[NC.3]
Date Due:_______________
Notes – Beta (β) Decay
 Read about beta decay on textbook page 294
 AFTER reading, read and complete the notes below
One of the particles that a radioisotope may emit is called a beta
particle
Beta particle – an electron emitted by an unstable nucleus.
Fold along this line
Glue this side of the page
into your ISN on page _____
using 6 small dots of glue.

Beta particles are produced by a neutron decomposing into
a proton and an electron (the beta particle)

Beta particles, like other electrons, have a 1- charge.

Because this electron is from the nucleus of the atom, it is
called a beta particle to distinguish it from the electrons
which orbit the atom.

Beta particles have a mass of ______ amu.

Beta particles are symbolized using:
o
the Greek letter beta: β
o
or, the isotope symbol:
0
1
e
Beta decay is a type of nuclear decay that releases a beta particle,
and is an example of a nuclear reaction.
Beta decay is somewhat more complex than alpha decay is. These
points present a simplified view of what beta decay actually is:
 A neutron inside the nucleus of an atom breaks down,
changing into a proton.

The parent nucleus emits an electron (the beta particle)
and an anti-neutrino (more on this later) which go zooming
out of the nucleus.
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

The atomic number goes UP by one and mass number
remains unchanged.
The following nuclear equation describes the beta decay of
thorium-234:
Th 
234
90
Pa * 
234
91
0
1
Beta Particle Symbol
Looking at the symbol for a beta particle 10 e you may be
wondering, “why is the atomic number of a beta particle -1?”.
Let’s take a look at the thorium decay equation again:
e  00 ν
Th 
234
90
Pa * 
234
91
0
1
e  00 ν
Remember that in beta decay, a neutron decomposes into a proton
and an electron.
• anti-neutrino
Since neutrons & protons are both nucleons, the mass number,
234, does not change: 234 – (1 neutron) + (1 proton) = 234
Because of this, the mass number of the beta particle is listed as
0
0:
1 e
However, since the number of protons increases by 1 during a beta
decay event, the atomic number of the beta particle is listed as -1:
0
1 e to balance the equation, because mass is conserved during the
reaction.
•
emitted anti-neutrino
Notice that the equation shows the conservation of mass:
Th 
Pa 
e ν

234
90

the mass number on the left (234) is the same as on the
right (234+0+0)

234
91
*
0
1
0
0
the atomic number on the left (90) is the same as on the
right (91 + -1 + 0)
Also notice that there is an asterisk next to the Pa* symbol. This
indicates that the nucleus is “excited” or still unstable. Unstable
daughter nuclei are likely to decay again.
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Even though a proton was gained, a neutron was lost; therefore
there is no overall change in mass number.
Neutrinos
Neutrinos are symbolized using the the Greek letter nu: ν
The line over the  indicates that it is an anti-matter particle.
Unfortunately, the study of neutrinos (and anti-matter!) is way
beyond the scope of this course.
If you’re interested in finding out more about neutrinos, stop in
after class and we’ll chat.
Otherwise check out:
http://icecube.wisc.edu/info/neutrinos/
 Make one AHA connection on notebook p.nnn-nnn
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