User manual

DECAY CURVES
For complete and easy evaluation of Radon-Thoron decay
curves, purchase MAKDECAY (see price list). It includes
many additional features and info.
If you observe the decay curve of Radon Daughters collected
with an Aware Fan-Filter, after turning off the fan, using AW-
GRAPH (or a spreadsheet program), you will notice what
appears to be a curve with a halflife of approx. 40 minutes.
This is due to the following:
The two materials generating a flux from the filter are Radium
B (halflife 26.8 minutes) and Radium C+C’ (halflife 19.9
minutes), both beta emitters (C’ alpha emmitter). Radium B
decays into Radium C, resulting in a curve with an apparent
halflife of approx. 40 minutes.
You can verify this by using a spread sheet program to plot
the decay curve of Radium B and Radium C as follows.
Given a certain quantity of radioactive material, if you know the halflife, you
can calculate the remaining quantity of the material after an elapsed amount
of time using the following formula:
E=E
o
* 2.71828
-( DecayConstant * t)
Where E is the remaining material,
E
o
is the initial quantity,
DecayConstant = 1/(halflife * 1.443),
t = elapsed time expressed in units the same as the halflife.
Fill four columns in the spreadsheet as follows. Fill column 1 with time
numbers (for example 0 1 2 3 4 5 6 etc.) for the x-axis.
Fill column two with the remaining quantity of Radium B using the corre-
sponding time number in column 1 and the Decay Constant of Radium B, by
applying the above formula. Start with an arbitrary amount of Radium B,
say 1000 units.
Fill column three with the remaining quantity of Radium C as above,
starting with an arbitrary amount of Radium C, say 700 units, but for every
row, add to the starting amount, the quantity of Radium B lost in the
corresponding row of column 2.
Fill column 4 with the sum of column 2 and 3.
Now generate a graph by assigning column 1 to the x-axis and column four
to the y-axis. You should get a curve with an apparent decay very similar
to that which you observe with real data when plotting Radon daughter
decay. For an exact match, use MAKDECAY program (see price list).
It is likely the Fan-Filter is collecting a little Thorium daughter as well. This
would be Pb-212. You can add a col. 5, col. 6 and col. 7. to the spreadsheet.
Fill col. 5 with decay info for Pb-212 (halflife: 10.64 hours), using the above
formula and the time info in Col. 1. Pb-212 is a daughter of Rn-220
(gaseous Radon isotope from Thorium, with halflife of 55.6 secs.). Fill col.
6 with the sum of col. 4 and 5. and add col. 6 to a y-axis graph series.
Import into col. 7 actual data collected from the fan-filter, and add this to a
y-axis graph series as well. Make sure the time increment in col. 1 equals
the time increment of the imported data in col. 7. Now observe the graph
then adjust the starting quantity of Ra B&C and Pb-212 so that col. 6 curve
matches col. 7 curve. This will reveal the percentage of Pb-212 collecting
on the filter.
X-RAYS FROM T.V.s and COMPUTER MON-
ITORS
Computer monitors, as well as TVs, operate with a high
voltage power supply generating voltages as high as perhaps
20,000 to 40,000 volts. This voltage has the potential of
generating X-Rays and Beta rays with electron volts as high
as the power supply voltage. The RM-60 is equipped with a
mica window (density 1.5 mg/sq. cm.). It can detect X-rays
with energies below 10,000 electron volts.
U.S. Department of H.E.W 21 CFR 1029.10 requires "Radia-
tion exposure rates produced by a television receiver shall not
exceed 0.5 milliroentgen per hour (500 microroentgens per
hour) at a distance of five (5) centimeters (1.97 inches) from
any point on the external surface of the receiver, as measured
in accordance with this section".
Normal background radiation levels average between 9 and 25
microroentgens per hour, depending on your location and
altitude. 500 microroentgens per hour is about 50 times
higher than background.
With the RM-60, a background radiation level of 10 micro-
roentgens per hour will generate an average of approx. 10
clicks per minute. A radiation level of 500 microroentgens
per hour will generate an average of approx. 500 clicks per
minute. It is evident that any radiation level approaching the
500 microroentgens per hour figure will be immediately and
obviously apparent given the large increase in click rate.
Therefore, one method of scanning a TV receiver (or com-
puter monitor) for excess radiation is to merely start the AW-
SRAD.EXE software collecting data in the ten second mode,
then slowly scan the surface of the receiver with the RM-60
holding it about two inches from the surface. If any increase
in click rate is observed, carry out a more detailed test to
determine the exact increase.
To run a more detailed check of a TV (or computer monitor)
for excess X-Ray generation, first place the RM-60 5 cm.
from the surface of the TV at the location that gave the
highest click rate observed as above, with the RM-60 window
pointing towards the TV. Start the radiation software and
gather radiation data for several TBU (ten second) periods.
Observe the average radiation level. Subtract the average
background radiation level for the site.
To eliminate alpha and beta emission from the test, place an
aluminum shield over the RM-60 window. A 5 mils thick
aluminum shield has a density of 35 mg./sq. cm. It will
shield all alpha emission and just about all beta emission with
energies less than 300,000 electron volts.
It would probably be a prudent decision to flag any TV (or
computer monitor) generating levels approaching 100 micro
roentgens per hour for a checkup by a technician who can
investigate the high voltage power supply, shielding, etc., of
the TV in question.
If you directed AW-SRAD to save the data to a file, you can
always reload the data and re-calculate the averages at your
leisure.
X-rays and gamma rays are composed of photons. They
differ only in their source. X-rays are generated from electron
beams hitting a metal obstruction whereas gamma rays are
emitted from radioactive materials. As stated above, the RM-
60 can detect X-rays (and gamma rays) with energies less
than 10,000 electron volts. The RM-60 system is calibrated
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