Chemistry Assessment Task: Research notes

Methods and Processes used to detect Radiation

Photographic Film On its own, a qualitative measure of radiation – indicates presence of Radiation, but not the

amount and type Used with plastic and metal shielding in monitors to determine amount of radiation nuclear

technicians are exposed to when working – film goes dark in presence of Gamma Radiation as most of the Alpha and Beta is already blocked out by the shielding

Geiger-Müller Counter A gas-filled device comprising of two electrodes that have a consistent potential difference

applied across them – Cathode is outer metallic surface, anode is the inner metallic electrode

The gas (usually Argon or other noble gases) present between the electrodes becomes ionized under the presence of radiation, which causes a discharge of electrons and ions

When a large enough voltage is applied, electrostatic attraction causes electrons to travel to the anode, whilst the positively charged ions move towards the cathode. This movement generates s a spark between both electrodes, which is then sent and recorded on a electronic counter (Units: Counts per minute)

Works best with alpha and beta emitters because of their high ionization power – but can also be used to detect gamma emissions

Better than Photographic film because it gives a quantitative measure of the amount of radiation being emitted in a room/source, but not its identity

Gamma Ray cameras (or Scintillation counter) Device that measures ionizing radiation using a crystal and a photomultiplier securely

encased in a tube Radiation enters the tube via an opening and collides with a crystal (Sodium Iodide (NaI))

which produces a “flash” of light – the greater the energy of the radiation, the flash of light is more intense

Flash is detected by a photomultiplier which amplifies them so that they can be recorded as a electrical signal (Units: Counts per minute/microentgens per hour

Used in medicine to detect Gamma ray emission from the body upon consumption of a radioisotope

Ionisation Chamber It is the simplest of all gas-filled radiation detectors - comprises of an outer metal conductor

and an inner, central anode, and low potential difference across them Utilises a principle very similar to that of the GM counter – radiation enters the chamber

and ionizes either pressurized air or carbon dioxide present between the electrodes, causing a discharge of electrons and ions that move to the electrodes and generate an electric current between them, producing a reading on an attached meter

Less sensitive than a GM counter because of low Voltage, and type of gas being used Used mainly for Gamma and X-Ray detection Common readout unit: roentgen per hour (R/hr)

Isotope How it is produced Uses Properties that complement its usageIn industry:Cobalt-60

Artificially produced in a nuclear reactor

Neutron bombardment of commonly found Cobalt-59 causes it to capture one:

59Co + 0n -> 60Co + ϒ Undergoes Beta decay to

form isotopic Nickel, releasing Gamma radiation in the process 60Co -> 60Ni + -1e + ϒ

Gamma radiography - used to detect cracks and defects in welds and joints without physically damaging the material - beams of radiation from sealed capsule pass through inspected metal from one side and onto a piece of photographic film on the other side- the pattern imprinted on the photographic film indicates whether there are cracks or defects in the welds or joints – this will be depicted by a higher concentration of gamma rays in those areas

Sterilisation of spices and certain foods, or medical equipment- Radiation is passed through suspicious food

or surgical equipment, which kills any live bacteria or living tissue without ionizing the rest of the substance

Strong Beta and Gamma emitter –as Gamma rays have low ionization power, it can pass through substances without ionizing those particles – good for both sterilization and radiography

Gamma rays have high penetration power – helps kill foreign bacteria in food and cells in medical equipment

As it is a Strong emitter, low amounts are required in order to be effectively used, therefore more economically viable in industry applications

Long half-life – 5.7 years Allows same isotope it to be used over a long

period of time and is low maintenance, provided it is placed in a sealed container

In medicine:Technetium 99m

Artificially produced from the beta decay of Molybendum-99, which itself is produced in nuclear reactors from Uranium-235

99Mo -> 99mTc + -1e + energy The “m” in Tc-99m stands

for metastable. Tc-99m naturally decays

to Tc-99 by emitting a gamma ray in the process

99mTc -> 99Tc + ϒ

Radioactive Tracer in medical diagnosis - Radiopharmacists, knowing that certain

chemicals are readily absorbed by particular parts of the body eg. Glucose by the brain, form compounds with Tc-99m to use as a tracer to pinpoint the location of tumors.

- When substance tagged with Tc-99m tracer is injected into the body, it travels to and concentrates immediately in the organ/tissue where the tagged substance is naturally absorbed

- As this happens, Tc-99m is decaying, releasing Gamma rays that can be detected, allowing its path and concentration to be traced out using a Gamma Ray Camera,

Very short half life (6 hours) – safe for the human body as it quickly decays during this time

Various oxidation states enable it to form compounds with chemical properties that lead to concentration in the organ of interest eg. heart, lungs, brain, liver and bones

Emits low intensity gamma rays and low energy beta particles – makes it less damaging to human tissue, but still powerful enough to be detected by the Gamma Ray Camera

allowing examiners to successfully diagnose that part of the body

Bibliography

http://www.ansto.gov.au/__data/assets/pdf_file/0018/3564/Radioisotopes.pdfhttp://www.ansto.gov.au/discovering_ansto/what_does_ansto_do/frequently_asked_questions/nuclear_medicines_and_radioisotopeshttp://www.epa.gov/radiation/radionuclides/cobalt.htmlhttp://www.evs.anl.gov/pub/doc/Cobalt.pdfhttp://www.furryelephant.com/content/radioactivity/alpha-beta-gamma-radiation/producing-technetium-99m/http://www.howstuffworks.com/radioactivity-info4.htmhttp://www.hps.org/publicinformation/ate/q1324.htmlhttp://www.hps.org/publicinformation/ate/faqs/radiationdetection.htmlhttp://www.kewpid.net/notes/chem9.2.pdfCarson P. Heffernan D. Loucopoulos P., Spotlight Chemistry: HSC Volume Textbook http://library.thinkquest.org/C003973F/Peace/Industry/radioisotopes%20in%20industry.htmhttp://www.techlib.com/science/ion.htmlhttp://www.world-nuclear.org/info/inf55.html