Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Materials Identification > inorganic GSR > Flashcards

inorganic GSR Flashcards

1
Q

what happens when the primer is struck

A

the initiator and additive materials instantly decompose producing a temperature and pressure in the region of 2000⁰C and pressure of 1400psi

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

what happens to the decomposed free metals

A

vaporise instantly forming a cloud of metallic vapour in ratios related to primer composition

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

what happens to the vapours upon nucleation

A

rapidly condense forming homogenous spheres of mixed metal alloy of ~2-10µm as they are super-saturated

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

what happens as the primary GSR is forming

A

the propellant begins to ignite causing a further increase in temperature and pressure

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

further increase in temp and pressure causes the production of what

A

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

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

what is a type of GSR particle that can be formed which is uncommon

A

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

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

what are the two presumptive tests for inorganics

A

sodium rhidizonate reaction

dithiooxamide reaction

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

sodium rhidizonate reaction - presumptive test for inorganic

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

dithiooxamide reaction - presumptive test for inorganics

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

what are two ways to detect GSR

A

neutron activation analysis

SEM and EDX

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

neutron activation analysis as a detection method for GSR

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

Requires a neutron source i.e. ISIS in Oxford

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

SEM and EDX as a detection method for GSR

A

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

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

SEM for GSR analysis

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

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

SEM image in GSR analysis

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

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

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

secondary electrons in SEM for GSR analysis

A

A result of inelastic scattering

Plentiful, therefore easy to detect

Reveal surface detail – 1-5nm depth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

back scattered electrons in SEM for GSR analysis

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

sample reception

A

GSR normally received on adhesive stubs or adhesive tape

Stubs with carbon tape are easiest to process

Many specialist companies manufacture specialist kits

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

coating

A

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

21
Q

class one morphology of GSR particles

A

Spherical bodies which may or may not include ‘nodules’ – most common type

22
Q

class 2 morphology of GSR particles

A

Irregular or fractures bodied – less common

23
Q

class 3 morphology of GSR particles

A

peeled oranges - uncommon

24
Q

morphology of GSR particles

A

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

25
Q

spherical Ba-Sb-Pb GSR particle

A

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

26
Q

Spherical Ba-Pb GSR partricle

A

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

27
Q

Ba-Sb-Pb oranges GSR particle

A

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

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

see pp for image

29
Q

size of GSR particle can vary significantly and depends upon what 4 things

A

Primer composition

Size of primer

Internal temperature/pressure

Where collected from

30
Q

size studies show what

A

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

31
Q

EDX

A

Frequently couple to SEM

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

32
Q

energy dispersive x-ray spectroscopy

A

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

33
Q

see pp for

A

EDX result

34
Q

GSR primer residue can be categorised into a number of types

A

Nomenclature not universal

Different systems have been used

35
Q

in the old FSS system, GSR falls into how many types

A

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

36
Q

you can define prime type by what 3 things

A

residue type
composition
evidential weight

37
Q

see pp for

A

primer types

38
Q

most UK ammunition use what composition

A

SINOXID

modern/3 component

Most will produce residue containing (Pb)-Ba-Sb

Pb not present if styphnate replaced by other primary such as Tetrazene

39
Q

rim fire ammunition

A

Often 2 component primer Ba-Sb

Frequently contains Silicon (SiO2) glass fractionator

40
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

41
Q

GSR traces

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

42
Q

name 3 indicative particles of GSR

A

fireworks
brake linings
electrical arc

43
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

44
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

45
Q

disadvantages of neutron activation analysis as a detection method for GSR

A

Potentially very costly

Slow TRT

Sample may remain radioactive for some time

Not industry standard!

46
Q

advantages of SEM and EDX as a detection method for GSR

A

Combined SEM-EDX equipment relatively cheap ~£150k

Rapid TRT

Cost per sample low

47
Q

disadvantages of SEM and EDX as a detection method for GSR

A

Sample may require coating

Requires high vacuum

48
Q

advantages of EDX

A

Inexpensive addition

Easy interpretation

49
Q

disadvantages of EDX

A

Sensitivity poor at low AMU

Unable to detect certain elements

H, He, Li, Be

Materials Identification (17 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions