CHAPTER 9 Nuclear Energy I. Radioactivity (pg ) I. Radioactivity (pg )

Radioactive Elements

A. Definitions  Radioactivity  Process of unstable nuclei of elements becoming stable through emitting particles or releasing energy away from the atom  Also called nuclear decay

DefinitionsDefinitions  During nuclear decay, the element can transform into a different isotope of the same element or to a different element completely.  Transmutation  process of changing one element into another element by nuclear decay

DefinitionsDefinitions  Nuclear radiation is the released energy and matter during nuclear decay.  This can have both positive and negative effects for life on earth.

DefinitionsDefinitions  Isotopes – elements that have the same number of protons but different number of neutrons in their nuclei.

IsotopesIsotopes  Carbon-12, Carbon-13, Carbon-14

Where does this take place?  Radioactivity (nuclear decay) happens in the nucleus of the atom.

B. Types of Radiation  Alpha (  )  helium nucleus paper 2+  Beta-minus (  -)  electron 1- plastic  Gamma (  )  high-energy photon 0 lead

Types of Radiation  Neutron emission (n) 1 0 n 0 charge

C. Nuclear Decay  Why some nuclei decay…  to obtain a stable ratio of neutrons to protons Stable Unstable (radioactive)

C. Nuclear Decay  Alpha Emission  Beta Emission TRANSMUTATIONTRANSMUTATION

ExampleExample  Actinium-217 decays by releasing an alpha particle. Write the equation for this decay process and determine what element is formed.  Step 1: Write the equation with the original element on the reactant side and products on the right side.

ExampleExample  217 A4 89 Ac  Z X + 2 He Step 2: Write math equations for the atomic and mass numbers. 217 = A = Z + 2

ExampleExample  Step 3: Rearrange the equations. A = 217 – 4Z = Step 4:Solve for the unknown value, and rewrite the equation with all nuclei. A = 213Z = 87

ExampleExample  Ac  87 Fr + 2 He This is an example of alpha decay.

D. Half-life  Half-life (t ½ )  time it takes for half of the radioactive nuclei in a sample to decay Example Half-lives polonium seconds lead hours iodine days carbon-145,370 years uranium billion years

Half-lifeHalf-life

If we start out with 1 gram of the parent isotope, after the passage of 1 half-life, there will be 0.5 gram of the parent isotope left.

D. Half-life  How much of a 20-g sample of sodium-24 would remain after decaying for 30 hours? Sodium-24 has a half-life of 15 hours. GIVEN: total time = 30 hours t 1/2 = 15 hours original mass = 20 g WORK : number of half-lives = 2 20 g ÷ 2 = 10 g (1 half-life) 10 g ÷ 2 = 5 g (2 half-lives) 5 g of 24 Na would remain.

Nuclear Forces There are two types of forces in the nucleus. Strong nuclear force – helps attract the protons and neutrons in the nucleus and keep them together. Repulsive force- protons repel each other because they are the same charge

Nuclear Forces In stable atoms, the attractive forces are stronger than the repulsive forces.

A. F ission  splitting a nucleus into two or more smaller nuclei  some mass is converted to large amounts of energy

A. F ission  chain reaction - self-feeding reaction

FissionFission  Chain reactions can be controlled and used to create electricity in nuclear power plants.  The minimum amount of a substance that can undergo a fission reaction and sustain a chain reaction is called critical mass.

B. Fusion  combining of two nuclei to form one nucleus of larger mass  produces even more energy than fission  occurs naturally in stars

FusionFusion

Nuclear Radiation in Life  Background radiation is nuclear radiation that is around you from natural sources like the sun, soil, rocks, and space.  A rem or millirem (1 rem = 1000millirems) is the unit for radiation.

Nuclear Radiation in Life  A safe limit is set at 5000 millirems/year.  Occupation – X-ray tech, flight attendant  Where you live- high elevation, near rocks  Activities - smoking

A. Nuclear Power  Fission Reactors

A. Nuclear Power  Fusion Reactors (not yet sustainable) Tokamak Fusion Test Reactor Princeton University National Spherical Torus Experiment

A. Nuclear Power  235 U is limited  danger of meltdown  toxic waste  thermal pollution  Hydrogen is abundant  no danger of meltdown  no toxic waste  not yet sustainable FISSIONFISSION FUSIONFUSION vs.

Other benefits to radiation  Smoke detectors  Disease detection  Ultra sound  CT scan  MRI  Cancer treatment