activity (nuclear waste)
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6
Q

how does nuclear radiation cause ionisation?

A
  • causes ionisation by bashing into atoms and knocking electrons off them. atoms with no overall charge are turn into charged ions… hence the term ‘ionisation’
  • the further the radiation can penetrate before hitting an atom and getting stopped, the less damage it’ll do a,one the way and so the LESS ionising it is.
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7
Q

Alpha particles

A

Alpha particles are HELIUM NUCLEI.

  1. they’re made up of 2 protons and 2 neutrons - they’re big, heavy and slow moving.
  2. they therefore don’t penetrate far into materials and are stopped quickly.
  3. because of their size they’re STRONGLY IONISING
  4. because of their positive charge alpha particles are deflected by electric and magnetic fields.
  5. emitting an alpha particle DECREASES the atom number of the nucleus by 2 and the mass number by 4.
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8
Q

BETA PARTICLES

A
  • an electron that’s been emitted from the nucleus of an atom when a neutron turns into a proton and an electron.
    1. when a beta particle is emitted, the number of protons in the nucleus increases by one. so the atomic number INCREASES BY ONE but the mass number stays the same.
  1. they move fast and are small, meaning…
    - they penetrate moderately before colliding
    - and are moderately ionising too
  2. because they’re charged negatively, beta particles are deflected by electric and magnetic fields.
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9
Q

GAMMA RAYS

A
  • in a way, the opposite of alpha particles. they have no mass and are just energy in the form of an EM wave.
  1. they can penetrate a long way into materials without being stopped.
  2. this means they are WEAKLY IONISING as they tend to pass through rather than collide with atoms- but eventually they hit something and do damage.
  3. they have no charge and so aren’t deflected by fields.
  4. you never get just gamma rays emitted
  5. has no effect on the atomic or mass numbers of an isotope
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10
Q

what are alpha particles blocked by?

A

paper, skin or a few cm of air.

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11
Q

what are beta particles blocked by?

A

thin metal eg aluminium

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12
Q

what are gamma rays blocked by?

A

very thick lead or concrete

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13
Q

how can you detect ionising radiation?

A

Geiger-Müller detector or photographic film

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14
Q

How do you balance an ALPHA-EMISSION equation?

A
  • mass number DECREASES BY 4

- atomic number INCREASES BY 2

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15
Q

How do you balance an BETA-EMISSION equation?

A
  • mass number STAYS THE SAME

- atomic number INCREASES BY 1

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16
Q

How do you balance an GAMMA-EMISSION equation?

A
  • mass number STAYS THE SAME

- atomic number STAYS THE SAME

17
Q

How do you balance an NEUTRON-EMISSION equation?

A
  • mass number DECREASES BY 1

- atomic number STAYS THE SAME

18
Q

DEFINITION OF HALF LIFE

A

time taken for half the original mass of a sample to decay

19
Q

what is the activity of a radioactive source measured in?

A

Becquerels (Bq)

20
Q

the activity of a radioactive source ________ over time

A

DECREASES

21
Q

half life is ________ for different radioactive isotopes

A

DIFFERENT.

for some isotopes it takes a few hours, for others it’s millions of years.

22
Q

short half life means…

A

… the activity falls quickly because lots of the nuclei decay quickly.

23
Q

long half-life means …

A

… activity falls more slowly because most of the nuclei don’t decay for a long time

24
Q

EXAMPLE TO CALCULATE HALF LIFE.

A

eg. the activity of a radioactive isotope is 640Bq. Two hours later it has fallen to 40Bq. find the half life.

  1. 640 (/2) INITIAL
  2. 320 (/2)
  3. 160 (/2)
  4. 80 (/2)
  5. 40

Tells us it takes 4 half lives for the activity to fall from 640 to 40. so 2 hours represents 4 half lives, meaning the HALKF LIFE IS 30 MINS

25
Q

how do you measure the half life of a sample using a graph?

A

-the half life is found from the graph, by finding the TIME INTERVAL on the bottom axis corresponding to a HALVING of the activity on the vertical axis.

(remember to - background count from all reading before plotting a graph)

26
Q

what are the uses of nuclear radiation?

A
  1. medical tracers use BETA or GAMMA radioactive substances (highly penetrating). source has to have a short half life.
  2. TREAT CANCER. kills cancer cells and stops them dividing- involves a high dose of gamma rays carefully directed to zap the cells in the tumour while minimising the dose to the rest of the body.
  3. STERILISE FOOD AND EQUIPMENT- kill microbes while leaving object unaffected. IRRADIATION.
  4. INDUSTRY TRACES AND THICKNESS GAUGES- gamma tracers used to detect leaks in underground pipes. (can pass through rocks or earth). beta used in thickness control of paper.
27
Q

what are the risks of nuclear radiation?

A
  • ionising radiation can damage cells and tissues.
  • beta and gamma can penetrate skin to reach delicate organs inside body.
  • alpha can’t penetrate but if it gets in the body it’s extremely dangerous as it does all damage in a localised area.
  • exposure to radiation = irradiation
  • contamination = radioactive particles getting onto objects
  • radioactive waste is difficult to dispose of safely.

Physics (14 decks)

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