Nuclear, i.e. pertaining to the nucleus

Nucleus Most nuclei contain p + and n 0 When packed closely together, there are strong attractive forces (nuclear forces) btw.. protons-protons protons-neutrons

Atomic Size The radius of an atom is 40 – 270 pm The nucleus has a radius of only pm, with an incredible density of 2 x 10 8 metric tons/cm 3 Remember, most of atom’s volume is taken by e - cloud

The Nucleus (aka Nuclide) Nucleus is made of p + and n 0, which are collectively called nucleons (p + and n 0 are types of nucleons) In nuclear chemistry, an atom is referred to as a nuclide and is identified by the number of p + and n 0 in its nucleus 228 Ra or Radium Nuclides can be written 2 ways.

Atomic Mass An atom is made of p+, n0, and e- So you could expect its mass to = Ex. Helium 2 p+(2 x amu) = amu 2 n0(2 x amu) = amu 2 e-(2 x amu) = amu total mass = amu

Mass Defect BUT, the atomic mass of the He atom has been measured at , NOT our calculated mass of Mass of helium atom is amu less than we expected The difference btw the mass of an atom and the sum of its “parts” is called the mass defect

Mass can be converted to energy What causes the “loss” in mass? According to E = mc 2, mass can be converted to energy and energy converted to mass The mass defect is caused by mass being converted to energy upon formation of the nucleus

E = mc 2 Using Einstein’s equation and the mass defect, we can calculate the energy released when a nucleus is formed (nuclear binding energy) It is also the energy required to break apart the nucleus

Nuclear Stability Binding energy per nucleon = the binding energy of the nucleus divided by the number of nucleons it contains The higher binding energy per nucleon, the more tightly they are held together and the more stable the nucleus Elements with intermediate atomic masses are the most stable.

Trends Among atoms with low atomic numbers, the most stable nuclides are those with a neutron:proton ratio of 1:1 (ex. He has 2:2) Increasing atomic numbers push the stable ratio closer to 1.5:1 (ex. Pb has 124:82) Stable nuclei tend to have even numbers of nucleons (p + and n 0 )

Opposing Forces in the Nucleus p + repel p + (electrostatic repulsion), except the ones very close to them (nuclear forces) As #p + increases, electrostatic repulsion overcomes nuclear forces, therefore more neutrons are required to increase the nuclear force and stabilize the nucleus

Vocabulary Recap Nucleon Nuclide Mass defect Nuclear stability Nuclear binding energy Electrostatic repulsion v. nuclear forces

Nuclear reaction = a reaction that affects the nucleus of the atom The number of protons and neutrons change! Large amounts of energy are given off Stability is increased p+ repel p+ (electrostatic repulsion), except the ones very close to them (nuclear forces) 9 Be + 4 He → 12 C + 1 n If the atomic number of the atom changes,……. Transmutation = a change in the identity of a nucleus A Be nucleus and a He nucleus fuse to form a C nucleus and a neutron

The spontaneous disintegration of a nucleus into a slightly lighter nucleus, accompanied by the emission of particles, electromagnetic radiation, or both Disintegration = breaking apartEmission = sending out Electromagnetic radiation, e.g. gamma rays, UV, visible light, x-rays, infrared waves, etc.

Nuclear Radiation = particles or electromagnetic waves emitted during radioactive decay ex. Uranium is a radioactive nuclide, and unstable nucleus that undergoes radioactive decay This week think of a neutron as a particle made up of a proton and an electron fused together mass similar to p + because mass of e - is negligible no charge because p + and e - cancelled each other out

5 Types of Radioactive Decay 1. Alpha Emission Restricted to heavy nuclei (large # of p + and n 0 ) Emits Alpha particles = He nuclei (2 p + and 2 n 0 bound together) to increase the stability of nucleus 210 Po → 206 Pb + 4 He A polonium nucleus is too large and therefore unstable. In radioactive decay, it emits an alpha particle to become lead, a smaller and more stable nucleus

5 Types of Radioactive Decay 2. Beta Emission occurs in nuclides with a high neutron:proton ratio To decrease the # of n 0, a n 0 can be converted into a p + and an e - and the e- is sent from the nucleus as a beta particle 14 C → 14 N + 0 β Atomic number increases by 1, but mass number stays the same. n 0 :p + decreases 1 n → 1 p + 0 β

5 Types of Radioactive Decay 3. Positron Emission Occurs in nuclides whose n 0 :p + ratio is too small Too decrease the number of p +, a p + can be converted into a n 0 by emitting a positron 1 p → 1 n + 0 β a particle that has the same mass as an electron, but has a positive charge ex. 38 K → 38 Ar + 0 β

5 Types of Radioactive Decay 4. Electron Capture Occurs in nuclides with a n 0 :p + ratio that is too small An inner e - is captured by its own nucleus and combines with a p + to form a n 0 0 e + 1 p → 1 n ex. 106 Ag + 0 e → 106 Pd

5 Types of Radioactive Decay 5. Gamma Emission Usually occurs following other types of decay, when particles (e.g. alphas, betas, positrons) leave the nucleus in an excited state Gamma rays (γ) are high energy electromagnetic waves emitted from a nucleus as it changes from an excited energy state to a ground energy state Ground state = the lowest energy state

Half-Life No 2 radioactive nuclides decay at the same rate More stable nuclides decay slowly and have long half- lives Less stable nuclides decay quickly and have shorter half- lives Half-life (t 1/2 ) = the time required for half the atoms in a radioactive nuclide to decay

Example Problem P-32 has a half-life of 14.3 days. How many mg of P-32 will remain after 57.2 days if you start with 4.0 mg? 1. Find number of half-lives that have passed. # of half-lives = (t 1/2 /t) 2. Reduce the original mass by half for every half-life that has passed. Final mass = initial mass x 0.5 for each half life that has passed t = time passed t 1/2 = half-life for the nuclide

Decay Series One nuclear reaction is often not enough to produce a stable nuclide A decay series = a series of radioactive nuclides produced by successive radioactive decay until a stable nuclide is reached All naturally occurring nuclides with atomic # greater than 83 are radioactive and belong to one of 3 natural decay series (U-235, U-238, Th-232)

Artificial Transmutations and Artificial Nuclides

Nuclear Radiation

Radiation Exposure

Radiation Detection

Applications of Nuclear Radiation

Nuclear Waste

Nuclear Fission

Nuclear Fusion