Transcript 4.4 Unstable Nuclei and Radioactive Decay

Types of Radiation and Unstable
Nuclei
I. Chemical and Nuclear Reactions
• Chemical reactions only involve an atom’s electrons
• Nuclear reactions involve changing an atom’s nucleus
• Nuclear reactions release a million times more
energy than chemical reactions
• Unlike chemical reaction, nuclear reactions are not
affected by temperature, pressure, or a catalyst.
II. Nuclear Vocabulary
• Radioactivity – the process of emitting radiation.
• Radiation - rays and particles emitted by a
radioactive source.
• Radioisotopes – isotopes of atoms with unstable
nuclei and emit radiation to obtain a more stable
nuclei
• Radioactive decay - Unstable nuclei losing energy
by emitting radiation in a spontaneous process.
• Nucleon – refers to both protons and neutrons
III. Which Isotopes are Radioactive?
• Small Nuclei - Atoms which contain up to 20 protons
(up to Calcium) are usually stable.
• Large Nuclei - Larger nuclei tend to be
radioactive. All nuclei with 84 or more protons
(Polonium and up) are radioactive. For example, all
isotopes of Uranium are radioactive.
• Atoms with more neutrons than protons - There are
radioactive nuclei that have less than 84 protons.
These nuclei have more neutrons than protons. For
example, Carbon-12 (6 protons and 6 neutrons) is
stable, while Carbon-14 (6 protons and 8 neutrons) is
radioactive.
IV. Why Does an Atom Undergo
Radioactive Decay?
• Radioactive atoms emit
radiation because their nuclei
are unstable.
• The stability of the nucleus
depends on the neutron to
proton ratio
• Neutrons vs. protons graph
stable nuclei found in a region
called the band of stability.
V. Types of Radiation – Alpha
Radiation
• Alpha radiation are attracted to the negatively
charged plate
• Alpha particles contain two protons and two
neutrons (A helium nucleus)
• Blocked by paper
• Least penetrating form of radiation (only travels a
few centimeter in the air)
• Carry +2 charge
4
4
• Symbolized by 2 He or 2 
VI. Types of Radiation – Beta
Radiation
• Beta radiation attracted to the positively
charged plate
• Carry –1 charge
• Beta particles are fast moving electrons
• Blocked by metal foil or wood
• Medium penetration power (travels a few
meters in the air)
• Symbolized by -10 e or -10 
VII. Types of Radiation – Gamma rays
• Gamma rays are high energy radiation that possess
no mass.
• Possess no electrical charge and are not deflected by
magnetic or electrical fields.
• Not completely blocked by lead or concrete
• The most penetrating and damaging type of radiation
• Carry no charge
• Symbolized by
0
0

IX. Electrostatic Force
• Electrostatic force is when like charges repel and opposite
charges attract.
X. Strong Nuclear Force
• The strong nuclear force or nuclear force is an
attractive force that acts between all nuclear
particles that are extremely close together.
• It keeps the nucleus together.
Remember Mass Number and
Atomic Number
Mass number
Atomic number
14
6
C
XI. Writing and Balancing Nuclear
Equations
• In a balanced nuclear equation, mass numbers
and atomic numbers are conserved.
Example
226
4
230
• 90 Th  88 Ra + 2 He
– Notice the mass numbers and atomic numbers
add up to the same on both sides of the equation
VIII. Electron Capture
• Electron capture occurs when a nucleus of an
atom draws in an electron.
•
81
37
Rb
+ - 01 e →
81
36
Kr
• Also known as Beta capture
Practice
1. 97
40 Zr 
0
-1
Po 
4
2
2.
218
84
3. ? 
4.
47
20
5.
244
96
222
86
e + ?
Ca 
Cm 
4
2
Nb
214
82
Pb
He
226
88
Ra
e + ?
47
21
Sc
240
94
Pu
He + ?
Rn +
0
-1
97
41
4
2
He + ?