Chemistry-Nuclear Packet Name:______Hour:____ Page 19
Chemistry A
Nuclear Chemistry
Worksheet #1 : Radioactivity
Chemical reactions involve changing one substance into another substance by rearranging atoms. However, during a chemical reaction atoms of one element cannot change into atoms of another element. The reason this change cannot occur is that chemical reactions only involve an atom's electrons – the nucleus remains unchanged.
Recall that an atom's identity is based on its number of protons. Since protons are in the nucleus and chemical reactions do not involve the nucleus, the atom remains unchanged. However, there are some reactions that do involve changes in the nucleus. These are called nuclear reactions and do change one atom of an element into an atom of a different element.
1. Fill in the table below as a review. You will need your periodic table for this! Remember the atomic number (or # of protons) determines the element. If you have four protons and seven neutrons you have beryllium. The same is true if you have four protons and six neutrons...you still have beryllium.
Isotope / Total Protons(Atomic #) / Total Neutrons
(Mass # - Atomic #) / Mass Number* / Total Electrons Outside Nucleus / Format for Nuclear Equation
K-40 / 19 / 21 / 40 / 19 /
Li-6 /
2 / 1
90 / 38
*NOTE: Do NOT use the mass numbers from your periodic table.
Radioactivity is when a substance spontaneously emits radiation. Radioactive atoms (or radioisotopes) emit radiation because their nuclei are unstable. Unstable nuclei lose energy by emitting radiation in a spontaneous process called radioactive decay. Unstable radioactive atoms undergo radioactive decay until they form stable nonradioactive atoms. There are several types of radiation emitted during radioactive decay.
Types of Radiation: Alpha, Beta, and Gamma
Three types of radiation have been discovered. The types are called alpha, beta and gamma. Alpha rays turned out to be small particles of matter with a charge of +2 and a mass of 4 amu. It has been proved that an alpha particle contains two protons and two neutrons – it is identical to the nucleus of a helium atom. In fact, when an alpha particle slows down and gains two electrons it becomes a helium atom. The Greek letter alpha (α) is used to represent this particle but in equations to keep track of mass and protons we must use. Betas were also found to be particles; they are simply high speed electrons. We use the Greek letter beta (β), but in equations is used. When a beta slows down it becomes an electron. Gamma rays (γ) are not particles; they are high energy electromagnetic radiation. They are photons (light) with no charge or mass so we simply write in our equations.
Example 1: Thorium-232 decays by emitting an alpha and a gamma.
à + γ +
Example 2: Uranium-239 decays by emitting a beta and a gamma.
à + γ +
In the above examples you should notice that the sum of the masses on the left of the arrow equals the sum of the masses on the right of the arrow and that the sum of the protons on the left equals the sum of the protons on the right.
2. Complete the following table.
Name / Charge / Mass / Greek Symbol / Equation Symbol / IdentityALPHA
BETA
GAMMA
When an atom undergoes radioactive decay the product nucleus is often unstable and undergoes further decay. This occurs until a stable nucleus is produced. (There is no way for a student to know how an atom will decay. We will always tell you the mode of decay for equations.)
3. Write the nuclear equations for the following radioactive decay series. Use the periodic table in your book.
uranium-235 emits an alpha ______
thorium-231 emits a beta and a gamma ______
protactinium-231 emits an alpha and a gamma ______
actinium-227 emits a beta ______
Th-227 emits an alpha and a gamma ______
Ra-223 emits an alpha ______
Rn-219 emits an alpha ______
Po-215 emits an alpha and a gamma ______
The product from above emits a beta ______
The product from above emits an alpha ______
The product from above emits a beta and a gamma ______
4. Using a full sheet of graph paper, graph this U-235 decay series. Have atomic number on the x-axis and mass number on the y-axis. Instead of dots make a circle and write the symbol for the element inside the circle. Connect the points as you make the graph, writing α, β or γ on the line to indicate the mode of decay. Make sure your graph has an appropriate title and covers at least half of the page.
Decay Series for U-235 Graph
Worksheet # 2: Half-life
1. What is a radioactive isotope_______
2. What is radioactive decay? ______
3. What is half-life? ______
4. If we start with 400 atoms of a radioactive substance, how many would remain after one halflife?______
after two half-lives? ______after three half-lives? ______after four halflives? ______
5. If we start with 48 atoms of a radioactive substance, how many would remain after one halflife?______
after two half-lives? ______after three half-lives? ______after four halflives?______
6. If we start with 16 grams of a radioactive substance, how much will remain after three half-lives?______
7. If we start with 120 atoms of a radioactive substance, how many will remain after three half-lives?______
Use the following graph to answer questions 8-11…
8. How long is a half-life for C-14?______
9. If only 25% of the carbon-14 remains, how old is the material containing the carbon-14? ______
10. If a sample originally had 120 atoms of C-14, how many atoms will remain after 16,110 years? ______
11. If a sample known to be about 10,740 years old has 400 carbon-14 atoms, how many atoms were in the sample when the organism died? ______
12. Which type of nuclear radiation (beta particles, gamma rays, or alpha particles) can be blocked by…
a) a piece of paper ______b) a sheet of aluminum ______c) a piece of lead ______
Use the following chart to answer questions 13-16…
Radioactive Substance / Approximate half-lifeRadon-222 / 4 days
Iodine-131 / 8 days
Radium-226 / 1600 years
Carbon-14 / 5730 years
Plutonium-239 / 24,120 years
Uranium-238 / 4,470,000,000
13. If we start with 8000 atoms of radium-226, how much would remain after 3,200 years? ______
14. If we start with 20 atoms of plutonium-239, how many would remain after 48,240 years? ______
15. If we start with 60 atoms of uranium-238, how many remain after 4,470,000,000 years? ______
16. If we start with 24 atoms of iodine-131, how many remain after 32 days? ______
Worksheet #3: Bombardment Reactions
So far, the equations we have written have involved natural radioactive decay and therefore natural transmutation (changing of one element into another element). However, we have learned to cause transmutation by bombardment of nuclei with high-energy particles. Bombardment allows us to prepare hundreds of isotopes that do not naturally exist, plus this is the method for the production of transuranium elements, all of the man-made elements that follow uranium on the periodic table.
Example: Boron-10 is bombarded with a neutron yielding an alpha and another product.
+ à +
Write nuclear equations for the following bombardment reactions.
a. Platinum-196 is bombarded by a deuteron (H-2), producing platinum-197 and a proton.
______
b. Nitrogen-14 is bombarded by a neutron, producing carbon-14 and a proton.
______
c. Plutonium-239 plus an alpha yields three neutrons and a transuranium element.
______
d. Uranium-238 plus a neutron yields a beta and another product.
______
Review of Nuclear Equations
You are to write out the complete nuclear equations for the following reactions. You will need to determine the identity of the unknown product.
***DON’T FORGET!!! Emission… is a word used to express that something is coming OUT of the nucleus. These should be placed on the RIGHT of the arrow and subtracted from the nucleus.
***DON’T FORGET!!! Bombardment is a word used to express some particle or radioisotope is forced INTO a nucleus. These should be added to the target on the LEFT of the arrow.
a. Iodine-131 decays by beta and gamma emission.
______
b. Polonium-218 decays into lead-214 and another product.
______
c. Uranium-235 decays by alpha and gamma emission.
______
d. Nitrogen-14 is bombarded with an alpha, producing a proton and oxygen-17.
______
Worksheet #4: Detection of Radioactivity
Radioactivity is not detectable by any of the human senses. You cannot see, feel, smell, taste, or hear alphas, betas, gammas, or neutrons. We have to detect the radiation emitted from unstable nuclei by the effects the radiation has upon matter--radiation ionizes matter and radiation causes some materials to scintillate (glow or flash light).
When alphas, betas, gammas or neutrons travel through matter they can knock electrons off atoms or molecules leaving a trail of positive ions behind them along their path. The material only stays ionizes for a short period of time before absorbing electrons and neutralizing again. Radioactivity was discovered because the emitted radiation exposes photographic film. When the radiation passes through the photographic emulsion it leaves a trail of ions and when the film is developed the silver atoms collect along this trail leaving visible evidence of where the radiation struck the film. Geiger counters detect the electricity created by these ions and produce a click, move a needle on a dial or move a number on a counter.
When ionizing radiation passes through a chamber filled with a gas saturated with a vapor a tiny trail of droplets collects on the trail of positive ions produced. This visible track can be photographed and studied and much of the research on fundamental particles within the nucleus was carried out this way in devices called cloud chambers. Computer analysis has replaced cloud chambers but they were very significant research detectors for many years.
Film badges also detect condensation created by radiation. They are worn by X-ray technicians, radiologists and anyone who works around sources of radiation. The badge tracks each person’s total exposure, and if a predetermined limit is reached the worker must be assigned to an unexposed workplace for a period of time to allow the body to recover from any damage due to the exposure.
When radiation strikes some materials it causes their electrons to become excited and to then emit visible flashes of light (photons). These materials are called phosphors and this process is called scintillation (or fluorescence). Different phosphors respond to different particles of radiation; zinc sulfide is an important phosphor for detecting alpha particles. In modern scintillation counters the individual flashes of light can be multiplied electronically and automatically counted. Scintillation counters are important detectors for modern research and medicine.
Cloud Chamber Film Badge Geiger Counter
Questions on Detection:
1. Which of the human senses can detect radiation?
2. What are the two properties of radiation that allow us to detect it?
3. How does radiation produce ions in matter?
4. What property of an ionized gas allows us to detect radiation?
5. Does a gas remain ionized forever?
For a long period of time?
What happens to the ions in a gas?
6. What element collects on the ions on photographic film?
7. What collects on the ions in a cloud chamber?
8. What is emitted when a material scintillates?
9. Give the name and formula for one material that will scintillate.
10. Name three professions that would involve wearing a film badge:
Worksheet #5: Nuclear Power Article and Questions
Commercial nuclear power plants are built to generate electricity. To understand how electricity is produced, it is necessary first to understand atoms, the fission process, nuclear fuel, and nuclear reactors, each of which is described below.
Atoms: The Foundation of Nuclear Energy
The process that produces the heat in nuclear power plants involves atomic energy. Atoms are made of protons, neutrons, and electrons.
Inside the nucleus at the center of each atom are positively charged protons. The number of protons in the nucleus determines which family or element the atom belongs to. For example, all carbon atoms have six protons.
The nucleus also contains uncharged particles called neutrons. Among atoms of the same element, it is the number of neutrons that distinguishes one atom from another. For example, the carbon-12 atom contains six protons and six neutrons in the nucleus; the carbon-14 atom has the same number of protons as carbon-12 (six), but has eight neutrons instead of six. Atoms of the same element containing the same number of protons but different numbers of neutrons are called isotopes. Isotopes are identified by a number after the element name that indicates the total number of protons and neutrons inside the nucleus. This is called the mass number.
Circling the nucleus of each atom at varying distances are tiny, negatively charged electrons. In most atoms there are the same number of electrons as protons, but if there are more electrons than protons the atom is said to have a negative charge. If there are more protons than electrons the atom is said to have a positive charge. If an atom carries either a negative or a positive charge it is called an ion. We can also say this atom is ionized/