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"We blew up a six inch balloon, rubbed it vigorously with cat fur, and suspended it from the ceiling. Using an RM-80 Radiation Monitor (Aware Electronics) we measured the background at about 17 counts per minute, probably due to cosmic radiation. Being somewhat impatient, we took down the balloon in about 10 minutes, and took a count. We measured 56 counts per minute to start with, and we were impressed. We continued to take counts, and found a half-life of somewhere around 45 minutes.
It was clearly worthwhile to do the experiment a bit more systematically. One of us took the equipment home and hung up a balloon in the basement of the house. After one hour, the measurements indicated a count of 484 counts per minute!
The next activity in our disorganized search into the presence of Radon daughters on balloons took place in the basement lecture preparation rooms in the Physics Building. We hung up a number of balloons, and measured the amount of radioactivity and found an average reading of 2440 counts per minute.
Now we were worried and contacted the Radiation Protection Officer, here at the university. He mentioned that he had performed random checks of radiation levels in a number of buildings across campus, including the Physics Building, and had found no unusual readings. However, he felt that he should come and check out this seemingly outrageous reading on our balloons. He placed a radon detector (a Sodium Iodide Scintillation Well Counter from Nucleonics) in one of the prep rooms, and we hung up a few more balloons. Two days later we received the results: The radon detector measured a decay rate equivalent to 1.4 pCi/l, which is much less than the Canadian allowable limit of 20 pCi/l ( the U.S. limit being a more stringent 4.0 pCi/l).
We now took one of our balloons to the Slowpoke Nuclear
Reactor Centre, The measurements revealed that most of the
radioactivity was due to the beta decay of Pb-214 and Bi-214, both
Radon-222 daughters, and that there was also a fair amount of activity
from Pb-212, one of the daughters of Rn-220, a member of the Thorium
The Canadian Nuclear Society uses RM-80s for their educational programs. They recently purchased a number of Acer Aspire One computers for about $300 each. Bryan White, one of their members e-mailed a few days ago: "These little netbooks come with an 8 GB solid state disk. I have stripped the software we don't need and inhibited all the extra hardware. They boot up with XP SP3 in reasonable time and do a good job".
Check out the CNS Ionising Radiation Workshop YouTube Channel that includes the very interesting Hot Balloon Experiment:
Generate random numbers. (A program is included with each RM unit, SEED.EXE, which
generates random numbers with seeds derived from RM unit pulses). Also see:
Our new Windows program Aw-Radw includes an advanced random number generator:
Professor R. Coisson has written a lesson on the Poisson process:
Demonstrate Beta-Gamma flux from potassium chloride.
Place one or more pieces of foam rubber, (or filter paper), in a jar with a piece of uranium bearing ore for 1 to 14 days. Radon and Thoron daughters plate out on the foam rubber. Next place the foam next to the RM unit and plot the decay curve of the collected daughters (alpha-beta emitters). Next use AW-GRAPH and MAKDECAY (or perhaps a spreadsheet) to separate the decay curve of Radon daughters (half-life approx. 25-40 mins) from Thoron daughters (half-life approx. 10-12 hours). (Ore available from Minerals Unlimited, P.O.B. 877, Ridgecrest CA 93556-0877, (760)-375-5279). Carry out the same experiment but instead of using uranium ore as a source of Radon, suck air through a coffee filter for two minutes with a vacuum cleaner, or use the Aware Fan-Filter assembly (described elsewhere). Either method could gather enough daughters from even outdoor atmosphere, (depending on location), to plot the decay curves. Check decay curve for other isotopes as well. Demonstrate Alpha emission versus Beta emission from the Radon daughters, by sliding a piece of paper between filter and RM window. This is a very interesting experiment.
Note: When a Radon source, such as uranium bearing ore, is placed within a sealed jar, the level of Radon within the jar will increase for approx. 14 days (half-life of Radon: 3.8 days x ~4). If one then opens the jar, the Radon will escape and it will take another 14 days to reach max. Radon levels.
New apparatus available (Aware V-TAC) for collecting decay products from uranium bearing ore (or other radioactive material). V-TAC includes a can, washers and a -1000 VDC power supply. A 700% increase in collection efficiency is demonstrated. With the V-TAC, maximum Radon decay concentration is achieved within a few hours, instead of 2 weeks. -1000 VDC power supply has a 4.7 meg. ohm output impedance to eliminate shock hazard. Power supply input: 2 to 35 volts DC at approx. 1 ma, so a 9 volt battery will run the unit for weeks. Excellent for a teaching environment.
DEMONSTRATE MUON DETECTION (from decay of cosmic ray generated pions) versus background gamma photons (from background radon, thoron, uranium, etc.) by orienting RM unit vertically then horizontally, and/or shield RM unit with lead bricks. The lead will block the photons but not the muons. Did you know the half life of muons is about two microseconds. They are created by cosmic-ray impacts at approx. 20 kilometers altitude. Light travels less than a kilometer over a few microseconds. How could it be the muons are alive and well at ground level given the fact that particles can't travel faster than light? Answer: Time dilation given the muon's velocity. (See "About Time" by Paul Davies, pg 55.)
New item available: Aware Coincidence Box Decoder: $85. Use with 2 RM units. Box includes 3 Mod. connectors (2 for RM units, 1 for computer) & CMOS logic gate. Only MUONS, positron-electron pairs, etc., will generate coincidence counts in both RM units. Short clicks: normal counts, long beep: coincidence count. Plot both normal and coincidence counts, real time, with AW-GRAPH. Very interesting.
DEMONSTRATE ALPHA PARTICLE DETECTION (Proton - Neutron). If you do not have an alpha source handy, collect Radon daughters from the air, or purchase the cheapest First Alert smoke detector. Open case to expose circuit board. Remove circuit board from plastic case by pushing back snap-in plastic tabs. Undo metal tabs holding ionization chamber hood onto circuit board. Fold back hood to expose inner metal and plastic Americium 241 holder.
Start the RM system. Bring alpha-beta window within an inch of the alpha source (americium in the case of the smoke detector). Notice readings increase to perhaps 20,000. Next slide a piece of paper between alpha source and alpha-beta window to demonstrate the inability of alpha particles to pass through the paper. (Note: You might want to decrease the geiger click duration to one, when measuring higher levels. With a beep duration of one and a reading of 20,000, the system makes a very attention getting whooshing - hissing sound which drops back to normal background clicking when the paper is in place.)
Be very careful when handling Americium 241. Although smoke detectors are useful devices, Americium is extremely dangerous. Therefore, do not dig out, prod, or otherwise disturb the Americium. Stress to students the health threats involved with breathing or ingesting alpha sources. Once lodged inside your body, an alpha emitter can remain there for extended periods of time, subjecting the cells surrounding the particles to continuous alpha bombardment. This can destroy and damage tissue, and can trigger cancers.
DEMONSTRATE BETA PARTICLE and GAMMA DETECTION (Electron - Photon) If you do not have a beta source handy, collect Radon daughters from the air, or purchase a camping lantern mantle at an Army-Navy store, Sears, etc. Be sure to purchase mantles dipped in thorium nitrate. Coleman has recently introduced a non- radioactive lantern mantle, so you would want to avoid it for the purposes of this experiment. Thorium nitrate dipped lantern mantles are usually made in India, and this will be stated on the bag. Normally, no mention is made, on the lantern mantle bag, of thorium, radioactive warnings, etc.
Start the RM system. Bring alpha-beta window within an inch of the beta source (thorium and daughters in the case of a lantern mantle). Notice readings increase to perhaps 200. Next slide a piece of paper between beta source and alpha-beta window to demonstrate the inability of paper to stop beta particles. Next, place a 1/16" thick piece of aluminum between source and alpha-beta window (like an aluminum frying pan, etc.). Note how the aluminum stops beta particles but allows the gamma rays to pass. Demonstrate measuring the thickness of a material by gamma flux attenuation.
Be very careful when handling lantern mantles. Leave them in the plastic bag. Stress to students the health threats involved with breathing or ingesting beta sources. Once lodged inside your body, a beta emitter can remain there for extended periods of time, subjecting the cells surrounding the particles to continuous beta bombardment. One should take great care when replacing a lantern mantle and particularly should avoid breathing lantern mantle ash.