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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
How does 'Blocking Temperature' work
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
What are discordant dates
The incorrect dating of rocks due to blocking temperatures resetting isotopic clocks
27
How is Lead used in dating
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
How does Carbon-14 dating work
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
What is fission track analysis
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
How does the dating of metamorphic events work
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
What is nuclear binding energy (in terms of how can you find it)
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
What equation do you use to find nuclear binding energy
E = mc2
33
What is fission
The splitting of a large nucleus into smaller peices
34
What is fusion
The joining of two nuclei at extrememly high temperatures and pressures
35
Do we do fusion or fission right now
Fission
36
Does the sun do fusion or fission
Fusion
37
What is MeV
Megaelectron volts
38
What is a nucleon
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
How to calculate the energy given from fission or fusion
The binding energy multiplied by the number of nucleons (things in the nucleus)
40
What is the most likely cause of fission
The absorption of a neutron which disturbs the nuleus structure.
41
42
What does fission produce
two fission nuclei (smaller), 2-3 free neutrons and energy (e.i. heat)
43
What are the factors that are important in inducing fission
Speed of the impacting neutron Structure of the nucleas being impacted
44
What can a fast neutron do to U-238
Transmutation - it absorbs it, beta decays and becomes neptunium-239
45
What happens if a fission reaction is uncontrolled
It becomes a 'runaway nuclear reaction' as the split neutrons continue to hit other nuclei - the basis for atomic weapons
46
What are used as moderators in nuclear reactors and why
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
What are 'thermal neutrons'
Moderated neutrons
48
Can nuclear fuel be none fissile
Yes BUT it must be transmuted via the gain of a neutron to become a fissile isotope
49
Why does fission produce energy
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
Why does fusion produce energy
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
What is the 'Rest Mass'
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
What is sum for mass defect
= the sum of the masses of protons and neutrons - the rest mass
53
What are the best fuels for fusion and what is the problem with them
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
What are the 4 benifits of fusion over fission and why
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
What happens if fusion occurs with elements heavier than Iron
Energy is consumed
56
Consumption (lifespan) stages of the Sun (the elements combined or created)
H - He - C - O - Si
57
How do we get elements heavier than Iron
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
What happens during a Supernova
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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