Demonstrations

Radioactive Discharge - Ionization

Code Number :	5D40.30
Disclaimer:	Reprinted by permission of Dick Berg, University of Maryland, for use on this website. The demonstrations contained and referenced herein are listed for the purposes of cataloging and describing physics demonstrations which should be conducted only under the direction of a trained instructional support professional or physicist. These demonstrations are not presented for the purpose of being conducted by persons unconnected to this Facility and/or persons not consulting with or being supervised by the recognized instructional support professional or physicist and his/her staff. The University is responsible only for those demonstrations carried out using its own equipment using established safety and scheduling policies, and bears no responsibility for those choosing to use this source material for their own purposes. All demonstrations described and contained herein are public domain, and can also be found in reference materials in libraries, bookstores, and electronic sources. Further information regarding legal liability in use of demonstrations and labs will be found on the web site Injuries in School/College Laboratories in USA. The University of Iowa Disclaimers: University of Iowa Disclaimer All Rights Reserved..
Condition :	Excellent
Principle :	Radioactive Discharge
Area of Study :	Electricity and Magnetism
Equipment :	Electrostatic voltmeter, parallel plate capacitor, high voltage power supply, americium source, polonium brush, Braun Electroscope, PVC rod, cat's fur.
Procedure :	Set the plate at about 2 cm separation and insert the electrostatic voltmeter probe as far as possible. Charge the parallel plates with the high voltage source to a potential of 1 to 2000 volts as measured by the voltmeter. Wait a few seconds to show that the voltage applied is not leaking off. Then bring the americium or polonium source toward the separation of the plates. When the source gets within 6 cm of the plate the voltage should start to decrease. The closer the source is to the plates the faster the discharge rate. NOTE: This works best during the winter months when there is lower humidity. A less intensive way to do this is to charge one of the electroscopes negatively with the cat's fur and PVC rod. Bring the brush that has the polonium 210 source in it near to the ball of the electroscope and observe the discharge. The brush with the Polonium 210 source can be purchased from the camera store. It is used to neutralize the static from dust so that it can be wiped away. The source will last for several years before it needs to be replaced. It is a very convenient source of alpha particles that can be used for several demonstrations.

References

S-130: "Dischg. - Flame & Radioactivity," DICK and RAE Physics Demo Notebook.

"Thoron Decay," The Demonstration Physicists Companion, Harvard University.

K.T. Bainbridge and J.C. Street, "Laboratory and Demonstration Experiments on the Law of Radioactive Decay and the Determination of the Disintegration Constant of Thoron, AJP, 6, 99, (1938).

"An Electrostatic 'Compass'," Physics From the Junk Drawer 3rd Edition, The Science House, North Carolina State University, p. 31.

Mail Questions and Comments to: Dale Stille