Integrated Science Chapter 25 Notes Radioactivity Integrated Science Chapter 25 Notes

I. What is Radioactivity? Radioactivity - Process by which an unstable nucleus emits one or more particles or energy Nucleus composed of protons and neutrons Electrons are outside the nucleus

I. What is Radioactivity? A. Nuclear decay Break down of an atom’s nucleus Element can become an isotope or a new element Isotopes – atoms of the same element with different numbers of neutrons Some isotopes are stable and never break down, while some are unstable and break down into a more stable atom.

Some reasons that an isotope of an element might be unstable are:  Too many neutrons in the nucleus  Too few neutrons in the nucleus  Nucleus is too big in size (too many neutrons and protons total)

Examples Carbon-12 (6 protons, 6 neutrons) is stable, but Carbon-14 (6 protons, 8 neutrons) is unstable. Beryllium-7 (4 protons, 3 neutrons) is unstable, but Beryllium-9 (4 protons, 5 neutrons) is stable. All elements atomic #93 and higher are unstable due to their large nucleus size.

I. What is Radioactivity? B. When a nucleus decays, it breaks down into a new nucleus, plus ejected nuclear radiation This is a naturally occurring / spontaneous event when a nucleus is unstable

I. What is Radioactivity? C. There is a “Strong Nuclear Force” present in the nucleus of an atom which holds the protons and neutrons together in the nucleus to remain stable.  Kind of like nuclear “glue”

I. What is Radioactivity? D. Types of Nuclear Radiation Nuclear radiation – charged or uncharged particles or energy emitted by unstable nuclei All radiation can interact with and affect surrounding matter

I. What is Radioactivity? Transmutation – change from one element into a new element plus nuclear radiation

I. What is Radioactivity? 4 Types of nuclear radiation 1. Alpha particles (α) – positively charged, made of 2 protons and 2 neutrons Most massive nuclear radiation particle Slow moving, and quickly loses energy

I. What is Radioactivity? 4 Types of nuclear radiation 2. Beta particles (β) – negatively charged, made of fast moving electrons - Little mass - Penetrate matter, but not deeply

I. What is Radioactivity? Beta Decay example

I. What is Radioactivity? 4 Types of nuclear radiation 3. Gamma rays (γ) – high energy, high penetrating power Not made of matter, no charge Electromagnetic energy like light or x-rays, but with more energy Stopped by 7 cm of lead Health hazard due to energy and penetrating ability

I. What is Radioactivity? 4 Types of nuclear radiation 4. Neutron emission – a single neutron with no charge Can penetrate up to 15 cm of lead

II. Nuclear Reactions A. Much energy released into the surroundings during a nuclear reaction B. In a nuclear reaction, the nucleus changes

II. Nuclear Reactions There are two types of nuclear reactions: 1. Nuclear Fission – process where a nucleus splits (or is split) into two or more smaller nuclei and releases energy

 Particles can cause chain reactions of nuclear fission in surrounding atoms  This is an example of a nuclear explosion

Some practical uses of fission reactions are: Nuclear reactors for a power source Weapons Medicine

II. Nuclear Reactions There are two types of nuclear reactions: 2. Nuclear Fusion – process where two nuclei combine at very high temperatures to form a larger nucleus and releases energy

Where does fusion happen? This occurs continuously in stars as hydrogen atoms (1 proton, 1 neutron) are joined together to form helium atoms (2 protons, 2 neutrons). During the process, a large amount of energy is also released.

Practical Uses of Nuclear Fusion We use this energy (solar energy) to warm the earth and homes, and plants use it to make food (photosynthesis), We can capture and convert solar energy into electricity .

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

C. Nuclear reactions, mass, and energy The Law of Conservation of Mass still applies, as matter (which has mass) is not created or destroyed, but the form is changed. During the change in form, energy is released as the matter becomes more stable, with less energy

III. Dangers and Benefits of Nuclear Radiation There are both positives and negatives to nuclear radiation and nuclear energy

III. Dangers and Benefits of Nuclear Radiation A. Dangers  can burn skin, can ionize living tissues, can destroy cells, can cause cancer, can cause genetic mutations in DNA, radiation pollution

III. Dangers and Benefits of Nuclear Radiation B. Benefits  can be used to treat diseases, used in smoke detectors, tracers used in medicine, agriculture, research, energy source

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

Half-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-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-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-life For example: If you have 100 atoms of a sample of Carbon-14, and the half-life of that isotope is 5730 years, how many atoms are left after 2 half-lives? 100 atoms  50 atoms  25 atoms 1st half-life 2nd half-life

Half-life If you started with 1000 atoms of a sample of Iodine-131, and you have 8 atoms left, how much time has passed? Half-life of Iodine-131 = 8.04 days

Half-life Step 1: Determine number of half-lives 1000 500 250 125 63 32 16 8 1 2 3 4 5 6 7 **7 half-lives** Step 2: What is the half-life of the isotope?  Half-life of Iodine-131 = 8.04 days

Half-life Step 3: Multiply # of half-lives and half-life time 7 half-lives x 8.04 days = 56.28 days half-life