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Nuclear radiation in medicine (Gamma cameras (Used to take images of…
Nuclear radiation in medicine
Radioactive tracers
Used to trace the flow of a substance through an organ
Tracer contains a radioactive isotope that emits gamma radiation, as it can be detected outside the body eg. doctors can use radioactive iodine to see if a patients kidney is blocked
Before the test, patient drinks water containing small amount of radioactive substance, and a detector then placed against the kidney
Radioactive substance flows in and out of normal kidney, so the detector reading goes up then down
For a blocked kidney, the reading goes up and stays up, as the radioactive substance cannot leave the kidney
Use radioactive iodine because:
Has half life of 8 days, so it lasts long enough for the test, but decays almost completely after a few weeks
Emits gamma radiation, which can be detected outside of the body
It decays into a stable product
Gamma cameras
Used to take images of internal body organs
Before the image is taken, patient is injected with a solution which contains an isotope that emits gamma radiation
Solution is then absorbed by the organ, and a nearby gamma camera detects the gamma radiation emitted by the solution
Gamma rays pass through the holes in the thick lead grid in front of the detector
The detector only detects gamma rays from nuclei directly in front of it
Detector signals are used to build up an image of where the isotope is located in the organ
The isotope must be a gamma emitter with a half-life long enough to give a useful image, but short enough so that its nuclei have mostly decayed after the image has been taken
Destroy cancerous tumours
In a narrow beam gamma rays can be used to destroy tumours
Radioactive isotope of cobalt used
Half life of 5 years
Gamma used as it can penetrate deeper in to the body than beta, and alpha in the body can cause cancer, not combat it
Radioactive implants
Used to destroy cancer cells in some tumours
Use beta or gamma emitting isotopes as either small rods or seeds
Permanent implants use isotopes with half-lives long enough to irradiate the tumour over a given time, but short enough so that most of the unstable nuclei will have decayed soon after
Reducing risk
Everybody is exposed to ionising radiation
Small risk to general public
Workers who use ionising radiation reduce exposure by wearing a radiation monitor, and hide behind a thick lead sheet