Cosmic Ray Workshop May 15, 2010 1 Cosmic Ray Detector Kit.

Cosmic Ray Workshop May 15, 2010

1

Cosmic Ray Detector Kit

Experiments


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Plateauing counters (this is essential)

Coincidence rates

Multiple cosmic ray hits

Solid angle dependence

Angular dependence

Dependence on horizontal spacing

Absorption (difficult: requires some engineering)

Muon lifetime

Muon velocity (advanced: requires some programming)

Curvature in Earth’s magnetic field (very advanced)

Come up with some of your own!

Plateauing counters


3

Purpose: make sure that PMT HV set correctly full efficiency without excessive noise

Setup: four counters stacked vertically

Program: justscounting

Configuration: enable: 1, 2, 3, 4 coincidence level: 1

coincidence window: 0.1 μs gatewidth: 0.2 μs

Procedure: set all PMT HV to 750 V adjust HV in steps of 25 V until approx. 1000 counts /min

do for all four counters

Result: At this rate about have of the singles counts will be noise and about half will be comic rays. This should guarantee that all counters will be fully efficient

Coincidence Rates


4

Purpose: Check that all counters are efficient Measure the flux of cosmic ray muons

Setup: four counters stacked vertically

Program: 2fold



Procedure: record and compare all six 2-fold coincident rates

Questions: Why do rates differ? If you count longer do they agree better? Why?

Why might there be some systematic difference? What is the accidenetal coincidence rate? Is it important?

Multiple Cosmic Ray Hits


5

Purpose: Determine how often two cosmic ray muons are measured in coincidence

Setup: two vertical stacks, two counters each (C1 on C2) and (C3 on C4)

Program: multifold



Procedure: measure 4-fold coincidence rate increase coincidence window keeping gatewidth twice as large compare indoors and outdoors (keep out of direct sun)

Questions: Why might rate change with coincidence window time? Why might rate be higher indoors compared to outdoors? Are single muon rates same indoors and out?

How can you measure the effect of accidental coincidences

Solid Angle Acceptance


6

Purpose: Learn about the concept of solid angle acceptance

Setup: two counters arranged vertically separated by adjustable distance

Program: 2fold

Configuration: enable: 1, 2 coincidence level: 2


Procedure: Measure 2-fold coincidence rate as function of the separation of the that 2 counters.

Questions: Why does rate decrease with increasing counter separation? Try to come up with a geometrical explanation. For a given separation, approximate the angular acceptance.

Angular Dependence


7

Purpose: Determine zenith angle dependence of cosmic ray flux

Setup: two counters separated by about 50 cm

Program: 2fold



Procedure: Measure 2-fold coincidence rate as function of zenith angle that 2 counter telescope is pointed at. Fit distribution to find angular dependence.

Questions: If cosmic rays are hitting the Earth isotropically, why are there fewer horizontal muons than vertical ones? Is there a dip right at zero degrees? If so what might it be due to? (this is a hard question) Is there any difference between NS and EW

Horizontal Spacing


8

Purpose: Get estimate of shower width by measuring rate of multiple hits as function of horizontal counter spacing

Setup: Four counters arrayed horizontally with variable spacing

Program: coincidence



Procedure: Measure 1-fold, 2-fold, 3-fold and 4-fold coincidence rates as function of horizontal counter spacing. It is best to do this outdoors to avoid a ceiling effect

Questions: What are the accidental backgrounds to the 1-fold, 2-fold, 3-fold and 4-fold rates? Are they significant?

Absorption


9

Purpose: Determine (roughly) the muon momentum spectrum by by measuring the fraction of muon absorbed by material of various thickness

Setup: Two counters stacked vertically. Place material of varying thickness above the counters

Program: 2-fold



Procedure: Measure 2-fold coincidence rate as function of material thickness

Thickness needed to absorb 0.1 Gev/c to 0.2 GeV/c muons

water: 10 cm to 50 cm bricks or Al: 5 cm to 25 cm steel: 2 cm to 10 cm

Muon Lifetime


10

Purpose: Measure lifetime of muon at rest

Setup: Three counters stacked vertically

Program: muon_lifetime

Configuration: enable: 1, 2, 3 coincidence level: 2


Procedure: Program will produce cvs file of number of muon decays as function of time Use Excel program to plot data and fit with an exponential

Determine exponential time constant

Questions: What are the sources of errors in your measurement? What is the most likely muon lifetime? Why don’t all muons decay at the same time? (this is at the heart of quantum mechanics)

Muon Speed


11

Purpose: Measure the speed of the incoming cosmic ray muons

Setup: Two counters separated vertically

Program: 2-fold



Procedure: Put the counter right on top of each other and take data. this run will give you the time offset

Separate the counters by at least 1 m then take another run.

Analyze the log files for the two runs and determine the time difference of the hits in the two counters. The first run with the two counters right next to each other will give the intrinsic offset of the two counters.

Questions: What is the speed of the muon? How far does a muon travel on average before it decays? Why can muons produced 10 km up in the atmosphere reach the ground. (this is at the heart of relativity)

Reading the Log File


Col 3: time of counter 1 (units of 1.25 ns) + 128

Col 4: time of counter 2 (units of 1.25 ns)

t2 – t1 = (Col2 - (Col1 – 128))*1.25 ns

New event whenever Col 1 > 128

Ignore lines for which Col 1 = 0

Cosmic Ray Workshop May 15, 2010 1 Cosmic Ray Detector Kit.

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