© The scientific sentence. 2010
Radioactivity studies the spontanuous transformations of unstable
nuclei; that is their spontanuous nuclear reactions.
In 1896, Becquerel, Antoine-Henri underlined the natural radioactivity
of the Uranium. He observed that photographic plates have been fogged
when exposed to radiation from a uranium salt.
Radiaoactive nuclei decay into another nucleus more stable, plus one or
more light particles.
In general, nuclei heavier than lead, and many isotopes of lighter nuclei,
have a finite probability of decaying spontaneously into another nucleus
plus one or more lighter particles.
The decay products may be:
An alpha-particle (α) that contains two protons and two neutrons. It
is the stable nucleus of a helium atom. The related process is written
(A,Z)X → (A-4, Z-2)Y + (4,2)He
(238,92)U → (234,90)Th + (4,2)He
A nucleus with more neutrons than it can maintain in stability may
decay by emission of an electron from the nucleus. This is the
beta-decay (β-). Along this process, a neutron is
converted to a proton:
n → p + e-
These electrons may emerge with a kinetic energy
of up to several MeV. The process of β- is:
(A,Z)X → (A, Z+1)Y + e-
(14,6)C → (14,7)N + e-
The third process β+ is encountred only for
the artificial nuclei, where a proton is converted to a
neutron plus a positron:
p → n + e+
The process of β+ is:
(A,Z)X → (A, Z-1)Y + e+
(74,33)As → (74,32)Ge + e+