Introduction to Nuclear Radiation

Learning Outcome: Make choices to reduce your exposure to ionizing radiation.

Activities for Learning:

  1. In the blue Chemistry In The Community textbook, read page 429 to list and describe units used to measure exposure to radiation. List and describe here:
  1. Go to to compute your personal annual exposure to radiation. (During class, if a computer is not available use the worksheet provided.)
  1. At the website, read and record the average annual radiation dose in the US. If computers are not available, use the worksheet provided in class.
  1. Answer these questions:
  1. How does your annual radiation dose compare to the US recommended limit of 500 mrem?
  1. How does your level compare to the national average?
  1. Why is it useful to monitor how many X-rays you receive annually?
  1. When choosing a place to live, what factors might decrease your annual ionizing-radiation dose?
  1. What are some lifestyle changes that could reduce a person’s exposure to ionizing radiation?
  1. Explain whether you feel that you need to make those changes or not.

NUCLEAR CHEMISTRY TASK 1: Writing Balanced Nuclear Equations

Learning Outcome: Write balanced nuclear equations.

  1. Read p. 6 - 8of this document and answer these questions or use the online resource
  1. What is the symbol for an alpha particle of radiation?

What does the top # represent?

What does the bottom number represent?

  1. What is the symbol for a beta particle of radiation?

What does the top # represent?

What does the bottom number represent?

  1. Read pp. 6-8 of this document and describe how nuclear equations are balanced.
  1. Complete the nuclear equations on p. 684 of MODERN CHEMISTRY, practice problems #1 and 2 and Section Review, #3. If you are working at home, complete the test questions following the tutorial at the website in #1 above and the problems below.

Alpha decay involves the emission of a Helium nucleus

  • decreases the atomic mass by 4
  • decreases the atomic number by 2

Beta decay involves the conversion of a proton to a neutron or a neutron to a proton.

  • The atomic mass does not change (remember neutrons and protons have the same mass!)
  • The atomic number increases or decreases by 1
  • To balance out the charges and electron can be lost or gained.

Complete the nuclear equations and label each of the following equations as alpha or beta decay

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NUCLEAR CHEMISTRY TASK 2: Comparing fusion and fission

Learning Outcome: Compare and contrast nuclear fission and nuclear fusion.

Activities for Learning:

  1. Read pp. 6-8 of this document and pp. 697 and 699in textbook Modern Chemistry and complete the Venn diagram below. If you are working at home, research the Internet to find the requested information I #2 below.
  1. Write a paragraph to compare and contrast fission and fusion nuclear reactions. Include the amount of energy released, radioactive products, examples of nuclear reactions, health concerns, and uses in society.

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NUCLEAR CHEMISTRY TASK 3: Solving Half-life Problems

Learning Outcome: Use a table that shows radioactive decay to solve half-life problems.

Learning Activities:

  1. Read pp. 6-8 of this document and define half-life.
  1. Complete the table below to determine the amount of radio-isotope left after 4 half-lives.

The half-life of polonium-210 is 138 days. How many milligrams of polonium-210 remains after 414 days if you start with 20 mg?

Time% of fraction ofamount of

original sampleoriginal sampleoriginal sample

0 100%120 mg

138 days 50%½10 mg

276 days _____%¼5 mg

____ days 12.5%______mg

  1. Use a table like the one in #2 above to complete p.689 practice problem #3 and #4. If you are working at home, complete the test questions following the tutorial at

NUCLEAR CHEMISTRY TASK 4: Radioactive Decay of Candium

Radioactive decay processes occur in accordance with first order kinetics. This simulation provides a simple example of the rate at which a radioactive isotope decays.

Materials: M&M™ candy pieces, resealable bag, paper towel, graph paper

Procedure

Place 50 atoms of candium (pieces of candy) in the bag.

  1. Seal the bag and gently shake.
  2. Gently pour out candy.
  3. Count the number of pieces with the print side up—and record the data. These atoms have "decayed".
  4. Return only the pieces with the print side down to the bag. Reseal the bag.
  5. Consume the "decayed atoms”.
  6. Gently shake the sealed bag for 10 seconds. (10 seconds represents the approximate half-life.)
  7. Continue shaking, counting, and consuming until all the atoms have decayed. Use only the number of half-lives needed to decay all the atoms. Add more if needed.
  8. On graph paper, graph the number of undecayed atoms on the y-axis (dependent variable) vs. time on the x-axis (independent variable).

Data and Observations

Half-life / Time / Total# of
Undecayed Atoms / Total# of
Decayed Atoms
0 / 0 / 50 / 0
1 / 10 sec
2 / 20 sec
3 / 30 sec
4 / 40 sec
5 / 50 sec
6 / 60 sec
7 / 70 sec
8 / 80 sec

Questions

  1. What is a half-life?
  1. At the end of two half-lives, what fraction of the atoms had not decayed?
  1. On the graph, draw lines to mark the actual half-life of Candium and label.
  1. Describe the shape of the curve on the graph.

Nuclear chemistry

Nuclear chemistry is the study of the break up of unstable nuclei, which results in the emission of radiation and the release of energy. This changes the unstable nuclei into more stable nuclei. The stability of a nucleus depends on the proton to neutron ratio or balance. Radioactive emissions change the neutron to proton ratio and at the same time releases energy.

Three types of radiation

There are 3 types of radiation, alpha (), beta () and gamma (). Their properties can be studied using an electrical field.

Alpha

- Slow moving positively charged particle, attracted to the negative plate.

Beta

- Fast moving negatively charged particle, attracted to the positive plate.

Gamma

- Electromagnetic radiation (travels at the speed of light). No deflection.

Radioactive penetration

Alpha particles are stopped by a hand, beta by thin aluminium and gamma rays by concrete

Alpha particles

Alpha particles come from the nucleus of a radioactive atom. They consist of 2 protons and 2 neutrons; hence have a 2+ charge. A few centimeters of air will stop them.

Alpha radiation consists of helium nuclei,

Beta particles

A beta particle is an electron, .

Since the nucleus does not contain electrons, it is thought that a beta particle is formed when a neutron splits up into a proton and an electron. While it will pass through air, it cannot penetrate thin metal foil.

Gamma waves

Gamma waves come from the nucleus of a radioactive atom. They are electronegative waves.

They do not change the nature of an atom. Thick lead or concrete will absorb gamma rays.

Radioactive emission

The emission of radiation from an atom will change its nature. Nuclear equations show the products of nuclear decay. In nuclear equations, the sum of the atomic number and mass number on each side of the equation should balance.

Alpha emissions

Beta emissions

Nuclear fission and fusion

Nuclear fission

In nuclear fission the nuclei of uranium or platinum break up into 2 smaller, lighter nuclei and release a large output of energy;

Nuclear fusion

Nuclear fusion is the reverse of nuclear fission. Two light nuclei are fused together to produce a heavier nucleus.

This reaction takes place in the center of stars, which have sufficiently high temperatures and pressures to allow this reaction to take place.

Half-life

Stability (or rate of decay) of a radioisotope is measured in half-life. The decay of an unstable nucleus is a random event and is independent of chemical or physical conditions. The half-life of a radioisotope is the time taken for the sample's activity to fall by half, and can be easily calculated.

Uses of radioisotopes

Radioisotopes of elements have a wide variety of uses.

Cobalt-60 / Used in medicine to treat cancer. rays can be focused on tumors.
Iodine-133 / Used to treat thyroid gland (in the neck). If the gland is enlarged, iodine-133 can be absorbed and will partially destroy it.
Carbon-14 / Used to date once-living materials.

Carbon dating

Every living organism contains the radioisotope carbon-14. Carbon-14 is formed when neutrons from cosmic radiation collide with nitrogen atoms in our atmosphere forming protons and carbon-14 atoms.

Carbon dioxide is responsible for carbon-14 entering the food chain.

Carbon-14 decays by beta-emission and has a half-life of 5730 years. This means that the beta-decay emissions can be monitored and the data used to calculate how long it has been since the material was alive.

Carbon 14 decay of a buried log. Its activity has dropped to 12.5% after 17,190 years.

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