Radioactivity and Nuclear Reactions

Name: ______CHAPTER 18 Radioactivity and Nuclear Reactions Guided Notes Section 1: Radioactivity  Why is it ______?  Radioactivity is ______because every element on the periodic table has some atomic nuclei that are radioactive.  New Vocabulary that you will learn in this section:  ______force  radioactivity What you’ll learn…  ______the structure of an atom and its nucleus  Explain what radioactivity is.  Contrast properties of ______and stable nuclei  Discuss the ______of radioactivity. The nucleus…lets review  Atoms are composed of ______, neutrons, and electrons.  Nucleus occupies only a tiny fraction of the ______in the atom. Contains almost all the mass of the atom  contains protons (+) and ______(neutral)  Total amount of protons= ______number (charge in a nucleus)  Electrons-located ______the nucleus (-) charge The Strong Force (p537)  How do you suppose protons and neutrons are held together so tightly in the nucleus?

The Strong Force cont…  1 of the 4 basic ______in nature and is about 100 times stronger than the electric force  ______force: long range force, so protons that are far apart still are repelled by the electric force  The total force between ______protons/neutrons depends on how far apart they are.  The strong force is a ______-range force: that quickly becomes extremely weak as protons and neutrons get farther apart Attraction and Repulsion  If a nucleus has only a ______protons and neutrons, they are all close enough ______to be attracted to each other by the strong force.  See Figure 4A  Protons and ______are held together less tightly in a large nuclei. (each protons and neutron is ______to only a few neighbors by the strong force)  See Figure 4B  All protons is a large nucleus exert a ______electric force on each other. Thus, the electric repulsive force on a proton in a large nucleus is larger than it would be in a small nucleus Radioactivity p. 538  When the strong force is not ______enough to hold a nucleus together tightly, the nucleus can decay and give off matter and energy. This process of ______decay is called Radioactivity.  Large nuclei tend to be unstable and can break apart of decay.  All nuclei that contain more than ______protons are radioactive. See 2nd paragraph (read as a class)  Almost all elements with more than ______protons do not exist naturally on Earth. Produced in labs (synthetic elements) Isotopes (p. 539)  Atoms of the same element that have different numbers of ______but the same number of protons  Ex). The elements Carbon 1  3 ______that occur naturally (Carbon nuclei can have 6,7, or 8 neutrons)  Look at figure 5 and identify the ratio of ______to neutrons in each isotope of helium  Answer: Helium-3 : 2 to 1; Helium-4 : 2 to 2 Stable and Unstable Nuclei  The ______of neutrons to protons is related to the stability of the nucleus  Less massive elements are ______when:  Ratio is 1 : 1  Heavier elements are stable when:  Ratio is 3 : 2  Nuclei is any isotopes that ______much from these ratios are unstable. (whether the elements are light or heavy)  Nuclei with too many or too few neutrons compared to the number of protons are radioactive

Nucleus Numbers  Atomic #: # of ______in nucleus  Mass #: # of protons and neutrons  See page 539 at the bottom The Discovery of Radioactivity (p. 540  1896 ______Becquerel  Uranium salt  1898 Marie and Pierre Curie  2 new elements: polonium and radium Self check  1). Describe the properties of the strong force 

 2). Compare the strong force between protons and neutrons in a small nucleus and a large nucleus.

 3). Explain why large nuclei are unstable.

Section 2 Nuclear Decay  Why it’s important?  Nuclear decay ______nuclear radiation that can both harm people and be useful What You Will Learn:  Compare and contrast alpha, ______, and gamma radiation  Define the ______-life of a radioactive material  Describe the process of ______dating Nuclear Radiation  Occurs when an ______nucleus decays, particles and energy called nuclear radiation are emitted from it.  3 types:  Aplha  Beta  ______Alpha Particles (p 541)  Alpha particle:  Made of ______protons and two neutrons is emitted from the decaying nucleus.  See Table 1  Compared to beta and gamma radiation, ______particles are much more massive

2  They have the most electric charge (therefore, lose energy more quickly when they ______with matter than the other types of nuclear radiation do). Damage from Alpha Particles (p.542)  Can be ______if they are released by radioactive atoms inside the human body.  A single alpha particle can damage many fragile ______molecules.  Can cause cells not to ______properly, leading to illness and disease.  Ex. Smoke detectors give off alpha particles that ionize the surrounding air. Transmutation (p. 542)  The process of changing ______element to another through nuclear decay  See Figure 8 on page 542 Beta Particles  When an electron is ______from the nucleus  Beta decay is caused by another basic force called the ______force.  Damage from Beta Particles  Beta particles are much ______and more penetrating than alpha particles  They can pass through paper but are stopped by a sheet of ______foil  Damage cells when they are emitted by radioactive nuclei inside the human body Gamma Rays  Electromagnetic waves with the highest frequencies and the shortest wavelengths in the electromagnetic spectrum.  Contain no mass and no charge  Travel at the speed of ______ Emitted from a nucleus when alpha ______or beta decay occurs.  See Table 3 on Page 543  What stops gamma rays?  Thick blocks of ______materials (lead and concrete)  They cause less damage to biological molecules as they pass through living tissue. Radioactive Half-Life  Half-life: The amount of ______it takes for half the nuclei in a sample of the isotope to decay.  Radioactive dating:  Geologists, biologists, and ______, among others, are interested in the ages of rocks and fossils found on Earth.  First: the ______of the radioactive isotope and its daughter nucleus in a sample of material are measured.  Second, the number of half-lives that need to pass to give the ______amounts of the isotope and its daughter nucleus is calculated.  Third, the number of half-lives is the amount of time that has passed since the isotope began to decay Carbon Dating  Carbon-_____ often is used to estimate the ages of plant and animal remains.  See page 545 Uranium Dating  Radioactive dating also can be used to estimate the ______of rocks.  Some rocks contain ______, which has two radioactive isotopes with long half-lives. Checks for understanding:  1. Infer how the mass number and the atomic number of a nucleus change when it emits a beta particle.

 2. Describe how each of the three types of radiation can be stopped.

Nuclear Reactions (p 551) 3  What you will learn…  Explain nuclear ______and how it can begin a chain reaction  Discuss how nuclear fusion occurs in the ______.  Describe how radioactive ______can be used to diagnose medical problems.  Discuss how ______reactions can help treat cancer. VOCABULARY: nuclear fission, ______reaction, critical mass, nuclear fusion, and tracer.

Nuclear Fission (p. 551)  Nuclear fission:  The process of ______a nucleus into several smaller nuclei  The word “fission” means to divide  Only large nuclei, such as the ______of uranium and plutonium atoms, can undergo nuclear fission.  Figure 16  The products of a fission reaction usually include ______individual neutrons in addition to the smaller nuclei Chain Reactions/Critical Mass (p. 552)  Chain Reactions:  The series of repeated ______reactions caused by the release of neutrons in each reaction  If the chain reaction is uncontrolled, an enormous amount of ______is released in an instant. However, it can be controlled by adding materials that absorb neutrons.  Critical Mass:  The amount of material required so that each ______reaction produces approximately one more fission reaction.  If ______than the critical mass of material is present, a chain reaction will not occur Nuclear Fusion (p. 553)  Nuclear Fusion:  2 nuclei with low masses are ______to form one nucleus of larger mass.  Fusion: ______atomic nuclei together  Fission: ______nuclei apart  For ______to occur: positively charged nuclei must get close to each other.  Example: The Sun  Most of the energy given off by the Sun is produced by a process involving the fusion of hydrogen nuclei. Tracer (p. 554)  Tracer:  A radioisotope that is used to find or keep track of ______in an organism.  Scientist can use tracers to follow where a particular ______goes in your body or to study how a ______organ functions.  Also used in agriculture to monitor the uptake of ______and fertilizers. Treating Cancer with Radioactivity  ______can be used to stop some types of cancerous cells from growing.  ______: a group of cells in a person’s body grows out of control and can form a tumor Summary:  Nuclear ______ Occurs when a neutron strikes a ______, causing it to split into smaller nuclei  A chain reaction ______a critical mass of fissionable material  Nuclear Fusion  Nuclear ______occurs when two nuclei combine to form another nucleus  Nuclear fusion occurs at temperatures of millions of ______which occur inside the Sun. Check for understanding:

4  Explain how a chain reaction can be controlled.

 Describe two properties of a tracer isotope used for monitoring the functioning of an organ in the body.