differentiation book, Summaries of Mathematics

Download differentiation book and more Summaries Mathematics in PDF only on Docsity!

Nuclear Physics

L2 Nuclear Fission

Fission There are two main types: Induced fission – happens by an external neutron being absorbed by a parent nucleus. E.g. Uranium- Spontaneous fission – happens naturally with no external factors e.g. Uranium-

Energy released by fission Very large atoms are unstable because their nuclei are too large to be held together by short-range nuclear forces very effectively. Taking away nucleons therefore increases their stability, binds them more tightly and releases energy. Q: Find the energy released when uranium-238 undergoes spontaneous fission into thorium according to the equation: mass difference = (238.05078) – (234.04360 + 4.00150) = 0.0568 u

m (U-238) = 238.05078 u; m (Th-234) = 234.04360 u;

m (α) = 4.00150 u

energy released = 0.0568 u × 931.3 = 52.898 MeV

Induced Fission An induced fission reaction is as follows:

1. The uranium 235 nucleus captures a neutron
2. Becomes highly unstable U-
3. The U-236 splits
4. Daughter nuclei, such as Barium-141 and Krypton-92 are produced
5. Three fast neutrons are produced IMPORTANT: The nuclear equation proton and neutron numbers should be balanced. There are NOT ALWAYS THREE neutrons produced – so be careful!

Fission Energy

The energy released is a combination of the Kinetic energy of the particle products and the energy of the photons and neutrinos.

Avoid a chain reaction? The control rods (made of boron) help to absorb neutrons to try and ensure only one slow neutron survives per fission event. The rods are lowered further into the reactor core to further slow the rate of reaction. The smallest amount of mass needed to sustain a chain reaction is called a critical mass.

Thermal Reactor The key components are the same for all reactors:

• (^) Fuel Rods - contain enriched Uranium (mainly 238, 2-3% U- 235)
• (^) Coolant – Used to remove thermal energy from the system
• (^) Moderator – Slow down fast neutrons produced by fission reactions (could be carbon or water)
• (^) Control Rods – Typically boron or cadmium

Energy from induced fission A nuclear reactor uses a controlled chain reaction to produce heat to produce steam for a generator. Apart from the source of heat, it works in the same way as a coal-fired power station.

1. Reactor produces heat. 2. Hot coolant from core heats water to produce steam. **3. Steam powers turbine generator.

1. Steam cooled and condensed by cooling tower.**

Environmental Impact

• (^) Uranium-238 readily absorbs neutrons of intermediate kinetic energies to eventually produce Plutonium-239 (Pu-239). The full process is as follows:
• (^) This is bad, Pu-239 is one of the most hazardous materials produced in nuclear reactors and is extremely toxic. It has a half-life of 24, years!
• (^) We cannot dispose of nuclear waste normally. It is an ethical and practical issue regarding the storage of high-level nuclear waste – one way is burying it deep underground so that these isotopes with ling half-lives do not enter the water supply. This means the location have to be decided on carefully, by geologists for example.

Taking a step back to Lesson 1!