1. Of the three main radioacti

1. Gamma rays have highest prenetration. So hardest to block.Most harmful to humans. Next are beta rays. Last are alpharays.

2.when radio active isotopes administered to body willaccumulate around certain type of cells like tumor or organ. Due totheir small half life, they disintegrate and emmit radiation whichcan be studied by imaging. If isotope has long half life thendoctor has to scan the body for a very long time to get properimage. These artificial isotopes are made in partical acceleratorsby colliding ions( eg is large hadron collider lhc).

3. Ct scan uses x rays to scan soft tissue like liver, lungs,tumors etc. Mri scan captures the magnetic fields and also usesradio waves to capture images. Pet scan uses radio active isotopesto make images of organs and tissues. The main deference betweenpet and other two is that, pet scan can also help understand themetabolic activity of scanned region. Depending on the requirementof part to be scanned different methods are used. Like brain scansare done by mri. But brain tumor scans are done by pet scan toidentify whether medication is altering metabolic activity oftumor. For a pnemonia patient lung scan is done by ct scan etc.