Chapter 23 Worksheet 1 (ws23.1)
Spontaneous and Induced Nuclear Reactions
Review of Atomic Structure
Atoms are composed of neutrons, protons, and electrons.
The neutrons and protons reside in a large, dense, central nucleus which is surrounded by a diffuse
electron cloud.
Particle
Neutron
Charge
Mass
1.00866492 amu
1.67492716 x 10-24 g
Proton
+1
1.00727646 amu
-19
+1.60217646 x 10 C 1.67262158 x 10-24 g
Electron -1
5.4857911 x 10-4 amu
-1.60217646 x 10-19 C 9.10938188 x 10-28 g
0
1 Å = 1 x 10-10 m
1 amu (atomic mass units) = 1.66053873 x 10-24 g
6.02214198 x 1023 amu = 1 g
(The mass of a carbon-12 nucleus is defined as 12 amu.)
Note: The masses of nuclei and sub-atomic particles are determined with high precision in a mass
spectrometer. See the figure on the last page of this document.
The electrons occupy regions of space called orbitals which are statistical descriptions of where electrons
may be found.
Particles that reside in the nucleus (neutrons and protons) are called nucleons.
The number of protons in a nucleus is called the atomic number (Z).
The atomic number also gives the number of electrons in a neutral atom.
The total number of nucleons (protons + neutrons) in a nucleus is called the mass number (A).
An element is defined by its atomic number. For example any nucleus with 6 protons is a carbon nucleus.
An element can exist in various forms called isotopes. Isotopes have the same number of protons (atomic
number) but a different number of neutrons so they have different mass numbers.
Elements in nature exist as a mixture of isotopes. The atomic mass given in the periodic table is the
average mass number + the mass of the electrons. The average mass number is calculated as follows:
Average mass number = (fractional abundance)i x (mass number)i
where i represents the ith isotope.
The nucleus of a particular isotope is called a nuclide.
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1. Two isotopes of carbon have mass numbers of 12 (carbon-12) and 13 (carbon-13). How many
protons, neutrons, and nucleons reside in the nucleus of each of these isotopes?
carbon-12:
# protons: _____
# neutrons ______
# nucleons ______
carbon-13:
# protons: _____
# neutrons ______
# nucleons ______
Symbols for nuclides and subatomic particles
A
The symbol for a nuclide is: Z X
where X is the symbol for the element, A is the mass number (number of nucleons), and Z is the atomic
number (or charge)
In the case of subatomic particles, the subscript still indicates the charge but will not correspond to the
0
number of protons. For example, an electron has the symbol 1 e indicating it has no nucleons and a
charge of -1.
2. Write symbols for the following:
(1) a proton: _______ or _________
(2) a neutron: _______
(3) a beta particle (same as an electron): _______ or _________
(4) an alpha particle (same as a helium nucleus): ________ or _________
(5) a positron (a positive electron): _______
(6) iron-59: _______
(7) uranium-235: _______
Balancing nuclear equations
A nuclear process will have a form similar to that shown below:
W  FB X  CG Y  HD Z
A
E
(1) the number of nucleons are conserved ( A+B = C+D )
(2) charge is conserved ( E+F = G+H )
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Spontaneous Nuclear Reactions: Radioactivity
Natural radioactivity is due to the decay of unstable nuclei. Radioactive atoms are called radioisotopes
and their nuclei are called radionuclides. There are five common types of natural radioactivity:
1) Alpha decay results in emission of an alpha particle (helium nucleus).
2) Beta decay results in the emission of a high speed electron and, in the nucleus, a neutron is converted into
a proton.
3) Positron emission results in the emission of a high speed positron and, in the nucleus, a proton is
converted into a neutron.
4) Electron capture occurs when an electron from the electron cloud gets pulled into the nucleus and
converts a proton into a neutron. (Notice that there are two ways to convert a proton into a neutron.)
5) Gamma radiation (is high energy (short wavelength, high frequency) electromagnetic radiation that
often accompanies nuclear decay. It represents the energy lost when a nucleus rearranges into a more stable
(lower energy) configuration or when a positron and electron annihilate each other.
3. Write balanced equations for the following natural radioactivity processes:
Alpha Decay of
Beta Decay of
238
92
60
27
U:
Co :
Positron Emission of
Electron Capture of
18
9
89
36
F:
Kr :
3
Induced Nuclear Reactions: Nuclear Transmutations
A stable nucleus can change identity when it is struck by a slow neutron or a high speed charged particle
such as another nucleus. Charged particles (such as alpha particles or protons) can be accelerated to high
speeds by alternating magnetic fields produced in cyclotrons or synchotrons The world’s most powerful
collider has recently gone on line at CERN near Geneva, Switzerland.
Neutrons can not be accelerated in a magnetic field but high speeds are not required for a neutron to
penetrate a nucleus. Nuclear bombardment is used to:
-
produce useful radioisotopes
create new elements
discover new sub-nuclear particles
initiate fission reactions
sustain fusion reactions
4. Insert the appropriate nuclear symbols in order to balance the equations for the following induced
nuclear processes:
Nuclear Transmutation:
Neutron capture:
14
7
2
1
O  11H  01 n  ____
N  01n  ____11p
Fission (2 step process):
Fusion:
18
8
[Product
(Occurs in upper atmosphere)
U  01n 236
92 U (unstable)  
235
92
1
U 144
56 Ba  ____  2 0 n
236
92
H  _____  24 He  01n
2
1
is used for positron emission tomography (PET)]
(There are many other possible products of fission.)
H is called “deuterium”. The 2nd reactant is _______________.
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How a Mass Spectrometer Works
This diagram illustrates the use of a mass spectrometer to determine the isotopic composition of a naturally
occurring sample of neon gas. Although the masses in this example are shown as whole numbers (20, 21,
22), a mass spectrometer can determine the mass of a particle with incredibly high precision.
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