Forensic Archaeology Flashcards
Define isotopes
Atoms with the same number of protons but a different number of neutrons
What is the difference between a chemical and nuclear reaction?
Chemical - change in valence electron configuration, no change in nucleus, no new elements created, independent of isotope
Nuclear - change in atomic nucleus, producing a new element, varies dramatically by isotope
What is alpha decay?
The product nucleus has an atomic number that is two or less, and a mass number that is four or less, than the original nucleus
How does alpha decay work in a smoke detector?
- A weak radioactive source ionises the air molecules in the chamber of the detector, creating a region of both positively and negatively charged particles
- A voltage is maintained between the plates inside the chamber, creating a current due to the flow of these positively and negatively charged particles
- As long as the current is maintained, the alarm is deactivated
- If smoke particles enter the chamber, these attach to the charged particles and slow down the flow, causing a drop in current, which triggers the alarm
What is beta decay?
A neutron is converted to a proton and an electron is ejected. The product nucleus has an atomic number that is one more than the original nucleus, and the mass number remains the same
What is positron emission?
Conversion of a proton to a neutron and a positron (positive electron). The product nucleus has an atomic number one less than the original nucleus
What is electron capture?
Conversion of a proton to a neutron. The product nucleus has an atomic number that is one less than the original nucleus
What is gamma emission?
When the radioactive decay results in a product nucleus in an excited state which goes to a lower state with the emission of electromagnetic radiation
What is spontaneous fission?
A heavy nucleus splits into lighter nuclei with the release of energy
What is the unit of radioactivity?
the Becquerel (Bq)
How many disintegrations per second is 1Bq?
One
What is a curie (Ci)?
A unit of activity equal to 3.7x10^10 disintegrations per second
What are the three ways of detecting radiation?
Ionisation (Geiger) counter, scintillation counter, accelerator mass spectrometry (AMS)
What is the equation for activity/rate of decay?
k x N
what is the half-life of C14?
5730 years
what is potassium argon dating useful for?
dating volcanic rocks
what is neutron activation analysis used for?
analysis of arsenic in human hair and to authenticate oil paintings
What is electron spin resonance (ESR)?
A repeatable dating method that measures the amount of unpaired electrons in the artefact that have been created over time by ionising radiation
What is thermoluminescence (TL)?
A non-repeatable dating method that depends on the presence of unpaired electrons in the artefact that have been created over time using ionising radiation
What is the paleodose?
Total radiation exposure
What is the process for taking the measurement for ESR?
- Sample is placed in a magnetic field. The unpaired electrons now have different energies depending on whether their spins are up or down
- Sample absorbs electromagnetic radiation in the microwave region of the spectrum to flip spins of unpaired electrons from low energy to high energy states
- The intensity of the ESR spectrum measures the concentration of unpaired electrons
Describe the process of TL dating?
- Heating sample, typically to 500 degrees, discharges the trapped unpaired electrons
- This is because heating gives electrons the activation energy to escape their trap sites so they become mobile and recombine with ions
- Energy stored in the solid is released as light
- The intensity of light emitted measures the concentration of unpaired electrons
What is the main difference between ESR and TL measurements?
TL measurement discharged the unpaired electrons so the dating measurement can be done only once, whereas ESR does not discharge the unpaired electrons so the dating measurement can be repeated
What is an F-centre?
A simple electron trapped in an anion vacancy
What does an alpha particle consist of?
2 protons and 2 neutrons, decreasing the atomic number by 2 when an alpha particle is emitted
What does beta emission mean?
The loss of an electron (beta particle) and a neutron is transformed into a proton in the nucleus. This increases the atomic number by 1
Why is X-ray fluorescence a good technique?
It can detect and quantify most elements in the periodic table, generally Na and above
Describe the principles of X-ray fluorescence
- The sample is bombarded with high-energy X-rays
- These X-rays will knock electrons out of the atoms
- These knocked out electrons, photoelectrons, will come from the inner electron shells of the atoms
- Therefore, there are holes in the atom
- Outer electrons will drop into the holes and there will be an emission of a photon in the X-ray regime
- These X-rays will be characteristic of the element and their intensity will be proportional to the concentration of the element
What does Moseley’s Law state?
The energy of a transition depends on (Z-1)^2, where Z is the charge on the nucleus
Define mass burial/grave
A mass of bodies in intimate contact with each other and deposited in the same grave
Define multiple burial
Simultaneous deposition of several bodies
Define collective burial
Deposition of multiple bodies over a period of time
Define primary burial
Buried once and that is where they are found
Define secondary burial
Buried once, dug up, and buried again
Define exhumation of human remains
The retrieval of the remains whether archaeological techniques were used or not
Define excavation of human remains
Results in the retrieval of the remains and ALSO the reconstruction of the human activity at the site and beyond
What is a harris matrix?
A tool used to depict the temporal succession of archaeological contexts
What are cadaver dogs?
Specially trained dogs to detect scene of human decomposition
What are the three types of probes and shovels, and what are they used for?
- T-bar - qualitative changes in soil compactness
- Penetrometer - quantitative changes in soil compactness
- Soil-coring - check for mixing of soil horizons
Once the outline of a grave is found, what do we do?
- Section grave
- Preserve the integrity of the grave
- Empty grave fill
What is the purpose of sectioning the grave?
- Adds depth to constraints of evcavation
- Allows lateral access to the grave and body
- General elements remain consistent
