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Materials identification > inorganic GSR > Flashcards

inorganic GSR Flashcards

1
Q

GSR formation

A
  • As 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 (~10,000Kpa)
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2
Q

what does the first stage of the GSR formation cause

A

the decomposed free metals to vaporise instantly forming a cloud of metallic vapour in ratios related to primer composition

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3
Q

what are the vapours

A

super-saturated and therefore upon nucleation rapidly condense forming homogenous spheres of mixed metal alloy of ~2-10µm
- This is perhaps the mechanism by which the majority of GSR particles are formed but this is not the end of the story

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4
Q

what happens as the primary GSR is forming

A

the propellant begins to ignite causing a further increase in temperature and pressure (~3000⁰C+ and 30,000psi+)

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5
Q

what can happens when the propellant ignites

A

cause the production of 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

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6
Q

what other type of GSR particles can be formed

A

peeled orange particle which consists of a central Barium-Antimony core with a peel or top layer consisting of lead – These are uncommon

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7
Q

Presumptive tests for inorganics

Sodium Rhidizonate reaction

A
  • 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
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8
Q

Presumptive tests for inorganics

Dithiooxamide reaction

A
  • 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
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9
Q

Detection methods of GSR

Neutron activation analysis (Uncommon)

A
  • 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
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10
Q

Neutron activation analysis (Uncommon)- Practical

A
  • Requires a neutron source i.e. ISIS in Oxford
  • Potentially very costly
  • Slow TRT
  • Sample may remain radioactive for some time
  • Not industry standard!
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11
Q

Detection methods of GSR

SEM and EDX

A
  • The material is imaged using the scanning electron microscope
  • This allow confirmation of morphology, an important requirement for GSR analysis
  • Each individual particles can then be analysed for electable composition by EDX
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12
Q

SEM and EDX- Practical

A
  • Combined SEM-EDX equipment relatively cheap ~£150k
  • Rapid TRT
  • Cost per sample low
  • Sample may require coating
  • Requires high-vacuum
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13
Q

SEM pros

A
  • 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
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14
Q

SEM image

A
  • 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
  • Many systems include an auto-scan function allowing GSR detection automatically, producing results in around 45 minutes per sample
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15
Q

most expensive instruments resolution

A
  • 0.4nm

- This can allow up to 500,000 x magnification

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16
Q

image

A
  • The image is produced by the interaction of the sample with the electron beam producing
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17
Q

secondary electrons

A
  • A result of inelastic scattering
  • Plentiful, therefore easy to detect
  • Reveal surface detail – 1-5nm depth
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18
Q

back scattered electrons

A
  • Elastically scattered
  • Can provide information on elemental distribution and may give greater contrast between sample and background
  • GSR particles show up as white dots
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19
Q

Practical applications

Samples – sample reception

A
  • Elastically scattered
  • Can provide information on elemental distribution and may give greater contrast between sample and background
  • GSR particles show up as white dots
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20
Q

Samples- SEM stubs

A
  • 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
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21
Q

sample preparation

A
  • 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
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22
Q

coating

A
  • Prevents the sample from being charged, coated with a conductive layer
  • This is normally by sputter coating
  • Carbon is most commonly used, although high-purity gold or platinum are excellent alternatives
  • Coating will affect elemental composition
23
Q

GSR under SEM

A
  • Spherical bodies which may or may not include ‘nodules’ – Most common type (Class 1)
  • Irregular or fractured bodies – Less common (Class 2)
  • Peeled oranges – Uncommon (Class 3)
  • A combination of the above
24
Q

morphology

A
  • Depends upon composition of primer
  • With certain types 70-100% of fall into the spherical category
  • Sintox or non-toxic primers less likely to yield spherical material often producing indistinct non spherical particulate materials
25
Q

GSR examples- Spherical Ba-Sb-Pb particle

A
  • Near perfect sphere 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
26
Q

GSR examples- Spherical Ba-Pb particle

A
  • Near perfect sphere from .22 LR rimfire
  • Back scattered electron detection
  • Note high contrast ideal for detection
  • Particulate containing heavier elements
  • shows up as white areas
  • 2.5 micron size
27
Q

GSR examples- Ba-Sb-Pb oranges

A
  • An unusual form of GSR particle
  • Barium and Antimony form inner core
  • Similar MP causes the two to coalesce together, barium may dominate the more central region
  • Ba – 730⁰C
  • Sb – 630⁰C
28
Q

Lead coalesces last to form an outer layer

A
  • This forms the peel of the GSR orange
  • This is due to the lower MP and likely greater levels
  • Pb – 330⁰C
29
Q

Casework example- Spherical Ba-Pb particle

A
  • Sample from sleeve of suspect at 500x Magnification
  • Note fibrous material (fibres shed from coat on sample collection)
  • BSE detection used to increase contrast
  • Unusual pitted olive shape

LOOK AT PPT FOR IMAGES OF EXAMPLES

30
Q

size of GSR depends on

A
  • Primer composition
  • Size of primer
  • Internal temperature/pressure
  • Where collected from…
31
Q

studies show that the size of the particles

A
  • Almost all particles fall between 0.5µm to 10µm in diameter
  • The greatest sub-population lie in the region between 0.5µm and 2µm
  • Class 2 and 3 GSR may be significantly larger in size (10-50µm)
  • Exceptionally large particles may indicate non-GSR source
32
Q

EDX-Frequently coupled to the SEM

A

Frequently coupled to the SEM

33
Q

what is edx designed to do

A

used to determine elemental composition of a sample even at microscopic level

34
Q

cons of EDX

A
  • Sensitivity poor at low AMU
  • Unable to detect certain elements
  • H, He, Li, Be
35
Q

pros of EDX

A
  • Inexpensive addition

- Easy interpretation

36
Q

energy dispersive X-ray spectroscopy

A
  • Sample irradiated with electrons
  • ~10-20 KeV
  • Penetration ~2µm
  • These force electron loss - Formation of a ‘hole’
  • The hole formed is unstable and is must be filled
  • Outer shell electron takes its place and in doing so releases energy
  • X-ray produced
37
Q

Energy of x-ray can be detected

A
  • 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- L to K, M to K etc…
  • Various types of interaction give rise to identifiable elemental peaks
38
Q

EDX result

A
  • Elemental composition
  • Elemental composition consistent with GSR
  • This particle consists of Ba-Pb (Probably oxides)
  • Small amount of Copper from the cartridge case and Silicon from frictionator – Rim-fire
39
Q

P- GSR types

• Categorisation

A
  • GSR primer residue can be categorised into a number of types
  • Nomenclature not universal
  • Different systems have been used
40
Q

In the old FSS system, GSR generally falls into one of how many types

A

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
41
Q

The following pages define primer type by type

A

 Residue type
 Composition
 Evidential weight
LOOK ON POWERPOINT FOR ALL THE TABLES

42
Q

Type IX

A
  • Relatively uncommon in recovered ammunition in UK
  • May be preferred due to non-toxic non-cumulative nature of residue
  • Therefore should be more common amongst firearms professionals and those using firearms more frequently however this is not the case
  • Most UK police forces are not yet using SINTOX primed ammunition due to concerns over reliability
43
Q

Most UK ammunition uses SINOXID composition

A
  • Modern/3 component
  • Most will produce residue containing (Pb)-Ba-Sb
  • Pb not present if styphnate replaced by other primary such as Tetrazene
44
Q

Older ammunition from Eastern Europe or Middle east

A
  • May be based upon mercury fulminate

- These are still in circulation

45
Q

Rim fire ammunition

A
  • Often 2 component primer Ba-Sb

- Frequently contains Silicon (SiO2) glass frictionator

46
Q

most UK ammunition uses

A

SINOXID composition

47
Q

A small but growing percentage of ammunition uses SINTOX or non-toxic compositions

A
  • 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
48
Q

All GSR

A
  • 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
49
Q

P-GSR other elements

A

look on ppt for table

50
Q

Indicative particles

• Other sources of GSR like particulate

A

fireworks

brake linings

electrical arc as a possible source too

51
Q

fireworks

A
  • Pb-Sb, Ba-Sb, Ba-Al often including K, Cu, Cl, Mg, Sr
  • Morphology generally inconsistent with GSR
  • Size often inconsistent with GSR
52
Q

brake linings

A
  • 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
53
Q

Non-GSR

A

• These particles look spherical – GSR? look on ppt for image
• The morphology is certainly consistent with GSR as is the general appearance and size (~3µm)
• Elemental composition however is not…
• Aluminium
• Chlorine
• Oxygen
• Clearly does not fall into the GSR
types previously mentioned

54
Q

non GSR- Aluminium Chloro-hydrate – AlCl(OH)5

A
  • This image (on ppt) is particulate material derived from a can of popular antiperspirant
  • The particles react with moisture to plug up pores and prevent sweating

Materials identification (21 decks)

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