APPLICATIONS OF ATOMIC AND NUCLEAR PHYSICS

What are applications? Applications are the uses of atomic and nuclear physics Applications make use of one or more of the properties of the isotope used Applications usually have benefits, but also have risks

Medical applications - diagnosis Radioactive substances are used to explore parts of the body that might be damaged or diseased They are usually added to a tracer – a compound that behaves in a specific way in the body The tracer carries the radioactive substance to the part of the body we’re interested in An external scanner then collects images to show what is happening

Technetium-99 Technetium-99 can be added to a tracer to find broken bones The tracer will accumulate more in places where a bone is healing itself The scanner will then find the places of high concentration of Technetium-99 Technetium-99 has a half-life of only six hours, so that it doesn’t stay in the body and damage it Technetium-99 is a gamma emitter, which means it can escape from the body and be seen It’s a low energy gamma emitter, so it doesn’t harm the body too much as it passes through

Iodine-123 Iodine-123 is used to detect thyroid problems, including cancer Iodine will accumulate in the thyroid and a scanner can then observe its activity If thyroid cancer has spread, the iodine will also accumulate in the other tumours and can be seen on the scanners Iodine-123 has a half-life of 13 hours Iodine-123 actually decays to Tellerium-123, which then decays immediately via gamma decay The gamma radiation is low energy so it doesn’t harm the body

Medical applications – nuclear medicine Radioactive isotopes are swallowed or injected Sometimes the isotope is enclosed in a case/capsule and placed on or in the body in the place needed These isotopes target specific body functions or organs Because this therapy kills cells (for tumours, cancers etc), the isotopes produce ionising radiation (usually beta radiation) The ionising radiation breaks chemical bonds in the target cells and kills them The radiation cannot travel far, so it only kills cells in the target area

Iodine-131 Iodine-131 is taken up by the thyroid almost exclusively Thyroid cancers that have spread will also take it up It produces beta and gamma radiation The beta radiation kills cells in the target area only because of its high ionising ability The gamma radiation escapes from the body Iodine-131 has a half life of 8 days before decaying to Xenon-131 The low amount of gamma radiation produced means you can see where the Iodine has been absorbed Excess iodine is eliminated in urine, which means the patient may have radioactive urine for some time

Iridium-192 Iridium-192 is used in brachytherapy, where it is put in a capsule or casing next to the target area It is commonly used for skin cancers, as well as other tumours which can easily be reached/targeted Iridium-192 has a half-life of 74 days, which means it can attack a tumour for a long time without needing replacement It emits beta and gamma radiation. The beta radiation kills the target cells and the gamma radiation escapes from the body It is a strong gamma emitter, so can cause damage to other cells if the amount is too much It decays to Platinum-192

Medical applications - radiotherapy Radiotherapy uses gamma radiation to target specific parts of the body It can be used to clear an area after surgery, or used with or instead of chemotherapy to reduce a tumour The radiation is applied in beams from different directions around the target area so that only the target gets a strong enough dose of radiation to kill large numbers of cells Because it is not applied inside the body, half life does not matter The gamma radiation kills cells by destroying their DNA

Cobalt-60 Cobalt-60 has a half-life of 5 years It decays to Nickel-60 via beta decay (the beta particles are captured in the machine), and the Nickel-60 then releases two gamma rays The gamma rays have different energies, depending on how excited the Nickel-60 was after the beta decay The gamma rays are very penetrating and can move through the body easily Gamma radiation can be very dangerous and can cause death in some circumstances, if too much is absorbed

Archaeology applications Radioactive isotopes can be used for dating items You have to know the half life of the isotope You have to know how much of the isotope was in the item when it was formed/made It works by measuring how much of the isotope is in the item you’re interested in and comparing it to how much it had when new Work out the percentage left and figure out from that how many half lives have passed This must be the age of the item

Carbon-14 Carbon-14 is formed by cosmic radiation hitting nitrogen in the air It is always present in about the same amount in the air and in living things, because the atoms are always being exchanged Once something dies, it can’t change atoms anymore, so the Carbon-14 can’t be replenished The half life is 5730 years, so it can date organic items less than 45,000 years old or so It decays via beta decay back into nitrogen

Uranium-235 and Uranium-238 These isotopes accumulate in rocks, where it substitutes for Zirconium in some zircon crystals in a predictable ratio Over time, both isotopes decay to lead following a complex pathway Uranium-235 has a half life of 700 million years, while Uranium-238 has a half life of 4.5 billion years The two isotopes allow one rock to be cross-checked for age The old rock is compared to other rocks of the same type whose ages are known

Smoke detectors Smoke detectors either use light or an ionising radioactive source to detect fires They work by passing a small current across a gap. If the current stops because of smoke, the alarm will go off The radioactive source must be carefully shielded The detector uses highly ionising radiation, but with low penetrating powers Ionising smoke detectors must be disposed of carefully because of the risk of radioactive contamination; some places have banned them for home use because of improper disposal

Americanium-241 Americanium-241 decays via alpha decay The alpha particles are released into a chamber. Because they are highly ionising, they will ionise the atoms in the air, which will then pass the current around the circuit If smoke enters the chamber, the alpha particles will ionise them instead, and the current will drop Americanium-241 has a half life of 432 years, which means it will outlast the casing Americanium-241 has to be disposed of very carefully or it can contaminate landfills

Irradiation and sterilisation Bombards objects with ionising radiation for the purpose of sterilising them Applied to food, where it stops spoilage and can kill insects and microbes that might be living in or on the food Applied to equipment, like medical instruments or industrial items, to kill microbes and avoid contamination Applied to insects, where it sterilises the males so they cannot impregnate a female, who therefore cannot lay eggs Irradiation uses gamma emitters to disrupt the DNA of insects and microbes, and to stop enzyme reactions in food

Cobalt-60 Cobalt-60 has a half-life of 5 years It decays to Nickel-60 via beta decay (the beta particles are captured in the machine), and the Nickel-60 then releases two gamma rays The gamma rays have different energies, depending on how excited the Nickel-60 was after the beta decay The gamma rays are very penetrating and can move through the body easily Gamma radiation can be very dangerous and can cause death in some circumstances, if too much is absorbed Different countries have different regulations on what foods/items can be irradiated

Industrial radiography Can be used to test welds and joins on pipes and storage containers, particularly if they will be pressurised Can be used to test machined parts, to test for weaknesses and leaks Can be used to test metal items for corrosion or faults Can be used to scan shipping crates Uses gamma radiation to build up a scan of the item The density shows how much of the radiation made it through, like an x-ray Places that are too light or too dark show faults This uses both Cobalt-60 and Iridium-192