Nuclear Notation Remember that an isotope is an atom that has the same number of protons, but a different number of neutrons. Since the number of protons is the same the identity of the element is the same, but the mass of the atom changes. We show different isotopes using the atomic/nuclear notation you learned earlier in the year.
Radioactive Decay - Radioactivity is the spontaneous emission of radiation by an unstable atomic nucleus. - The release of radiation by radioactive isotopes (radioisotopes) is called decay - Radioactive decay occurs when the nuclei of the isotopes are unstable - There are three types of nuclear decay and each changes the nucleus in its own way. - They are alpha, beta and gamma.
1. Alpha Decay • Alpha radiation consists of a stream of alpha particles • An alpha particle is a helium nuclei consisting of two protons and two neutrons • Alpha particles can be represented as:
• When alpha decay occurs the decaying nucleus loses 2 protons and 2 neutrons and turns into the nucleus of an element with an atomic number that is 2 less and a mass number that is 4 less than that of the original. • Uranium-238 decays spontaneously (in a long series of steps) into Thorium-234 by alpha decay • When an element decays into another element a transmutation occurs
• Another example showing the nuclear notation is below.
• Alpha radiation does not penetrate deeply into matter and is easily stopped by a thin layer of material like paper or clothing.
2. Beta Decay • This type of decay results in beta radiation. • In beta decay a high energy electron with a 1- charge is released. • Beta particles can be represented as:
• The beta particle that is released is the result of a neutron being broken down into a proton and electron • Results in transmutation because this reaction causes a neutron to change into a proton, so the atomic number to increase by one. • The mass number remains the same.
• Beta particles pass through matter more easily than alpha particles. They can be stopped only by thick materials such as stacked sheets of metal, blocks of wood, or heavy clothing.
3. Gamma Decay • This type of decay results in gamma radiation • A gamma ray is a high energy form of electromagnetic radiation without mass or charge. • The symbol for Gamma rays are:
• During gamma decay, only energy is given off. • Gamma radiation is often omitted from nuclear equations because it does not affect mass number or atomic number • Does not cause transmutation • Generally doesn’t occur alone but accompanies other modes of decay. • Example 1:
• Example 2:
• Example 3:
• Because it’s high energy gamma rays have a high penetrating ability and can cause great harm to living cells. • Gamma rays are much harder to stop than alpha or beta and can pass easily through most types of materials, and stopping them requires blocks of lead or even thicker blocks of concrete.
Half-Life • Method of measuring radioactivity • The half-life is the time required for a substance to decay to one-half of its initial value. • An example is iodine-131 which has a half-life of approximately 8 days. If you start with 16mg its decay over a period of time is as follows:
16mg ------→ 8mg ------→ 4mg…….. 8days 8days Nuclear Energy • In the decay reactions we have studied so far, only minor changes to the target nuclei occurred • When a major nuclear change occurs it usually releases a great deal of energy. • The origin of nuclear energy is the conversion of a small amount of matter into radiant energy. • The two principal reactions used as sources of energy are nuclear fission and nuclear fusion.
1. Nuclear Fission • Occurs when an atomic nucleus is split into two or more larger fragments. • Caused by bombarding the atom with neutrons • Releases large amounts of energy • Here is a typical reaction for uranium fission
• Nuclear fission can often result in a chain reactions which is why it is so dangerous. The neutrons released from the first reaction can go on to attack other atoms. • Formula example of fission:
2. Nuclear Fusion • Occurs when two or more nuclei combine to form a larger nucleus • The fusion of two nuclei with lower masses than iron generally releases energy, while the fusion of nuclei heavier than iron absorbs energy. • Nuclear process that produces energy in stars like our sun • The reaction in the sun occurs when two different isotopes of hydrogen combine to form helium and a neutron.
NUCLEAR CHEMISTRY QUESTIONS
1. Define the following terms: (These words will be on your vocab quiz this week) • Radioactive Decay:
• Alpha Decay:
• Beta Decay:
• Gamma Decay
• Half Life
2. Directions: Identify the following as alpha, beta, gamma, or neutron.
1 a. 0 n 0 b. −1 e 4 c. 2 He 0 d. 0 γ
e. Nuclear decay with no mass and no charge
f. An electron
g. Least penetrating nuclear decay
h. Most damaging nuclear decay to the human body
i. Nuclear decay that can be stopped by skin or paper.
j. Nuclear decay that can be stopped by aluminum.
3. Complete the following nuclear equations and identify the type of nuclear reaction.
4. Answer the following questions about the equation below
a) Complete the equation b) Which type of decay is this? c) Is this an example of fission or fusion? Explain.
5. Identify the following as fission or fusion
Multiple choice Questions
1. Bismuth-210 decays directly to polonium-210 .Which of the following must be emitted during this radioactive decay? A. alpha particle
B. beta particle
2. A hospital buys a compound that contains an isotope of barium. Several months later, most of the barium has changed to the element lanthanum.Which of the following is responsible for this change? A. exposure to air
B. radioactive decay
C. reactions with the container wall
D. absorption of moisture from the air
3. Which of the following statements applies to a nuclear fission reaction? A. The reaction has no commercial applications.
B. The reaction takes place only at very high temperatures.
C. The reaction produces only short-lived radioactive waste.
D. The reaction releases large amounts of energy when nuclei split apart.
4. Uranium forms thorium and helium, as shown in the equation below.
Which of the following does this equation represent?
A. decomposition reaction
B. physical change
C. radioactive decay
D. synthesis reaction
5. Which of the following statements accurately describes alpha particles in terms of charge and mass?
A. Alpha particles are positivelycharged and less massive than beta particles.
B. Alpha particles are negatively charged and less massive than beta particles.
C. Alpha particles are positively charged and more massive than beta particles.
D. Alpha particles are negatively charged and more massive than beta particles.
7. An equation is shown below.
Which kind of reaction does the equation represent?
A. alpha decay
B. beta decay
C. nuclear fission
D. nuclear fusion
8. The equation below shows the radioactive decay of thorium (Th).
Which of the following particles is released in this reaction?
9. The three main types of nuclear radiation are alpha, beta, and gamma. Which of the following lists these types of radiation from highest penetrating power to lowest penetrating power?
A. alpha, gamma, beta
B. beta, alpha, gamma
C. beta, gamma, alpha
D. gamma, beta, alpha
13. Radium-223 is part of a radioactive decay series that gives off alpha, beta, and gamma radiation.
a. Identify the charges on alpha radiation, beta radiation, and gamma radiation.
A sample of radium-223 is placed in a lead block and the emitted radiation passes between charged plates, as shown below.
b. Describe the path of each type of radiation as it passes between the charged plates.
If several sheets of aluminum are placed in the path of the radiation emitted from the sample of radium-223, as shown below, some radiation would be blocked.
c. Identify which type of radiation the aluminum sheets would least likely block. Explain your answer.
d. If Radium-223 has a half life of 36 years. If you start with a sample of 347g of radium-223 how much would you have after 180 years.