Radioactivity is as easy as Alpha, Beta, and Gamma
In today's lab we will explore some properties of nuclear radiation. We will
examine how the intensity of the radiation measured depends on the distance from the source to the detector and on shielding placed between the source and the detector. We will also examine the difference between two types of radiation.
The radioactive materials that you use will not hurt you, but you should observe some simple precautions that will be explained to you.
You will be using a Geiger-Mueller detector that is attached to an instrument that supplies the high voltage to the detector along with counting the amount of radiation received. Please be careful and do not touch the back of the instrument or move the detector with the voltage on since there is anywhere between 600 to 800 volts supplied to the detector. Now with these warnings out of the way let's have some phun!!
As we have seen in class there is radiation around you that exists naturally. If we want to study radiation we first need to measure this "background radiation" that is always present and subtract its effects from our results.
Part 1: Measuring the background: Make sure that the counter is set to read for 0.1 minutes (6 seconds) and don't change that for the rest of the measurements throughout the lab. Turn the power on and press reset. Turn the voltage up to 720 Volts using the course and fine settings. Measure the background radiation five times, write down your results for each and then take the average. Notice that the numbers are sometimes not the same this is because the emission of radiation is random. The average background radiation number you just measured is important since for all the future measurements you make you will substract your background number from the measurements.
Part 2: Observing the effect of distance on intensity: Measure the distance from the entrance of the detector to each selve level using the unit of centimeters. Place a red or orange source with the label pointing downwards (aways make sure that the label is pointing downwards). in the tray closest to the detector and count. Do this for each level in the holder and remember to substract the background from your results. You should have six different measurements. Using as much of the graph paper as possible plot the number of counts on the y axis versus the distance on the x axis. If you are uncertain about making a graph ask for help. Does the shape of your graph remind you of something?
Part 3: Without making a graph repeat the above experiment with a green source.
Part 4: Observing the effects of shielding on radiation: Choose a red or orange source and place it in the fourth lowest selve. Place the other provided holder on the second level. Take a measurement. This represents the radiation received without any shielding. Now place in the second selve the thinnest lead shield and take a reading. Continue to do this for all the lead shields. What do you oberve?
Part 5: Repeat the above experiment only this time use the plastic shields instead of the lead shields. What do you observe?
Part 6: Repeat parts 4 and 5 only this time use the green sources, remembering to have the label pointing downwards, instead of the red or orange sources. What do you observe for the green?
Part 7: What general observations can you make about radiation? Was there any difference between the red or orange and the green source?