Radiotherapy

If radioisotopes are injected into the blood stream of someone seeking treatment . To find out the activity of the radioisotope , the nurse would probably draw lets say 10 ml of blood and measure the activity. After a few days the process is repeated to measure the activity again. It is obvious the the same 10 ml of blood should be drawn to measure its activity.If for some reason only 5 ml is drawn than the activity must be multiplied by 2 . The activity must be taken from the same amount of sample so that it can be compared correctly.
The same goes with carbon dating. 1C14 to 2000000 (fresh wood) and 1 C14 to 4000000 (old wood)would actually mean initial N (fresh wood) = 2 and old wood to be N=1 . Hence the age of the old wood is one half life.
This principle must be employed at all times in dealing with any kind of application.

Count rate vs Activity

Count rate is only proportional to activity. Count rate is proportional to number of radioactive atoms. Activity is also proportional to number of radioactive atoms but you can calculate Activity if you know the half life and number of radioactive atoms using the formula A = (0.693/half life) N.

Frustration over units of quantities

The unit for decay constant should be in per second. If you who want to put the examiner to test you may try giving it in per year without omitting the unit.But ...
Don't set a trap for yourself ! You use the decay constant in per year and use it to calculate the activity A = lamda N and give the unit as per second or Bq.
To prevent further traps set by yourself always use per second in whatever calculations. There is no point saving time and getting wrong answers. Take a longer route to get everything in seconds and be 100% sure of your own calculations.

Polonium 210 poisoning

Polonium is a alpha source and it was the radioisotope that killed the russian Litvenenko recently. He had a meeting with an associate and detectives tracked down the existence of a hot teapot discovered by hotel staff. Here are more information about polonium: Because of its short half-life and rapid decay, a small quantity of polonium-210 is intensely active. Its "specific activity" is 4490 curies/g (166 TBq/g). Thus 4 millicuries (a minimal lethal dose for 80 kg person) is 0.89 micrograms, an almost invisible speck of matter.A detail story can be found here

More elementary particles

An antiproton (blue) enters a bubble chamber from bottom left and strikes a proton. The released energy creates four positive pions (red) and four negative pions (green). The yellow streak at the far right is a muon, a decay product of the adjacent pion. (The dark blue curlicues are low-energy electrons knocked from atoms, not involved with the antiproton.)pic taken from www.lbl.gov/Science-

Three types of radiation

pic taken from library.thinkquest.org

Alpha and beta tracks in cloub chamber

pic taken from practicalphysics.org

Bubble chamber tracks

It is a difficult task indentifying the particles that produces the tracks.