Introduction to Radioactivity and the 3 types of Nuclear Radiation

Today’s Objective Define and understand the following terms Radioactivity Repulsive Force Nuclear Force Isotope Be able to describe/explain why some atoms are radioactive Be able to describe and balance Positive alpha radiation α equations Negative beta radiation β equations Neutral gamma radiation γ equations

7.1 – Atomic Theory and Radioactive Decay Natural background radiation exists all around us. This radiation consists of high energy particles or waves being emitted from a variety of materials. Like the sun, radio stations, electronic devices, TV’s, cell phones, lights, etc... Being exposed to radioactive materials can be beneficial or harmful

Beneficial (good) radiation exposure Light! X-rays Radiation therapy (cancer treatment) Electricity generation (nuclear power plants)

Harmful (bad) radiation exposure Too much of any radiation... Can cause Cancer Skin cancer from sun (UV) radiation Body cancer from high amounts of radiation Can cause genetic mutations Radiation affects and mutates the DNA in our body cells and then causes mutations in offspring

WHAT IS RADIATION?? Radioactivity (radiation) is the release of high energy particles or waves from unstable nuclei When atoms lose high energy particles and waves, ions or even new atoms can be formed High energy waves and particles are called ‘radiation’ when they leave the atom

Why are some Nuclei Radioactive? Note: Radioactive = Unstable Recall the structure of an atom. What lives in the nucleus? Protons Neutrons REPULSIVE FORCE P+ N P+ P+ NUCLEAR FORCE N P+ N N P+ N

Repulsive and Nuclear Forces The nucleus is full of positive protons Like charges want to repel= REPULSIVE FORCE Fortunately the neutrons are there to help hold the nucleus together= NUCLEAR FORCE Sometimes there are not enough neutrons in the nucleus. This means the balance between repulsive forces and nuclear forces is off!

UNSTABLE NUCLEI When the forces do not balance, the nucleus will make adjustments by kicking out particles or energy out of their nucleus. This is called RADIATION

The Electromagnetic Spectrum The higher the frequency of radiation (ie. the shorter the wavelength) = The more harmful the radiation is for you!

Searching for Invisible Rays Radiation is everywhere, but can be difficult to detect Roentgen named X-rays with an “X” 100 years ago because they were previously unknown Becquerel realized uranium emitted seemingly invisible energy as well Marie Curie and her husband Pierre named this energy radioactivity Early discoveries of radiation relied on photographic equipment Later, more sophisticated devices such as the Geiger counter were developed to more precisely measure radioactivity

Isotopes and Mass Number Isotopes are different atoms of the same element, with the difference between the two atoms being the number of neutrons in the nucleus, the number of protons is the same. Isotopes have the same number of protons and therefore the same atomic number as each other. By having different numbers of neutrons, isotopes have different mass numbers.

Representing Isotopes Isotopes are written using standard atomic notation. Chemical symbol, atomic number & mass number. Potassium has three isotopes

Wait a MINUTE... MASS ATOMIC # Periodic Table Nuclear Symbol CHEMISTS PHYSICISTS

C C Calculating Neutrons 14 12 6 6 6 8 It is now much easier because of the physicists C 6 12 C 14 6 MASS ATOMIC # 6 8 # Neutrons

Practice! Work with a partner to do the practice problems on page 291 in your notebook. (Don’t write in your textbooks!!!) Check your answers on page 592

Radioactive Decay Unlike all previously discovered chemical reactions, radioactivity sometimes resulted in the formation of completely new atoms. Radioactivity results from an atom having an unstable nucleus When these nuclei lose energy and break apart, decay occurs Radioactive decay releases energy from the nucleus as radiation Radioactive atoms release energy until they become stable, often ending up as different atoms For example: uranium-238 (parent nucleus) decays in several stages until it finally becomes lead-206 (daughter nucleus) An element may have only certain isotopes that are radioactive. These are called radioisotopes. Carbon-13 is an example.

Three Types of Radiation When atoms are unstable, they break apart to become new, more stable atoms and release radiation... There are 3 types that can be released. Positive alpha radiation α Negative beta radiation β Neutral gamma radiation γ

Alpha (α) radiation Alpha radiation is a stream of alpha particles These particles are the same as a helium nucleus so we represent α radiation as: Because it has two protons, it has a charge of 2+ The release of alpha particles is called alpha decay Alpha particles are slow and penetrate materials much less than the other forms of radiation. A sheet of paper will stop an alpha particle

** Notice – the product side atomic masses add up to the reactant side (as well as the atomic numbers) You try: Ac  Fr + He Decays to + ____ 4 ____ 87 2 221 89

Beta (β) Radiation (Beta decay) Beta radiation is a stream of beta particles Beta particles are the same as an electron. So we represent radiation as: Beta decay occurs when a neutron changes into a proton + an electron. The proton stays in the nucleus and the electron is released. Beta particles are faster than alpha particles. A sheet of aluminum foil will stop a beta particle.

** Notice – the product side atomic masses add up to the reactant side (as well as the atomic numbers) You try: Hg  Tl + β Decays to + O -1 ___ 201 0 80 ____ -1 201 81

Gamma (γ) Radiation Gamma radiation is a ray of high energy, short-wavelength radiation no charge and no mass the highest energy form of electromagnetic radiation Occurs when nucleus is in excited state (shown by by *) after emitting an alpha or beta particle, and needs to release more energy. It is shown by: It takes thick blocks of lead or concrete to stop gamma rays Sometimes reactions can release more than 1 type of radiation. For example: Uranium-238 decays into an alpha particle and also releases gamma rays

Gamma Radiation Uranium is releasing an Alpha particle and Gamma Radiation Nickel is decaying and giving off just Gamma Radiation Notice – no change in atomic mass or number!

Try some radioactive decay questions... (Copy in your notes) Pa  Ac + ___ C  ___ + β U  Cs + ____ + γ 227 231 ____ 4 91 ____ 2 α / He 89 14 14 ____ 0 6 ____ -1 N 7 Rb 92 235 143 ____ 0 92 55 ____ 0 37

Assignment Try practice problems on page 295 and 296. Check your answers.