Chapter 10

Complete the table to indicate how many protons and neutrons are in the nuclei of the following atoms:

radioactivity - process by which an unstable nucleus emits one or more particles or energy in the form of electromagnetic radiation

nuclear radiation - particles that are released from the nucleus during radioactive decay ◦ There are different types of nuclear radiation.

Nuclear Energy Nuclear energy – energy that exists within

the nucleus of an atom Nuclear fission – process of breaking

apart subatomic bonds which releases large amounts of energy

Disadvantage of nuclear energy:• Produces radioactive waste• In short supply (100-200 years at current

consumption rate)• Extremely expensiveSafety concerns:• Produces radioactive waste• Extremely dangerous if explodes – which will

contaminate thousands of miles of land

An example of nuclear fission is the explosion of an atomic bomb

The first atomic bomb was dropped by the U.S on Hiroshima, Japan during WWII

Nuclear materials are an extraordinarily rich energy source

One gram of uranium-235, the most common nuclear fuel, delivers about as much energy as 3.5 metric tons of coal

Nuclear energy does not produce carbon dioxide

Nuclear Explosion at Chernobyl

                               

16 years later the soil is still being tested

The nuclear reactor at Chernobyl was covered up with concrete and steel to stop any more radiation from escaping

In the United States a massive effort to build an atomic bomb was launched in 1942. The code name was the Manhattan Project. This project was carried out in extreme secrecy On July 16, 1945, in the desert near Alamogordo, New Mexico, the US successfully conducted the world's first nuclear test.

Nuclear fusion – lightweight atomic nuclei combining to form a heavier nucleus, basically the opposite of nuclear fission•Process which powers the stars, which includes our sun – temperature up to 10,000,000oC

•It is a safer energy source than nuclear fission

•Difficult to achieve

Quark – subatomic particle theorized to be among the basic units of matter

Transuranium elements – having an atomic # greater than 92

Plasma – state of matter in which atoms have been stripped of their electrons◦ Exists at high temperatures

Alpha particles consist of protons and neutrons.• An alpha particle is a positively charged atom

that is released in the disintegration of radioactive elements and that consists of two protons and two neutrons.

Beta particles are electrons produced from neutron decay.• A beta particle is a charged electron emitted

during certain types of radioactive decay, such as beta decay.

Gamma rays are very high energy.◦ A gamma ray is a high-energy photon emitted by

a nucleus during fission and radioactive decay.

Neutron radioactivity may occur in an unstable nucleus.• Neutron emission consists of matter that is

emitted from an unstable nucleus.• Neutrons are able to travel farther through matter

than either alpha or beta particles.

In nuclear decay, the sums of the mass numbers and the atomic numbers of the decay products equal the mass number and atomic number of the decaying nucleus.

A nucleus gives up two protons and two neutrons during alpha decay.• The process of the alpha decay of radium-226 is

written as follows.

88226Ra

86222Rn

24He

888622262224

A nucleus gains a proton and loses a neutron during beta decay.◦ A beta decay process occurs when carbon-14

decays to nitrogen-14 by emitting a beta particle.

614C

714N

Š10e

67(Š1)14140

Nuclear Decay Actinium-217 decays by releasing an alpha particle. Write the equation for this decay process, and determine what element is formed.

1. Write down the equation with the original element on the left side and the products on the right side.Use the letter X to denote the unknown product. Note that the mass and atomic numbers of the unknown isotope are represented by the letters A and Z.

89217C

ZA X

24He

89217C

ZA X

24He

2. Write math equations for the atomic and mass numbers.217 = A – 4 89 = Z – 2

3. Rearrange the equations.A = 217 – 4 Z = 89 – 2

4. Solve for the unknown values, and rewrite the equation with all nuclei represented.A = 213 Z = 87The unknown decay product has an atomic number of

87, which is francium, according to the periodic table. The element is therefore

87213Fr.

89217C

87213Fr

24He

The half-life is the time required for half of a sample of a radioactive substance to disintegrate by radioactive decay or by natural processes.◦ Half-life is a measure of how quickly a substance

decays.

Half-life Radium-226 has a half-life of 1599 years. How long would it take seven-eighths of a radium-226 sample to decay?

1. List the given and unknown values.Given: half-life = 1599 years

fraction of sample decayed = 7/8Unknown: fraction of sample remaining = ?

total time of decay = ?

2. Calculate the fraction of radioactive sample remaining.To find the fraction of sample remaining, subtract the fraction that has decayed from 1.

fraction of sample remaining = 1 Š fraction decayed

fraction of sample remaining = 17

8

1

8

3. Calculate the number of half-lives.

Amount of sample remaining after one half-life = 1

2

Amount of sample remaining after two half-lives = 1

2

1

2

1

4

3. Calculate the number of half-lives

Amount of sample remaining after three half-lives

= 1

2

1

2

1

2

1

8Three half-lives are needed for one-eighth of the sample to remain undecayed.

4. Calculate the total time required for the radio-active decay.Each half-life lasts 1599 years.

total time of decay = 3 half-lives

1599 y

half-life4797 years

Nuclei are held together by a special force.◦ Protons and neutrons are tightly packed in the

tiny nucleus of an atom.• strong nuclear force causes protons and

neutrons in the nucleus to attract each other. This attraction is much stronger than the electric repulsion between protons.

Fission is the process by which a nucleus splits into two or more fragments and releases neutrons and energy.◦ One type of fission of uranium-235 can be repre-

sented by the following equation.

92235U

01n

56137Ba

3684Kr 15

01n energy

Energy mass speed of light

E mc

2

2

The equivalence of mass and energy observed in nature is explained by the special theory of relativity

Neutrons released by fission can start a chain reaction.

nuclear chain reaction is a continuous series of nuclear fission reactions.

critical mass is the minimum mass of a fissionable isotope that provides the number of neutrons needed to sustain a chain reaction.

Nuclear fusion is the process in which light nuclei combine at extremely high temperature, forming heavier nuclei and releasing energy.

11H

11H

12H two particles

12H

11H

23He

00

23He

23He

24He

11H

11H

Background radiation - the nuclear radiation that arises naturally from cosmic rays and from radioactive isotopes in the soil and air.

rem - the quantity of ionizing radiation that does as much damage to human tissue as 1 roentgen of high-voltage X rays does.◦ Radiation is measured in units of rems.

Exposure varies from one location to another.

Some activities add to the amount of nuclear radiation exposure.

Nuclear radiation is used to detect diseases.• A radioactive tracer is a radioactive material that

is added to a substance so that its distribution can be detected later.

• Radioactive tracers are widely used in medicine.

Normal brain Alzheimer’s brain