The Physics Blog

Mark Scheme for Radioactivity Test

Here is the markscheme for all of the questions that you did for the tests this week.

Download Radioactivity Test Markscheme

The Geiger-Muller Tube.

The instrument that we can connect to a counter in order to measure the activity of a radioactive sample (or the background).

The Wiki page on the GM tube explains how it works, the sensitivity depends on the p.d. you put across the anode and the cathode.

Reading on Scattering

Here are a few pages to read on Elastic and Deep Inelastic Scattering. The questions in the exam are very descriptive on these so being familiar with the concepts and then making sure you can write our a definition or description in your own words will prepare you well for them.

Elastic Scattering is what is responsible for the results of the Rutherford, Geiger, Marsden experiment, here is the Oxford University page on it.

Wiki Deep Inelastic Scattering is a good link and then there is the Oxford University page to look at.

Remember too that the HYPERPHYSICS webpages are a very good resource for your revision and understanding.

Radioactive (Random) Decay using Dice

Below is the file of data from the combined dice experiment. On it you can draw lines for an initial number of dice (you choose) and then half that number in order to find the half life for dice. Remember if you are asked to do this in an exam that you have to draw THREE SETS of lines and then take and average for the half life.

Download Radioactive Decay Modeled by Dice

Hal life is the time taken for the number of original nuclei to halve, or the number of original nuclei at any instant to halve. It can also be expressed in terms of activity since the activity (number of decays per second) of a sample is proportional to the number of nuclei, so half life is also the time for the activity of a sample to fall to half its value.

After one half life the activity of a sample drops to half. After two half lives the activity drops by half AGAIN or to a quarter of the original value.

Number of half Lives ------------------------ Fraction of Original Nuclei Remaining.

0 ----------------------------------------------------------------------------- 1
1 ---------------------------------------------------------------------------- 1/2
2 ---------------------------------------------------------------------------- 1/4
3 ---------------------------------------------------------------------------- 1/8
4 ---------------------------------------------------------------------------- 1/16

n ---------------------------------------------------------------------------- 1/(2)^n

Example Questions to do:

1. A sample of Radon 220 has a half life of 55.6 seconds. Approximately what fraction of the original sample is left after 12 minutes?

2. The activity of a radioactive sample is 3600 Bq. In one hour the activity has dropped to 360 Bq. Approximately, what is the half life of the sample?

3. Approximately what is the half life of a radioactive sample which has lost 96% of its activity in 1 hour?

4. A sample has an activity of 24000 Bq and a half life of 2.5 seconds. What will be the activity in 2 minutes? Will you be able to detect this? Explain.

5. The half life of C 14 (used for radio Carbon dating) is 5730 years with an uncertainty of 40 years. Read up on carbon dating and rite down in 5 sentences or less the key details of how it works as a method of aging organic material.

Set of Notes for Radioactivity

Here are some additional notes for you to have that support what we have been doing in class.

Download Radioactivity Notes

Radioactivity Introduction (safe)

The Cloud Chamber

The BIG cloud chanber at the San Fransisco Science Exploratory

University of California, Berkeley Lecture on the concepts of Radioactivity