The second type of muon beam is often called the "surface" or "Arizona" beam (recalling the pioneer works of Pifer "et al." from the University of Arizona). Here muons are used that arise from pions decaying at rest still inside, but near the surface, of the production target. Such muons, which are 100% polarized, ideally monochromatic and have a very low momentum of 29.8 MeV/c, which corresponds to a kinetic energy of 4.1 MeV, have a range width in matter of the order of 180 mg/cm2. Hence the paramount advantage of this type of beam is the possibility to use relatively thin samples.