Cosmic Ray induced Electromagnetic Cascades in metals

[hardhacker]

In a 1964 publication Bruno Rossi describes an experiment where cosmic rays could penetrate dense materials. Finding that cosmic radiation at sea level could penetrate over 1m of lead. In these same experiments he was also surprised to record a higher rate of detection, as many as 35 per hour as the thickness of lead increased peaking at 1.5cm and then falling slowly.

http://teachers.web.cern.ch/teachers/archiv/HST2000/teaching/expt/muons/cascades.htm

I'd like to conduct a similar experiment using other metals like Aluminium being safer and cheaper, I'm a thinking it would be approximately 4 times eg 60mm is there some kind of guide to shielding comparisons for different non-magnetic metals?

 

[Bob S]

For the interactions of charged particles in matter, review the Berkeley Particle Data Group publication section on Passage of Particles through Matter:

http://pdg.lbl.gov/2009/reviews/rpp2009-rev-passage-particles-matter.pdf

In particular, review Section 27.4 on radiation length. Note in particular in eq 27.22 that the radiation length X₀ scales inversely as Z². This is due to the Z² dependence of pair production and bremsstrahlung.

Review Section 27.5 on electromagnetic cascades. Look especially at the depth-dose buildup for 30-GeV electrons in lead in Fig 27.18. The peak is at about 5 radiation lengths (about 2.8 cm).

Review Section 27.6 on muon energy loss at high energies. Muons are the primary component of cosmic rays at sea level. Note in Fig. 27.20 that the two primary contributions to muonic electromagnetic cascades are pair production and bremsstrahlung, whose cross sections are roughly proportional to Z². Fig. 27.21 shows that the Bethe Bloch dE/dx ionization is the most important energy loss below about 100 GeV (very roughly 2 MeV per gram/cm²), and radiation (electromagnetic cascades) above 100 GeV.

For a list of radiation lengths in various materials, see the table in

http://pdg.lbl.gov/2009/reviews/rpp2009-rev-atomic-nuclear-prop.pdf

Look at the column labeled X₀ (Radiation length) for a long list of metals and other materials. Aluminum is a poor choice of a lead substitute in demonstrating electromagnetic cascades. Copper is twice as good per gram, and six times better per unit volume. Nearly all the cosmic ray muons you will detect at sea level are below 100 GeV, and their primary energy loss is ionization. Only cosmic ray electrons and positrons (both from muon decay) will produce electromagnetic cascades in your detector.

Bob S

 

[hardhacker]

Wonderful information Bob, thank you I just find learning more about this area fascinating.

This forum is an invaluable resource.

Regards

Robert