section 19.1 radioactivity 1.students will be able to describe the factors that lead to nuclear...
Post on 19-Jan-2016
217 Views
Preview:
TRANSCRIPT
Section 19.1
Radioactivity
1. Students will be able to describe the factors that lead to nuclear stability.
2. Students will be able to describe types of radioactive decay.
3. Students will be able to write equations to show radioactive decay.
Objectives
Section 19.1
Radioactivity
• nucleons – particles found in the nucleus of an atom – neutrons – protons
• atomic number (Z) – number of protons in the nucleus
• mass number (A) – sum of the number of protons and neutrons
• isotopes – atoms with identical atomic numbers but different mass numbers
• nuclide – each unique atom
A Review of Atomic Terms
Section 19.1
Radioactivity
Nuclear Stability
• Small atoms tend to have neutron-proton ratios ~ 1:1
• The ratio approaches 1.5:1 as the atomic number increases
• Explained by the relationship between strong nuclear forces and electrostatic repulsion
Section 19.1
Radioactivity
Nuclear Stability
• Strong nuclear forces act over very short distances
• As the # of protons increases, the electrostatic force between protons increases
• More neutrons are needed to stabilize the nucleus
Section 19.1
Radioactivity
A. Radioactive Decay
• radioactive – nucleus which spontaneously decomposes forming a different nucleus and producing one or more particles
• nuclear equation – shows the radioactive decomposition of an element
Section 19.1
Radioactivity
A. Radioactive Decay
• Alpha-particle decay • Alpha particle – helium nucleus
– Examples
Types of Radioactive Decay
• Common for heavy isotopes
Section 19.1
Radioactivity
A. Radioactive Decay
• Beta-particle decay
Types of Radioactive Decay
• Net effect is to change a neutron to a proton.
• Beta particle – electron – Examples
Section 19.1
Radioactivity
A. Radioactive Decay
• Gamma ray release
Types of Radioactive Decay
• Net effect is no change in mass number or atomic number.
• Gamma ray – high energy photon – Examples
Section 19.1
Radioactivity
A. Radioactive Decay
• Positron production
Types of Radioactive Decay
• Net effect is to change a proton to a neutron.
• Positron – particle with same mass as an electron but with a positive charge – Examples
Section 19.1
Radioactivity
A. Radioactive Decay
• Electron capture
Types of Radioactive Decay
– Example
Section 19.1
Radioactivity
A. Radioactive Decay
Section 19.1
Radioactivity
A. Radioactive Decay
Decay series
Section 19.1
Radioactivity
Sample Problems
1. Silver-116 undergoes beta particle decay.
2. Bismuth-211 undergoes alpha particle decay
3. An isotope undergoes alpha particle decay and produces the isotope Polonium-218
4. Silver 106 undergoes electron capture.
5. Potassium-38 undergoes positron emission.
Section 19.1
Radioactivity
Detection of Radioactivity and the Concept of Half- life
Objectives• Students will be able to define the term half-life and
explain how it relates to the stability of the nucleus. • Students will determine the half-life of an isotope or
the fraction of the isotope that remains given appropriate data.
Section 19.1
Radioactivity C. Detection of Radioactivity and the Concept of Half- life • Half-life – time required for half of the original sample of
radioactive nuclides to decay
Section 19.1
Radioactivity
Half Life Problems:
1. Phosphorus-32 has a half-life of 14.3 days. How many days will it take for a radioactive sample to decay to one-eighth its original size.
2. Iodine-131 has a half life of 8.0 days. How many grams of an original 160 mg sample will remain in 40 days?
3. Carbon-14 has a half life of 5715 years. It is used to determine the age of ancient objects. If a sample today contains 0.060 mg of carbon-14, how much carbon-14 must have been present in the sample 11,430 years ago>
Section 19.1
Radioactivity
B. Nuclear Transformations
• Nuclear transformation – change of one element to another
Section 19.1
Radioactivity
B. Nuclear Transformations
Discovery of Protons:
• Rutherford performed the first artificial transmutation, by bombarding nitrogen gas with alpha particles (1919)
HOHeN 11
178
42
147
Section 19.1
Radioactivity
B. Nuclear Transformations
Discovery of Neutrons
• Chadwick discovered the neutron by bombarding Be with alpha particles. (1932)
nCHeBe 10
126
42
94
Section 19.1
Radioactivity
B. Nuclear Transformations
Section 19.1
Radioactivity
B. Nuclear Transformations
Production of Neptunium and Plutonium
UnU 23992
10
23892
eNpU 01
23993
23992
ePuNp 01
23994
23993
Section 19.1
Radioactivity
B. Nuclear Transformations
• Transuranium elements – elements with atomic numbers greater than 92 which have been synthesized
Section 19.1
Radioactivity C. Detection of Radioactivity and the Concept of Half- life • Geiger-Muller counter – instrument which measures
radioactive decay by registering the ions and electrons produced as a radioactive particle passes through a gas-filled chamber
Section 19.1
Radioactivity C. Detection of Radioactivity and the Concept of Half- life • Scintillation counter – instrument which measures the
rate of radioactive decay by sensing flashes of light that the radiation produces in the detector
top related