inorganic GSR Flashcards
what happens when the primer is struck
the initiator and additive materials instantly decompose producing a temperature and pressure in the region of 2000⁰C and pressure of 1400psi
what happens to the decomposed free metals
vaporise instantly forming a cloud of metallic vapour in ratios related to primer composition
what happens to the vapours upon nucleation
rapidly condense forming homogenous spheres of mixed metal alloy of ~2-10µm as they are super-saturated
what happens as the primary GSR is forming
the propellant begins to ignite causing a further increase in temperature and pressure
further increase in temp and pressure causes the production of what
larger GSR particles (>20µm) which may be the result of coalescence of smaller particles and are generally less homogenous than their smaller cousins with areas of greater lead density and may even include gas pockets
what is a type of GSR particle that can be formed which is uncommon
peeled orange particle which consists of a central Barium-Antimony core with a peel or top layer consisting of lead
what are the two presumptive tests for inorganics
sodium rhidizonate reaction
dithiooxamide reaction
sodium rhidizonate reaction - presumptive test for inorganic
Test reagent for Lead and other heavy metals
Both found in primer and bullet materials
Spray area with Sodium Rhidizonate
- Normally present as 0.2% w/w solution
Neutralise background colour with pH 2.8 buffer
- Pink colour indicative of heavy metals e.g. Barium etc.
Spray area with dilute hydrochloric acid
- Blue/Violet – Lead
- Bashinski transfer for dark coloured items
dithiooxamide reaction - presumptive test for inorganics
Test reagent for both Cu and Ni
Both found in bullet jacketing or cartridge cases
NH4OH filter paper transfer lift of residue
Reaction with dithiooxamide
- Reagent generally sprayed onto test area
- Colour change noted
- Green/Grey – Copper
- Blue/Pink – Nickel
what are two ways to detect GSR
neutron activation analysis
SEM and EDX
neutron activation analysis as a detection method for GSR
The material is bombarded by high-energy neutrons from a high-flux source
This causes the material to form radioactive isotopes
It is the decay of these isotopes that can be analysed, allowing elemental composition to be determined
Requires a neutron source i.e. ISIS in Oxford
SEM and EDX as a detection method for GSR
The material is imaged using the scanning electron microscope
This allow confirmation of morphology, an important requirement for GSR analysis
Each individual particle can then be analysed for electable composition by EDX
SEM for GSR analysis
Can produce scale images of individual GSR particles ideal for presentation in court
Excellent high-resolution high depth of field images
Morphology of particles obvious
Size of particles easily ascertained
Minimal training required
EDX can provide full elemental composition at levels more than sufficient for GSR analysis
Generally limited to surface level detail
SEM image in GSR analysis
A high energy beam of electrons is scanned in a raster pattern across the sample surface
The beam is typically of an energy between 1-40 kV and can be focussed to a spot of 0.5nm or less
In the most expensive instruments, this can give a resolution of 0.4nm
This can allow up to 500,000 x magnification
Many systems include an auto-scan function allowing GSR detection automatically, producing results in around 45 minutes per sample
The image is produced by the interaction of the sample with the electron beam producing
secondary electrons in SEM for GSR analysis
A result of inelastic scattering
Plentiful, therefore easy to detect
Reveal surface detail – 1-5nm depth
back scattered electrons in SEM for GSR analysis
Elastically scattered
Can provide information on elemental distribution and may give greater contrast between sample and background
GSR particles show up as white dots
sample reception
GSR normally received on adhesive stubs or adhesive tape
Stubs with carbon tape are easiest to process
Many specialist companies manufacture specialist kits
SEM stubs
Small aluminium mushrooms with an adhesive carbon layer
These are repeatedly dabbed onto the suspect surface, with 100 contact being typical before exhaustion
These are then sealed ready for processing
Once received they require minimal preparation
sample preparation
Despite the use of carbon tape, non-conducting samples can become charged which seriously affects results
The charged (-ve) stubs may deflect negatively charged electrons preventing interaction and degrading the image
coating
where necessary samples are coasted with a conductive layer
This is normally sputter coating
Carbon is most commonly used, although high-purity gold or platinum are excellent alternatives
Coating will affect elemental composition
class one morphology of GSR particles
Spherical bodies which may or may not include ‘nodules’ – most common type
class 2 morphology of GSR particles
Irregular or fractures bodied – less common
class 3 morphology of GSR particles
peeled oranges - uncommon
morphology of GSR particles
Depends upon composition of primer
With certain types 70-100% fall into the spherical category
Sintox or non-toxic primers less likely to yield spherical material often producing indistinct non spherical particulate materials
spherical Ba-Sb-Pb GSR particle
Near perfect shape from sinoxid primer
Secondary electron image
Poor contrast of SE shows excellent surface detail
2 micron in size typical of GSR produced in the initial stages of primer detonation
see pp for image
Spherical Ba-Pb GSR partricle
Near perfect shape from .22 LR rimfire
Back scattered electron detection
Note high contrast ideal for detection
Particulate containing heavier elements
2.5 micron size
see pp for image
Ba-Sb-Pb oranges GSR particle
Barium and antimony from inner core
Similar MP causes the two to coalesce together, barium may dominate the more central region
Ba – 730⁰C
Sb – 630⁰C
lead coalesces last to form an outer layer
This forms the peel of the GSR orange
This is due to the lower MP and likely greater levels
Pb – 330⁰C
see pp for image
size of GSR particle can vary significantly and depends upon what 4 things
Primer composition
Size of primer
Internal temperature/pressure
Where collected from
size studies show what
Almost all particles fall between 0.5um to 10um in diameter
The greatest sub-population lie in the region between 0.5um and 2um
Class 2 and 3 GSR may be significantly larger in size (10-50um)
Exceptionally large particles may indicate non-GSR source
EDX
Frequently couple to SEM
A spectroscopic method used to determine elemental composition of a sample even at microscopic level
energy dispersive x-ray spectroscopy
Sample irradiates with electrons
10-20KeV
Penetration – 2um
These force electron loss – formation of a hole
The hole formed is unstable and must be filled - outer shell electron takes its place and in doing so releases energy
X-ray produced
energy of x-ray depends on the energy gap in inner and outer shell electrons
Related to element present
Can be attributed to specific elements
There is more than one way for gaps to be filled
Various types of interaction give rise to identifiable peaks
see pp for
EDX result
GSR primer residue can be categorised into a number of types
Nomenclature not universal
Different systems have been used
in the old FSS system, GSR falls into how many types
one of nine
Each has its own characteristics and composition
Each has an associated level of evidential weight
Characteristic or Indicative
This is quite logical so although not universal is what I will consider
you can define prime type by what 3 things
residue type
composition
evidential weight
see pp for
primer types
most UK ammunition use what composition
SINOXID
modern/3 component
Most will produce residue containing (Pb)-Ba-Sb
Pb not present if styphnate replaced by other primary such as Tetrazene
rim fire ammunition
Often 2 component primer Ba-Sb
Frequently contains Silicon (SiO2) glass fractionator
A small but growing percentage of ammunition uses SINTOX or non-toxic compositions
Ti-Zn GSR is common
Sr is common in some ammunition types such as CCI Blazer lead free
Note strontium is also a component of some fireworks
GSR traces
May contain traces of other firearms associated particulate
Traces of cartridge material is common
Tin materials may be the result of foil primer capping materials or the results of the tin component of the bullet
Iron may also be present, which may be environmental or a result of barrel wear
name 3 indicative particles of GSR
fireworks
brake linings
electrical arc
fireworks
Pb-Sb, Ba-Sb, Ba-Al often including K, Cu, Cl, Mg, Sr
Morphology generally inconsistent with GSR
Size often inconsistent with GSR
brake linings
Pb-Ba-Sb in low concentration
Always including Fe and sometimes S, Mg, Si, Ti
Morphology generally inconsistent with GSR
Be aware of this – Mechanics potentially prone to false +ve’s
disadvantages of neutron activation analysis as a detection method for GSR
Potentially very costly
Slow TRT
Sample may remain radioactive for some time
Not industry standard!
advantages of SEM and EDX as a detection method for GSR
Combined SEM-EDX equipment relatively cheap ~£150k
Rapid TRT
Cost per sample low
disadvantages of SEM and EDX as a detection method for GSR
Sample may require coating
Requires high vacuum
advantages of EDX
Inexpensive addition
Easy interpretation
disadvantages of EDX
Sensitivity poor at low AMU
Unable to detect certain elements
H, He, Li, Be
