RadioactivityRadioactivity

Integrated Science Integrated Science

Chapter 25 NotesChapter 25 Notes

I. What is Radioactivity?I. What is Radioactivity? RadioactivityRadioactivity - Process by which an - Process by which an

unstable nucleus emits one or more unstable nucleus emits one or more particles or energyparticles or energy

Nucleus composed of protons and neutronsNucleus composed of protons and neutrons Electrons are outside the nucleusElectrons are outside the nucleus

I. What is Radioactivity?I. What is Radioactivity?

A. Nuclear decayA. Nuclear decay Break down of an atom’s nucleusBreak down of an atom’s nucleus Element can become an isotope or a new Element can become an isotope or a new

elementelement IsotopesIsotopes – –

atoms of the same atoms of the same

element with different numbers of neutronselement with different numbers of neutrons Some isotopes are stable and never break Some isotopes are stable and never break

down, while some are unstable and break down down, while some are unstable and break down into a more stable atom.into a more stable atom.

Some reasons that an isotope of an Some reasons that an isotope of an element might be unstable are:element might be unstable are:

Too many neutrons in the nucleusToo many neutrons in the nucleus

Too few neutrons in the nucleusToo few neutrons in the nucleus

Nucleus is too big in size (too Nucleus is too big in size (too manymany

neutrons and protons total)neutrons and protons total)electron

neutron

proton

ExamplesExamples Carbon-12 (6 protons, 6 neutrons) is Carbon-12 (6 protons, 6 neutrons) is

stable, but Carbon-14 (6 protons, 8 stable, but Carbon-14 (6 protons, 8 neutrons) is unstable.neutrons) is unstable.

Beryllium-7 (4 protons, 3 neutrons) is Beryllium-7 (4 protons, 3 neutrons) is unstable, but Beryllium-9 (4 protons, 5 unstable, but Beryllium-9 (4 protons, 5 neutrons) is stable.neutrons) is stable.

All elements atomic #93 and higher are All elements atomic #93 and higher are unstable due to their large nucleus size.unstable due to their large nucleus size.

I. What is Radioactivity?I. What is Radioactivity?

B. When a nucleus decays, it breaks down B. When a nucleus decays, it breaks down into a new nucleus, plus ejected nuclear into a new nucleus, plus ejected nuclear radiationradiation

This is a naturally occurring / spontaneous This is a naturally occurring / spontaneous event when a nucleus is unstableevent when a nucleus is unstable

I. What is Radioactivity?I. What is Radioactivity?C. There is a “Strong Nuclear Force” present C. There is a “Strong Nuclear Force” present

in the nucleus of an atom which holds the in the nucleus of an atom which holds the protons and neutrons together in the protons and neutrons together in the nucleus to remain stable.nucleus to remain stable.

Kind of like nuclear “glue”Kind of like nuclear “glue”

I. What is Radioactivity?I. What is Radioactivity?

D. Types of Nuclear RadiationD. Types of Nuclear Radiation Nuclear radiation – charged or uncharged Nuclear radiation – charged or uncharged

particles or energy emitted by unstable particles or energy emitted by unstable nucleinuclei

All radiation can interact with and affect All radiation can interact with and affect surrounding mattersurrounding matter

I. What is Radioactivity?I. What is Radioactivity?

Transmutation – change from one element Transmutation – change from one element into a new element plus nuclear radiationinto a new element plus nuclear radiation

I. What is Radioactivity?I. What is Radioactivity?

4 Types of nuclear radiation4 Types of nuclear radiation 1. 1. Alpha particlesAlpha particles (α) – (α) – positively charged, made positively charged, made of 2 protons and of 2 protons and 2 neutrons2 neutrons

Most massive nuclear radiation particleMost massive nuclear radiation particle Slow moving, and quickly loses energySlow moving, and quickly loses energy

I. What is Radioactivity?I. What is Radioactivity?

4 Types of nuclear radiation4 Types of nuclear radiation 2. Beta particles (β) – negatively charged, 2. Beta particles (β) – negatively charged,

made of fast moving electronsmade of fast moving electrons

- Little mass- Little mass

- Penetrate matter, but- Penetrate matter, but

not deeplynot deeply

I. What is Radioactivity?I. What is Radioactivity?

Beta Decay exampleBeta Decay example

I. What is Radioactivity?I. What is Radioactivity?4 Types of nuclear radiation4 Types of nuclear radiation 3. Gamma rays (γ) – high energy, high 3. Gamma rays (γ) – high energy, high

penetrating powerpenetrating power Not made of matter, no chargeNot made of matter, no charge Electromagnetic energy like Electromagnetic energy like light or x-rays, but with more light or x-rays, but with more energyenergy Stopped by 7 cm of leadStopped by 7 cm of lead Health hazard due to energy and Health hazard due to energy and

penetrating abilitypenetrating ability

I. What is Radioactivity?I. What is Radioactivity?4 Types of nuclear radiation4 Types of nuclear radiation 4. Neutron emission – a single neutron with 4. Neutron emission – a single neutron with

no chargeno charge Can penetrate up to 15 cm of leadCan penetrate up to 15 cm of lead

II. Nuclear ReactionsII. Nuclear ReactionsA. Much energy released into the A. Much energy released into the

surroundings during a nuclear reactionsurroundings during a nuclear reaction

B. In a nuclear reaction, the nucleus B. In a nuclear reaction, the nucleus changeschanges

II. Nuclear ReactionsII. Nuclear Reactions There are two types of nuclear reactions:There are two types of nuclear reactions:

1. Nuclear Fission – process where a nucleus 1. Nuclear Fission – process where a nucleus splits (or is split) into two or more smaller splits (or is split) into two or more smaller nuclei and releases energynuclei and releases energy

Particles can cause chain reactions of Particles can cause chain reactions of

nuclear fission in surrounding atoms nuclear fission in surrounding atoms

This is an example of a nuclear explosionThis is an example of a nuclear explosion

Some practical uses of fission Some practical uses of fission reactions are:reactions are:

Nuclear reactors for a power sourceNuclear reactors for a power source

WeaponsWeapons

MedicineMedicine

II. Nuclear ReactionsII. Nuclear Reactions There are two types of nuclear reactions:There are two types of nuclear reactions:

2. Nuclear Fusion – process where two 2. Nuclear Fusion – process where two nuclei combine at very high temperatures nuclei combine at very high temperatures to form a larger nucleus and releases to form a larger nucleus and releases energyenergy

Where does fusion happen?Where does fusion happen? This occurs continuously in stars as This occurs continuously in stars as

hydrogen atoms (1 proton, 1 neutron) are hydrogen atoms (1 proton, 1 neutron) are joined together to form helium atoms (2 joined together to form helium atoms (2 protons, 2 neutrons). protons, 2 neutrons).

During the process, a large amount of During the process, a large amount of energy is also released. energy is also released.

Practical Uses of Nuclear FusionPractical Uses of Nuclear Fusion We use this energy (solar energy) to warm We use this energy (solar energy) to warm

the earth and homes, and plants use it to the earth and homes, and plants use it to make food (photosynthesis), We can make food (photosynthesis), We can capture and convert solar energy into capture and convert solar energy into electricity .electricity .

C. Nuclear reactions, mass, and C. Nuclear reactions, mass, and energy energy

In both fission and fusion reactions, a In both fission and fusion reactions, a small amount of matter is converted into a small amount of matter is converted into a large amount of energy during the large amount of energy during the reaction. reaction.

C. Nuclear reactions, mass, and C. Nuclear reactions, mass, and energy energy

The Law of Conservation of Mass still The Law of Conservation of Mass still applies, as matter (which has mass) is not applies, as matter (which has mass) is not created or destroyed, but the form is created or destroyed, but the form is changed. changed.

During the change in form, energy is During the change in form, energy is released as the matter becomes more released as the matter becomes more stable, with less energy stable, with less energy

III. Dangers and Benefits of Nuclear III. Dangers and Benefits of Nuclear RadiationRadiation

There are both positives and negatives to There are both positives and negatives to nuclear radiation and nuclear energynuclear radiation and nuclear energy

III. Dangers and Benefits of Nuclear RadiationIII. Dangers and Benefits of Nuclear Radiation

A. Dangers A. Dangers can burn skin, can ionize can burn skin, can ionize living tissues, can destroy cells, can cause living tissues, can destroy cells, can cause cancer, can cause genetic mutations in cancer, can cause genetic mutations in DNA, radiation pollution DNA, radiation pollution

III. Dangers and Benefits of Nuclear RadiationIII. Dangers and Benefits of Nuclear Radiation B. Benefits B. Benefits can be used to treat can be used to treat

diseases, used in smoke detectors, tracers diseases, used in smoke detectors, tracers used in medicine, agriculture, research, used in medicine, agriculture, research, energy sourceenergy source

III. Dangers and Benefits of Nuclear RadiationIII. Dangers and Benefits of Nuclear Radiation Natural sources of radiationNatural sources of radiation

Half-lifeHalf-life

Some radioisotopes decay to stable atoms in less than a second.

However, the nuclei of certain radioactive isotopes require millions of years to decay.

A measure of the time required by the nuclei of an isotope to decay is called the half-life.

Half-lifeHalf-life• The half-life of a radioactive isotope is the

amount of time it takes for half the nuclei in a sample of the isotope to decay.

• The nucleus left after the isotope decays is called the daughter nucleus.

Half-lifeHalf-life Half-lives vary widely

among the radioactive isotopes.

The half-lives of some radioactive elements are listed in the table.

The number of half-lives is the amount of time that has passed since the isotope began to decay.

Half-lifeHalf-life For example: For example:

If you have 100 atoms of a sample of Carbon-14, If you have 100 atoms of a sample of Carbon-14, and the half-life of that isotope is 5730 years, and the half-life of that isotope is 5730 years, how many atoms are left after 2 half-lives?how many atoms are left after 2 half-lives?

100 atoms 100 atoms 50 atoms 50 atoms 25 atoms 25 atoms

11stst half-life half-life 22ndnd half-life half-life

Half-lifeHalf-life

If you started with 1000 atoms of a sample If you started with 1000 atoms of a sample of Iodine-131, and you have 8 atoms left, of Iodine-131, and you have 8 atoms left, how much time has passed?how much time has passed?

Half-life of Iodine-131 = 8.04 daysHalf-life of Iodine-131 = 8.04 days

Half-lifeHalf-lifeStep 1: Determine number of half-livesStep 1: Determine number of half-lives

10001000 500 500 250 250 125 125 63 63 32 32 16 16 8 8

11 2 3 4 5 6 7 2 3 4 5 6 7

**7 half-lives****7 half-lives**

Step 2: What is the half-life of the isotope?Step 2: What is the half-life of the isotope?

Half-life of Iodine-131 = 8.04 daysHalf-life of Iodine-131 = 8.04 days

Half-lifeHalf-life

Step 3: Step 3:

Multiply # of half-lives and half-life timeMultiply # of half-lives and half-life time

7 half-lives x 7 half-lives x 8.04 days8.04 days = = 56.28 days56.28 dayshalf-lifehalf-life