What is so dangerous about nuclear energy? Journal 14  What is so dangerous about nuclear energy?

Nuclear Chemistry Nuclear Chemistry Bravo – 15,000 kilotons

Chapter 21 Atomic nuclei are made of protons and neutrons. Collectively known as nucleons. An atom of an element (or an isotope) is called a nuclide and can be represented by the nuclear symbol or the hyphenated symbol. Example: Radium

Mass Defect Because an atom is made of protons, neutrons and electrons, you would expect the mass to be the sum of the masses of those particles. BUT the actual mass of an atom of an element is less!!!!!! Why? This difference in mass is called the MASS DEFECT.

What causes loss in mass? Einstein said E = mc2 Mass can be converted to energy Some of the mass of the atom has been used as energy to hold the nucleus together. This is called nuclear binding energy.

Nuclear Stability Nuclear binding energy is a measure of nuclear stability. We measure it in binding energy per nucleon. Binding energy per nucleon = binding energy # of nucleons Elements that have intermediate sized nuclei have the greatest binding energies and therefore are the most stable.

Nuclear Binding Energies

Elements that are larger or smaller have unstable nuclei. In order to become stable they must either lose or gain mass by ejecting particles This is known as radiation!

Nuclear Stability and Decay Unstable isotopes will undergo decay to achieve a more stable ratio of neutrons to protons The type of decay depends on the ratio of neutrons to protons Too many neutrons, turn neutrons to protons Too many protons, capture electrons and turn protons to neutrons, this emits a positron

Nuclear Stability Isotopes with low atomic numbers fig 28.6 Isotopes with low atomic numbers The stable ratio is 1 neutron to 1 proton Isotopes with high atomic numbers The stable ratio is 1.5 neutrons to 1 proton This creates the band of stability

Nuclear Stability Isotopes in Region A Isotopes in Region B Region C Alpha decay fig 28.6 Isotopes in Region A Have too many n, use beta decay to turn neutrons  protons Isotopes in Region B Have too many p+, use positrons to turn p+  neutrons Isotopes in Region C Have too many p+ & n use alpha decay to reduce the numbers Region A beta decay Region B positron

Radioactive decay All nuclei with atomic numbers greater than 83 are radioactive These nuclei have too many neutrons and too many protons to be stable So most undergo decay losing energy by emitting radiation

CA Standards Students know the three most common forms of radioactive decay (alpha, beta, and gamma) and know how the nucleus changes in each type of decay. Students know alpha, beta, and gamma radiation produce different amounts and kinds of damage in matter and have different penetrations. Students know some naturally occurring isotopes of elements are radioactive, as are isotopes formed in nuclear reactions.

Types of Radiation Radiation Alpha particles Beta Positron Gamma When we are looking at any type of radiation or radioactive decay we must remember that matter is conserved!

Nuclear Symbols Element Mass number symbol (p+ + no) Atomic number (number of p+)

Alpha Particle Emission Beta Particle Emission Gamma Ray Emission Symbol or Mass Heavy Light No Mass How it changes the nucleus Decreases the mass number by 4 Decreases the atomic number by 2 Contains 2 protons and 2 neutrons Converts a neutron into a proton Send off a fast moving e- (β) Increases atomic number by 1 -High energy radiation –just energy! (gamma rays) -No change to the nucleus -emitted with alpha & beta radiation Penetration Low Medium High Protection provided by… Paper, clothing Cardboard, wood Lead Danger Low, slow moving Medium, fast

Types of Radioactive Decay alpha production (a, He): helium nucleus beta production (b, e): gamma ray production (g):

Alpha Radiation Alpha decay is limited to VERY large, nuclei such as those in heavy metals. (a, He): helium nucleus

Alpha particles in a reaction Alpha radiation is emitted from U-238 23892U →23490Th + 42He Is matter conserved? Yes! Now you try! Alpha radiation is emitted from Rn-222 22286Rn → Yes 21884Po+ 42He

Gamma particles in a reaction 23090Th→22688Ra + 42He + γ When the alpha particle is released a huge amount of energy is also released (the gamma particle)!

Beta Radiation Beta decay converts a neutron into a proton and an e- (β) is released

Beta particles in a reaction C-14 is a beta emitter, show the decay process 146C →147N + 0-1β What Happened? np+; so atomic mass is still 14 a new p+= atomic number of 7 (now N) A β-particle flies out of the atom 0-1 β is the same as 0-1 e

Now you try What Happened? np+; so atomic mass is still 40 4019K → 4020Ca + 0-1 β What Happened? np+; so atomic mass is still 40 a new p+= atomic number of 20 (Ca) A β-particle flies out of the atom 0-1 β is the same as 0-1 e

Positron Particle Same mass as an electron Neutrons can be formed by protons that emit a positron They have a negligible mass Consequently they are more penetrating than alpha particles They have a charge of +1

Positrons in a reaction Potassium-38 will emit a positron, show the decay. 3819K → 3818Ar + 0+1β What Happened? p+  n; atomic mass is still 38 p+  n; atomic number decrease by 1; 18 (Ar) A positron flies out of the nucleus Now you try 137N → 136C + 0+1β

CA Standards Students know protons and neutrons in the nucleus are held together by nuclear forces that overcome the electromagnetic repulsion between the protons. Students know the energy release per gram of material is much larger in nuclear fusion or fission reactions than in chemical reactions. The change in mass (calculated by E = mc2) is small but significant in nuclear reactions.

Fission- big to small Fission - Splitting a heavy nucleus into two nuclei with smaller mass numbers.

Fusion Reaction- small to big Example:Deuterium – Tritium Fusion - Combining two light nuclei to form a heavier, more stable nucleus.

Energy and Mass Nuclear changes occur with small but measurable losses of mass. The lost mass is called the mass defect, and is converted to energy according to Einstein’s equation: DE = Dmc2 Dm = mass defect DE = change in energy c = speed of light Because c2 is so large, even small amounts of mass are converted to enormous amount of energy.

A Fission Reactor

Practice band of stability p 703 # 9 & 10

Discovery of Radiation Wilhelm Conrad Roentgen had discovered X rays Pierre & Marie Curie Discovery of several radioactive elements Coined “Radioactive” Nobel Laureates Brainpop- marie curie