Physics and Engineering of Radiation Detection

56 Chapter 1. Properties and Sources of Radiation

and^9438 Sr.
235
92 U+2n→

236

92 U

∗→ 140

54 Xe+

94

38 Sr+2n (1.6.9)

Here^23692 U∗is an unstable isotope of^23592 Uthat eventually breaks up in fragments and
releases 2 neutrons. These fission fragments are themselves unstable and go through
aseriesofβ-decays till they transmute into stable elements.^14054 Xeeventually decays
into cerium-140 while^9438 Srdecays into zirconium-94. Because of their highβ-yields,
these fission fragments and their daughters are regarded as extremely hazardous and
special precautions must be taken while handling them.

1.6.H Muons,NeutrinosandotherParticles

H.1 Muons..............................

Muon is one of the elementary particles according to the Standard Model of Par-
ticle Physics and is classified as a Lepton. Muons carry the same electrical charge
(positive or negative) as carried by protons or electrons but they are approximately
9 times lighter than protons. Because of their lower mass, they can penetrate larger
distances in the material than protons and are therefore extensively used in probing
the magnetic properties, impurities and structural defects of different materials.

Basic Properties of Muons

Rest mass = 1. 783 × 10 −^36 kg= 105. 66 MeV/c^2

Electrical charge = ± 1. 6 × 10 −^19 C

Mean life = 2. 19 × 10 −^6 s

Internal structure : Believed to have no internal structure.

With a flux of about 1 muon per square centimeter per second , they are the most
abundant of charged particles at sea level that enter the Earth’s atmosphere from
outer space. The main production mechanism of these muons is the interaction of
primary cosmic rays with material in the upper atmosphere. The mean energy of
these muons is about 4GeV. They lose about 2MeVperg/cm^2 of energy as they
pass through the atmosphere which suggests that their original energy is around 6
GeV.
Muons can also be produced in the laboratory by hitting a target (such as
graphite) with high energy protons.

H.2 Neutrinos

Neutrinos are also elementary particles belonging to the leptonic category. They
come in three distinctflavors: electron-neutrino (νe), muon-neutrino (νμ), and tau-
neutrino (ντ). Flavoris a real term used in Standard Model of particle physics to
characterize the elementary particles. Recent experiments have proved that these
three types can transform into one another (1). Standard Model does not assign