Radiation/Properties:

Radioactive Elements - elements whose nuclei spontaneously disintegrate into new nuclei and emit nuclear radiation

Geiger Counter - a machine that detects ionizing radiation

When radiation enters a counter, the radiation ionizes atoms by knocking out electrons. These freely moving electrons create electrical pulses which are deleted by clicking sounds

Types of ionizing radiation: fast-moving charged particles and high energy electromagnetic radiation

Types of Decay:

Alpha - ⁴₂He stopped by skin or paper

Beta - ⁰₋₁e stopped by thick Al sheet

Positron - ⁰₁e same as beta particle

Gamma - ⁰₀Ɣ stopped by thick concrete or lead

Electron Capture -  ⁰₋₁e (but on left side of arrow)

Half-Life:

Time it takes for a radioactive isotope to fall to half its original value

Artificial/Induced Transmutation:

1925: Partick Blackett discovers protons

1932: James Chadwick discovered the neutron

1934: Enrico Fermi bombards lots of nuclei with neutrons in hopes of making nuclei heavier than Uranium. He detects some odd half-lives and chemical properties of his products but he is not successful at confirming the formation of any heavier nuclei (neutrons would be better than alpha particles at causing transmutation becuase neutrons are more penetrating since neutrons are neutral/no replusion)

1940: Np and Pu were synthesized. A particle accelerator was used to smash U-238 with fast neutrons (12,000 mps) to create U-239. This then goes by beta decay to Np-239 which then goes through beta decay to Pu-239.

1950s/1960s: More new elements are made using even more powerful particle accelerators

Radioactive Decay - spontaneous transmutation of one radioactive isotope into a more stable isotope

Induced Transmutation - humans cause this change from one element to another by bombarding a nucleus with another nucleus or particle

Bombardment of alpha

Particle Accelerator - a device that used electromagnetic fields to confine beams of charged particles and collide at high speeds

LHC - large hadron collider

CERN - council european research nuclear

Alpha bombardment is on the left side (just like electron capture)

Nuclear Fission:

1938: Lise Meitner becomes interested in Fermi’s results and works with Otto Hanh to continue to bombard U. They find that the isotopes act like barium (through halflives). A reaction with slow neutrons (1.4 mps) seem to break apart the atom, which seemed impossible but turned out to be fission.

Fission - a large nucleus splits into two medium-sized nuclei releasing lots of heat

1. Greater force is SNF because of the small distance

2. The slow neutron is bombarded

3. Critical deformation occurs

4. Collision causes the nucleus to expand

5. SNF weakens because of distance

6. Electric force becomes dominant

7. Repulsion spits the nucleus

Atomic bombs/fission bombs usually have U-235 or PU-239

Always 3 neutrons or more each time, so 3 or more reactions every fission

No sustained chain reactions occur with natural uranium with a small percentage of U-235 because there is a little chance that neutrons produced will hit a U-235.

An expanding chain reaction is possible for weapons-grade U with a large percentage of U-235 because there is a good chance that every neutron produced will his U-235.

To have a sustained expanding chain reaction, fissionable material must have supercritical mass.

To have supercritical mass, the fissionable material must be large enough, pure enough, and dense enough to cause a chain reaction to accelerate.

Critical mass - the smallest amount of fissile material needed for a sustained nuclear chain reaction (number of n escaping = number of n produced)

Supercritical mass - sustained chain reaction accelerates because fewer number of n escape than n produced

Subcritical mass - chain reaction stops because most neutrons escape before reacting

First Atomic Bomb Used: Little Boy

• US dropped on Hiroshima Japan 8/6/1945

• U Gun type: 2 pieces of subcritical, U-235 are brought together to form a supercritical mass

• Consisted of 92.6 lbs of weapons-grade U

• Had explosive power of 12,500 tons of TNT

• Compared to an equal mass of TNT, Little Boy released 2,5 million times more energy

Second Atomic Bomb Used: Fat Man

• US dropped on Nagasaki Japan 8/9/1945

• Implosion type: consisted of weapons-grade plutonium

• A subcritical mass of plutonium is compressed to form a supercritical mass

• Had explosive power of 22,000 tons of TNT

Mass Defect and Nuclear Binding Energy:

Proton - 1.00783 amu

Neutron - 1.00866 amu

This mass defect exists in all stable nuclei. The energy corresponding to the mass defect obtained by substituting the mass defect into the equation E=mc^2 is the nuclear binding energy.

Binding energy - the amount of energy required to break apart the nucleus into component nucleons (MeV)

1 amu = 931.5 MeV

Mass defect = mass of all protons (top number times 1.00783) + mass of all neutrons (atomic number minus protons times 1.00866) - mass of the isotope

Binding energy = mass defect converted to MeV

Nuclear binding energy per nucleons = binding energy/number of nucleons (atomic number)

SNF helps sustain nuclear binding energy

More energy out of musion than fission

Larger mass defect and binding energy, more stable the nuclei

Nuclear Fusion:

2 atoms form a larger nucleus

Need a very high temp plasma and high density

High temp gives enough energy to bring 2 positively charged nuclei close enough for SNF to overcome electrostatic repulsion

High temp therefore high speed (KE)

Higher charges have stronger repulsion, require more energy, higher temperatures

Element Abundance:

Even number elements are more common

Odd + odd = even

Even + even = even

Even + odd = odd

Uranium?

Stars ran out of fuel and exploded ejecting outer layers = supernova

Odd elements are formed when elements capture or with ¹₁H or ⁰₁n because ⁰₁n → proton

Fusion occurs when two atoms slam together to form a heavier atom, like when two hydrogen atoms fuse to form one helium atom.

Stability of Nuclei:

S-32 and S-35 have the same number of p but S-35 has more neutrons. Since S-32 is stable S-35 must be unstable because its n/p ratio is too high. Thus, S-35 will decay by a process by which a n turns into a p (beta decay).

Na-23 and Na-22 have the same number of p but Na-22 has fewer n than Na-23. Since Na-23 is stable, Na-22 must be unstable because itsn/p ratio is too low. This Na-22 will decay by a process by which a p turns into a n (positron emission).

Band of Stability - shows n/p ratio for all nuclei

n/p ratio is too high: too many n compared to p (beta decay)

n/p ratio is too low: too few n compared to p (positron emission)

Total number of nucleons is too high: too large nucleus(alpha decay)

Gravity - all objects with mass are attracted, weakest, very long distances

Electric Force - opposite charges attract same repel, medium, medium distances

Strong Nuclear Force - all combinations of nucleons attract, strong, tiny distances

The weak force - interaction involved with changing one type of quark into another type of quark, weak, very tiny distances

Two p close together: SNF is stronger

Two p far apart: Electric force is stronger

Smaller nuclei tend to be stable with about equal amounts of p and n

Large nuclei tend to need more neutrons than p

Added neutrons increases the SNF because it has more nucleons, n change in p repulsion, so nucleus gets more stable

Mass Change and E=mc^2:

If substances get more stable energy is released and mass must be lost. Mass is being converted into energy through E=mc^2. Think of mass and energy as two forms of the same thing.

Fpr favorable chemical reactions we usually assume that mass is conserved but in reality an extremely tiny unmeasurable amount of mass is lost and is converted into a small amount of energy. For a favorable nuclear reaction a tiny but measurable amount of mass is lost but converted into lots of energy.

Calculate initial mass of reactants (left side of arrow)

Calculate final mass of products (right side of arrow)

Calculate mass change by subtracting final and initial

Convert mass change (amu) to kg (1 amu = 1.6605 * 10^-27 kg)

Calculate amount of energy by multiplying kg by speed of light squared in J (E=mc^2) (3.00 * 10^8) ^2

Convert J/atoms to J/mol (1 mol = 6.022 * 10^23 atoms)

Nuclear Reactor:

• The main job of a reactor is to house and control nuclear fission—a process where atoms split and release energy.

• Reactors use uranium for nuclear fuel. The uranium is processed into small ceramic pellets and stacked together into sealed metal tubes called fuel rods.

• Inside the reactor vessel, the fuel rods are immersed in water which acts as both a coolant and moderator. The moderator helps slow down the neutrons produced by fission to sustain the chain reaction.Control rods can then be inserted into the reactor core to reduce the reaction rate or withdrawn to increase it.

• The heat created by fission turns the water into steam, which spins a turbine to produce carbon-free electricity.

• The Chernobyl disaster occurred when technicians at nuclear reactor Unit 4 attempted a poorly designed experiment. They shut down the reactor’s power-regulating system and its emergency safety systems, and they removed control rods from its core while allowing the reactor to run at 7 percent power. These mistakes, compounded by others, led to an uncontrolled chain reaction that resulted in several massive explosions.