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physics > chapter 25 - Radioactivity > Flashcards

chapter 25 - Radioactivity Flashcards

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1
Q

What are the three types of radiation?

A

alpha, beta, gamma

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2
Q

What is ionising radiation?

A

Radiation that removes electrons from atoms, creating positive ions

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3
Q

What is alpha decay?

A

When an alpha particle (2 protons and 2 neutrons) is emitted from the nucleus

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4
Q

What are the properties of alpha radiation?

A
  • Very ionising
  • Very short range
  • Very low penetrating
  • Charged (+2e)
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5
Q

What’s beta- decay?

A

Decomposition of down quark into up quark (neutron into proton) to make an electron and antineutrino

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6
Q

What’s beta+ decay?

A

Decomposition of up quark into a down quark (proton into neutron) to make a positron and neutrino

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7
Q

What are the properties of beta radiation?

A
  • Ionising
  • Short range
  • Low penetrating
  • Charged (-1e or +1e)
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8
Q

Whats gamma decay?

A

Emission of high energy gamma photons from an unstable atoms nuclei

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9
Q

What is the wavelength of gamma rays?

A

Less than 10^-13

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10
Q

What are the properties of gamma radiation?

A
  • Low ionising
  • Long range
  • Highly penetrating
  • No charge
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11
Q

How can you use electric fields to distinguish between radiations?

A
  • Beta- radiation (electrons) will be deflected towards +ve plate because they’re -ve
  • Beta+ radiation (positrons) and alpha radiation (helium nuclei) will be deflected towards -ve plate as they’re both +ve ( alpha deflected less due to its heavier mass)
  • Gamma radiation (photons) won’t be deflected at all as they have no charge
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12
Q

How can you use magnetic fields to distinguish between radiations?

A
  • Beta- radiation (electrons) will be deflected downwards as they’re -ve
  • Beta+ radiation (positrons) and alpha radiation (helium nuclei) will be deflected upwards as they’re both +ve
  • Gamma radiation (photons) won’t be deflected at all as they have no charge
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13
Q

How do you stop alpha?

A

A few centimetres of air or a thin sheet of paper

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14
Q

How do you stop beta?

A

1 meter of air or 1-3 mm of aluminium

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15
Q

How do you stop gamma?

A

A few centimetres of lead

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16
Q

Why is radiation dangerous?

A

Ionising which causes damage to living cells

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17
Q

What is the alpha decay equation

A

A: X :Z → A-4: X :Z-2 +4He2

226Ra88→222Rn86+4He2

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18
Q

What kind of nuclei undergoes beta minus decay?

A

One with too many neutrons to be stable

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19
Q

What kind of nuclei undergoes beta positive decay?

A

One with too many protons to be stable

20
Q

What kind of nuclei undergoes beta positive decay?

A

One with too many protons to be stable

21
Q

What’s the beta- decay equation?

A

A: X :Z → A: X :Z+1 + e− + anti-neutrino

14C6→ 14N7 + e− + anti-neutrino

22
Q

What’s the beta+ decay equation?

A

A: X :Z → A: X :Z-1 + e+ + νe

23Mg12 → 23Na11 + e+ + νe

23
Q

What kind of nucleus emits gamma radiation?

A

One with a surplus of energy (especially just after alpha or beta emission)

24
Q

What’s the gamma decay equation?

A

A: X :Z → A: X :Z + γ (photon)

137 56Ba→137 56Ba+γ

25
Q

What is a decay chain?

A

A parent nuclei decays into a radioactive daughter nuclei, which then becomes the
parent for a subsequent decay process until it has a stable nucleus

26
Q

How do you describe radioactive decay?

A

As a random and spontaneous event

27
Q

Why is radioactive decay random?

A
  • Cannot predict when a particular nucleus in a sample will decay
  • Cannot predict which nucleus will decay next
  • Each nucleus in a sample has the same chance of decaying per unit time
28
Q

Why is radioactive decay spontaneous?

A
  • Not affected by presence of other nuclei in sample

- Not affected by external factors (like temperature or pressure)

29
Q

What’s half life?

A

The time taken for the radioactivity of a specified isotope to fall to half its original value

30
Q

How do you calculate half life?

A

Half life = ln(2)/λ

31
Q

How can you simulate half life with dice?

A
  • Throw a large number of dice at the same time (e.g. 100 dice)
  • Remove all the dice showing a particular number from the group and record the number removed
  • Throw the lower number of dice again and repeat
  • Once you’ve gotten down to one or so dice you stop
  • Plot a graph of number dice threw against the number of throws
  • You can use the graph to see that you should have a relatively stable half life
32
Q

What is activity?

A

The rate at which a source of unstable nuclei decays

33
Q

What is the unit of activity?

A

Becquerel (Bq) = s^-1

34
Q

What is activity reliant on?

A

Number of undecayed nuclei and half life

35
Q

How do you calculate activity?

A

A = λN

36
Q

What’s the decay constant?

A

The probability of decay of an individual nucleus per unit time

37
Q

What’s the decay constant?

A

The probability of decay of an individual nucleus per unit time

38
Q

What are the units for decay constant?

A

s^-1 or h^-1 or y^-1

39
Q

What is the exponential decay equation for activity?

A

A = Ao x e^(-λt)

A = activity
Ao = initial activity
λ = decay constant
t = time
40
Q

What is the exponential decay equation for number of undecayed nuclei?

A

N = No x e^(-λt)

N = number of undecayed nuclei
No = initial number of undecayed nuclei
λ = decay constant
t = time
41
Q

Why does activity decrease exponentially?

A

Because activity is directly proportional to the number of undecayed nuclei. Since the number of undecayed nuclei is decreasing exponentially, the activity also has to decrease exponentially

42
Q

How can you determine the half life of protactinium?

A
  • Find the background count
  • Shake protactinium bottle for 15 seconds to dissolve the protactinium
  • Place a GM tube directly in front of the bottle without touching it
  • Take a ten second count of decaying protactinium every 30 seconds
  • Make sure to zero the count right before every 10 second count
  • Take the background count away from each of the 10 second counts
  • Plot graph of corrected count rate against time
  • You can then find half life by seeing time it takes for count rate to half
43
Q

Why is protactinium difficult to use and transport?

A

It has a very short half life so has decayed before you get to use it

44
Q

How can you make protactinium?

A

Get a bottle filled with Uranyl(VI) nitrate and organic solvent

  • Uranium-238 in uranyl nitrate decays into Thorium-234
  • Thorium-234 decays into Protactinium-234
  • Protactinium-234 is soluble in organic solvent so dissolves and rises to top of the bottle
45
Q

What is carbon dating?

A

The process of using the radioactive isotopes in carbon 14 to calculate the age of an artifact

46
Q

How does carbon dating work?

A
  • Living organisms take in carbon-12 and carbon-14 in known ratios while alive
  • After it dies the carbon-14 isotopes continue to decay while carbon-12 stays same
  • Therefore the ratio of C-12 to C-14 in fossils can be measured and their age calculated
47
Q

What are the limits of carbon dating?

A
  • Assumes ratios of carbon-12 and carbon-14 have stayed same over time
  • Carbon-14 in small amounts so activity is comparable to the background rate

physics (18 decks)

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