(Links to PHOTOS, DATA GRAPHS, DATA TABLES, SUGGESTIONS
FOR MORE RESEARCH, and RESOURCES are at the bottom of this
page.)
Primary cosmic rays striking the
upper atmosphere of the earth produce a cascade of secondary
particles. Many of the secondary particles are muons. A muon is about
206 times heavier than an electron and it has a lifetime of about 2
microseconds. In traveling the distance from the higher parts of the
atmosphere, muons arrive at the surface of the earth and below after
their lifetimes have expired. But because the muons are traveling
near the speed of light, a time dilation effect allows them to
complete their journey.
Magnetic fields affect the arrival
directions of the primary cosmic rays which in turn affect the
arrival directions of muons which are also spread out from the
creation of the particle cascade. The constant arrival of muons on
the surface of the earth results in a muon flux which varies with the
coordinates of the arrival location. This is a result of the magnetic
fields and the muon flux variation and has been calculated by J. F.
Ziegler (see resources) for various locations on the earth using New
York as a base reference value of one. The Ziegler article was
written as study of how cosmic radiation affects the failure rate of
computer chips at different locations.
Geiger counters detect the muon
flux which is around 5% to 10% of the total background radiation
which is picked up. This is not an accurate way to find the muon flux
rate and its variations. A better way is to place two geiger counters
together and connect them with a coincidence counter (c-box). Only
those muon particles that go through both geiger counters at the same
time interval are counted with the help of the c-box.
During the past year, I have
consulted many websites and several books on the subject and I have
found much theory and calculations but little on the actual study of
the muon count variations on the surface of the earth. There seems to
be many sophisticated experiments on measuring the various components
of cosmic radiation but little on actually measuring and monitoring
the muons reaching the surface of the earth at various locations and
times. Despite the magnetic fields which change their directions, I
think that it is worthwhile to study the variations in the peaks of
the muon flux on the surface of the earth with the location and local
and sidereal time.
The sources of cosmic radiation
which could affect the muon flux variation are the sun, our galaxy,
and the rest of the universe. Variations in the radiation from the
sun could affect the muon flux variation after large solar flares
which tend to suppress the cosmic radiation reaching the earth while
they are active. I think that a better candidate would be the cosmic
radiation reaching the earth from the center of our galaxy. The
galactic center has a strong radio source (Sagittarius A at around RA
17 deg. 45 min and DEC -28 deg. 48 min.).
I am interested in finding changes
in the muon flux which can be related to solar activity, activity
from the center of our galaxy, and unusual events that may occur
anywhere in the universe. This project is concerned with gathering
background data on the feasibility of measuring muon flux variations
related to the above events. This project is also intended to be
educational and perhaps will facilitate a number of investigators
sharing their data online to be able to develop an accurate model for
explaining the variations of the muon flux on the surface of the
earth.
Accuracy and expense are 2
important aspects of this project. The setup that I am using makes
use of the following items (shown in the top photo without the
computer): 1) A PC computer with a free serial port input, 2) Two
RM-60 geiger counters and software from Aware Electronics (see
Resources), 3) Coincidence box (c-box) from Aware Electronics, 4)
Several elastic bands, 5) Compass, 6) Level, 7) Protractor, and 8)
Pile of index cards or other device for changing the angle of the
array. The Photo section will show how these items are used. The
computer hookup directions are available from Aware Electronics.
Optional items could include a GPS device to indicate the exact
location and a barometer. It is possible that the muon count rate
could be affected by the density of the air which is related to
barometric readings but it is possibly a very small variation.
The RM-60 geiger counters have
geiger tubes which have a higher pickup rate from the sides. The
geiger counter is housed in a plastic box (see Photos). The 2 geiger
counters are placed on top of each other with the sides of the geiger
tubes parallel to each other. They are secured with 3 elastic bands.
The geiger counters and c-box and computer port connector all make
use of standard phone plugs and jacks. The 2 geiger counters are
connected to the c-box with phone line cords and the c-box is
connected to the computer serial port with another phone line cord
(refer to Aware Electronics directions for the proper connection
sequence as the c-box may not work properly if their connection
sequence is not followed). The software from Aware Electronics
includes a program (aw-srad.exe) which finds the counts from the
geiger counter and shows the counts as an updating bar graph. This
can be saved as a file and viewed as a bar graph or line graph using
another program (aw-graph.exe). I recorded the data for this project
and viewed it with the aw-graph.exe program which enables screen
capturing of the graph displayed on the screen. You can see an
extensive collection of data graphs by clicking on the screen below.
There are 19 small graphs each which can be viewed in a large,
detailed format. (Give the Data Graphs page time to load.)
I placed the 2 geiger counter array
at a straight up (90 deg.) angle for some parts of this project. That
is the position for the maximum muon count rate. The muons do not
have enough energy to come from the direction of the earth so that
only the ones from the overhead sky are counted. To prove this one
would have to place many lead blocks below the geiger counter array.
When turned sideways (0 deg. angle) which can be indicated as N/S,
E/W etc. the muon count drops to around 10 % or less of its straight
up angle. I used angles of 40 deg. and 20 deg. South for some of the
counts. The average count rate for 20 deg. S was 20 % of the straight
up angle rate and for 40 deg. S was around 35% of the straight up
angle rate. The 20 deg. S angle was the optimum direction for
pointing towards the center of our galaxy.
The accuracy of the data in this
project is related to the size of the geiger tubes and their capture
rate. More or larger geiger tubes would increase the accuracy but
would also increase the cost. Another way to increase the accuracy is
to average the data counts over one or two hour periods instead of
just one minute periods. This can be done automatically by the
aw-graph.exe program. This results in reliability factors in the high
ninety percents for many of the peaks on the muon graphs that were
made as a part of this project. The values given in the project
graphs are in counts per minute. These values need to be multiplied
by 60 for the hour graphs and 120 for the 2 hour graphs before
calculating the probability statistics.
To calculate the probability of the
curve of interest on a graph being significant, the following math
can be used: 1) Determine the average counts per time period and take
the square root of it - this is the standard deviation. 2) Find the
difference between the curve of interest in counts per time period
and the average counts per time period. 3) Divide the difference by
the standard deviation. 4) Use the results of the division to look up
the areas in a standard curve table which will give the probability
that the curve of interest was not caused by random variations.
As an example of the above, I will
use the curve in muon graph # 02. The curve of interest has a value
of 1.68 counts per minute and it took place at 5:45 AM EDT on
7/04/01. The average muon flux for this graph is 1.22. The graph is
done in intervals of one hour each so the counts per minute need to
be multiplied by 60 first to get the counts per hour. The curve of
interest becomes 1.68 X 60 = 100.8. The average muon flux becomes
1.22 X 60 = 73.2. The square root of the average muon flux is 8.56
and the difference between the curve of interest and the average is
27.6. The next step is to divide the 27.6 by the standard deviation
of 8.56 and that equals 3.22 which has a probability of 0.9994 in the
standard curve table. The table is available from an online link at
Aware Electronics but quick estimates in the 90 % range can be made
from the following. 1.29 = 0.9015, 1.65 = 0.9505, 2 = 0.9744
Using the above example, the curve
which peaked at 5:45 AM EDT on 7/04/01 was not due to chance but was
caused by a source definitely increasing the muon count rate. In
order to connect muon count increase with a definite celestial event,
it needs to be related to the sidereal time of the event and it needs
to be in a repeating pattern. If the repeating pattern is not
apparent, then corrections for other factors (for example, the
magnetic field) need to be taken into account. It could also be a
one-time event which could be correlated to the observations of
others at the same time.
This project is meant to be a
starter project giving the basic instructions for assembling the
components and some idea on the values to be received under different
conditions. The large data graphs together with all of the
explanations given in this report, should enable you to draw some
ideas involving the times of the significant events on the graphs. My
analysis of the data is given on the DATA TABLE, ANALYSIS,
SUGGESTIONS FOR MORE RESEARCH page. I hope that we can collaborate in
this project to further investigate this unknown area of knowledge.
Perhaps a network could be set up to share the data. Feel free to
contact me for any questions that you may have regarding the project.
Also check out the RESOURCES page of this report, the PHOTO page, and
DATA GRAPH page.
