Modern Physics > Nuclear Physics > Radioactive Decay DCS# 7D10.25

SEQUENTIAL DECAY OF RADON PRODUCTS

graph of count rate vs time


APPARATUS
 
modified counter and geiger-muller tube 214-02-B
vernier interface 113
1/4" stereo - BNC cable 101-13-C
laptop 206
balloon 202-14-E4
rabbit fur 202-18-D5
rubber band 111
paper clamp 111
masking tape
111


DESCRIPTION
This demonstrates both the presence of radon products in the air, and shows the decay curve that results from the sequential decay of two members of the radon decay chain.  

The charged balloon picks up dust containing decay products of radon.  Fasten the dust-laden balloon securely around the GM tube.  Plot count rate vs time (corrected for background) and/or ln count rate vs time for the duration of the class period.

The main sources of the detected radiation are the decay of lead-214 ( t1/2 = 27 min) and its product, bismuth-214 (t1/2 = 20 min) .  As the lead decays, the amount, and therefore the activity, of bismuth increases.  The decay curve represents the combined activity of both:


NOTES
Blow up, clamp, and charge the balloon 60 minutes before counting is to start.  Leave it in the machine shop until it is needed.

The experiment file is set up to do two-minute counts for 120 minutes.  The "corrected counts" column = counts/min - background counts/minute, where background was measured to be 20 +/- 1 in room 201.   

The modified counter outputs a 0-5 VDC TTL pulse with each event.

See the decay series of radon for the half-lives of the radon progeny.
 

REFERENCES
AJP 30, 120 (1962).