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written by David B. Pengra
Counting statistics of cosmic rays is explored using a LabVIEW based computer program on a computer connected to a National Instruments data acquisition unit. The program collects the interval times between successive coincident pulses from a stack of plastic scintillator detectors. Analysis of the data set allows students to see the distribution of N-pulse intervals for various values of N; this is the Erlang distribution. With N = 1, the Erlang
distribution is exponential with a characteristic time equal to mean count interval t. When N is increased, the distribution becomes peaked at Nt with a fractional width proportional to 1/?N. This is an instance of the central limit theorem. Students may also examine the data set according to the distribution of numbers of pulses recorded for a series of fixed-length intervals, which for random pulses follows the Poisson distribution. Again, as the length of the interval increases, the distribution conforms to the central limit theorem: it becomes normal with a well-defined mean and width, both related to mean and width of the underlying distribution.

The software also allows students to simulate pulse-intervals that follow a uniform distribution (e.g., any real number between 0 and 1 has equal probability) or a Gaussian one.  In these cases, one can see that the counts per fixed interval length do not follow the Poisson distribution, although all types become normal at longer intervals or greater numbers of pulses per interval length. This serves to drive home the point that cosmic ray counts are truly a Poisson process and also to illustrate the significant power of the central limit theorem-- that regardless of the underlying probability distribution function, when N becomes large the distribution becomes normal with a well-defined mean and width.

Presented at the 2013 AAPT Summer Meeting
in Portland, Oregon.
W36: Advanced Labs Workshop
Subjects Lab Level Resource Types
- Fundamentals
= Atomic and Nuclear Physics
- Instrumentation
Modern Physics
- Nuclear Physics
= Particle Detectors
Other Sciences
- Mathematics
- Advanced Undergraduate
- Instructional Material
= Instructor Guide/Manual
= Laboratory
Material Category Formats Ratings
- Lab Manual
- application/pdf
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Access Rights:
Free access
© 2008 University ofWashington
Central Limit Theorem, Coincidence measurements., Cosmic rays, LabVIEW, Point processes, Poisson statistics, Scintillator detectors
Record Creator:
Metadata instance created July 9, 2013 by Ramon Torres-Isea
Record Updated:
July 9, 2013 by Ramon Torres-Isea
Last Update
when Cataloged:
July 9, 2013
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AIP Format
D. Pengra, (2008), WWW Document, (
D. Pengra, Cosmic Ray Statistics using LabVIEW (2008), <>.
APA Format
Pengra, D. (2013, July 9). Cosmic Ray Statistics using LabVIEW. Retrieved April 20, 2014, from
Chicago Format
Pengra, David B.. Cosmic Ray Statistics using LabVIEW. July 9, 2013. (accessed 20 April 2014).
MLA Format
Pengra, David B.. Cosmic Ray Statistics using LabVIEW. 2008. 9 July 2013. 20 Apr. 2014 <>.
BibTeX Export Format
@misc{ Author = "David B. Pengra", Title = {Cosmic Ray Statistics using LabVIEW}, Volume = {2014}, Number = {20 April 2014}, Month = {July 9, 2013}, Year = {2008} }
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%A David B. Pengra
%T Cosmic Ray Statistics using LabVIEW
%D July 9, 2013
%O application/pdf

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%0 Electronic Source
%A Pengra, David B.
%D July 9, 2013
%T Cosmic Ray Statistics using LabVIEW
%V 2014
%N 20 April 2014
%8 July 9, 2013
%9 application/pdf

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