proton mass, mp

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proton mass, mp 1.672 6231 x 10-27 kg 1.007
2765 u
neutron mass, mn 1.674 9286 x 10-27 kg 1.008
6649 u
electron mass, me 9.109 3897 x 10-31 kg 0.000
548 579 90 u
1 u 1.660 5402 x 10-27 kg
1 u 931.494 32 MeV
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The mass of a nucleus is always less than the sum
of the uncombined masses of the constituent
particles. The difference is called the nuclear
mass defect.
The mass defect can be converted into an
equivalent nuclear binding energy using the
relationship 1 u 931 MeV.
Divide the binding energy by the number of
nucleons to get the binding energy per
nucleon. This value is used to determine
the stability of that atoms nucleus.
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RADIOACTIVITY
the spontaneous uncontrollable decay of an
unstable atomic nucleus with the emission of
particles and/or rays
An unstable atomic nucleus will decay naturally
(emit particles and/or rays from the
nucleus) until it becomes stable. The danger of
radioactive decay products depends on
their charge and energy.
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Alpha Decay

• alpha particle a doubly
• ionized helium atom or simply a helium
  nucleus
• written a, a ,or He

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4 2
4 2

• Z gt 82 for alpha decay possible
• have relatively slow speeds (0.1 c)
• can be stopped by a few cm of air or
• an ordinary sheet of paper
• natural as have energy between 4 and 10 MeV
• half-lives from 10-6 s to 1010 yr

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Beta Decay
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0 -1
0 -1

• electron, written e or b
• or positron, written e or b

0 1
0 1

• occurs primarily in light nuclei
• penetrates many meters of air
• or thin sheets of metal
• high speed (approach speed of light)

or
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Gamma Decay

• high energy photons
• (electromagnetic radiation)
• written g
• penetrates 2 km air or 30 cm lead
• short lifetimes
• energy range of keV to MeV
• have short wavelength (high frequency)

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Proton Decay
Neutron Decay
When balancing nuclear equations, mass number and
nuclear charge must be conserved. These equations
are generally simpler to write than chemical
equations.
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The rate of radioactive decay depends on the
amount of nuclei present. The equation for
the number of radioactive nuclei present at
any time t is given by the equation
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• N(t) radioactive nuclei
• present at time t
• N0 number initially present
• the disintegration constant,
• which is equal to (ln 2)/T1/2 ,
• where T1/2 is the half-life
• of the decaying nucleus

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Click here, here, and here to run simulations
of radioactive decay.
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Often, the product of a decaying nucleus is also
unstable and subsequently decays at some other
rate. The amount of each nucleus present depends
on the amount of initial nuclei present and on
the decay rates of the parent and daughter nuclei.
View a typical decay chain here.