Physics and Engineering of Radiation Detection

52 Chapter 1. Properties and Sources of Radiation

HereFFrepresents fission fragments. Although most of these neutrons are used up
to induce more fission reactions, still a large number manages to escape the nuclear
core.

Radioactive Sources of Neutrons

There are no known naturally occurring isotopes that emit significant number of
neutrons. However it is possible to produce such isotopes by bombarding neutron
rich isotopes by other particles such as protons. The problem is that these isotopes
have very short half lives making them unsuitable for usual laboratory usage.

Table 1.6.5: Common neutron sources and their decay modes.

Source Isotopes Reaction Type

Californium^25298 Cf Spontaneous Fission

Deuterium-Helium^21 D-^32 He Nuclear Fusion

Tritium-Helium^31 T-^42 He Nuclear Fusion

Uranium^23592 U Nuclear Fission

Lithium^73 Li Spallation

Beryllium^94 Be Spallation

Plutonium-Beryllium^23894 Pu-Be (α, n)

Plutonium-Beryllium^23994 Pu-Be (α, n)

Americium-Beryllium^24195 Am-Be (α, n)

Americium-Boron^24195 Am-B (α, n)

Americium-Fluorine^24195 Am-F (α, n)

Americium-Lithium^24195 Am-Li (α, n)

Radium-Beryllium^22688 Ra-Be (α, n)

Antimony-Beryllium^12451 Sb-Be (γ, n)

Perhaps the most extensively used source of neutrons is californium-252. It has
two decay modes:α-emission (96.9%) and spontaneous fission (3.1%). The latter