NUCLEAR ENERGY



NUCLEAR ENERGY

NUCLEAR STRUCTURE

Nuclei of atoms contain positively charged protons and neutral neutrons.

atomic number (Z): # protons

atomic mass (A): # protons + # neutrons

isotopes -Atoms of the same element that have a different number of neutrons.

3 isotopes of hydrogen

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|hydrogen |deuterium |tritium |

|0 neutrons |1 neutron |2 neutrons |

RADIOACTIVE DECAY

Some isotopes are unstable because they have too many or too few neutrons.

In radioactive decay, unstable isotopes release small particles to reach a stable configuration.

ALPHA DECAY (α)

In alpha (α) decay, a helium nucleus is spontaneously emitted from the parent nucleus.

An alpha particle is a helium nucleus consisting of 2 protons and 2 neutrons.

BETA DECAY (β) -Beta (β) decay is a type of nuclear reaction that involves the emission or capture of a beta particle.

BETA-NEGATIVE DECAY -In beta-negative decay a neutron spontaneously decays into a proton and electron; the electron is emitted from the nucleus.

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BETA-POSITIVE DECAY

In beta-positive decay a proton changes into a neutron and a positron and the positron is emitted.

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ELECTRON CAPTURE

An electron is absorbed by a nucleus and combines with a proton to form a neutron.

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GAMMA RADIATION (g)

A photon is emitted. A photon is a particle with zero mass and a high level of energy

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example 1

Fill in the missing information and state the type of decay.

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example 2

Fill in the missing information and state the type of decay.

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7.3 hALF-LIFE

Half-life is the amount of time required for half of the number of unstable nuclei in an isotope to decay.

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A= amount remaining M= mass remaining N = number remaining

Ao = initial amount Mo = initial mass No =initial number

t = time elapsed

T = half life time

Example

1. Gold-198 has a half life of 2.6days. What percentage remains after 1 day? 1 week?

RADIOACTIVE DATING

CARBON-14

▪ Carbon molecules are the basis for life on Earth.

▪ Carbon-14 undergoes beta decay to form Nitrogen-14.

▪ Carbon-12 is completely stable.

▪ When living matter dies, carbon-14 gradually decays.

▪ By comparing the portion of carbon-14 in a bone fragment, scientist can estimate the age of the bone.

7.4 mASS ENERGY EQUIVALENCE

Mass can be transformed into energy and energy can be transformed into mass.

E = mc2

E - energy in joules (J)

m - mass in kilograms

c - speed of light (3.00x108 m/s)

Nuclear technologies transform mass into energy.

Nuclear reactions can produce very large amounts of energy from very small amounts of fuel.

exampleS

1. How much mass must be converted to energy for a nuclear reaction to release 3.6x106 J (1kWh) of thermal energy?

2. Binding energy is the energy that keeps the subatomic particles together in an atom. It’s based on the difference in the calculated vs. atomic mass.

How much binding energy is in a helium atom with mass of 4.002603u?

Proton = 1.007 276u STEPS:

Neutron = 1.008 665u 1. Find the # of p, n, e

Electron = 0.000 549u 2. Find the atomic mass of the

Mass conversion: 1 u = 1.66 x 10 -27 kg p, n, e in atomic mass units

Joules to MeV: 1.602 x 10 -13 J = 1MeV 3. Convert mass to kg.

4. Find the difference between the

calculated vs. given mass (mass defect)

5. Use the mass from step #4 to find E.

6. Convert the energy into MeV (mega electron volts)

3. How much energy is released in the following nuclear fission reaction?

235 U + 1 n = 94 Zr + 139 Te + 3( 1 n)

92 0 40 52 0 STEPS:

U = 235.044u 1. Find the mass defect/difference

Zr = 93.906u between products and reactants

Te = 138.935u in atomic mass units (u).

n = 1.008665u 2. Convert mass to kg.

3. Use the mass from step #3 to find E.

4. Convert the energy into MeV (mega electron volts)

Alternate Method – instead of converting mass to kg, keep mass in amu and use

c2 = 930 MeV/u in the equation E=m c2

7.4-7.5 NUCLEAR REACTIONS

▪ Fission and fusion are nuclear reactions which release so much energy that the energy can be harnessed and used as heat to turn a turbine to generate electricity.

▪ Controlled fission reactions are used in nuclear reactors.

▪ Fusion is the main source of energy production in the Sun.

NUCLEAR FISSION

A heavy nucleus splits into lighter atoms and releases nuclear potential energy.

The process occurs naturally but it can occur more quickly if a neutron is added to the original nucleus.

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NUCLEAR FUSION

Combining of two light nuclei to form a single larger nucleus with a release of energy.

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GENERATING NUCLEAR POWER

Canada's nuclear power industry generates about 15 per cent of the electricity used in Canada. It is very important in Ontario, where it supplies more than half of the province's electricity.

How it works- Nuclear power plants use uranium as fuel to boil water and create steam. This steam spins turbines which are connected to a generator, which produces electricity.

Basic Components of Nuclear Reactors - The reactors used in Canada are CANDU reactors. This stands for Canada Deuterium Uranium reactor.

Fuel - Uranium has two main isotopes: uranium-235 (235U) and uranium-238 (238U). The uranium used in nuclear power is often made from a combination of these two isotopes. The critical mass is the smallest amount of fuel needed for a stable and sustained nuclear chain reaction.

Moderator - The fission chain reaction must be stable so there is no increase in the number of free neutrons within the reactor. A moderator is necessary to slow down the fast neutrons created during fission to increase their efficiency in causing further fission. The moderator in a CANDU reactor is heavy water, which is formed with the heavier deuterium isotope of hydrogen.

Coolant - A coolant is necessary to absorb and remove the heat produced by nuclear fission and maintain the temperature of the fuel. It can then transfer the heat to drive electricity-generating turbines. If water is used as the coolant, the steam produced can be fed directly to the turbines.

Control rods - Control rods are made of materials that absorb neutrons (example: boron, silver, cadmium) so the reaction don’t go out of control. The rod can be lowered or lifted into the reactor to regulate the reaction.

Managing used nuclear fuel and wastes

Once nuclear fuel bundles have been in the reactor for a period of time generating the steam that leads to creating electricity, they must be removed and safely managed. They have high levels of radioactivity.

Used fuel is stored in water for 5-10 years and then placed in large concrete and steel containers at the nuclear facility.

EXAMPLE

4. How much energy is released in the following nuclear fussion reaction?

2 H + 3 H = 4 He + 1 n + Energy

1 1 2 0 STEPS:

2H = 2.014 10u 1. Find the mass defect/difference

3H = 3.016 05u between products and reactants

He = 4.002 60u in atomic mass units (u).

n = 1.008 67u 2. Use E=m c2 to find energy released.

c2 = 930 MeV/u

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