Introduction to Forensic Science - week 2
the act is not culpable unless the mind is also guilty.
15/11/24
Introduction to atomic structure?
poisoning - suspected lead, arsenic or chromium poisoning, analyze body fluids
determining time of death - analyzing chemistry of bones can tell how long those remains were in the ground
bullets also
Robert Boyle’s proposal is that elements are substances that can neither be created or destroyed
elements are substances that cannot be broken down into simpler materials, they are basic building blocks for the world around us
there are 93 naturally occuring elements. there are additional elements that are created by nuclear technology.
paper is made of cellulose, cellulose consists of elements, carbon, hydrogen and oxygen. so the atoms are assembled in a particular way which makes cellulose.
if you burn the piece of paper, the carbon turns into carbon dioxide and the hydrogen will turn into water. the atoms of carbon are still there they just turned into carbon dioxide.
human bodies are made of carbon, hydrogen, oxygen, a little nitrogen, phosphorous, calcium, sulfur, sodium, potassium, iron and more.
any object will contain small amounts of impurities. even bullets are most likely to just be 99% lead.
when we are talking about analysis of elements. we are talking about 2 things. determining the bulk composition. but also determining the trace impurities. and often it is the latter that is more informative.
one picogram which is one trillionth of a gram would still contain 100 billion atoms.
Structure of the atom
the key to doing analysis at such a small level is spectroscopy.
helium became the first element discovered outside of the earth.
at the end of the 19th century, a model of the atom was created called the plum pudding model
the model showed the atom as a large positively charged object with negatively charged electron embedded in it. THIS MODEL WAS DROPPED
Rutherford proposed a the planetary model, the atom consisted of a small positively charged nucleus, which was later to be found to be made up of neutrons and protons. almost all of the mass of the atom is concentrated in that nucleus. the negatively charged electrons orbit around that nucleus.
there was a problem with this model cause this positive nucleus surrounded by negative electrons would result in the atom destroying itself. because the nucleus would attract the electrons and they would just collapse in the nucleus.
but atoms dont destroy themselves, they are stable.
Bohr’s model, the electrons did not move around freely they were restricted to specific energy levels. this is because energy is quantized. energy is not a continuous function.
however the electrons can move from one level to another. if the electron receives enough energy it can jump from one level to another. by absorbing that energy.
same thing an electronic can drop down a level by releasing energy.
the energy thats absorbed or released is usually in the form of electromagnetic radiation, such as visible light, ultraviolet light, or infrared radiation, depending on the energy difference between the levels.
the amount of energy musth match between the 2 energy levels.
the color of the visible light is determined by the frequency.
when you get to the right frequency as you scan through the light sources frequencies, the electron can absorb the energy and be promoted to a higher energy level. this is called the excited state.
Analysis of microscopic objects 18/11/24
microscopy is to analyzes extremely small objects. like gunshot residue. use a scanning electron microscope, which uses electrons instead of light which most microscopes do.
SEM fires a beam of electrons at the object of interest.
Napoleon case:
died in fifties. it was a respectable age. rumors that his death was not natural.
funeral happened, buried and nobody could take it out.
but we had samples of his hair. when someone famous died, u cut his hair off to keep as a memento, which can later be used for forensic analysis to determine factors such as cause of death or potential poisoning.
analysis done in 1952, and arsenic was found, so it must’ve been murder!
but whats the motive? many wanted him dead, was it the british? french government didnt want him either.
in 1980, dr david jones, asked what color was napoleons wallpaper was? someone listening to radio, called in said they knew and had a piece of it.
its a historic sample, so u cant destroy it. no dissolving in acid, cannot do atomic absorption spectroscopy because the owner will want it back.
advantages of SEM-EDX is that it is not destructive and u can see specific microscopic objects in sample.
if theres arsenic in the wallpaper how does it go from there to napoleon?
st helena is humid, so mold grows. some of the mold can take arsenic and release it as gas, which is how he could’ve been poisoned.
we have autopsy result, and it tells us he died from stomach cancer, and eyewitnesses.
JFK Assassination case:
JFK was shot by a man called Lee Harry Oswald.
since the death, many theories have gone about what happened that day.
one of the questions, is did he act alone? or were there others?
Assassin fired 3 times. one missed completely, 2 shot the president.
so we examine the car to find how many bullets there are. but its not as simple cause bullets can break apart and fragment as they hit the target.
they didnt find 2 bullets, but all fragments of bullets, its not a jigsaw puzzle because they deform, thats why elemental analysis is necessary.
we are not interested in bulk composition, but trace composition.
which is silver and antimony.
five fragments were found, the level of silver is about the same.
but if you look at the antimony concentration, you see a huge difference.
you have 2 different groups, first with a higher level of antimony about 800ppm
and a lower group with 600ppm.
so most likely conclusion is that higher level group came from one bullet, the other from another bullet.