Firearms Flashcards

Question

What does the DTO Test test for? | What is a positive test?

Answer 1

Copper and Nickel Positive Cu = dark green-black Positive Ni = blue-pink Cu confirmation test: pink, back to dark green False positives = green for Fe and orange for Zn

Answer 2

Filter paper moistened with ammonium hydroxide solution Moistened side pressed against exhibit Residue transfer photographed Lift sprayed with DTO Confirmation against false positives with 2-NN

Answer 3

Nickel plated bullets | Positive = bright red

Answer 4

Filter paper is prepared with a DMG solution Suspected bullet hole is treated with ammonium hydroxide (looking for path of bullet) Pretreated DMG filter pressed on exhibit and removed If nickel red DMG complex seen immediately

Answer 5

Within 18” firing distance.

Answer 6

``` SEM-EDS AAS GFAAS ICP XRF ```

Answer 7

``` Raman IR GC-MS LC-MS CE ```

Answer 8

Information of physical nature of sample surface | Higher resolution than optical microscopes because of smaller wavelengths - smaller diffracted effects

Answer 9

Electron beam production Focussing electron beam Image production Detection

Answer 10

Tungsten filament (super hot solid ejects electrons) Crystals Electrons accelerated by positive anode, produces smaller, more cohesive beam Smaller eV gives better topographical information Larger eV gives deeper information

Answer 11

Electromagnetic lenses and apertures reduce beam diameter Pathways bent by electromagnetic radiation Focal length controlled by varying current in coils Electrons accelerated through objective and condenser lenses, reduce diameter Condenser converges electron beam to spot below, height impacts spot diameters (low = large, high = small) Resolution cannot be better than diameter of incident beam

Answer 12

Raster scanning - uses two pairs of deflection (scanning) coils within objective lens Beam moves across sample Electrical signal to coil controls movement Coils deflect beams in X and Y direction, respectively Size of rastered area gives rise to magnification

Answer 13

Multiple detector types: secondary electron detector, Backspatter electron detector, x-ray detector Everhart-thornley: positive bias to attract and accelerate electron to a scintillator Electrons are converted to photons Photons pass through photomultiplier tube - amplifies signal

Answer 14

Penetration of sample surface - electron beam produces secondary electrons, Backspatter electrons, xrays, and Auger electrons The depth the electron come to rest within the solid is the penetration depth The volume of sample containing most of these electrons is the interaction volume Shallow depth = escape depth

Answer 15

1-5 keV = delicate or uncharted samples 5-10 keV = coated biological samples 10-30 keV = physical science samples Higher the beam the more BSEs in addition to SEs

Answer 16

Conductive samples = easiest to study - minimize buildup of charge - buildup causes distortion of signal and image Non-conductive samples = grounded or coated with conductive materials to minimize surface charging: copper tape, carbon paint, THIN metallic coatings (Os, Au, Pt, Ag)

Answer 17

Investigates the elemental or chemical characteristics of a sample Z > 3 (carbon and beyond) When an electron beam interacts with a sample x-rays are emitted from the whole interaction volume

Answer 18

Characteristic x-rays | Bremsstrahlung (continuum) x-rays

Answer 19

X-rays produced due to interaction of electron with electric field atomic nuclei Electrons are slowed, they lose energy, energy is converted to x-rays which are emitted Sharper turn = higher energy x-rays, and vice versa Lose energy in single interaction or many interactions Whale shape: many low energy x-rays are absorbed by sample, x-ray intensity decreased at low energy

Answer 20

High energy electrons fill lower energy vacancies Incoming electrons knock electrons in K and L shells shells, higher energy electrons fall down When electron falls to lower shell an x-ray is emitted at equal energy to delta E L -> K = Ka M -> K = Kb M -> L = La N -> L = Lb a=1 shell difference, b=2 shell difference

Answer 21

X-rays fluorescence lines have been tabulated for K and L lines Energies independent of chemical form due to electron structure of atom Characteristic x-rays have discrete energies but signal is averaged so line becomes peak Energies of characteristic x-rays used to identify elements present Ensure that both K lines or both L lines are present in the right ratios (Ka/Kb 5:1, La/Lb 1:1) Quantitative information only for flat, polished, bulk samples

Answer 22

Analysis of the particulates in GSR be conducted with SEM/SEM-EDS SEM - morphology determination : spherical agglomerates EDS - elemental profiles of individual particles Identification on unique presence of Pb-Sb-Ba (Characteristic vs Consistent)

Answer 23

On environmental exposure bullets and cartridges may acquire films or undergo corrosion processes that cast obscure striation patterns or impressions and markings Lead alloys react with atmospheric oxygen, water, and carbon dioxide to produce PbO, PbCO3, Pb3(CO3)2(OH)2 and other salts -> comparative analysis of bullets

Answer 24

1. Ultrasonication in DI for 30s 2. Transfer to perchloric acid until bubbling stops 3. Ultrasonicate in acid 10s 4. Rinse with DI Removes corrosion products while leaving striation marking on bullet

Answer 25

1. Sonication in MilliPore water 2. After drying sonicate in reagent grade trichloroethylene 3. Sonicate in HPLC-grade acetone 4. Sonicate 50 C in aqueous metasilicate and ethylene glycol monobutyl, pH 12.5 5. Immersion in acid cleaning solution - H2SO4, thiourea, sodium lauryl sulphate, pH 1.5 6. Sonicate in MilliPore water

Answer 26

Cu-Zn alloys (brass) are susceptible to dezincification Preferential Zn dissolution Simultaneous dissolution, redisposition of Cu as spongey Cu Zn preferentially dissolves as anode

Answer 27

Used to provide investigators with the ability to trace the original purchaser of a firearm Above trigger and removable barrels Damaged areas (mechanical deformation) etch at a different rate which is what allows for identification of the serial number

Answer 28

Chemical etching Electrochemical etching Magnetic particle restoration - depends on damaged crystals

Answer 29

Reagent 1: Fry’s reagent | Reagent 2: most common (HNO3 and H2O)