Nuclear and environmental chemistry Flashcards
When did french scientists Pierre and Maire Curie discover the radioactive elements?
1898
When did french physicist henri becquerel discover radioactivity in uranium?
1986
What are stable isotopes
atoms of elements can have multiple isotopes with different numbers of neutrons in the nucleus
What does radioactive isotopes mean?
isotopes have an unstable nucleus - occurs when the nucleus of an atom has an excess of protons or neutrons
the emit particles/radiation to regain stability
What does radioactivity refer to?
to unstable atomic nuclei which spontaneously disintegrate and simultaneously emit nuclear radiation
What does the term disintegration refer to?
one nuclide (atom) changing into another nuclide
What does the term nuclear radiation refer to?
the emitted particles or high frequency light
What are 3 types of nuclear radiations?
alpha particle - when a radioactive isotope releases decay. A helium nuclei. 4 protons and 2 neutrons.
Beta particle - negatively charged electron
Gamma rays - photon (short wavelength)
Decay series
some radionuclides need to undergo a series of disintegrations before reach a stable nuclide
This can involve several different radionuclides and types of nuclear radiation emitted
How is radioactive detected?
a geiger-mueller counter
What is the SU unit called?
becquerel - defined number of disintegrations it undergoes
The activity of radioisotope is proportional to the number of radioactive nuclei
Radioactive decay - what does half-life refer to?
processes are first order kinetic process
Half life refers to the time required for half the original sample of nuclei to decay
What is the term transmutations? and how is this achieved?
refers to the conversion of one
type of element to another type following particle bombardment
naturally occuring and can physically change it with;
- Accelerators
- Cyclotrons
- Nuclear reactors
What is the main principle radiometric dating?
radionuclides undergo disintegration at a constant rate, which differs between each radionuclide
carbon-14 for radiometric dating on shorter timescales
Naturally occuring carbon - 3 isotopes
12C - 98.93%
C13 - 1.07%
C14 - 0.00000001%
reliable detection of radioisotopes occurs up to ten half-lives
How is carbon-14 incorporated into radiocarbon dating?
nitrogen is atmosphere collides with cosmic rays, transmute nitrogen into carbon 14 isotope - continuous production. When that transmutation occurs, that C14 atom then taken up by plants - animals eat the pants. consistent ratio consumed into molecules. Once created - starts to decay.
when animals dies, the carbon 14 begins to decay, this ratio with change relative to the ration.
What is isotopic dilution? and what are the 3x assumptions made in regards to this?
Way to assess amount of in a poll in a large pool - take a sub sample, mark it, return capture, dilutions occurs, period of time later, resample, and calculate marked individuals.
- assumptions associated with this; the chance of capturing unmarked and marked individuals must be equal
- the proportion of unmarked to marked individuals remains constant
- Population size does not increase or decrease
estimating blood volume
soil phosphorus kinetics
Counting fish in a large pool
Tracer - giving a unique fingerprint
What issues occur for labeling/tracer?
if added to soil - if taken up by animals. Radioactive substance inside of animals now.
How is radioactivity found in the environment? and what are four factors to consider?
Found in the environment
1. the energy of radiation
2. the penetrating ability of radiation
3. the ionising ability of the radiation
4. the chemical properties of radiation source
How does ionising radiation cause damage?
Produces a free radical that can damage your DNA - small scale you body has mechanisms to repair it. however, larger amounts/ higher concentrations, your body can’t handle the amount.
What are 3 photochemical reactions?
- photodissociation - refers to the rutpure of a chemical bind following the absorption of a photon - the minimum energy required to break the bond between two oxygen atoms is equal to the bond energy
Calculations - review.
- photoionisation - refers to a molecule absorbing energy resulting in an electron being rejected - ionisation energy.
- Ozone in the atmosphere in stratosphere
compound absorbing photons with wavelengths from240 - 310nm
continuous formation and decomposition (cycle - releasing heat)
how can the ozone layer be affected?
- natural events - volcanic eruption, affects the processes and raise temperature
- production of CFCs - trying to remove CFCS found in fridge AC aerosols etc. Photodissociation of CFCs - releases cholrine, binds with ozone - creating high energy radiation (breaks down ozone)
What are 4 anthropogenic events?
- heavy metals (Cd, Pb and Hg)
- detergents and fertilisers
- acid water
- Pharmaceuticals
