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Board Work
1. What is the electrical interaction betweena. a proton and another proton in a nucleus?
b. a proton and a neutron in a nucleus?
c. a neutron and another neutron in a nucleus?
Objectives
• Describe the different types of nuclear reactions and identify the properties of nuclei undergoing them.
• Identify reactions and products in the nuclear power cycle and nuclear weapons.
Nuclear Forces
• Electrostatic force (Coulomb’s Law)– Protons repel protons
• Strong nuclear force– Nucleons attract at short distances
Identifying Nuclei
• Number of protons = atomic number Z– determines the element
• Number of neutrons N– Isotope: same Z, different N
• N + Z = mass number A
• Isotope name: Name-A (e.g. Carbon-12)
Board Work
2. Find the elements with these atomic numbers:
a. 11
b. 23
3. Find the atomic numbers of the following elements:
a. Chlorine
b. Magnesium
Poll Question
The fraction of parent nuclei remaining after two half-lives is
A. None — it has all decayed.
B. 1/2.
C. 1/4.
D. 1/8.
Alpha Decay
• Nucleus emits an alpha particle = 2 p + 2 n(helium-4 nucleus)
• Daughter nucleus has Z – 2, N – 2, A – 4
Poll Question
After alpha decay, the atomic number of a nucleus is
A. larger
B. smaller
C. the same
as before.
Poll Question
After alpha decay, the mass number of a nucleus is
A. larger
B. smaller
C. the same
as before.
Beta decay
• n = neutron• p+ = proton• e– = electron (beta particle)• e = electron anti-neutrino
• e–, e escape, p+ remains in nucleus• Daughter has same A, Z + 1, N – 1
n p+ + e– + e
Poll Question
After beta decay, the atomic number of a nucleus is
A. larger
B. smaller
C. the same
as before.
Poll Question
After beta decay, the mass number of a nucleus is
A. larger
B. smaller
C. the same
as before.
Gamma Emission
• Excited nucleus emits a high-energy photon (gamma-ray)
• Occurs only after another decay type
Source: Griffith
Poll Question
After gamma emission, the atomic number of a nucleus is
A. larger
B. smaller
C. the same
as before.
Think Question
Which kind of atomic nuclei tend to undergo alpha decay?
A. Nuclei with large mass number A.
B. Nuclei with too many neutrons.
C. Very light (low Z) nuclei.
D. Nuclei with too many protons.
Think Question
Which kind of atomic nuclei tend to undergo beta decay?
A. Nuclei with large atomic number Z.
B. Nuclei with too many neutrons.
C. Very light (low Z) nuclei.
D. Nuclei with too many protons.
Fusion
• Two nuclei combine to make a larger nucleus
• Neutrons usually released as well
• Requires extremely high energies (temperature) to overcome nucleus-nucleus electric repulsion
Binding Energy
Source: Georgia State U., Hyperphysicshttp://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html
fission
fusion
Think Question
What sort of nuclei release energy by fission?
A. Nuclei lighter than iron.
B. Nuclei about as heavy as iron.
C. Nuclei heavier than iron.
Summary
• Nuclei contain positive protons and neutral neutrons.
• Nuclear stability is a balance between electrostatic repulsion and the attractive strong force.
Summary
• Radioactive atoms can emit alpha particles, beta particles, and gamma rays.
• Nuclei can also split apart (fission) and combine (fusion).
• Reaction types depend on nuclear characteristics.