Nuclear Reactions

Chapter 18 Sec 1

Nucleus

• Composed of protons and neutrons which comprise most of the atom’s mass

What holds these particles together in the nucleus?

• The strong force causes protons and neutrons to be attracted to each other in the nucleus.– Strong force is powerful when neutrons and

protons are packed closely together– Protons and neutrons in a large nucleus are held

less tightly by the strong force than protons and neutrons in a small nucleus

Radioactivity

• Nuclear decay which happens when the strong force is not large enough to hold the nucleus together– The nucleus will give off matter and energy

FYI

• All nuclei that contain more than 83 protons are radioactive

• All nuclei that contain more than 92 protons do not exist naturally on Earth– These can only be produced in laboratories and

are called synthetic elements (man-made)– These synthetic elements are unstable, and decay

soon after they are created

Isotopes role in radioactivity

• Isotope – atoms of the same element with varying numbers of neutrons

• A nucleus that contains too many or too few neutrons compared to protons is radioactive.

The Discovery of Radioactivity

• 1896 – Henri Becquerel– uranium

• 1898 – Marie and Pierre Curie– polonium and radium

SECTION 2Chapter 18

Nuclear Radiation

• Particles and energy are released from a decaying nucleus

Three types of nuclear radiation

• Alpha – release particles– Consists of two protons and two

neutrons• Beta – release particles– A beta particle is an electron and is

emitted when a neutron decays into a proton

• Gamma – electromagnetic wave– Gamma rays are electromagnetic waves

of very high frequency that usually are emitted when alpha decay or beta decay occurs

Penetration strength increases from alpha to beta to gamma

Transmutation

• Process of one element’s changing to another element through nuclear decay

Half-life

• The length of time it takes half of the atoms of a sample of the radioactive isotope to decay

• Can vary from fractions of a second to “billions of years”

Radioactive Dating

• Uses half-life of isotopes to determine ages of materials.– Carbon dating is used to date once-living materials• Uses Carbon-14 Isotope

– Uranium dating is used to figure ages of rocks

Example of radioactive dating

• Half life of Iodine-131 is 8 days• How much of a 5-g sample will be left after 32

days?

Example of radioactive dating

• Half life of Iodine-131 is 8 days• How much of a 5-g sample will be left after 32

days?

• Answer: 0.3 grams of Iodine-131 will be left after 32 days

Chapter 18 Section 3

Detecting Radioactivity

• Radiation detectors are instruments used to identify ions formed when radiation passes through matter.

• Some instruments that can be used– Cloud chamber– Bubble chamber– Electroscopes

Measuring Radiation

• Important to monitor the amount of radiation a person is being exposed to because large doses of radiation can be harmful to living tissue.– Ex. Geiger counter – measures radioactivity by

producing an electric current when radiation is persent

Chapter 18 Sec 4

Nuclear Reactions

Nuclear Fission

• Process of splitting a nucleus into two nuclei with smaller masses; a large amount of energy is released

Chain reactions

• A chain reaction in nuclear fission is when there is an ongoing series of fission reactions

• If this reaction goes uncontrolled an enormous amount of energy is released.

• For a chain reaction to occur, a critical mass of material that can undergo fission must be present, this critical mass is the amount of material required so that each fission reaction produces approximately one more fission reaction.

Chain reaction

Nuclear Fusion

• Nuclear fusion occurs when two nuclei with low masses are combined to form one nucleus of larger mass.– Nuclear fusion can happen only when nuclei are

moving fast enough to get close to each other– Temperatures in stars (millions of degrees Celsius)

are high enough for fusion to occur

Nuclear fusion