Nuclear+Chemistry

=**Nuclear Chemistry**=

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//Using chemistry to make new materials that are useful to human society, we turn to radioactive materials. These are particularly useful in **medicine** (diagnosis and therapy) and **industry** (as tools for monitoring processes)// (Textbook)

**BOS Dot Points**

 * Distinguish between stable and radioactive isotopes and describe the conditions under which a nucleus is unstable
 * Describe how a transuranic elements are produced
 * Describe how commercial radioisotopes are produced
 * Identify instruments and processes that can be used to detect radiation
 * Identify one use of a named radioisotope
 * in industry
 * in medicine
 * Describe the way in which the above named industrial and medical radioisotopes are used and explain their use in terms of their chemical properties

Definitions and Terms

 * **Radioactivity**
 * Spontaneous emission of radiation by certain elements
 * **Radioactive Isotopes/Radioisotopes**
 * Rather than than talk about "Radioactive elements", we talk about radioactive isotopes, this is due to the fact that certain elements have both stable and unstable isotopes
 * **Stable Nuclei**
 * The nuclei is not radioactive (won't spontaneously decay/emit α or β radiation)
 * **Unstable Nuclei**
 * The nuclei is radioactive and dependant on its size will decay and emit α or β radiation
 * **Zone (or band) of stability**
 * Once all known isotopes are plotted on a graph (with neutrons on the y-axis, protons on the x-axis), there will be an area of stable isotopes, this appears to be a "band".
 * **Alpha rays/particles**
 * First known as heavy postively charged particles.
 * They were then discovered to be helium nucleus, charge of 2+ and a mass of 4 (relative atomic mass), it has low penetrating power. They're so heavy that a sheet of paper can stop them
 * **Beta rays/particles**
 * First known to be lightly negatively charged particles
 * They were discovered to be electrons, charge of 1-, mass of 1/2000 (relative atomic mass), they have moderate penetrating power. can penetrate the sheet of paper and 0.5mm sheet of aluminium, but they will be stopped by 0.5mm of lead
 * **Gamma rays/particles**
 * First believed to be like X-rays and thought to be genuine radiation.
 * They're now known to be electromagnetic radation, with a charge of 0, mass of 0 (relative atomic mass), they have high penetrating power. They can penetrate all previous sheets but will be stopped by 5cm thick sheet of Lead of 15cm sheet of concrete
 * **Nuclear Reaction**
 * A reaction in which change occurs to the nucleus of an atom (Note: The difference between a chemical/physical reaction and a nuclear one. Whilst physical changes the structure of the atoms, chemical changes the bonds, Nuclear reaction changes the atom itself)
 * **Nuclear Fission**
 * Process in which neutrons bombard atoms and cause them to split into roughly two equal fragments
 * **Transuranic elements**
 * Artificial elements whith an atomic number greater than 92, an example would be Americium or Curium
 * **Half-life**
 * The amount of time required for half the atoms in a given sample to undergo radioactive decay

How to prepare/obtain commercially useful isotopes
2 major methods of producing useful isotopes
 * Nuclear Reactor
 * Due to the number of neutrons produced in a fission reaction, they can be used to create isotopes
 * An example would be the production of Technetium-99//m// (m indicates an unstable form of the isotope) from the fission of Uranium-235
 * Cyclotron
 * Cyclotrons accelerate positive particles by passing them through alternating positive and negative fields
 * There are cyclotrons in major hospitals in Sydney, Melbourne and Brisbane which are used to produced isotopes for medical diagnosis
 * An example would be the production of Fluorine-18 from the bombardment of Nitrogen-14 with alpha particle.

Detection of radiation
Radiation can be detected using the following methods Example of a Cloud Chamber Another example of a Cloud Chamber made from a Starbucks cup Part 1 of a Geigar Counter explanation Example of a Geiger-Muller Counter in use
 * Photographic film
 * Radiation darkens the film
 * Still used in "radiation badges" by laboratory workers
 * Cloud Chamber
 * A sealed environment containing a supersaturated(*) vapour of water or alcohol, w hen ionising radiation passes through, it ionises the air
 * These ions act as a nuclei upon which droplets of liquid form, so their path can be made clear
 * Alpha Particles - Straight, dense tracks
 * Beta Particles - Less dense, zig-zag tracks
 * Gamma Particles - Even fainter tracks
 * Geiger-Müller counter
 * Using the ionising properties of radiation, a beta ray enters through the thin end window of the Geiger tube, hits a gas molecule (generally a noble gas, i.e. Argon) and ionises it, knocking an electron out of it
 * High voltage accelerates the electron towards central electrode, since it is gaining speed it will ionise more argon atoms (so it forms a cascade effect) which will eventually reach the electrode
 * These are electrical pulses which are amplified and measured by generating clicks in an audio amplifier
 * Particularly good for measuring beta particles
 * Scintillation counter
 * A brief localised light flash is producued in phosphor when ionising radiation (i.e. Gamma or Beta rays) "hit" it, these flashes are converted into electric pulses through a "photomultiplier" and counted (as audible ticks)

Further reading
 * @http://www.darvill.clara.net/nucrad/detect.htm
 * //Supersaturated refers to a solution that contains more dissolved material than could be dissolved by the solvent//

Uses of Radioisotopes
Radioisotopes have many uses
 * Quantity of naturally occuring radioactive **tritium (H-3)** can be used to determine the age of underground water
 * Tracking techniques (using **scandium-46** or **lanthanum-140**) can be used to aid investigation and control of termites
 * **Copper-64** can be used to investigate how the body handles copper and provide a treatment for Menkes disease
 * **Gold-198** can be used to trace the dispersal of disposed effluent, sewage and movement of silt and sand in waterways

Medical

 * **Cancer Treatment**
 * A method of treating cancer is to irradiate the affected areas of the body with gamma rays which kill cancer cells
 * Common source for radiation therapy is **cobalt-60**, it is made by neutron bombardment of **cobalt-59** (it then disintergrates into **nickel-60**, gamma rays accompany this decay)
 * **Diagnosis**
 * Medical isotopes have many uses within diagnosing patients.
 * **Fluorine-18**can be used to study brain function and to diagnose epilepsy, some cancers and heart disease
 * Prepared by bombarding nitrogen with high-speed helium nuclei ( α particles) and has a half-life of 110 minutes
 * Technetium-99//m// can be used to trace liver-bile to determine to functioning of the bile duct, it can also be used to diagnose thyroid abnormalitites
 * A property which makes it good for medical diagnosis is that its half-life is 6 hours

Industrial

 * **Thickness gauges**
 * A radioactive source and detector can be used to monitor and control the thickness of materials such as sheets of steel, paper, aluminium foil, plastic film. The amount of radiation the detector receives is dependant //(dependent?)// on the thickness of the material (i.e. thicker materials absorb more radiation, etc. etc.) and the rollers which flatten the material can be adjusted electronically
 * Isotopes chosen are based of their properties such as having a **fairly low energy emission** (since we want the material to absorb the radiation and it is safer to use) and a **long half-life** (since we don't want to replace it frequently), this leads to **Strontium-90** (half-life 28 years), **caesium-137** (half-life 30 years) and **cobalt-60** (half-life 5.3 years) being used
 * **Leak Detectors**
 * Radiation can be added to water pipes and underground oil pipelines, by adding a suitable radio tracer (i.e. **Sodium-24** (half-life of 15 hours)) into the liquid and scanning the pipe
 * Since no radiation should be detected from the isotope due to the pipe, a crack or leak can be found if radiation is detected.
 * The properties of the isotopes required are that it is short-lived, quickly decays, so if there is a leak the radiation is obvious and the liquid becmes usable quickly and and does not decontaminate the environment
 * **Irradiation of Medical Supplies and Food**
 * Since gamma radiation is effective in destroying large biological molecules such as DNA (oh noes!), it has been useful to kill bacteria and sterilise medical supplies (such as dressing and bandages).
 * Food can also be irradiated to extend shelf-life and destroy micro-organisms, the radioisotopes requires properties such as emitting gamma radiation with sufficient energy to destroy bacterium but not enough energy to irradiate the food, they also must have a reasonably long half-life, this leads to **caesium-137** and **cobalt-60** being used
 * Arguments for this process are that it destroys bacteria and moulds, so it keeps the food "fresher"
 * Arguments against this process are that it won't kill all the bacteria and mould and that it desstroys some of the vitamin content of the food

Benefits and Problems
There are benefits for both **industry** and **medicine** in using radioisotopes such as;
 * **Medicine**
 * To do diagnosis and treatment procedures non-invasively, in the form of radiation therapy (to treat cancer)
 * **Industry**
 * To do things (i.e. sterilisation of medical equipment) more efficiently and reliably
 * Ability to make monitoring equipment more sensitive, precise and reliable (to examine buildings and machinery for weld and structural faults)

There are also issues and problems with using radioisotopes, this arises from the fact //radiation from radioisotopes is harmful to people//, all types of radiation can cause undesirable reactions in living tissue and upset the delicate balance. More information on radiation exposure
 * **Tissue damage**
 * Immediate, can show up as skin burns/nausea or as radiation sickness (can lead to death with enough exposure)
 * **Cancer**
 * Doesn't show up until 10 or 20 years after exposure, usually in the form of lung cancer or leukaemia
 * **Genetic damage**
 * Which will lead to deformities in offspring

Safety precautions when using radioisotopes are; http://www.ted.com/talks/kirk_sorensen_thorium_an_alternative_nuclear_fuel.html
 * Radioactive material **must be stored in well-shielded containers**
 * Equipment that uses radioactive material must be designed to ensure that radiation is directed only where it is required and that there is no stray radiation
 * People using equipment or material are well trained to handle such things in a safe manner
 * People working in and around radiation facilities must wear radiation monitors (badges) that record the cumulative amount of radiation they have received