A small amount of radioactive material is put into the patient's body. The radiographer puts a detector around the body to detect any gamma rays or beta particles that pass out of the patient's body.

treating cancer (MRI):  

Gamma rays damage cells whether they are normal or cancerous, so gamma rays must be focused on the tumour. One way of doing this is to use a wide beam of gamma rays, but to rotate the beam around the patient, keeping the tumour at the centre. This concentrates the gamma rays on the cells that need to be killed.

cancer therapy (cobalt)

Radiation therapy works by damaging the DNA (genetic material) of cells. A radiation beam of photons, electrons, protons, or neutrons can be used to disrupt the growth of tumour cells by directly or indirectly ionizing the DNA (deoxyribonucleic acid). The cell with damaged DNA dies during cell division.

http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/radiation/treatmentrev4.shtml

https://www.britannica.com/story/how-radioactive-isotopes-are-used-in-medicine

 

Many different radioactive isotopes and techniques are used for dating. All rely on the fact that certain elements (particularly uranium and potassium) contain a number of different isotopes whose half-life is exactly known and therefore the relative concentrations of these isotopes within a rock or mineral can measure the age. For an element to be useful for geochronology (measuring geological time), the isotope must be reasonably abundant and produce daughter isotopes at a good rate.

Either a whole rock or a single mineral grain can be dated. Some techniques place the sample in a nuclear reactor first to excite the isotopes present, then measure these isotopes using a mass spectrometer (such as in the argon-argon scheme). Others place mineral grains under a special microscope, firing a laser beam at the grains which ionises the mineral and releases the isotopes. The isotopes are then measured within the same machine by an attached mass spectrometer (an example of this is SIMS analysis). 

There are a few different types of radioactive dating such as:
* radiocarbon dating - this is the most common technique
*  Rubidium-Strontium dating 
* Potassium-Argon dating 
* Samarium-Neodymium 

Food irradiation is the application of ionizing radiation to food this makes food more durable and safer to eat by eliminating microorganisms and insects from inside or outside of the product, it is the same concept of pasteurizing milk and canning fruits and vegetables it makes it safer to consume the food. The FDA (Food and Drug Administration) is the administration responsible of regulating the radiation used on foods and will only do so if determined that irradiating the food is safe.