What is the difference between shelf life and half life?

Answer 1

An isotope of a chemical element is an atom that has the same number of protons (this also means this atom has the same atomic number) and electrons, but has a different numbers on neutrons. The isotope is radioactive if it has too many neutrons in the nucleus and because of this the isotope is unstable.

The half-life of a radioactive isotope is a time period. When the isotope is at the end of the period it's weight will be the half of the starter weight.

Answer 2

The difference between count rate and activity of a radioactive sample is simply geometry - geometry as in the ratio of disintegrations versus observed counts.

It is true that activity is proportional to activity. One curie is defined as 3.7x1010 disintegrations per second (DPS), or one microcurie is more commonly defined as 2.2x106 disintegrations per minute (DPM). The problem is that not all of the disintegrations get counted. After all, the detector does not completely surround the source and, even if it did, still not all of the disintegrations will be counted.

During calibration, a known activity is presented to the detector in a known geometry, and the count rate is measured. Lets say that 0.01 microcurie yields 1x104 counts per minute. We would say, then, that the instrument's absolute efficiency is 0.45%, which is the ratio of 1x104 over 2.2x106. If you then measured an unknown activity and got 5x103 counts per minute, you could reasonable assume that the sample was 0.005 microcuries.

These number are all examples, "picked out of the air", to illustrate the principle. Actual detector design and geometry is a complex science and other factors, such as emergy absorbtion, pulse nullification, and linear vs avalanche mode, just to name a few, factor into the proper design and calibration of a detector.

Answer 3

• Shelf life: Time that something (e.g. food, batteries) can stay good in storage, unused (aka on the shelf). This is a rough estimate that depends on various conditions (e.g. temperature, humidity).
• Half life: Time that something unstable (e.g. radioisotope) takes to decay to half its previous quantity. This is a physical constant for every item having this property.

Answer 4

Count Rate: Counts for radioactive emissions for a given period of time.

Half-life: Time it takes for half a given radioisotope to decay.