Skip to 0 minutes and 1 second [Alternative Radioactive sources] Some schools, particularly new schools, may not have any radioactive sources available for physics experiments. There are alternatives that you can use that are easier to come by, since they have low activity and are not controlled substances. In all cases, schools should refer to the appropriate guidance for their country, [CLEAPSS in England, Wales and Northern Ireland, SSERC in Scotland]. Bringing in materials that some students may be familiar with, will also give some context to your discussions. One such material is low sodium salt. This is readily available in any supermarket. Low sodium salt contains Potassium Chloride in addition to Sodium Chloride.
Skip to 0 minutes and 53 seconds Potassium-40 makes up a small percentage of naturally occurring potassium, and is both a beta and a gamma emitter. It is important that students understand that radiation is always present in an environment, and in fact our bodies contain potassium. The levels of radiation produced by low sodium salt are safe and in the levels consumed by an average adult would be below background radiation levels. Although low, the radiation from low sodium salt can be detected with a Gieger-Muller tube. To perform this experiment, it is important that students first measure the background radiation count over a period of say 5 minutes.
Skip to 1 minute and 36 seconds They can then calculate the background count, which is normally about 15- 20 counts per minute. The experiment should then be repeated with the tube inserted into the salt. For our low sodium salt, we’ve detected 2 to 3 times the background level in our radiation experiments. Another source that it is possible to buy are thoriated welding rods. These rods are used for arc welding to join metals together, for example in the manufacture of bicycles or aircraft. These rods contain thorium, which is an alpha emitter. Again the radiation levels from these rods are low but they should not be given to students because they could be harmful if broken and ingested or inhaled.
Skip to 2 minutes and 38 seconds This experiment should be performed over several minutes and compared to background radiation levels.
Skip to 2 minutes and 48 seconds Thoriated rods can also be used in an alternative source in cloud chambers.
Novel sources of radiation to use in school
Radioactive sources can be hard to come by, particularly in new schools, and can normally only be used in a demonstration by the teacher. The sources used in this video can be used with students in the laboratory and can be purchased cheaply in a supermarket or online. Both low sodium salt (Potassium Chloride) and thoriated welding rods can be used as weak radioactive sources.
As with the smoke alarm, students must be careful to take into account background radiation levels, over several minutes, when measuring the count rate from these sources. The count rate is low and so must be measured over a period of at least 5 minutes to ensure an appreciable difference above background. A possible task for the students whilst taking measurements could be to order statements as to the process from decay to detection, including the decay formula and the function of the Geiger-Müller tube.
Using low sodium salt as a source should help them to appreciate that we are constantly exposed to low levels of radiation in our environment and it is only harmful if we receive dose levels that are too high. This is a good opportunity to discuss medical and dental X-rays and the increased radiation dose from high-altitude flights on aircraft.
At the end of the video we mention cloud chambers. Take a look at this STEM Learning resource to find out how to make your own cloud chamber in the classroom.
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