unpaired electron methods

Question 1

Electron spin resonance (ESR)

Answer 1

measures the amount of unpaired electrons in the artefacts that have been created over time by ionising radiation
repeatable because it does not discharge the electrons

Question 2

Thermoluminescence (TL)

Answer 2

depends on the presence of unpaired electrons in the artefact that has been created over time by ionising radiation
unrepeatable because it discharges the electrons

Question 3

total radiation exposure (aka paledose)

Answer 3

Age (years) = paledose / annual dose

Question 4

Additive irradiation method

Answer 4

• sample irradiated with several measured radiation dose
• ER intensity then plotted
• extrapolate back to zero to find paledose

Question 5

Xray fluorescence

Answer 5

can detect and quantify most elements in the periodic table
non destructive
specialised elements can be differentiated between oxidation states

Question 6

what makes a suitable artefact?

Answer 6

it must be an electrical insulator

Question 7

how does unpaired electrons build up?

Answer 7

exposure to high energy ionising radiation causes unpaired electrons to build up and become trapped in their structures
isotopes that cause this:
- K 40
- Th 232
- U 238

Question 8

when is the unpaired e- conc at its max?

Answer 8

at 1 million years, all the trapping sites are occupied. reaches SATURATION

Question 9

What can be dated since their formation?

Answer 9

bones, teeth, shells, carbonate deposits

Question 10

when can you date flints?

Answer 10

from the time since heated (ie can date the formation of the tool the flint is used in)
same for clay –> pottery

Question 11

why cant metals be dated?

Answer 11

because they are conductors and electrons cant be trapped.

Question 12

How does ESR measure?

Answer 12

put in a magnetic field, electro magnetic radiation absorbed
the spins of unpaired e- change from low to high energy state
the ESR spectrum intensity measures the conc of the unpaired electrons

Question 13

How does TL measure?

Answer 13

Heat to 500 C
electrons escape their trap sites and recombine with ions
this causes energy to be released as light
the intensity of this light emitted measures the conc pf unpaired e-

Question 14

how does X ray fluorescence measure?

Answer 14

the sample is bombarded with high energy x rays
electrons are knocked out
outer electrons drop into the space left behind
emits rays characteristics of the element. proportional to concentration