Title: Nuclear Physics
1Nuclear Physics
2Radioactivity
- Radioisotopes are unstable isotopes whose nuclei
gain stability by spontaneously undergoing
changes. - These changes are accompanied by the emission of
large amounts of energy. - Radioactive decay is the process by which
materials give off this energy. - The penetrating rays and particles that are
emitted during these changes are called
radiation. - Eventually unstable radioactive isotopes are
transformed into stable isotopes of a different
element.
3What holds the nucleus together?
- The nucleus contains the positively charged
protons and neutral neutrons. - There is a repulsive force between the protons
(like charges repel). - The strong nuclear force (also called the strong
force) acts between the protons and neutrons in
the nucleus holding them together. - This strong force is 100 times stronger than the
repulsive force between protons. - The range of this force is so short that in large
nuclei the repulsive force is greater resulting
in an unstable nuclei. - When a radioactive isotope decays, some of the
energy holding the nucleus together is released
in the form of a radioactive particle with mass
and kinetic energy.
4Radioactive Isotopes
- All elements consist of at least one radioactive
isotope. - Isotopes that have too many or too few neutrons
(atomic mass larger or smaller than the average)
tend to be radioactive. - All isotopes with an atomic number greater than
83 are radioactive.
5Identify the radioactive isotope
6Identify the radioactive isotope
- Chlorine-35
- Carbon-12
- Lead-207
- Potassium-40
7Types of Radiation
- Alpha radiation
- Beta radiation
- Gamma radiation
8Alpha Radiation
- Alpha radiation consists of helium nuclei that
are emitted from a radioactive isotope. - Alpha particles consist of two protons and two
neutrons. - Alpha particles have a 2 charge.
- The symbol for an alpha particle is 42He or a.
- Alpha particles are the most massive of the
radioactive particles (4 amu), the most damaging,
and are the least penetrating (easily stopped by
a piece of paper).
9What is the product when plutonium-238 undergoes
alpha decay?
- Uranium-234
- Thallium-206
- Lead-206
- Radium-226
10What is the product when bismuth-210 undergoes
alpha decay?
- Radium-226
- Lead-206
- Thallium-206
- Uranium-232
11What is the product when polonium-210 undergoes
alpha decay?
- Bismuth-206
- Lead-206
- Radium-206
- Thorium-206
12Beta Particles
- Beta particles consist of fast moving electrons
formed by the decomposition of a neutron in an
atom. - The neutron decomposes into a proton and an
electron-the proton remains in the nucleus and
the electron is emitted. - Beta particles have a 1- charge.
- The symbol for a beta particle is o-1e or ß.
- Beta particles are 8000 x lighter than an alpha
particle, are less damaging, but are more
penetrating (stopped by aluminum foil or thin
pieces of wood).
13What is the product when carbon-14 undergoes beta
decay?
- Carbon-13
- Nitrogen-14
- Oxygen-14
- Boron-10
14What is the product when strontium-90 undergoes
beta decay?
- Rubidium-90
- Krypton-91
- Strontium-91
- Yttrium-90
15What is the product when potassium-40 undergoes
beta decay?
- Calcium-40
- Scandium-40
- Argon-40
- Chlorine 40
16Gamma Radiation
- Gamma radiation is high energy electromagnetic
radiation. - Gamma rays are emitted along with alpha or beta
particles. - Gamma rays have no mass or charge.
- The symbol for gamma rays is oo?
- Gamma rays are extremely penetrating and
potentially dangerous (stopped only by several
meters of concrete or several centimeters of
lead).
17Other Nuclear Reactions
- Fission-when a large nucleus is bombarded with
neutrons, a division of the nucleus into 2
smaller nuclei occurs resulting in a large
release of energy. - This energy is used in nuclear power plants and
in atomic bombs. - Fusion-nuclei with small masses combine to form a
nucleus with a larger mass. - This type of reaction occurs in the sun and in
hydrogen bombs. - The high temperature needed to start a fusion
reaction is produced by a fission reaction.
18Nuclear Decay Puzzle
- Uranium-238 is a radioactive isotope. Through a
series of 14 nuclear reactions, the unstable
uranium isotope undergoes radioactive decay until
it forms a more stable isotope of lead-206.
19Unstable isotopes formed during the process
- Uranium-234
- Thorium-234
- Thorium-230
- Protactinium-234
- Radium-226
- Radon-222
- Polonium-218
- Polonium-214
- Polonium-210
- Lead-214
- Lead-210
- Bismuth-214
- Bismuth-210
20Radiation emitted during the process
- Eight alpha particles
- Six beta particles
21Procedure
- Write the isotope symbol for each of the
radioactive isotopes involved in the problem.
Put one symbol on each card. (There should be 15
total) - On eight cards, write the symbol for alpha
radiation. - On six cards, write the symbol for beta
radiation. - Put the cards in the correct order to determine
the steps in going from uranium-238 to lead-206. - After they are in the correct order, write the 14
nuclear equations that illustrate the steps.
22Radioactivity and Half-Lives
- Purpose To simulate the conversion of a
radioactive isotope over a period of time. - Data
-
23Analysis
- Use graph paper and plot the number of isotopes
remaining (y-axis) vs. the trial number
(x-axis). - Examine your graph. Is the number of isotopes
remaining over time linear or nonlinear? Is the
rate constant over time or does it change? - By approximately how much did the number of
isotopes remaining decrease with each trial? - Define half-life. What represented one half-life
during this lab?
24Half-Life
- A half-life is the time it takes for one -half of
the nuclei of a sample of radioactive isotopes to
undergo radioactive decay. - Half-lives may be as short as a fraction of a
second or as long as billions of years. - For examples, see the chart on page 810.
25Graph the following data
26How much remains after 3 days?
27What is the half life of the isotope?
- 5 days
- 10 days
- 15 days
- 20 days
28If 25 g remains, how much time has elapsed?
- 5 days
- 10 days
- 15 days
- 20 days
29How many half-lives have occurred when 25 g
remains?
30Determining Half-Lives
- In order to solve problems involving half-lives,
the following equation may be used -
- of half-lives total time/time of one
half-live - To determine the amount of sample left, the
following equation may be used -
- amount left starting amount/ 2 of half-lives
31The half-life of carbon-14 is 5700 years. If a
10 gram sample undergoes decay for 17,100 years,
how many half-lives has the sample undergone?
32Cobalt-60 is a radioactive element used as a
source of radiation in the treatment of cancer.
Cobalt-60 has a half-life of five years. If a
hospital starts with a 1000-mg supply, how much
will remain after 10 years?
- 1000 mg
- 750 mg
- 500 mg
- 250 mg
33Homework
- p. 810 pr. 24-25 and p. 829 pr. 73, 74, and 78