QuarkNet
Cosmic Ray Muon Detector
User’s Manual
Series "6000" DAQ

Jeff Rylander, Glenbrook South High School
Tom Jordan, Fermilab
Jeremy Paschke, York High School
Hans-Gerd Berns, U. Washington

January, 2010
Version 1.1

Classroom Cosmic Ray Muon Detector User’s Manual

QuarkNet
Cosmic Ray Muon Detector
User’s Manual
Series "6000" DAQ
January, 2010
Version 1.1
This manual provides information for setting up and using a cosmic ray muon detector(CRMD) with the QuarkNet Version 2.5 Data Acquisition (DAQ) board and ancillary
hardware. It serves both beginning and advanced users.
This January, 2010 version includes an extensive rewrite of the original "Cosmic Ray
Detectors User's Manual, Version 2, August, 2008" which applied to the Series "200" and"5000" DAQs.
Much of the technical information was originally compiled in a user’s manual written by R.
J. Wilkes. Hans Berns, Rik Gran, Sten Hansen, and Terry Kiper contributed some of thetechnical documentation with input from the practical experience of many beta testers.1
Although some of the components of your cosmic ray muon detector may have come fromvarious sources, the heart of the detector is the QuarkNet DAQ board. The development of
this board is a collaborative effort involving Fermilab, the University of Nebraska and the
University of Washington. Appendix A has a description of the history of this project.
DAQ Development Team
Fermilab: Sten Hansen, Tom Jordan, Terry Kiper
University of Nebraska: Dan Claes, Jared Kite, Victoria Mariupolskaya,
Greg Snow
University of Washington: Hans Berns, Toby Burnett, Paul Edmon,
Rik Gran, Ben Laughlin, Jeremy Sandler, Graham Wheel, Jeffrey Wilkes

1

For more technical documentation on the DAQ board, see <http://www.phys.washington.edu/~walta/qnet_daq/>.

iClassroom Cosmic Ray Muon Detector User’s Manual

Table of Contents
Chapter 1

In the Classroom
Cosmic Ray Experiments within the Classroom
How Can I Use Cosmic Ray Muon Detectors in My Classroom?
What Experiments Can My Students Perform?

Chapter 2

Hardware Introduction
Hardware Overview
The DAQ Readout Board
Power Supply
GPS Receiver
Scintillation Counters
Cables for Connecting to PC

Chapter 3

Data Display
Data Display on a PC
Keyboard Commands

Chapter 4

The DAQ Card
GPS Observation
Singles and Coincidence Rate Measurement
Data Collection

Chapter 5

Data Upload and Analysis
QuarkNet Website Overview
Data Upload to the Server
Analysis Tools

Chapter 6

Advanced Topics
Counter Plateauing
Data Words
Coincidence Counting Variations
On-board Barometer Calibration

Appendices
Appendix A: History of Card Development
Appendix B: Schematic Diagrams
Appendix C: Terminal Emulator Setup
Appendix D: Precise Event Time Calculation Algorithm
Appendix E: Details of Time Coincidence and Data HandlingAppendix F: Acronym and Jargon DictionaryiiClassroom Cosmic Ray Muon Detector User’s Manual1Classroom Cosmic Ray Muon Detector User’s Manual

Chapter 1: In the Classroom
p + n  p + p + π+ + π- + π-

Cosmic Ray Experiments
For most of today’s particle physics
experiments, large accelerators accelerateparticles to very high energies. However, it
is possible to do high-energy physics in yourschool without a particle accelerator! Natureserves as an accelerator for cosmic rays—
particles that are of astrophysical origin andseem to be everywhere throughout theuniverse. Astronomers are presently
researching the origin of energetic cosmic
rays. Scientists at the Pierre Auger
Observatory, in Las Pampas, Argentina,
point to black hole activity at the centers of
distant galaxies.

andp + n  p + n + π+ + π° + π-.
The products of such interactions are called“secondary” particles or “secondary” cosmic
rays. Some of these products, however, arevery short-lived and generally decay intodaughter particles before reaching theearth’s surface. The charged pions, forinstance, will decay into a muon and aneutrino:π-  µ - + !

“Primary” cosmic rays, which are mainly
protons (and a few heavier nuclei), interact
with nucleons in the earth’s upper
atmosphere in much the same way that fixed
target collisions occur at particle physics
laboratories. Some primary cosmic rays canexceed human-made particle detector
energies a million-fold. When these primaryparticles interact with nucleons in theatmosphere, they produce mainly pions andkaons. In the collisions, if most of theincoming momentum is transferred to an
atmospheric proton, the following reactions
are common:µorπ+  µ+ + ! .
µAlthough these reactions are not the only
possibilities, they are examples of common
reactions that produce secondary particles
and their daughters. Counting all secondary
particles detected at sea level, 70% aremuons, 29% are electrons and positrons and
1% are heavier particles.
If these secondary particles have sufficientenergy, they may in turn interact with otherparticles in the atmosphere producing a“shower” of secondary particles. The
particles in this shower will strike a wide
area on the earth’s surface (perhaps several
m2 or even km2) nearly simultaneously.
Figures 1 and 2 illustrate these showers.

p + p  p + p + π+ + π° + πandp + p  p + n + π+ + π+ + π-.
If most of the momentum is transferred to aneutron, then these reactions are common:2

Classroom Cosmic Ray Muon Detector User’s Manual

cosmic rays. See the Auger site for recent
information. <http://www.auger.org/>

How Can I Use a Cosmic Ray
Muon Detector in My
Classroom?
The very nature of cosmic ray experiments
is quite different from traditional labs thatcan be completed in a single lab period.
Cosmic ray experiments typically require agreat deal of run time to collect data. Extra
class time, however, is not something mostteachers have in an already full course. You
may also wonder how to provide each
student time to do an experiment when you
have only one setup. These are realistic
questions. As a possible solution, thefollowing approach allows you not only toincorporate these experiments into yourcourse but also to help your students
discover how high-energy physics
experiments are really done.

Figure 1: An ultra-high-energy proton triggers acascade of secondary particles in this animationfrom the Auger array.

Organize the cosmic ray experiments as along-term project that spans a quarter oreven more. If students work on this projectintermittently, you can run these cosmic ray
experiments in parallel with your standard
curriculum, setting aside a day or two
periodically for cosmic ray muon detector(CRMD) work.

Figure 2. A cosmic ray shower produced bya primary cosmic ray entering the earth’s
atmosphere.

After an introduction to cosmic rays, theequipment, and the research questions thatphysicists ask in this field, have student
groups write up a proposal for theexperiment that they want to perform.
Background articles and animations
describing the equipment and cosmic rays ingeneral can be found at the QuarkNet
Cosmic Ray e-Lab website<http://www.i2u2.org/elab/cosmic/>.
These experiments might include calibrationand performance studies, muon lifetime

Although your students can do several
cosmic ray experiments with a single
classroom setup, the QuarkNet cosmic ray
website <http://www.i2u2.org/elab/cosmic/>
provides student access to data frommultiple cosmic ray muon detectors to study
larger showers. Several professionalversions of this same experiment are taking
data that may help determine the origin ofsome of these highly energetic primary3

Classroom Cosmic Ray Muon Detector User’s Manual

calibrations to study the response of thecounters and the board. Calibration studies
include plateauing the counters, threshold
selection and barometer calibration. These
are discussed in Chapter 5. A PowerPoint
slideshow and Excel template make theplateauing process even easier. You may
download these files from:<http://www.i2u2.org/elab/cosmic/library/resources.jsp>. Additionally, the QuarkNet
online analysis tools include a“performance” study for uploaded data. The
details of this study are outlined in Chapter 5
and on the website.

experiments, shower studies, or flux studies
as a function of one of many variables, e.g.,time of day, solar activity, east/west
asymmetry, angle from vertical, barometricpressure, etc. Your students can also look
for particles that are strongly correlated intime and may be part of a wide-area shower.
Once proposals are accepted, give each
student “collaboration” a few days to a week
to run their experiment. In some cases, twogroups might pool their time and share thesame data but for different physics goals.
This is not unlike how real high-energy
physics experiments are done! If time
permits, students can do a second run withthe student-suggested modifications.

Flux Experiments
Your students can do a variety of flux
experiments investigating such things ascosmic ray flux as a function of time of day,solar activity, east/west asymmetry(showing the µ+/µ- ratio by assuming thesecharged particles will bend in the earth’s
magnetic field), angle from vertical,
barometric pressure, altitude. The list goeson. Flux experiments are especially exciting
because students select the factors that theywant to test. Chapter 5 discusses flux studies
in more detail.

While one group is using the hardware,other groups can design their setup, analyze
their data (or other data), visit the “Poster”
section of the QuarkNet cosmic ray website
to research the results of other student
groups, etc. Having your students post theirwork here and/or having them give oralpresentations (sometimes with guest
physicists!) may make for a great summary
to the project.

What Experiments Can My
Student Perform?

Muon Lifetime Experiment to
Verify Time Dilation

There are four categories of experiments thatstudents can do with the cosmic ray muon
detectors:

A classic modern physics experiment toverify time dilation is the measurement of
the muon mean lifetime. Since nearly all of
the cosmic ray muons are created in theupper part of the atmosphere (~30 km above
the earth’s surface), the time of flight forthese muons as they travel to earth should be
at least 100 µs:

1. Calibrations and performance studies
2. Flux experiments
3. Muon lifetime experiments
4. Shower studies

Calibrations and Performance
Studies

30x10 3 mt flight === 100µ s .
vmuon 3x108 m / sdBefore students can “trust” the cosmic ray
equipment, they can and should do some4Classroom Cosmic Ray Muon Detector User’s ManualThis calculation assumes that muons aretraveling at the speed of light—anythingslower would require even more time. If a
student can determine the muon lifetime (asdescribed in Chapter 5) and show that it issignificantly less than this time, they arepresented with the wonderful dilemma thatthe muon’s time of flight is longer than its
lifetime!

tools of the e-lab can check for multiple
detectors firing in coincidence.
The QuarkNet online analysis tools allow
students to not only look for showers but tomake predictions about the direction fromwhich the shower (and thus the primarycosmic ray) originated. Details for doing
shower studies can be found in Chapter 5
and in the QuarkNet Cosmic Ray e-Lab.
See:
http://www.i2u2.org/elab/cosmic/analysisshower/tutorial.jsp

This time dilation “proof” assumes that allmuons are created in the upper atmosphere.
Although this is actually a good
approximation, your students cannot test it.
However, by using the mean lifetime value
and by measuring flux rates at two
significantly different elevations, you candevelop experimental proof for time
dilation. This experiment requires you tohave access to a mountain, an airplane, or
collaboration with a team from anotherschool that is at a significantly different
altitude! Here is a wonderful opportunity forschools to work together proving time
dilation. A very thorough explanation of thisexperiment is outlined in the 1962 classroom
movie titled, “Time Dilation: An
Experiment with Mu Mesons.”2 This movie
helps you (and your students) understandhow the muon lifetime measurement (alongwith flux measurements at two different
altitudes) can be used to verify time dilation.

Shower Studies
With the GPS device connected to yourDAQ board, the absolute time stamp allows
a network of detectors (at the same site or atdifferent schools) to study cosmic ray
showers. Your students can look for small
showers over their own detectors, or
collaborate with other schools in the area tolook for larger showers. The online analysis
2This 30-minute movie can be ordered on CD for $10
from http://www.physics2000.com/.

5

Classroom Cosmic Ray Muon Detector User’s Manual

Chapter 2: Hardware Introduction
5. GPS module.
6. GPS antenna.
7. Temperature sensor.
8. 5 VDC power supply.
9. PDU power cable.
10. Power distribution unit, PDU.
11. Power extension cables for PMTs.
12. USB cable.
13. Personal Computer.

Hardware Overview
See Appendix G for alternate setup.
Figure 7 shows QuarkNet’s most recent
cosmic ray muon detector (CRMD) setup
composed of:
1. Counters – Scintillators,
photomultiplier tubes and PVC
housing.
2. BNC signal extension cables.
3. QuarkNet DAQ data acquisitionboard.
4. CAT-5 network cable.

9

13

8

12

7

5
10

3

4

6

11

1
2

Figure 7. The components of the 6000 series QuarkNet cosmic ray muon
detector.

6

Classroom Cosmic Ray Muon Detector User’s Manual

For this setup, the DAQ board takes thesignals from the counters and provides
signal processing and logic basic to mostnuclear and particle physics experiments.
The DAQ board can analyze signals from up
to four PMTs. (We show two in the figure.)
The board produces a record of output datawhenever the PMT signal meets a predefined trigger criterion (for example, when
two or more PMTs have signals above somepredetermined threshold voltage, within acertain time window).

and environmental sensor data (temperatureand pressure).
This chapter includes an overview of eachmajor component shown in Figures 7 and 8.
Additional details regarding somecomponents are in the appendices.

DAQ Readout Board
Figure 8 is a picture of the DAQ board withseveral major components numbered.
1. GPS input
2. GPS fanout to another DAQ board
3. Board reset button
4. Coincidence counter display
5. Inputs for 4 counters (channels 0-3)
6. CPLD (programmable fast logic)
7. Time-to-digital converter (TMC)
8. USB port (output to PC)
9. 5 VDC input
10. 5 VDC output to power distribution
unitThis board is the logic link between the
scintillation counters and the PC. The board
provides discriminators and trigger logic for
four channels of PMTs. The board includes
five built-in scalers, allowing simultaneous
counts of singles on each channel, plus
triggers at whatever logic level you specify(2- to 4-fold majority logic).

The output data record, which can be sent
via a standard USB cable to any PC,
contains temporal information about the
PMT signals. This information includes:
how many channels had above-thresholdsignals, theirrelative arrival times (precise to 0.75 ns),
detected pulse. In addition, an external GPS
receiver module provides the absolute UTC
time of each trigger, accurate to about 50 ns.
This allows counter arrays using separate
DAQ boards—such as different schools in awide-area array or two sets of counters at thesame site—to correlate their timing data.
Keyboard commands allow you to define
trigger criteria and retrieve additional data,such as counting rates, auxiliary GPS data,

9
5

6

10
8

7

4

2

1
3
Figure 8. Close-up view of the DAQ: dataacquisition card..

7

Classroom Cosmic Ray Muon Detector User’s Manual

A standard USB interface can be connected
to any PC (Windows, Linux or Mac). The
datastream consists of simple ASCII textlines readable by any terminal emulation
program. In addition, a GPS clock provides
accurate event time data synchronized to
Universal Time (UTC), so widely separated
sites can compare data. In datastream mode,
the DAQ board outputs a series of text lines
reporting event data: trigger time in UTC(with 10 ns resolution and absolute accuracy
about 100 ns), leading and trailing edge
times for each pulse recorded within the

coincidence time window (with 1.25 ns
precision), and data from the GPS andinternal clocks. Additional keyboard
commands allow reading of temperature,barometric pressure and other sensors.

Board Components
Figure 9 is a block diagram of the QuarkNet
DAQ v2.5 board. (See Appendix B for aschematic diagram.)

Figure 9. Block diagram of the QuarkNet DAQ v2.5 board..

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Classroom Cosmic Ray Muon Detector User’s Manual

Discriminators
PMT signals are first pre-amplified by afactor determined from a set of changeable
resistors (Amplification factor x10 is used
for QuarkNet DAQ.) Discriminators are
implemented using voltage comparator chips
with the reference threshold voltage varied
through the terminal emulator program andthe TL command. Default settings on the
DAQ card are -300-mV threshold. It is
important to remember that the voltage
comparators look at the amplifier output, so
raw PMT signal levels are multiplied by any
amplification factor present before being
compared. For example, if you used a-30 mV threshold with NIM discriminatorsand have x10 amplification, your thresholdlevel on the QuarkNet DAQ board should be
set to -300 mV.

time intervals (pre-6000 DAQ: 0.75 ns). If
the trigger criterion is satisfied, the TDC
data are latched and read out, giving leading
and trailing edge times for each channel
relative to the trigger time in units of 1.25
ns. This allows you to calculate PMT pulse
widths (time over threshold, or ToT; see
Figure 10) as a crude estimate of pulse area
and thus energy.

Figure 10. Typical PMT pulse from which
the time over threshold (ToT) can be
determined.

Complex Programmable Logic Device(CPLD)
Trigger logic is implemented using a CPLD
chip. Software revisions for this chip must
be prepared using special software but canbe downloaded via the serial port. This
flexibility allows the engineers to distribute
updates that alter the fast logic, if necessary.
Any trigger logic level from singles to 4fold can be set by keyboard commands tothe board. Majority logic is used: any
combination of three active channels causesa trigger at the 3-fold level, for example.
Time-to-Digital Converters (TDCs)
Discriminator output pulses are fed into
TDCs3 which measure the arrival time ofleading and trailing pulse edges. TDCs keep
track of their state (high or low) at 1.25 ns
3“TDC” is a generic term in particle physics technology. The
specific chips used on the board are TMCs (“Time Measurement
Chips”). You may see this designation in some documentation.

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Classroom Cosmic Ray Muon Detector User’s Manual

Microcontroller (MCU)
The MCU is really just a special-purpose
CPU that provides the onboard “slow” logic(with a time scale of microseconds, notnanoseconds) to interface the board to you
via a terminal window or equivalent on yourPC. At present, the MCU can be
reprogrammed to redefine functionality only
by using special software and burn-in
hardware.

Board Functionality
Threshold Detection and Setting
After amplification, the PMT signals are fed
to voltage comparators. The comparators set
a HIGH logic level whenever the amplified
PMT signal exceeds their negative thresholdvoltage setting as shown in Figure 11. This
logic level has 1.25 ns resolution. Thismeans that we can measure the timedifference between pulses on different
channels at the same site down to less than ananosecond! We depend on the GPS clocks,
with 10 ns resolution (pre-6000 DAQ: 24ns), for timing between school sites.

Auxiliary Sensors
There is a temperature sensor built into themicrocontroller chip. This sensor is present
so that CPU temperature can be measured.
This temperature and the supply voltage arereported whenever the board is started up.
While the board components are rated fortemperatures between –20 °C and +80 °C,
the board temperature should not normallygo above +50 °C.

ReferencegroundSignal after
amplification

A second temperature sensor is located on
the booster board built into the GPS cable’s“far-end” DB9 connector. This sensor canbe used to log outdoor temperature at thecounter locations, and is read out with akeyboard command. The GPS module may
be damaged if its temperature goes below–40 ºC or above +85 ºC.4

User determinedthreshold

Figure 11. A typical negative PMT pulse
showing the user-defined threshold value
compared to reference ground.

A barometric pressure sensor is built into theboard as well. It can also be calibrated andread out (in units of millibars) with akeyboard command.

4

At DAQ card power-up or reset, the temperature on the DAQ card
(actually, inside the MCU chip) is reported. Note that this is not agood indicator of air temperature at the card site, even if the card islocated outdoors, since the chip generates considerable heat while
operating. It is a useful way to make sure the card is healthy,
however! Temperatures over +40 ºC may be dangerous to thecard’s chips.

10Classroom Cosmic Ray Muon Detector User’s Manual

Setting the threshold level too high will missall but those events that correspond to alarge amount of energy deposited in thedetector; setting the threshold too low will
result in background noise within theelectronics being mistaken as event counts.

The plot shows the singles rate in thatchannel as a function of threshold value.
You can see that the counting rate decreases
as the threshold setting increases. Once thethreshold value became as high as 0.5 V, thecounting rate decreased much more slowly.
The “kink” in the graph suggests that noisecontaminated the counting rate when thethreshold was set below 0.5 V. Operatingslightly above this value is probably the
optimum threshold value to choose.

So how do you determine the appropriate
threshold setting? Consider the graph in
Figure 12 below as a “ballpark”
determination of the optimum thresholdvalue to use for a channel. For the data
shown in this graph, the PMT voltage was
set to that determined by plateauing thecounter (see section 6.1 for help on how thisis done) and kept constant throughout theexperiment.

Change the threshold by using the TL
command from hyperterm. For instance,
TL 2 500 will set the threshold of channel 2
to -500 mV. The command TL 4 800 will set
all four channels to a threshold of -800 mV.
The default threshold equals -300mV.

Frequency(counts/minute)

Threshold Determination
900
800
700
600
500
400
300
200
100
0
0

0.1

0.2

0.3

0.4

0.5

0.6

Threshold (V)Figure 12. A graph of frequency vs. threshold for a counter used todetermine threshold setting.

11

0.7

0.8

Classroom Cosmic Ray Muon Detector User’s Manualmodular switching power supply, of the typeused for many small electronic devices, is
supplied with the board. Replacements arereadily available at Radio Shack or a similarelectronics store.

Coincidence Logic
The DAQ board can also determine whether
signals in separate channels are coincident intime. For example, if the trigger criterion is
set to 2-fold, then as soon as any channel
goes above threshold, a time window is
opened. (Window time width is adjustable.)
If any other channel goes above threshold
during this time window, all event data arelatched and outputted for the overlap timeinterval when both are active. Notice that
pulse data are reported for a time intervalthat is not of fixed length but just covers theoverlap period when two or more channels
are active. Leading and trailing edge times
are reported for any active channels (not justfor the two channels that launched thetrigger), with empty data entries forchannels that remained inactive during thetrigger window. For a single event trigger,
the DAQ board may need to output several
lines of data. The first line has an “eventflag” for identification. Any following lines
without this flag are simply additional data
for the same event.

PMT bases provided by QuarkNet can be
powered by the same +5 VDC power supply
that is plugged into the DAQ board. The
PMTs are connected to the board through a
power distribution unit (PDU: item #10 in
Figure 7). This simple box of four
potentiometers allows one to easily change
the voltage to each independent PMT for
optimal settings.
Note: It is important to distinguish theseDAQ power supply modules from otherunits used for computers or other electronic
devices requiring DC voltage. Connection of
the wrong power supply to your DAQ board
will probably damage it with too muchcurrent or voltage.

GPS Receiver

Rate Counters
The card has five built-in counters,
numbered 0 through 4: counters 0 through 3
record the singles count for each channel,
and counter 4 records the trigger count for
whatever coincidence level you have set. By
zeroing these counters with a softwarecommand (RB), then running the board for a
fixed length of time and reading out thecounters at the end, you can obtain singles
rates for each channel as well as thecoincidence rate.

Figure 13. The GPS unit consists of a
100-ft. CAT-5 network cable (green
cable), a GPS module (gray box), an
antenna (black cable), and atemperature probe (gray cable, red
end).

Power Supply
The board requires a stable +5 VDC power
supply, with 800 mA or greater output
current. A 110 VAC to 5 VDC/2.4A
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Classroom Cosmic Ray Muon Detector User’s Manual

The GPS unit shown in Figure 13 isconnected to the DAQ with a standard
Ethernet cable. An external temperature
sensor and the GPS antenna plug into one
side of the GPS module (a circuit board),
while the Ethernet cable plugs into the otherside. The GPS antenna is weatherproof withmagnetic backing, but the module should beprotected.

and longitude down to the equivalent of afew 10 s of meters.

The “1PPS” Signal
The stock NavSync GPS module wasmodified slightly for our application toallow the more precise timing we need down
to 10 s of nanoseconds (eight decimal places
following integer seconds). The GPS
receiver outputs a logic pulse at the
beginning of each UTC second, called the
1PPS (1 Pulse Per Second) signal.

GPS Startup

The GPS receiver sends two types ofdatastreams to the board. The first is RS-232
ASCII data telling what time it is, at what
latitude, longitude and altitude the receiveris, and information about the satellites thereceiver is using. The other data is a 5 V,
100-ms pulse telling exactly when the datais true. Each stream of 5 V, 100-ms pulses
arrives every second, thus the 5 V pulse isnamed 1 pulse per second (1PPS). The
microcontroller on the board records thecounter value during which the pulse isreceived. The time is according to a counter
running at ~25 MHz.

Once powered-up, the GPS module should
quickly “find itself” if it is in a location witha clear view of at least half the sky. Usually
it does not work well through windows andshould be physically outdoors. The receiverwill lock onto four or more satellites,
download the data needed to operate
accurately and start averaging its positionand clock settings at one-second intervals.
Within a few minutes after startup, you
should obtain accurate GPS data. The unit’s
LED display blinks red when first poweredup and searching, and changes to long green
followed by short greens for number ofsatellites when it has acquired enoughsatellite data to locate itself accurately. Timedata are not accurate until then.

In principle, the leading edges of 1PPS
signals from GPS receivers anywhere in theworld are all in synch, to within theaccuracy of the non-military GPS system(about 100 ns.) This feature allows accurate
time synchronization between school sites.
The special connector and cable attached tothe commercial GPS module transmits the
1PPS signal about 100 ft. or more without
excessive timing degradation.

The GPS module provides several kinds ofdata. The commercial GPS module directly
supplies the date and “coarse” time (in UTC,not local time) down to milliseconds, or
three decimal places after seconds, andreports its geographic location in latitude

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Classroom Cosmic Ray Muon Detector User’s Manual

millisecond, but there is a delay of a fractionof a second relative to the 1PPS edge. For
example, when the 1PPS signal says it isexactly 12:01:25.000000000, the GPS time
field in the data record may say it is12:01:24.850. This delay (reported as+0.150 sec in this example) will cause you
to associate the wrong integer second withthe event time if you are not careful. (TheGPS time delay may be negative, i.e., aforward shift, with the ASCII time dataahead of the 1PPS signal.) The DAQ board
is programmed to list the delay inmilliseconds for each data record so thereported time in seconds can be corrected tomatch the 1PPS data. The algorithm
described in Appendix D implements thesecalculations.

How to Calculate Event Times
The DAQ board has onboard a 25 MHz
oscillator, which “ticks” every 40
nanoseconds (1/25 x 106 sec). Such a device
does not maintain its frequency very
accurately, and our oscillator’s frequency
may drift by 10-100 Hz from its nominal
value (perhaps even more under extreme
temperature changes). A counter (scaler)
keeps counting the clock ticks. Wheneverthis 32-bit counter reaches its maximum
capacity of 4.3 billion, approximately every
100 seconds, it just “rolls over” back to zero,
like an old car’s odometer, and continues
counting. Clock calibration occurs in theinternal clock counter every time a 1PPS
signal arrives.
Find the precise event time by getting thedate and time down to the nearest second
from the GPS module’s coarse time (withone correction described below), finding thenumber of clock ticks between the last 1PPS
and the event trigger, and dividing by the
number of clock ticks between the last two
1PPS pulses to get the fraction of a second
down to 40 ns precision. Of course, youhave to know whether the counter rolled
over during the last second when doing thearithmetic.

For people who like really deep-down
details, the delay mentioned above, which
you can determine and correct, is not thewhole story. There is an additional delay of150-250 ms, which is unresolvable, since it
is buried in the manufacturer’s firmware.
Luckily, it is too small to cause the rounding
procedure described above to go wrong.
Remember, all this is just about determining
the integer seconds part of the time.
Nanosecond-level timing is not affected.
Also, we have not discussed corrections forthe antenna cable delay—the event time
calculated is when coincidence occurs at theDAQ board, not at the counters. This is ofno consequence as long as all school sites inan array use approximately the same cable
lengths, within a few 10 s of meters. The
algorithm showing how to get the precise
event time is shown in Appendix D.

There is a caveat to the previous paragraph:
If the data rate is very slow—less than about
one event per 100 sec—the internal countermay roll over more than once between
readings. In this case, all bets are off, andthe seconds cannot be reliably calculated.
The next firmware update will includecommands to produce an output line at each
1PPS, and/or automatic DG commands atregular intervals, ensuring that the necessary
information is logged between counterrollovers.
One minor correction is also needed: theGPS module reports the time down to the14Classroom Cosmic Ray Muon Detector User’s Manual

traverses is not discussed in this manual.
This phenomenon, however, is an important
one in helping your students understand theoperation of the detectors.

Power Supply

A typical counter used in this experiment isshown in Figure 15. A counter is comprisedof a plastic scintillator wrapped in foil and a
PMT. The PMT provides the necessary
operating voltage and sends an electricalsignal to the DAQ board when a light pulse
is “seen” by the PMT. QuarkNet glues anoptical “cookie” to a corner of thescintillators and the user then joins thecookie to the PMT and wraps it all in lighttight material. The PVC tube allows for easy
manipulation and transportation of thecounters.

Figure 14. Power distribution unit.
One black and four yellow test
points allow one to check voltage
on the PMTs.

A power distribution box (shown in Figure14) has taken the place of the previous
power supply option. The PMT/counters are
powered by stereo audio cables from thebox. The power distribution box isconnected to the DAQ and is attached via amono cable. This box provides 0.3 to 1.8 V
which scales by 103 to represent the voltage
on the PMT.

Scintillation Counters

Figure 15. The latest version of the cosmic ray
counter consists of scintillator, cookie (the flat
paddle region), PVC pipe support (white
cylinder, partially wrapped in black tape), and
the PMT (black wrapped portion of the PVCpipe).

Since muon flux at sea level is ~1 x 10-2
muons/cm2/sec, and since these compriseabout 70% of the cosmic rays at sea level, adetector of significant surface area will help
to increase the counting rate to 10 s or even
100 s of events each minute. If shower
experiments or flux studies are of interest,
then increasing surface area is the primary
way to increase the counting rate. If muon
lifetime experiments are of interest,
however, then increasing the thickness ofthe scintillator will also increase thecounting rate since only the muons that havestopped and decay within the detector can beused for lifetime studies.

It will be necessary to “plateau” yourcounter before the counting rate can betrusted. Small fluctuations in the highvoltage can offer significant variations incounter response if the operating voltage is
not near the voltage plateau. Details for how
to plateau a counter are in Chapter 6. Whencalculating the surface area of the active
portion of your detector, use the entire
square portion.

The process by which a scintillator
scintillates light when a changed particle

15

Classroom Cosmic Ray Muon Detector User’s Manualplateau. QuarkNet Cosmic Ray e-Lab
provides an informative PowerPoint
slideshow and an Excel template to help
with the plateauing process. See:
http://www.i2u2.org/elab/cosmic/library/
resources.jsp

PMT
Along with the newer versions of the GPS
and other components, QuarkNet andFermilab have gone to a PMT which has abuilt in power base. (See Figure 16.) The
P30CW5 requires the same power input of+5 V, 35 mA as the previously used PMT;
however, the HV is now contained within
the black cylinder.
BNC signal extension cables, which are thincoaxial cables carry the PMT signal to the
DAQ board.

Figure 16. The newest version of the PMT
has no high-voltage base.

The potentiometer is located in the power
distribution box, not on the end of the PMT.

Plateauing the Counters
To determine the operating voltage for aparticular counter, you must “plateau thecounter.” To do this, set up double
coincidence and stack the detectors. Run the
top counter as the trigger and the next
counter as the one to be plateaued. Record
the voltage as you increase it. Run for 2-3
minutes at each voltage and record thenumber of coincidences. You want yourtrigger counter to be set high enough that it
takes a good number of hits but not so muchthat it records a lot of noise. Setting it
around 0.7-0.9 volts is a good range. Make
sure the trigger is set constant at all times
during the testing of the array. Run thedetector you are plateauing from 0.5 to 1.5
volts (in 0.1 V steps) and record the numberof coincidences (the S4 column). A plot ofcounts per time vs. voltage will show the16

Classroom Cosmic Ray Muon Detector User’s Manual

Chapter 3: Data Displaythat a single event may result in more than
one line of data. In this section, we discuss
the meaning of some of the keyboard
commands that you can type in order tomodify or view various values of the board.

Data Display on a PC
View the data with a terminal emulation
program such as Zterm (Mac or Windows),
Hyperterminal (Windows) or a “homemade”
Unix-based program you can downloadfrom the QuarkNet website. See Appendix C
for details on setting up these terminal
emulation programs.

Your PC is capable of sending commands to
the DAQ board in addition to receiving thedatastream from the board. Figure 18 shows
an example of three keyboard commands
that you type in order to measure thetemperature at the GPS sensor, the value ofthe scalers, and to display GPS data.

Keyboard Commands
Once the terminal emulator is initialized andthe scintillation counters and board are
powered, you should begin to see data on
the screen that looks something like thatshown in Figure 17.

The help commands “H1” and “H2” send asummary of all keyboard commands.
Figures 19 and 20 show these commandsummaries.

The meanings of these “words” arediscussed in great detail in Chapter 6. Note

Figure 17. Sample screen of datastream from DAQ board when viewed with a terminal
emulation program.

17

Classroom Cosmic Ray Muon Detector User’s Manual

Figure 19. A list of keyboard commands viewable by typing “H1.”Figure 20. A list of keyboard commands viewable by typing “H2.”Some of the most commonly usedcommands are discussed in Table 1. See
Chapters 4 and 6 for more detailed

descriptions of how and when to use
these and other commands.

18

Classroom Cosmic Ray Muon Detector User’s Manual

Keyboard
Command
H1, H2
CD

CE
DS

RB
RE
TH
BA
DG
V1, V2
DC, DTST 3 5
SA 1

Description
Help Commands. Listing of all DAQ commands; see Fig.19, 20.
Counters Disabled. Does not write event lines on the PC monitor
even though the scalars will still increment. This is useful when you do
not want to “see” all the data coming in.
Counters Enabled. Writes event lines on the PC monitor. This
command has the opposite effect of the CD command.
Display Scalars. Displays values of the scalars in hexadecimal.
Scalars 0-3 store the singles rates for channels 0-3, and counter 4
records the number of n-fold coincidences, where “n” is whateverlevel you set. These counts are running totals since the last time thecounters were zeroed.
Reset Board. Resets scalars and TMC only.
Reset Everything. Resets everything (including card setup parametersthat you may have modified); will zero all scalars.
Thermometer. Reports reading of temperature sensor on the GPS
module connector, about 3 feet from the GPS module itself.
Barometer. Read and adjust barometer.
GPS Data. Displays current date, time, GPS position, and number ofsatellites visible.
Setup Registers. View registers in readable form.
Setup Registers. View registers in hexadecimal form.
Status Line. Show status line plus counts: channels & coincidence.
Important: run this command for each data session.
Save. Save any configuration changes.

Table 1. Commonly used DAQ commands.

19

Classroom Cosmic Ray Muon Detector User’s Manual

Chapter 4: The DAQ Card, V2.5
GPS Observation

If you connect the GPS module directly toyour PC’s serial port, as discussed before,
you can also use a software package
provided to display sky maps of satellites
and other interesting data. This can be foundonline.
<http://www.phys.washington.edu/~berns/archive/Leadtek/GMonitor.exe>

To read out the current GPS time, latitude,
longitude, altitude and number of satellites
in view, type “DG” as shown in the previous
section. You can also directly monitor the
GPS module’s serial datastream by sending
the command “NM 1.” This command willpass all data from the GPS module directly
to your PC. Normally, the board’s MCU
reads, interprets and distills the raw GPS
information to produce the DG command
output. Although this will continue to betrue even after you send the “NM 1”
command, you will get many more lines ofdetailed data (in the GPS industry’s standard
NMEA format). Refer to the link tounderstand this data format.

Singles and Coincidence Rate
Measurement
Two methods:
1) Important measurements you want tomake are the rate at which an individual
counter is hit (“singles rate”) as well as therate at which a 2- to 4-fold coincidence
occurs (“coincidence rate”). To determine
these, type the following commands shownin Table 2:<http://www.phys.washington.edu/~berns/archive/Leadtek/GPS_Protocol_ReferenceMa
nual.pdf>
To disable NMEA data forwarding andreturn to normal operation, send thecommand NM (i.e., no “1”).
CD
RB
DG
DS
DG

Counter Disabled. Prevents the datastream from off your screen.
Reset Scalars. But immediately after type . . .
Display GPS Data. Gives the initial time—when you began counting. (You
could use a stopwatch to measure the elapsed time instead.)
Display Scalar. After an adequate amount of time has passed (say 5 minutes
or so) take the final reading of the scalers and then immediately type . . .
Display GPS Data. Give the final time.
Table 2. The keyboard command sequence performed for determining
counting rate.

20

Classroom Cosmic Ray Muon Detector User’s Manual

The counting rates for any particularscaler (0-3) can be determined by
dividing the hex-valued scaler by thedifference of the beginning and endingtimes. The number of n-foldcoincidences that occurred within theelapsed time is recorded in scaler 4.
Dividing the number of coincidences by
the elapsed time will yield thecoincidence rate. Figure 21 illustrates
this command sequence and thecorresponding board outputs. As an
example of the singles rate, consider thedata in which the counting rate forchannel 0 was BCFHex = 3023dec. The
elapsed run time was 21:35:45 –21:30:46 = 4:59 or 4.98 minutes. Thus,
the singles rate is:

Rsin gles =3023counts
counts.
= 607
4.98minmin!

Initial GPS time

Scaler values after elapsed time

Ending GPS time

Figure 21. An example of keyboard commands and board responses used todetermine the singles counting rate in a particular channel.

21Classroom Cosmic Ray Muon Detector User’s Manual2) One can also display the counts using
the “ST 3 1” command. The middle
number “mode 3” will reset the countersafter each display. The final number isthe time interval in minutes. Figure 22
shows what the computer displays after
an ST sequence.

data as a text file that can be analyzed
later. The data will be written to this filecontinuously. For example, opening thistext file while data is being saved will
display all the data collected up to thatmoment.
When you want to stop a run (which
could be minutes, hours, or even weeks
later!), use the stop command for yourparticular emulator. (See Appendix C for
this command.) This file can be
uploaded to the server and the data
analyzed.

Data Collection
Once you have set up and tested yourequipment and have plateaued thecounters, you are ready to collect andsave data for a run. Although thecommands for starting and stopping a
run vary slightly with each terminal
emulation program (see Appendix C forthese commands), the idea is the same:Once the datastream appears on yourmonitor, select the command that willallow you to begin capturing text. You
will be prompted to type a name and afolder into which these data will besaved. Your emulator will save these

Each data collection should include thefollowing commands at the beginningand end of a data session:
H1, H2, DG, DC, DS, DT, BA, TH, TI,
V1, V2, ST 3 5, SA 1

Figure 22. Display of scalar counts from an ST command.

22

Classroom Cosmic Ray Muon Detector User’s Manual

Chapter 5: Data Upload and Analysis

Figure 23. The QuarkNet Cosmic Ray Collaboration webpage serves as the student homepage
for the Cosmic Ray project.

<http://eddata.fnal.gov/lasso/quarknet_g_act
ivities/view.lasso>.

QuarkNet Website Overview
Teacher Pages
The QuarkNet teacher activities database isfound at

By selecting the “Grid Cosmic Ray
Collaboration” link, you can find out more

23

Classroom Cosmic Ray Muon Detector User’s Manual

Before students can upload data to theserver, you will need to register yourdetector as part of the cosmic rayinvestigations network. This is easily doneon the teacher website. Registration will
require you to enter the serial number of thedetector found on the bottom of the DAQ
card itself, or by typing the keyboard
command “SN” in the terminal emulator.

about this project and use online tools for
implementing this project in your classroom.
You will find a page to register their schoolas part of the cosmic ray investigations
network so that your students may upload
data from their detector. A link to thestudent homepage is also located here.

Student Pages

By selecting the “Upload” link from the<http://www.i2u2.org/elab/cosmic/data/upload.jsp> page, you will see instructions and links for
uploading data. (You do not need to worry about
uploading data that may be “contaminated” by
keyboard command lines typed during theoperation of this run, as the analysis software will
create a new file for this data using only data linesthat are the complete 16 words across.)

The student homepage for this project is<http://www.i2u2.org/elab/cosmic/home/>(Figure 23).
Among many resources, students will find: Studies – Interesting questions alongwith ideas to answer these questions
through experiment.
 Resources – Links to related projects,
physicists and other student groupcontacts.
 Upload Data – Links to upload data andgeometry files.
 Data Analysis – Powerful analysis tools
to analyze data for a variety ofexperiments. Even students without adetector can analyze data.
 Poster Session – A method for students
to share their results, search the work ofother students and collaborate withstudents at other schools.

Once you have uploaded data, to see that it
has been loaded successfully, select the“Data” link. You can “View” your data inyour school’s folder. The link to view thisdata lists the date the data was collected. If adata run spans more than one day, the data
will be broken into separate files labeledwith the appropriate date.

Analysis Tools
Once your students have collected anduploaded the data, there are four studies they
can do. Analyze data from your detector aswell as any other detector that has uploaded
data. You can even look for coincidences
between your school and other schools if run
times overlap! This section will explain thenature of each study/analysis and provide aframework from which you can get started.

Data Upload to the Server
While many of the cosmic ray muon
detector experiments that your students cando require only the equipment at your local
site, analyzing the data is cumbersome with
software such as Excel. Working locallydiscourages student collaboration like thatfound in real high-energy experiments.
Accordingly, QuarkNet is developing a
website that allows data uploads andanalysis. This simplifies the analysis ofthese complex data and supports student
collaboration.

System Performance
The main objective of the “system performance”
study is to understand the quality of the data thatyou have collected or want to analyze.
24Classroom Cosmic Ray Muon Detector User’s Manualdeposited in the scintillator. To keep the costdown, however, a TDC (Time to Digital
Converter) was used. (See Chapter 2 formore on the TDC.). Since taller pulses(pulses with more energy) are generally
wider, there is a correlation between thetime that the pulse exceeded the thresholdvalue and the amount of energy deposited in
the scintillator.

Number of Events

Number of Events

The primary technique used to evaluate datain the performance study is a histogram of
the number of events as a function of timeover threshold (ToT, see Chapter 2). In avery loose sense, ToT is a measure of theamount of energy deposited in the
scintillator for a given event. Ideally, theDAQ board would have been equipped withan analog-to-digital converter (ADC) tomeasure pulse height and thus the energy

Time over Threshold (ns)Time over Threshold (ns)

a

(ns)

b

Figure 24. (a) The Gaussian distribution expected from an “ideal” system performancegraph; (b) an actual system performance graph.

Figure 24 (a)5 shows the ideal, Gaussianshaped distribution about a mean value forthe time over threshold; Figure 24(b) showsan actual data run plot.

and threshold settings used in our
experiment). This actual data, however,appears more skewed than Gaussian. Thishistogram may tell us that there is “good”
data in our actual run data, but that it iscontaminated with short pulses (a.k.a. noise)that were just above threshold. Increasing
the threshold value may “clean-up” thischannel in the future.

The actual data run histogram peak does
occur around 12 ns (which is typical for the1/2”-thick scintillator, the PMT efficiency,
5

There is probably a large portion of the actual run
data in Figure 18(b) that represents actual muons
traversing the counter. No real data histogram will
ever look perfectly Gaussian, but a shapesomewhat resembling that of Figure 18(a) can be

Figure is used with permission. Eric W. Weisstein.
"Gaussian Distribution." From MathWorld--A
Wolfram Web Resource.
http://mathworld.wolfram.com/GaussianDistribution.
html

25

Classroom Cosmic Ray Muon Detector User’s Manuala reasonable indicator that much of your data is“good” and represents real muons.
One factor you can modify in plotting ahistogram is the number of bins into which
the data are divided. Choosing a different
number of bins for the same dataset cansignificantly change the shape of the graphand may help evaluate the quality of thedata.
Figure 25. Cosmic ray flux
(events/detector area/sec) vs. time
graph over a period of two hours.

Flux Experiments
Cosmic ray flux, ! CR , can be defined as! CR =

events.
(time )(area )In analyzing flux study data, students selectthe dataset and channel(s) to be analyzed.
The analysis tools produce a histogram offlux vs. time similar to the one shown in
Figure 25. Students can juxtapose data
regarding their independent variable as afunction of time to look for correlations.

Since the area of your detector will probably
not be varied during an experiment, flux
studies ask the question, “How does the rate
at which cosmic rays pass through mydetector depend on __ ?” Since there aremany ways to complete this question, thisstudy is a fairly straightforward yet excellent
open-ended research question for yourstudents.

3
Muon Lifetime
Experiments

Flux experiments may include several
geometries of your detectors such as (1) asingle counter, (2) multiple counters placedin the same plane to increase detector area,(3) closely stacked counters that requirecoincidence, and (4) separated, stacked
counters that require coincidence used tolook at flux from only a particular directionof the sky. There are several interesting
variables to test in flux studies. Have yourstudents generate the questions that theywant to study.

1
Figure 26. A three-counter muon lifetime2detector system using the older version ofcounters.

A classic modern physics experiment is themeasurement of the muon mean lifetime.
This experiment has historical significanceas the very first experimental evidence oftime dilation. Chapter 1 discusses how the
lifetime measurement can be used to verify

26

Classroom Cosmic Ray Muon Detector User’s Manual

time dilation. Here we develop the muon
lifetime measurement itself.

Muon Lifetime Decay PlotMay 28, 2004

Consider Figure 26. When a muon enters acounter, a signal is generated in that counter.
If the muon traveled through counter 1 andinto counter 2, both of these counters shouldhave a signal at approximately the sametime. If the muon has stopped within counter2, however, it will “wait around” until it
decays and generate a second signal incounter 2 upon decay. The time tDECAY, thetime between the two signals in counter 2,
can be extrapolated from the data file. Sinceno signal occurred in counter 3, this is astrong indication that a muon did indeed
decay in counter 2. Theory suggests that themuon lifetime exhibits the characteristic
exponential decay that is common to otherphysical phenomena, such as radioactive
decay. In the case of radioactive materials,
the decay expression is given by"

Figure 27. A lifetime graph showing
number of number of decays as a function
decay from when the muon entered thescintillator. Fitting this data to an
exponential decay function can yield thelifetime.

It should also be mentioned here that the
muon’s time of flight before it entered thedetector is of no concern. Though tDECAY is
not its entire lifetime, plotting the number ofdecays as a function of decay time will yield
the same exponential decay shape fromwhich lifetimes can be found. The common“zero time” that we use here is when eachmuon entered the detector. If a large numberof decays are collected in the manner
described above, a plot can be produced
using the web analysis tool. (See Figure 27.)t!

N (t ) = N 0 e ,where N0 is the initial population, N(t) is the
population after time t, and τ is the mean
lifetime. The fact that muons in our
experiment do not coexist, whereas they doin radioactive materials, does not change thedecay expression. This does, however, givea slightly different meaning to N(t) and N0.
In this experiment, N0 is not the number ofmuons present at t = 0 but represents thetotal number of muons that were captured
and decayed within the detector. N(t) is then
the number of these muons with tDECAY > t.

While doing a lifetime study, no coincidence
level should be set locally. Instead,coincidence levels may be requested in the
web analysis. Students select the data file tobe analyzed, the coincidence level, and thetime interval between which coincidencesmust have occurred. The lifetime can be
determined by fitting this decay plot with an
exponential decay function of the form
described above. It is also possible forstudents to estimate the background valuethat should be subtracted from each bin
before fitting. (See Figure 27 pink line.)27

Classroom Cosmic Ray Muon Detector User’s ManualShower Studies
With the absolute time stamp that GPS
offers, a network of detectors (at the same
site, or at different schools) can study
cosmic ray showers. The web analysis tools
allow students to make predictions about
which direction in the sky the shower (andthus the primary cosmic ray) came from.
Students select the specific datasets toanalyze (these may be from different
locations) the coincidence level required,
and the time interval between whichcoincidences must have occurred. A 3-D
plot of position on the earth (xy) is graphed
as a function of signal time (z). This graphallows them to “see” the direction fromwhich the shower came. (See Figure 28.)

(ns)

Figure 28. Shower study plot showing
coincidences within a 70 ns time window.

28

Classroom Cosmic Ray Muon Detector User’s Manual

Chapter 6: Advanced Topics
Use a digital multimeter at the power
distribution box to find the voltage applied
to the PMT that you are plateauing. On a
regular basis note the scalar output from thePlateauing Counters
In order to determine the operating voltageof each of your counters, it is necessary to
perform a procedure in which you “plateau
the counter.” This step is necessary at least
once a year because counting variations due
to drifts in the tube gain or voltage occur
over time. By using an operating voltage
near the center of the plateau, drift effects
are minimized. QuarkNet Cosmic Ray e-Lab
provides an informative PowerPoint
slideshow and an Excel template to help
with the plateauing process. See:
http://www.i2u2.org/elab/cosmic/library/
resources.jsp

counter. Use the DS command to display
scalers and RB to reset the counters.
Continue the process for many different
voltages (potentiometer settings) to produce
a graph similar to the one shown in Figure
29. Remember that the scalar increments arein hexadecimal format when they aredisplayed in the terminal emulator. Also,
note that the channels are numbered 0, 1, 2,
and 3 respectively on the monitor and theboard. This numbering scheme (startingfrom 0 instead of 1) is consistent withengineering and computer programming
practice.

How to Plateau a Counter
There are two methods to plateau a counter:
1) Plateauing using a single counter
2) Plateauing using multiple counters
The first technique is simpler, however, it
may make “seeing” the plateau morechallenging.

Counter Plateau Plot

Singles Frequency(counts/minute)100000

Plateauing Using a Single CounterTo plateau a single counter, choose athreshold value for the discriminator andhold this constant for your experiment.
(Chapter 2 discusses how to choose athreshold value.) Turn on the DAQ board
and connect it to your computer so that you
can view the datastream on your monitor
using a terminal emulation program. (SeeAppendix C for help setting up a terminal
emulation program.) Once you see thedatastream, convince yourself that lower
potentiometer dial values result in a lower
counting rate while higher settings produce avery high datastream rate on your monitor,
or a fast increase of numbers on the DAQs
on-board scalar display.

10000
1000
100
10
1
4

4.5

5

5.5

6

6.5

7

7.5

Potentiometer Value

Figure 29. Example of counter plateau graph(log scale) used to determine optimal
operating voltage of PMT.

The optimum operating voltage is where thesemi-log graph looks the most horizontal.
For the graph shown, this occurs around 5.5
V. Sometimes it is difficult to “see” theplateau with this technique. If multiple
counters are available, the second techniqueoutlined below will make the plateau more
apparent.

29

Classroom Cosmic Ray Muon Detector User’s Manual

Plateauing Using Multiple Counters
Consider the four-counter setup in Figure
30. Let’s plateau counter 1. (This can occur
even if the other counters have not beenplateaued.) Set up an experiment toinvestigate the coincidence frequency
between counters 0 and 1 as a function of
the potentiometer setting on the base ofcounter 1. (See Figure 31.)

You can also plot singles of the counter
being plateaued along with the coincidences.
The graph is shown in Figure 32. Set thevoltage not far after the plateau begins.

Figure 30. Shown here is a four-counter setup usedin plateauing counters using the multiple countermethod. Each counter is paired with another andcoincidences are plotted over increasing voltages.

Since the coincidences between 0 and 1
should remain relatively constant over theexperiment, this can serve as a baseline fromwhich to find the plateau, and therefore theoptimal operating voltage.

Data Words
This section explains the meaning of each of
the data “words” that appear as a result of asingle event. It is not imperative for you tounderstand these words in order to collectand analyze data, but understanding thesewords can help as you attempt to evaluate
the quality of your data.

Counts per Minute

Coincidence Rate
800
600
400
200
0
0.6

0.7

0.8

0.9

1

1.1

Ch 1 Tube Voltage

The datastream from the DAQ board is in
ASCII format. Each data line contains 16
words as shown are a sample set of data in
Figure 33. Words 1-9 are in hex format. The
data shown below is for a single event—asingle event can span several lines of data!

Figure 31. Example of a multiple-counter plateau
graph used to determine the optimal operating
voltage of counter 1.

29Classroom Cosmic Ray Muon Detector User’s Manual

80EE0049 80 01 00 01 38 01 3C 01 7EB7491F 202133.242 080803 A 04 2 -0389
80EE004A 24 3D 25 01 00 01 00 01 7EB7491F 202133.242 080803 A 04 2 -0389
80EE004B 21 01 00 23 00 01 00 01 7EB7491F 202133.242 080803 A 04 2 -0389
80EE004C 01 2A 00 01 00 01 00 01 7EB7491F 202133.242 080803 A 04 2 -0389
80EE004D 00 01 00 01 00 39 32 2F 81331170 202133.242 080803 A 04 2 +0610

Figure 33. A sample event containing five lines of data. Each line is comprisedof the same 16-word format with each word separated by a space.

Below is a brief description of each of the“words.”Word 3: TMC count of Falling Edge at
input 0 (FE0). The format used is shown
below:

Word 1: A 32-bit trigger count of the 25
MHz CPLD clock mounted on the DAQ
board with a range from00000000...FFFFFFFF. Its resolution (1LSB increment) is 10 ns.6,7 A trigger countof 00000000 means that the DAQ card isstill in the initialization phase, i.e., the GPS
receiver has not started to generate 1PPS
pulses yet. Do not use the initial data until
the trigger count becomes nonzero!

Bits 0-4 = TMC count of falling edge.
Bit 5 = channel edge tag (1 = valid fallingedge, 0 = no falling edge).
Bits 6-7 = not used, always 0.
Word 4: TMC count of rising edge at input
1 (RE1); same format as RE0, except bit 7 isalways 0.
Word 5: TMC count of falling edge at input
1 (FE1); same format as FE0.

Word 2: TMC count of the Rising Edge at
input 0 (RE0). It is also the trigger tag. The
format used is shown below:

Word 6: TMC count of rising edge at input
2 (RE2); same format as RE1.
Word 7: TMC count of falling edge at input
2 (FE2); same format as FE1.

Bits 0-4 = TMC count of rising edge;
resolution = 1.25 ns (=10 ns/8).
Bit 5 = channel edge tag (1 = valid risingedge, 0 = no rising edge).
Bit 6 = not used, always 0.
Bit 7 = trigger tag (1 = new trigger, start ofa new event; 0 = follow-up data of a
trigger event).

Word 8: TMC count of rising edge at input
3 (RE3); same format as RE1.
Word 9: TMC count of falling edge at input
3 (FE3); same format as FE1.
Word 10: A 32-bit CPLD count of the mostrecent 1PPS (1 pulse per second) time markfrom the GPS receiver. This hex word
ranges from 00000000...FFFFFFFF and has
a resolution of 10 ns just like word 1.8

610.00 ns if the CPLD clock is exactly 25 Hz. It is reasonable toassume that an error within ±1000 ns is acceptable for a school
network if the schools are more than 1 mile apart from each other.
7

The CPLD clock frequency fluctuates slightly over time,depending on temperature changes and oscillator ageing drifts.
Therefore, in order to achieve high accuracy (±50 ns) in computing
the absolute trigger times, you need to poll the current CPLD
frequency at a regular basis (say once every 5 minutes) withcommand DG (Display GPS data). If the event rate is high enough(at least 1 event per 100 seconds), the CPLD frequency can becomputed from the 1PPS counter numbers of consecutive events.

Word 11: UTC time of most recent GPS
receiver data update. Although one update issent each second, it is asynchronous with the
830

The same uncertainty comments apply here as in word 1.

Classroom Cosmic Ray Muon Detector User’s Manual

1 = Current or last 1PPS rate is not within
25 CPLD clock ticks. (This is a result ofa GPS glitch, the DAQ uC being busy, or
the CPLD oscillator not tuned
correctly.)

1PPS pulse. The format used is shown
below:
HHMMSS.mmm
where: HH = hour [00...23]
MM = minute [00...59]
SS = second [00...59]
mmm = millisecond [000...999]

Word 16: The time delay in milliseconds
between the 1PPS pulse and the GPS datainterrupt. A positive number means 1PPS
pulse is ahead of GPS data, and negative
number means GPS data is ahead of 1PPS.
To get the actual GPS time to the nearest
second, round (word 11 + word 16/1000) tonearest full second. This gives the actual
GPS time at the last 1PPS pulse.

Word 12: UTC date of most recent GPS
receiver data update. The format used isshown below:
ddmmyywhere: dd = day of month [01...31]mm = month [01...12]
yy = year [00...99]
e.g., [03=2003]

See Appendix F for the interpretation of thedata for the previous example.

Word 13: A GPS valid/invalid flag.
A = valid (GPS data OK).
V = invalid (insufficient satellite lock for 3D positioning, or GPS receiver is ininitializing phase); time data might be
OK if number of GPS satellites is threeor more and previous GPS status was"A" (valid) within the last minute.
Word 14: The number of GPS satellites
visible for time and position information.
This is a decimal number between 00…12.
Word 15: This hex word is a DAQ statusflag. The format used is shown below:
Bit 0: 0 = OK.
1 = 1PPS interrupt pending. (Warning flag:
If DAQ card is busy, then 1PPS countmight lag behind or get mismatched.)
Bit 1: 0 = OK.
1 = trigger interrupt pending (possibly hightrigger rate; if continues, then data
might be corrupted).
Bit 2: 0 = OK.
1 = GPS data possibly corrupted while DAQ
uC was/is busy.
Bit 3: 0 = OK.

31

Classroom Cosmic Ray Muon Detector User’s Manualexperiments and typical parameter values
for each.

Coincidence Counting
Variations

Muon Telescope Flux Experiments
Set d = 4 and w = 10.
If you want to build a muon telescope withcounters less than a meter apart, TTRG is thetime it takes a muon to go from the top
counter to the bottom counter. Since thesemuons travel at essentially the speed of light(≈ 1 ft/ns), the TTRG is only a few ns so you
set d to the minimum value of four clock
ticks, or 40 ns. Similarly, to simply countmuons, you are only interested in a shorttime window for edges, so you could take
TWIDTH = 100 ns as well. The DAQ default
values would work well for this experiment.

Setting with Keyboard Commands
Chapter 4 discusses how to use somekeyboard commands to read scaler values
over a known period of time in an effort todetermine basic counting rate. That simple
calculation does not discuss two
parameters—gate window and TMC delay(w and d respectively). The gate window, w,
refers to how close in time pulses must be tocause a trigger. The TMC delay, d, moredifficult to define, determines which pulse
edges get read out into the datastream whena trigger occurs, by delaying thisinformation until the trigger actually
happens. (See Appendix E for a full
explanation of each quantity and the detailsof time coincidence and data handling.)

Muon Lifetime Measurements
Set d = 4 and w = 400.
If you want to look for muons that stop anddecay (2.2 µs mean lifetime) in a counter,you look for the decay electron pulses
several microseconds after the trigger, so
you have TWIDTH = 400 (10240 ns, or about
10 µs).

Consider the actual physical quantities andrelate them to the two parameters, d and w.
 TTRG: This quantity is the maximum
time window during which real physics
processes might cause a trigger. In otherwords, if you set the card for 2-foldcoincidences, and one channel receives asignal at t = 0, at least one other channelmust show a signal before t = TTRG or
you will not receive any information
about that pair of pulses. The examples
in Appendix E may help.
 TWIDTH: This quantity is the duration
after the first pulse in a trigger during
which you want to record all rising andfalling edge times. The channel in whichthese extra pulses occur does not matter;all of them will be saved.

Cosmic Ray Showers
Set d = 50 (= 1.2 µs) and w = 100.
In extensive air showers, the main“pancake” of arriving particles should be
between 10 m and 200 m thick. The earliest
and latest particles might arrive at thecounters about 0.6 µs apart, for a verticalshower. Thus you want TTRG to e about 1 µs.
TWIDTH can be about the same.
However, you should not set huge time
windows “just to be safe.” Doing this causes
the card to be busy all the time, and its
effective dead time will become a serious
problem. The values of d and w should be as
small as possible for the given physics goals.

The physical quantities TTRG and TWIDTH are
the values for d and w you set on the board.
You set TTRG and TWIDTH based on the typeof experiment that you want to perform.
Below is a list of several types ofDefault values, effective when the DAQ
card is powered up, are d = 40 ns and w =32Classroom Cosmic Ray Muon Detector User’s Manual

100 ns. These values may be restored usingcommand 'SA 2'. Modifying these values isprobably unnecessary for muon telescope
flux experiments. However, for air shower
detectors or muon lifetime experiments, you
should set them at larger values. TheseRE
CD
WT 01 00
WT 02 32

Resets the card by setting all counters to zero and returns everything todefaults.
Disables the counters and TMC.
Sets the time register with read pointer (register 01) = 00 and the write
pointer (register 02) to d, in hexadecimal. The TMC delay d will be thedifference of these values (so in fact you could set 01 to some value nn, and
02 to nn + d). This example sets d = 50; 500 ns. We have set register 02 to
32 = 50 . The maximum is 7F = 127 .
Sets the coincidence level and enable desired channels. Set control
registers with the WC (Write Control register) command. Register 0 sets thecoincidence level, using its first (left) hex character. Here, 0 means singles,
1 means 2-fold, and n-1 means n-fold coincidence level is to be required.
This is different from how coincidence is described in the data analysis
software found online. The second (right) hex character represents thedesired pattern of enabled/disabled channels in its bits, with 0s for disabledchannels and 1s for enabled channels. In this example, 1F means set 2-foldcoincidences with all four channels enabled: F = 1111. If you wanted todisable channel, 2 you would use 1101 = D . If you wanted to enable 3-foldcoincidences with channel 2 turned off, you would use WC 00 2D.
Sets the value of w (gate width). Registers 2 and 3 hold the gate width
setting in integer clock ticks (units of 10 ns). The lower 8 bits of the binary
number representing w go in register 2, and the higher 8 bits in 3. Thus, thedesired gate width w is given as abcd and is typed as:
WC 02 cd
WC 03 abAs an example, to get w = 100 clock ticks (100 = 0064 = 0000 0000 0110
0100 ) you would type what is shown to the left; 1000 ns.
Re-enables the onboard counters.
Displays the scaler values.
H

WC 00 1F

values serve as a good guide. If you want to
use the values of d = 50 and w = 100, Table
3 shows how to set the DAQ card to thesevalues:

10

H

10

H

H

WC 02 64
WC 03 00

10

H

2

CE
DS

Table 3. A keyboard command sequence that allows for coincidence counting
variations of the gate window and TMC delay.

33

Classroom Cosmic Ray Muon Detector User’s Manual

time has past, you type “DS,” the card will
return the scaler values for each channel as
discussed previously. In addition, the “S4=”line returns the value of the 2-foldcoincidences. This number is also inhexadecimal. The screen capture on the next
page (Figure 34) illustrates these commands
and outputs.

Interpreting Coincidence Data fromthe DAQ Board
This example shows how to interpret thecoincidence data from the board. Assume
you are looking for 2-fold coincidence
between any two of the inputs. As discussed
in the previous section, “WC 00 1F” will set
up this 2-fold coincidence. If, after someRB resets the scalers and TMC.
WC 00 1F sets up 2-fold coincidence between any of
the four channels.
Board responds that coincidence is set as specified.
DS displays the scalers for channels 0-3 (@00 through@03), displays the number of coincidences (@04)
present for above defined criteria, displays the 1PPS
signal (@5).
Figure 34. A sample terminal emulation window displaying how to set coincidence
levels and how to read this coincidence data.

34

Classroom Cosmic Ray Muon Detector User’s Manualbarometer (or some way to retrieve actualpressure in the local area). The actual
barometer reading should be recorded every
time the command “BA” is typed on the
keyboard. The “BA” command displays anumber that represents the ADC (analog-todigital converter) count readout of the onboard barometer. Figure 35 illustrates thiscommand. Notice that the value changes
each time the “BA” command is typed due
to fluctuations in local air pressure. If you
take actual barometer readings each time the
ADC count is recorded (over a period ofsignificant fluctuation in air pressure), agraph similar to the one shown in Figure 36
can be produced.

On-Board Barometer
Calibration
Air Pressure (kPa)

Pressure Sensor Calibration Plot
99
98.8
98.6
98.4
98.2
98
97.8
97.6
97.4
97.2
1900

y = 0.0188x + 61.33

1920

1940

1960

1980

2000

2020

ADC Counts

Figure 36. Calibration plot used to convert ADC
counts to air pressure in kPa.

You can measure air pressure with abarometer on the DAQ board. The
barometer sensor must be calibrated before
it can yield pressure in units of kPa. To
calibrate the sensor, you will need a real

Figure 35. The ADC count is displayed each timethe “BA” command is typed.

35

Classroom Cosmic Ray Muon Detector User’s Manual

Determine the slope and y-intercept for the
best-fit line and input those values into theboard via a keyboard command and yourpressure sensor is calibrated.

the reciprocal of the slope#& 1= 53.2 ! is what the software calls$"% 0.0188“gain,” while the y-intercept (61.3) is what
the software calls “baseline.”

Figure 37 illustrates the command sequence
used in the barometer calibration. Note that

HB is barometer help command.

User types inputs “baseline” and “gain” from graph informat asked for (see above).

Values are stored in board.
Figure 37. Command sequence used to calibrate thebarometer.

36Classroom Cosmic Ray Muon Detector User’s Manual

Appendices
Appendix A: History of Card Development
programmable logic and time digitizer
chips—similar to ones used in Rylander’sexperiment—to put cosmic ray experimentsin the hands of QuarkNet teachers aroundthe country. At Tom’s request, Fermilab
engineers Sten Hansen and Terry Kiper
developed a prototype front-end card for a
simple tabletop cosmic ray demonstration
detector. This “Version 1” QuarkNet board
put together components that were cheap,
reliable and highly capable of integrating ona small board the discriminator, logic andscaler functions of NIM modules for four
PMT channels, and a universal PC interface.
However, only relatively coarse (~20 ns)
pulse timing information could be provided.

After participating in the 1994 Teacher
Research Associates (TRAC) Program at
Fermilab under the mentorship of Dane
Skow, high school physics teacher Jeff
Rylander was excited about his experience
doing high-energy physics research andwanted to bring a real high-energy physics
experiment back to his classroom. During
the next year, Jeff collected the equipment
needed to perform a cosmic ray muon
lifetime experiment in his class. Fermilabelectrical engineer Sten Hansen developed alow-cost circuit board for the setup thatserved as the logic board to analyze a single
counter output and then deliver a readable
signal to a classroom computer. In 1996,high school students at Maine East HighSchool in Park Ridge, Illinois did this muon
lifetime experiment.

At the SALTA Workshop, held as part of
the Snowmass 2001 meeting, QuarkNet
joined CROP and WALTA to plan an
improved Version 2 board. The goals were: Nanosecond local timing.
 <100 nanosecond absolute timing.
 Reporting of all pulse edge times withina reasonable time window.
 Up to 4-fold majority logic.
 Total cost per board under US$500.

Independent of Rylander’s experiment,
projects like CROP and WALTA began
supplying schools with NIM crates andmodules, on loan from Fermilab, toparticipants in school-network cosmic ray
muon detector projects. The loaned
equipment had a book value of about$10,000 per school. Although most of themodules were obsolete and no longer indemand for current experiments, the large
cost drove the need to provide a very lowcost set of front-end electronics to theseteachers. Also, off-the-shelf NIM modules
could not handle GPS timing data and PC
interfacing. Thus, while adequate fortraining teachers, these wide-area network
projects could not begin taking real data inschools with the NIM hardware.

Remarkably, these goals were quickly
achieved! A team at KEK, the Japaneseequivalent of Fermilab, had developed atime-to-digital module for the ATLAS
particle physics experiment using a custommade ASIC chip called TMC (TimeMeasurement Cell). Samples, available at
Fermilab, are used in the new board design
to provide the detailed, precise timing dataneeded for air shower detectors. In addition,
the TMC chips allowed for time-overthreshold (ToT) estimates of pulse area.
University of Washington engineer Hans

During 2000, Tom Jordan of Fermilab
worked on the possibility of using new37

Classroom Cosmic Ray Muon Detector User’s ManualBerns designed and implemented an onboard system to integrate data from a very
low-cost (US$100) GPS receiver module.
This provided the final piece of missing
functionality. The Fermilab team revised theboard and its firmware to better encompass
the needs of air shower experiments. Afterlab-testing prototypes, QuarkNet distributed
the production specimens of the Version 2
cards in the summer of 2003.

Currently, Fermilab is helping to produce
several hundred DAQ boards and PMTbases for distribution to QuarkNet teachers
around the country. A software development
team has developed a web interface by using
grid computing tools and techniques toallow cosmic ray data networks nationwide.
Now students across the country are able tocollaborate as they perform real HEP
experiments. See:
http://www.i2u2.org/elab/cosmic/home/38

Classroom Cosmic Ray Muon Detector User’s Manual

Appendix B: DAQ V2.5 Board Schematic Diagrams

39Classroom Cosmic Ray Muon Detector User’s Manual

Appendix C: Terminal Emulator Setup
Hyperterminal

Once this program is opened, a window
appears that asks for a name for theconnection that you are making. Enter aconvenient name so that in the future you
will not have to go through the initial setup
routine each time you want to establish aconnection.

Hyperterminal, a terminal emulation
program, often comes with a Windowsbased PC or can be downloaded from theInternet. Hyperterminal allows the PC’smonitor to display the data that is sent fromthe DAQ board to the PC’s serial port orUSB port. Note: Hyperterminal no longer
comes as a standard application with
Windows Vista or Windows 7. Contact theCosmic Ray e-Lab HelpDesk for solution:
https://www.i2u2.org/elab/cosmic/teacher/fo
rum/HelpDeskRequest.php

Once you select “OK,” the window shownin Figure 38 appears. You need to select the
COM port that the DAQ board is connected
to on the back of your computer.

Choose the COM port that the DAQ
board is plugged into on the back ofyour computer (Serial port is COM1and USB is COM3 for this computer.)
COM3, the USB port, is selected here.

Figure 38. This window illustrates where the COM port selection is made,which tells the computer to which port the DAQ board is connected.

You need to change two settings from theirdefault values on the next screen. These
modifications are shown in Figure 39.

for the text file to which the datastream will
be written. Once a file name and folder forthat file have been selected, the “Start”
button begins the process of writing data to
the text file. As long as the connection is
open, data is written to the file. This text filecontains data for later analysis. To stop
writing data to the file, select “Capture

Once these settings have been made, selectthe “Capture Text” → “Start Capture”
command from the “Transfer” menu. A
window appears in which you type a name41

Classroom Cosmic Ray Muon Detector User’s Manual

Text” → “Stop Capture.” The connection
may be closed, and the text file is ready for

analysis.

Figure 39. Where baud rate and low control settings are modified for
Proper reading of the DAQ datastream with Hyperterminal.

the shift button while Zterm is opening. This
opens a window showing all possible
devices that are connected. You can selectthe USB device or serial port connection.

Zterm
Zterm is a terminal emulation program thatcan be downloaded and used on either aMac- or Windows-based PC. This program
allows the computer to display the data thatis sent from the DAQ readout board to thecomputer’s serial port or USB port.

Select the “Settings” → “Connection”
menus. The window shown in Figure 33
appears. You need to change two values
from the default settings: Data Rate =115000 bits/sec and Flow Control =Xon/Xoff.

Once this program is installed and openedon your machine, the computer should auto
detect the port your DAQ board is connected
to. If this is in question, you can hold down

42

Classroom Cosmic Ray Muon Detector User’s Manual

Change Data Rate to115200 for “6000” DAQ.

Figure 40. Where baud rate and flow control settings are modified
for proper reading of the DAQ datastream with Zterm. Note: theData Rate should be set o 11520 for the “6000” series DAQ.

“Dial” menu or just quit Zterm. The
connection is closed, and the text file isready for analysis.

Once the settings have been made, select the“Start Capture” command from the “File”
menu. A window appears in which you typea name for the text file to which thedatastream will be written. Once a file nameand folder for that file have been selected,
the “Start” button begins the process ofwriting data to the text file. As long as theconnection is in place, data is continually
written to the file. This text file contains
data to be analyzed. To stop writing the data
to the text file, select “Hang Up” from theUnix/LinuxThe application 'screen', standard on mostLinux distros, allows the capture of DAQ
data coming to a USB port. Contact theCosmic Ray e-Lab HelpDesk for details:
https://www.i2u2.org/elab/cosmic/teacher/fo
rum/HelpDeskRequest.php

43Classroom Cosmic Ray Muon Detector User’s Manual

Appendix D: Precise Event Time Calculation
Algorithm

triggered by a pulser. One was captured on alaptop and one on a PC. For the purpose of
discussing the data format, each column islabeled with a letter. The lines are split inhalf for readability.

Example Calculation
Note: this example uses data from theprevious generation DAQ (clock: 41.66
MHz). The following two simultaneous
events were recorded by two boards

LaptopPC

LaptopA
Trigger Count
1BB7FB6A
1BB7FB6D

B
RE0
B7
01

C
FE0
01
24

D
RE1
37
01

E
FE1
01
24

F
RE2
00
00

G
FE2
01
01

H
RE3
00
00

I
FE3
01
01

1BB7FB52
1BB7FB55

B5
01

01
21

35
01

01
21

00
00

01
01

00
00

01
01

J
1PPS Count

K
Time
(GMT)
210727.72
7210727.72
7

L
Date

M
Valid?

N# Satellites

O
Error Bits

P
Correction

110603

A

06

A

+0096

110603

A

06

8

+0096

110603

A

06

A

+0450

110603

A

06

8

+0450

1B1F27A0
1B1F27A0

PC

1B1F2787
1B1F2787

210727.37
2210727.37
2

Table 4. Example event data from PC and laptop used to illustrate how to
calculate precise event times.

44Classroom Cosmic Ray Muon Detector User’s Manual

Column A is the clock value at which thetriggers came. Columns B through I
contain timing information in fractions of aclock period. Each input has data for therising edge (RE) and falling edge (FE) of thepulse for each channel. Column J is theclock value at which the 1PPS arrived.
Column K is the time and Column L thedate at which the 1PPS arrived. This value
must be corrected by Column P androunded to the next second. Column M is
“A” when the GPS data in a row is valid and“V” when it is invalid. Column N is thenumber of satellites the receiver is using.
Column O is four error bits, each of whichindicates the trigger IRQ status. Bit 0
indicates that the 1PPS interrupt is pending,
bit 1 that the trigger interrupt is pending, bit
2 that the GPS data could be corrupt (write
in progress during readout), and bit 3 thatthe current or last 1PPS pulse was not withintolerance of clock ticks.
To calculate the absolute time of the 1PPS,
we must add K to P and round to the nearest
integer second, first converting to seconds
after midnight. Separate K into hours,
minutes, seconds, and milliseconds.
Multiply by 3600 for hours and 60 for
P #&minutes. Round $ K sec + m sec ! = T1PPS .
1000 "%
To calculate the relative time between the
input pulses, you must understand the edge
data represented in columns B through I.
Each column contains a tag bit (bit 5) toindicate whether the column contains data.
Bits 0-4 are the data. Bit 6 is always 0. Bit 7
of column B only indicates whether a new
trigger is contained in the line; for columns
C through I, bit 7 is always 0. See bit map.

7

6

5

4

3

2

1

0

0 (Trig tag for RE0)

0

Channel Tag

Data

Data

Data

Data

Data

Table 5. Bit map for columns B through I for event data shown in Table 4
above.

Bit 7 of Column B indicates a new trigger.
To calculate the time of each trigger, therelative time between the 1PPS and thetrigger must be found. This can becalculated by subtracting the counts in
Column J from those in A (first converting
to decimal). A " J = !Tclk . The data fromcolumns B through I may be added but givesuperfluous precision (for small datasets)
given the 1PPS is measured only in integer
clock periods. To calculate the absolute timeof column A, convert !Tclk to seconds(multiply by the reciprocal of the clock' 1 $"" = !Tsec , and add tofrequency), !Tclk %%& f clk #T1PPS . Thus the absolute time of the trigger

is: T1PPS + !T = Tabs . The long form is:

P $ (A ! J )'Round % K sec + m sec " += Tabs . In thisf clk
1000 #&
case the triggers happen at the following
times in seconds after midnight:

45

Classroom Cosmic Ray Muon Detector User’s ManualPC:

450 # (465042258 - 455026567 )&= 76048.240376582 sec
Tabs = Round $ 76047.372 +!+
1000 "
41666667%
after midnight.
Laptop:0096 # (465042282 - 455026592)&= 76048.240376558 sec
Tabs = Round $ 76047.727 +!+
1000 "
41666667%
after midnight.
Note: for "6000" series DAQ, fclk = 25 MHz
for all older DAQ, fclk = 41.666667 MHz
The difference between the two times in thisexample is the length of one clock period.
This is to be expected because the clock
period is the limit of the resolution of thetriggers. By writing a program to examine
the files containing readout data, you caneasily check the time difference for each
event. For these data, the time differs no
more than two clock periods verifying that
the GPS data can be used in correlating data
between QuarkNet DAQ v2 cards.

46

Classroom Cosmic Ray Muon Detector User’s Manual

Appendix E: Details of Time Coincidence and Data
Handling
This appendix explains the operation of thecard’s time coincidence and data handling ata deeper level. To keep the cost low, theproject engineers created a very cleverscheme for handling the tasks needed withminimal resources. Of course, “clever” alsomeans “not simple.” For this reason, the way
in which triggering is handled differs insome details from what one might expect for
simple modular fast electronics like NIM
coincidence units. The card handles
coincidences as described below.

processes that we want to study mightcause a trigger. In other words, if we set
the card for 2-fold coincidences and one
channel gets a signal at t = 0, at least one
other channel must show a signal before
t = TTRG or you lose detailed information
about that pair of pulses. The examples
below may help.
 TWIDTH: This quantity is the duration
after the first pulse in a trigger during
which we want to record all rising andfalling edge times. The channel in whichthese extra pulses occur does not matter;all of them are saved.

Descriptions of Gate Window
and TMC Delay

Set the values of w and d as follows: Set d > TTRG, but no smaller than twoclock ticks.
 Set w > TWIDTH + d – 1.

We define two parameters, which you canset:
1. w = Gate Window: Just like the “width”
setting in a NIM module, the gatewindow determines how close together
pulses must be to cause the card to
trigger. Note: In digital electronics, theterm “gate” means a signal used toenable (“open the gate for”) passage ofother signals or data.
2. d = TMC Delay: This quantity
determines which pulse edges get readout into the datastream when a trigger
occurs by delaying this information until
the trigger actually happens.

Whenever an above-threshold voltage is
detected on any channel, that channel turns
on an internal trigger bit for w clock ticks (wx 10 ns). At the end of that time the internal
trigger bit is reset to zero.
The card’s startup default setting is for 1fold coincidence, which means it
triggers on singles: any above-thresholdsignal on any channel produces output data.
Unless your PMTs are extremely quiet,
actually triggering on singles will quickly
overwhelm the card.

Both w and d are measured in units of 10
nanoseconds, the internal clock tick interval.

When the card is set for 2-fold coincidences,a trigger is declared any time that two or
more channels' trigger bits are “1”simultaneously. If the card is set for 3-foldcoincidence, then it requires three channels

Consider the actual physical quantities andrelate them to the two parameters listed
above.
 TTRG: This quantity is the maximum
time window during which real physics

47

Classroom Cosmic Ray Muon Detector User’s Manual

three ticks. (Again, the trigger is still on.)Because both edges appear when the trigger
is on, they appear in the datastream sent tothe computer.

with their bits set simultaneously, andsimilarly for 4-fold.
The trigger bits must overlap by at least one
10 ns clock tick to activate a trigger. If one
channel's bit drops and another rises, notrigger occurs. Also, the trigger is active forexactly the overlap period. The card has a
TRG output that goes high when a trigger
occurs. You can watch this on theoscilloscope and see its duration change as
the signals are closer or further apart.

Examples of Event Timing
Diagrams
Below are four examples of event timing
diagrams showing 2-fold coincidences, with
d = 6, w = 10. In each case, pulses of width
two clock ticks (10 ns) arrive at inputs 0 and
1, but with different time separations in eachexample. The timing diagrams show thediscriminator output, the channel trigger
gate, and the TMC output after delay d, foreach channel, plus the coincidence trigger
gate, and the edge time information obtained
from the TMC upon readout.

The TMC delay d is very different than thealmost-just-like-NIM coincidence describedabove. The reason for this is that we want to
do more than count triggers; we also want torecord all the edges that contributed to agiven trigger. It is hard to program thecircuits inside the board to look back in timeto the first pulse that contributed to thetrigger when the second pulse might havearrived a significant amount of time later. (Itwas also hard to make the old NIM modules
do this.) Instead, we separate the part thatgenerates the trigger from the part that reads
out the timing information and then wedelay this detailed timing information sothat it is read out after the trigger isgenerated. The card needs to save only
information that happens when the gatesoverlap.

Example A
The signal in channel 1 arrives two clock
ticks (20 ns) after the signal in channel 0.
Figure 41 illustrates that the trigger gate iseight ticks long (overlap time of the two tentick channel gates). All edges get reported.

Consider the card’s startup default settings,
d = 6 and w = 10. Imagine a physics event
where one pulse arrives three clock ticks
after another. The trigger will occur when
the second pulse arrives—three clock ticks
after the first. At this point, the card detects
trigger bit overlap, and the TRG output goeshigh. Internally, however, pulse edge time
information is delayed six clock ticks (d =6), so the information about that first pulse
is available after just three more clock ticks(the trigger is still on). The information
about the second pulse arrives after another

Example B
The signal in channel 1 arrives three clock
ticks (30 ns) after the signal in channel 0. In
this case, the trailing edge of the delayed
TMC signal for channel 1 lies outside the48

Classroom Cosmic Ray Muon Detector User’s Manual

this looks like a random background eventthat you have to eliminate or ignore when
you analyze the data.

card trigger gate (overlap time of theindividual channel gates), so only its leadingedge is reported. This is illustrated in Figure
42.

The next example is an actual event
recorded by the DAQ card, on Aug. 8, 2003,
with a mini-array of four counters. In thisexample, the card was set with d = 6, w = 10
(the default startup values), and for 2-fold or
greater coincidence level. (Theinterpretation of the data words for thisevent can be found in Appendix F.)

Example C (Figure 43)
The signal in channel 1 arrives five clock
ticks (120 ns) after the signal in channel 0.
Note that the delay value is six clock ticks(144 ns). In this case, both edges of thesignal on channel 1 lie outside the trigger(overlap) window and are not reported. If
your physics application involves simply
counting triggers (as in a muon telescope),
this does not present a problem. However, if
you are analyzing edge time data, as in amuon decay or air shower experiment, thiswould appear to be a 1-fold event! If thissituation represented a real physics process
you wanted to study, you would need tolengthen the values of d and w to accept all
the edges in this event. If this is not done,

Example D (Figure 44)
Notice the datastream had five lines of data
for this single event.

80EE0049 80 01 00 01 38 01 3C 01 7EB7491F 202133.242 080803 A 04 2 -0389
80EE004A 24 3D 25 01 00 01 00 01 7EB7491F 202133.242 080803 A 04 2 -0389
80EE004B 21 01 00 23 00 01 00 01 7EB7491F 202133.242 080803 A 04 2 -0389
80EE004C 01 2A 00 01 00 01 00 01 7EB7491F 202133.242 080803 A 04 2 -0389
80EE004D 00 01 00 01 00 39 32 2F 81331170 202133.242 080803 A 04 2 +0610
Figure 44. A sample event containing five lines of data. Each line iscomprised of the same 16-word format with each word separated by a space.

49

Classroom Cosmic Ray Muon Detector User’s Manualis asserted. If no further signals arrived,
the trigger would stay on for ten 10 ns
time bins (100 ns) since the signals onchannels 2 and 3 arrived inside the same
clock tick.

The pulse-timing diagram, Figure 45, shows
the four PMT channels’ trigger bits as afunction of time in nanoseconds.
(Remember, channels are numbered 0
through 3). Pulse edge times are recordedwith 1.25 ns precision. Recall, however, thatthe trigger logic works in time bins of 10 ns.

4. In 10 ns time bin 2, pulses arrive inchannels 0 and 1, setting their trigger
gates for 10 ticks. Thus, the 2-foldcoincidence requirement is met
continuously from time bin 1 until timebin 11, a total of 11 clock ticks or 110 ns(shaded area in Figure 46).
5. At the end of this interval the trigger
gates for all channels are down, so the
TRG gate is dropped. The pulse edge
times stored during the time the trigger
was on are read out of the TMC chip andreported.

Figure 45. Discriminator output timing
diagram for Example D.

Figure 46 shows the channel trigger bits as afunction of time, in units of 10 ns.

6. Only edges that are within the trigger
interval after they have been delayed bysix ticks are put into the datastream.
Thus, all the pulses in Figure 43 arerecorded, but the second falling edge ofchannel 3 (which is off the figure to theright) will fall outside the shaded area in
Figure 46 and will not be recorded.
Note: The actual values encoded in thedatastream represent the delayed times. If it
is vital to get the actual time for each edge,
then each of them actually arrived d x 10 ns
earlier than the time given in the data record.
Usually only relative timing matters, andthis kind of accuracy is not necessary.

The following sequence of events occurs:
1. The first pulse arrives on channel 2 at t =1 (in units of 10 ns). Trigger gate 2 is set
for 10 ticks. The TMC records thepulse’s leading edge at 3 ns relative tothe last 10 ns clock tick.
2. Three nanoseconds later, a pulse arrives
on channel 3. Trigger gate 3 is set for 10
ticks. The TMC records this pulse’s
leading edge at 6 ns.
3. Trigger gates 2 and 3 are set
simultaneously, so a trigger gate (TRG)
50

Classroom Cosmic Ray Muon Detector User’s Manual

Appendix F: Acronym and Jargon Dictionary
Acronym or
Term
1 PPS
AC
ASCII
ASIC
ATLAS

Binary

Bit
Byte

BNC

Coincidence

Counter
CPLD

CPU
CROP

DAQ
DB9

Description
One Pulse Per Second. GPS signal used for precise time synchronization.
Alternating Current.
American Standard Code for Information Interchange. Numeric code fortext files.
Application-Specific Integrated Circuit. A custom-made chip, like the
TMC chip used in the DAQ board.
A Toroidal LHC ApparatuS. A large international collaborative
experiment at the Large Hadron Collider (LHC) at CERN Laboratory in
Switzerland. <http://atlas.web.cern.ch/>Base 2 number system with only 2 digits: 0 and 1. For example, thedecimal numbers 1, 2, 3, and 4 are written 1, 10, 11, and 100 respectively
in binary notation. To distinquish a binary number from a decimal (base10) number, a subscript “2” follows the number: 1002 is the same as 410.
Binary Digit. Component of a number expressed in the binary systemusing only 0s and 1s.
A block of four binary bits which can store one ASCII character. Also, aunit of capacity for computer storage devices (hard drives, memory
chips, etc.).
Either Bayonet/Neill-Concelman (the inventors of the BNC connector),or Berkeley Nucleonics Corporation (opinions differ). The name for acommonly used connector for coaxial cable.
In high-energy and nuclear physics, a set of events that occur“simultaneously” (i.e., within some small period of time). For example,“3-fold coincidence” means particles are detected simultaneously in three
separate detectors.
The detector element in high-energy physics experiments. Refers to thescintillator, light guide, photomultiplier tube (PMT) and base assembly.
Complex Programmable Logic Device. A general-purpose integrated
circuit chip which can be used in many ways, as programmed by theuser.
Central Processing Unit. The “heart” of a computer.
Cosmic Ray Observation Project. Nebraska-based project to study large
scale cosmic ray showers.
<http://physics.unl.edu/~gsnow/crop/crop.html>
Data Acquisition.
Serial Communications D-shell connector with 9 pins. Used on the GPS

51

Classroom Cosmic Ray Muon Detector User’s ManualDC
Discriminator

DOE
Event

FIFO
FNAL
FPGA
Gate
GPS
HEP
Hex

HV
KEK

LED
LEMO
MCU
NIM
NMEA
ns
NSF
Op-Ampdevice.
Direct Current.
In high-energy and nuclear physics, an electronic circuit that produces an
output pulse only when its input voltage exceeds a selected (threshold)level.
United States Department of Energy. <http://www.doe.gov/>
In high-energy and nuclear physics, a coincident pattern of detectedparticles that is likely to be of interest, and should be recorded. (Derived
from the use of the same term in special relativity: an occurrence at aparticular point in space and time.)
First In, First Out. A type of memory buffer where data is taken out inthe same order as it is put in.
Fermi National Accelerator Laboratory. Also known as Fermilab.
<http://www.fnal.gov>
Field-Programmable Logic Array. One variety of CPLD.
In digital electronics, a signal that enables another signal to betransmitted. The digital equivalent to a toggle switch.
Global Positioning System. <http://tycho.usno.navy.mil/gps.html>
High-energy physics. The branch of physics that studies the nature andbehavior of high-energy particles.
Hexadecimal. A number system with base 16. Use the characters 0-9 andA-F to represent numbers with decimal values of 0-15. Widely used incomputers, since one hex digit represents 4 binary bits. Data storage in‘bytes’ of 4 bits or multiples of 4 (8, 16, 32, etc.) is very common.
Example: A37FH = 4185510 = 1010 0011 0111 11112. The subscript “H”
denotes a hex number.
High Voltage
Koh-Enerhughi-Ken-Kyu-Sho. A high-energy accelerator researchorganization in Tsukuba, Japan. The Japanese equivalent to Fermilab.
<http://www.kek.jp/intra.html>
Light-Emitting Diode(Company name) Miniature coax cable connectors—serve the samefunction as BNCs.
Micro Controller Unit. (See also “CPU.”)
Nuclear Instrument Module. A standard for interchangeable nuclear
physics electronic modules dating back to the 1950s.
National Marine Electronics Association. Commonly used data
specification with navigation instruments, e.g., GPS receivers.
Nanosecond = 1 billionth (10-9) of a second.
National Science Foundation. <http://www.nsf.gov/>
Operational Amplifier. An integrated circuit element that amplifies a52

Classroom Cosmic Ray Muon Detector User’s ManualPC
PMT
QuarkNet
RS-232SALTA
Scaler
TDC
TMC
ToT
TRG
UNL
USB
UTC
UW
VAC
VDC
WALTA

signal. Op-amps are the building blocks of many kinds of digital circuits.
Personal Computer. A generic term that covers Windows-, Mac-, orLinux-based computers.
Photomultiplier Tube. Vacuum tube that converts extremely low lightlevels (down to single photons) into electrical signals.
National science outreach program funded by NSF and DOE.
<http://quarknet.fnal.gov>
Recommended Standard 232. A connector commonly used for computer
serial interfaces.
Snowmass Area Large-scale Time-coincidence Array.
<http://faculty.washington.edu/~wilkes/salta/>
Pulse counter.
Time-to-Digital Converter.
Time Memory Cell. Name of the specific TDC chip used in the DAQ
board. <http://research.kek.jp/people/araiy/TEG3/teg3.html>
Time over Threshold.
Trigger. In high-energy and nuclear physics, the digital signal thatindicates an event of interest has occurred and data should be logged.
University of Nebraska, Lincoln.
Universal Serial Bus.
Universal Time Coordinated. Formerly known as Greenwich Mean Time
(GMT).
University of Washington, Seattle.
Volts of Alternating Current system. Most U.S. appliances use 110 VAC.
Volts of Direct Current system. The DAQ board used 5 VDC.
Washington Large-scale Time-coincidence Array.
<http://www.phys.washington.edu/~walta>53