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Environmental Radioactivity > Lectures 1, 2 and 3 > Flashcards

Lectures 1, 2 and 3 Flashcards

1
Q

What does the nucleus contain

A

Protons and Neutrons

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2
Q

What defines the chemical element

A

Number of protons

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3
Q

What defines the isotope of the element

A

Number of neutrons

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4
Q

What determines the chemical bonding behaviour of the element

A

Electrons

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5
Q

What determines whether an element can be radioactive

A

The relative number of protons and neutrons, which determines the stabiity of the nucleus

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6
Q

What forces create nucleus instability

A

Coulombic repulsions and short-range attractions

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7
Q

What occurs when the attractive forces outweigh the repulsive forces

A

Stability

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8
Q

What happens when the repulsive forces outweigh the attractive forces

A

nucleus loses stability and spontaneously disintegrates, emitting particles and/or elecromagnetic radiation

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9
Q

what is the term that describes the quantitative measure of nuclear stability

A

nuclear binding energy

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10
Q

what is the principal factor for determining nucleus stability and what is it

A

neutron to proton ratio
the energy required to split a nucleus into its componenet protons and neutrons

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11
Q

What ratios of n:p create instability

A

ratios greater than 1

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12
Q

Why does the band of stability veer off of the N=Z line

A

At higher atomic number a larger number of neutrons is needed to counteract the strong repulsions between protons

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13
Q

What is the process of rearranging in the structure of the nucleus commonly referred to

A

Radioactive decay

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14
Q

What are the 5 types of ionising radiation

A
  1. Alpha
  2. Beta
  3. Gamma
  4. Positron emission
  5. Electron capture
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15
Q

What does alpha decay emit

A

A helium nucleus is emitted from the nucleus

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16
Q

What does beta decay emit

A

a high speed electron/positron as well as a neutrino

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17
Q

What does the conservation of mass and charge mean

A

The sum of the mass numbers and charges before and after the radioactive decay must be the same

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18
Q

What dies a becquerel (Bq) describe

A

Radioactive decay - one bequerel is equal to one decay per second

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19
Q

What is half life

A

The time taken for half of the initial number of nuclei to disintegrate in a radioactive substance

t1/2 = 0.693/k
k - decay rate

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20
Q

What is decay rate (k)

A

The speed at chich a substance disintegrates

ln(N/N0) = -kt
N - nuclei remaining
N0 - nuclei initially
k - decay rate
t - time

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21
Q

How can you use half lives to measure the age of rocks, and therefore the earth

A

By measuring the ration of daughter to parent isotopes with in the rock, this tells you how man half lives have passed and then if you know how long a half life is you can date the rock

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22
Q

How long is the U-238 half-life

A

Approximately the age of the Earth

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23
Q

What is the final, and stable, daughter of U-238

A

Pb-206

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24
Q

What is ‘Blocking Temperature’

A

The temperature at which the atomic clock is ‘reset’

25
Q

How does ‘Blocking Temperature’ work

A

If Igneous and Metamorphic rocks are heated to high enough temperatures, they no longer act as ‘closed systems’. Some of the daughter products ‘leak’ out of the primary mineral via diffusional migration. This changes the ratio of daughter to parent and gives an incorrect age for the rock.

26
Q

What are discordant dates

A

The incorrect dating of rocks due to blocking temperatures resetting isotopic clocks

27
Q

How is Lead used in dating

A

Ratios of the three radiogenic lead isotopes to the non-radiogenic lead-204 all change BUT at DIFFERENT RATES. These ratios can be used to date rocks

28
Q

How does Carbon-14 dating work

A

In the upper atmosphere Nitrogen is cosmically bombarded so that it emits a proton and becomes C-14. C-14 is radioactive with a half life of 5,730 years.

Plants and animals ingest C-14 while they are alive. When they die they stop taking it in. The C-14 clock then begins to count down and by looking at ratios of C-14 in plants and animals, their age can be discerned.

29
Q

What is fission track analysis

A

When an atom of U-238 disintegrates and emits an alpha particle (He), the massive Helium nucleus causes structural damage to the crystal which can be revealed by chemical etching

30
Q

How does the dating of metamorphic events work

A

During a metamorphic event there is some redistribution of the daughter atoms out of the crystal into adjacent rock. Dating the crystal would then reveal the age of the metamorphic event, wheras dating the whole rock would provide the original age of the crystal and rock.

31
Q

What is nuclear binding energy (in terms of how can you find it)

A

It is the difference between the sum of the masses of protons and neutrons in the nucleus - it in the energy that holds the nucleus together

32
Q

What equation do you use to find nuclear binding energy

A

E = mc2

33
Q

What is fission

A

The splitting of a large nucleus into smaller peices

34
Q

What is fusion

A

The joining of two nuclei at extrememly high temperatures and pressures

35
Q

Do we do fusion or fission right now

A

Fission

36
Q

Does the sun do fusion or fission

A

Fusion

37
Q

What is MeV

A

Megaelectron volts

38
Q

What is a nucleon

A

A proton or neutron - for example if you were to count all of the nucleons in a Helium, there would be 4 (2 protons and 2 neutrons)

39
Q

How to calculate the energy given from fission or fusion

A

The binding energy multiplied by the number of nucleons (things in the nucleus)

40
Q

What is the most likely cause of fission

A

The absorption of a neutron which disturbs the nuleus structure.

41
Q
A
42
Q

What does fission produce

A

two fission nuclei (smaller), 2-3 free neutrons and energy (e.i. heat)

43
Q

What are the factors that are important in inducing fission

A

Speed of the impacting neutron
Structure of the nucleas being impacted

44
Q

What can a fast neutron do to U-238

A

Transmutation - it absorbs it, beta decays and becomes neptunium-239

45
Q

What happens if a fission reaction is uncontrolled

A

It becomes a ‘runaway nuclear reaction’ as the split neutrons continue to hit other nuclei - the basis for atomic weapons

46
Q

What are used as moderators in nuclear reactors and why

A

Water, D2O (heavy water) and Graphite

They slow the released neutrons from fission via collisions, so that the neutrons travel at a speed that allows for the continuation of fission (instead of the neutrons wizzing around and passing through everything)

47
Q

What are ‘thermal neutrons’

A

Moderated neutrons

48
Q

Can nuclear fuel be none fissile

A

Yes BUT it must be transmuted via the gain of a neutron to become a fissile isotope

49
Q

Why does fission produce energy

A

The mass of the two fission fragments is less than the mass of the reactant, this mass difference is converted to energy

Can be calculated by E = mc2

50
Q

Why does fusion produce energy

A

The mass of an atomic nucleus is always smaller than the sum of all of its protons and neutrons (binding energy) - so the mass difference (or mass defect) is the energy released

51
Q

What is the ‘Rest Mass’

A

the ‘rest mass’ of an object is the inertial mass that an object has wehn it is at rest (perfectally stationary) - the MINIMUM MASS

52
Q

What is sum for mass defect

A

= the sum of the masses of protons and neutrons - the rest mass

53
Q

What are the best fuels for fusion and what is the problem with them

A

Heavy isotopes of Hydrogen - deuterium and tritium
There is a limiting supply of tritium currently and new ways of making much more need to be developed

54
Q

What are the 4 benifits of fusion over fission and why

A

U-238 is not used and since it is only a fertile material and not a fissile material, this reduces costs as well as the number of radiactive isotopes produced its transmutation

Pu–244 - a very long half-life radioactive isotope and which can be used in the production of nuclear weapons

He is produced which is inert and not radioactive compared to the wide range of radioactive isotopes created via fission

A loss of coolent (LOCL) accident is much less likely to occur due to the strict conditions that fusion requires are not maintained, meaning chance of meltdown is much less likely

55
Q

What happens if fusion occurs with elements heavier than Iron

A

Energy is consumed

56
Q

Consumption (lifespan) stages of the Sun (the elements combined or created)

A

H - He - C - O - Si

57
Q

How do we get elements heavier than Iron

A

Supernovae

At the end of the lifespan of a very large star (Supergiant), when there is nothing less to fuse a supanova will typically occur causing a very large explosion

58
Q

What happens during a Supernova

A

Flood of neutrons is created and elements heavier than Fe are formed via the rapid capture of neutrons on seed nuclei at rates greater than disintegration through radiactivity

Environmental Radioactivity (11 decks)

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