# Cosmic rays and their detection

1. Aug 18, 2010

### { imp }

Greetings,

currently I'm working with cosmic rays (merely researching, not so much as working) and now I have a question regarding cosmic rays and cosmic rays detectors (specifically, Cherenkov detectors). How is the number of photons detected by the PMT's (photomultiplier tubes) related to the direction and composition of the original cosmic ray (as the PMTs detect the photons produced by the Extensive Air Shower, not the cosmic ray itself)? Is there a formula for this?

Also, if you know of any other source of information regarding technical aspects of cosmic ray detection, that would be very much appreciated.

2. Aug 18, 2010

### malm1987

I'm not sure if this is what you are looking for, but perhaps you could find the answer to atleast one of your questions: http://wogsland.org/physics/hep/cherenkov_detectors.html
(really summarized, but has some links to more specific pages).

Quite oftopic now, but you don't happen do be a part of the research group at BAUT.com?

3. Aug 18, 2010

### Bob S

The theory of Cerenkov radiation is reviewed in Schiff "Quantum Mechanics", pages 267-271. The number of photons per cm is

N = 370[1-1/n2β2]ΔE photons per cm,

where n is the index of refraction, β=v/c, ΔE is the energy range of detected photons in eV. (6000 Angstroms to 3000 Angstroms is [STRIKE]1[/STRIKE] ~2 eV).

The photons all are on the surface of a cone of half angle θ = cos-1(1/nβ)

Any non-scintillating transparent material can be used as a Cerenkov radiator; air or other gas under pressure, water, glass, Lucite (UVT), FC-75, etc.

Common Cerenkov electromagnetic shower detectors are alternate layers of 1 cm of lead and 1 cm of Lucite, often over 5 radiation lengths long. Lucite transition pieces to PMTs should be on alternate sides to prevent detection of particles missing the lead-Lucite sandwitch. Air Cerenkov detectors are often over 1 meter long. Muons do not produce showers, so a high energy (β=1) muon will produce ~740[1-1/1.52] = 400 detectable photons (6000 to 3000 Angstroms) per cm in Lucite. [added] After folding in the light collection efficiency (guess 20%) and photocathode efficiency (guess 20%), you will have ~16 photoelectrons (not very many).

[added] A single incident high energy electron can produce over 100 radiating secondary electrons in a single layer of Lucite after several radiation lengths of detector. The exact shower development should be calculated using GEANT4 or equivalent program.