20.7 – Applications of Radioactivity

Some applications of radioactivity are:

Medical Diagnosis

- Small quantities of the radioactive element are injected into the patient to allow for imaging of internal organs.

Medical Treatment

- Iodine-131 injected into the body gets concentrated in the thyroid gland which will start killing cells in the thyroid. This is used as a thyroid cancer treatment.
- γ-ray sources are directed through the body towards a cancer. Usually several beams are sent from different directions so that the cancer receives a high dose of radiation but the surrounding tissues receive a lower dose.

Killing of Microbes with γ-rays

- Medical equipment can be sterilised by being bombarded with γ-rays. This is often used for equipment that can’t be heated to sterilise such as bandages or plastic syringes.
- Food can be irradiated to kill any bacteria that may be present on it. The food will then keep for much longer before going bad.

Dating Ancient Objects

- Carbon-14 is found all around as a naturally occurring isotope of carbon. When a living organism dies it stops taking in carbon-14 and slowly any carbon-14 it contains will decay to the more stable isotopes. By determining the percentage of carbon-14 in the object its age can be determined. Carbon-14 has a half-life of 5700 years. Carbon-dating can determine the age of objects up to about 100,000 years old.
- Uranium-238, with a half-life of 4.5 billion years, is used by geologists in a similar manner to determine the age of rocks.

Smoke Detectors

- Americium-241 produces α-particles which cause a small current to flow when they strike a detector. Smoke particles will stop the α-particles and trigger the alarm.

Industrial Use – Thickness Monitoring

- Materials that need to be produced at a constant thickness (paper, glass, metal sheets, etc.) can be monitored by passing a beam of β-particles through them. If the material gets too thick, the count rate of β-particles passing through them will drop and so corrections can be made to the machinery.

Example
(a) Why are isotopes with short half-lives (e.g. 2 hours) usually used for medical imaging? So that the level of activity will decay to nothing within a short period of time. This will minimise unwanted effects due to radioactivity taking place within the body. (b) Why it is safe to eat strawberries that have been irradiated with γ-rays? The γ-rays will kill all the bacteria present on the strawberries. But, being just electromagnetic waves, they will not leave the strawberries radioactive. (c) Why can carbon-dating not be used to determine the age of dinosaur bones? Dinosaur bones are millions of years old. With carbon-14 having a half-life of just 5700 years, so many half-lives will have passed since the dinosaurs died that there will not be any measurable carbon-14 left in the dinosaur bones.

Example

(a) Why are isotopes with short half-lives (e.g. 2 hours) usually used for medical imaging?

So that the level of activity will decay to nothing within a short period of time. This will minimise unwanted effects due to radioactivity taking place within the body.

(b) Why it is safe to eat strawberries that have been irradiated with γ-rays?

The γ-rays will kill all the bacteria present on the strawberries. But, being just electromagnetic waves, they will not leave the strawberries radioactive.

(c) Why can carbon-dating not be used to determine the age of dinosaur bones?

Dinosaur bones are millions of years old. With carbon-14 having a half-life of just 5700 years, so many half-lives will have passed since the dinosaurs died that there will not be any measurable carbon-14 left in the dinosaur bones.

Links
YouTube Video: Using Radiation in Medicine

Physics with Mr Shone