Part 4- Isotope Geochemistry Flashcards

0
Q

How does radiogenic isotope variation occur?

A

The radioactive decay of unstable nuclides.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
1
Q

What are the two principle processes that generate isotopic variations?

A

Radiogenic and stable isotope geochemistry.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How do stable isotopic variations occur?

A

Variations for physical, chemical or biological processes that change the isotope compositions of elements in a mass dependent manner.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are isobars?

A

Elements with the same mass number but different combinations of protons and neutrons.
E.g. 110Cd and 110Pd.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What does amu stand for and what does it represent?

A

Atomic mass unit.
1/12th of the mass of 12C
6

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is Gram Atomic Weight?

A

Mass of 1 mole of a particular molecule/element.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How does one work out the atomic weight of an element?

A

The masses of the naturally occurring isotopes multiplied by the molar isotope abundances then added together.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What does the horizontal trend on the chart of nuclides show?

A

Isotopes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What does the diagonal trend on the chart of nuclides show?

A

Isobars.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the products of beta/negatron decay?

A

The new ‘stable’ element.
An electron/beta particle.
An anti-neutrino.
Decay energy (Q).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What happens to the original mass and atomic numbers in beta decay?

A

The mass number remains the same

The atomic number increases by 1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the products of Positron decay?

A

The new ‘stable’ element.
A positron.
A neutrino (v).
Decay energy.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

For which type of nuclides does beta decay occur?

A

Neutron rich.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

For which type of nuclides does positron decay occur?

A

Proton rich.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is electron capture decay?

What happens to the atomic/mass numbers?

A

A reaction between an electron and a proton to form a neutron therefore mass the same atomic down by 1.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What type of nuclides does electron capture decay occur in?

A

Proton rich.

16
Q

What is branched decay?

A

Decay of a nuclide by two or more pathways.

17
Q

What are the products of alpha decay?

What type of nuclides decay by this?

A

The new element.
A helium nucleus (alpha particle).
Decay energy.

Heavy nuclides (protons > 58).

18
Q

What is spontaneous fission?

Which nuclides undergo this?

A

The break-up of a nuclide into 2 or more fairly heavy daughter nuclides.

Only the heaviest e.g. Thorium and Uranium.

19
Q

In terms of half-lives, within how many are most radioactive decay systems useful?

A

Within 5 half-lives.

20
Q

Give the basic equation of geochronology and name each term.

A

D = Do + N(e^lt - 1)

D: total number of daughter atoms

Do: number of daughter atoms present at time of formation (original no.)

N: no of parent atoms in sample

l: lambda, decay constant
t: time

21
Q

How are the abundances of daughters or parents input to the equation?

A

The abundance measured relative to a stable non-radiogenic isotope.

22
Q

How do scientists work out Do?

A

Analyse 2 or more samples from the same unit.

Plot the D values- will create a sloping line: isochron.

Draw line across at t = 0.

Where they intercept is value of Do.

23
Q

What conditions are required for the isochron method to be successful?

A

Isotopic homogenisation at t=0.

Closed system behaviour through time.

Sufficient trace element fractionation.