## Nuclei

# Nuclear Force and Nuclear Energy

- NUCLEAR FORCES are very strong attractive forces. They are charge independent and spin dependent.
- Nuclear forces are short ranged i.e., they are applicable only when the separation of nucleon is of the order of 10
^{−15}m. - The nuclear forces does not act along the line joining the centres of the nucleons.
- Nuclear force is due to the exchange of π meson between nucleons.
- The conversion of one element into another by artificial means is called ARTIFICIAL TRANSMUTATION of the element
- The phenomenon of splitting up of a heavy nucleus into lighter fragments emitting large energy is called NUCLEAR FISSION.
- Nuclear fission reaction by a thermal neutron is
_{92}U^{235}+_{0}n^{1}→_{56}Ba^{141}+_{36}Kr^{92}+ 3_{0}n^{1}+ Q - The average number of neutrons released per fission in U
^{235}is 2.5 - Fission of Uranium and thorium is also possible with the high speed protons of energy 6.9 MeV or with deuterons of energy > 8 MeV
- CHAIN REACTION is characterized by neutron multiplication factor "K"

\tt K = \frac{Number \ of \ neutrons \ in \ present \ generation}{Number \ of \ neutrons \ in \ previous \ generation} - NEUTRON MULTIPLICATION FACTOR, K : If K < 1, then the reaction is said to be under critical.
- If K = 1, then the reaction is said to be critical and energy will be produced at a steady rate.
- If K > 1, then the reaction is said to be super critical (explosive)
- The combination of two or more lighter nuclei forming comparatively heavier nucleus is called NUCLEAR FUSION.
- Nuclear fusion takes place at a very high temperature (approx. 10
^{6}K) - Carbon – Nitrogen cycle 4
_{1}H^{1}→_{2}He^{4}+ 2_{+1}e^{0}+ energy (26.7 MeV) - Proton – Proton Cycle 4
_{1}H^{1}→_{2}He^{4}+ 2_{+1}e^{0}+ energy (26.7 MeV) - When a γ-ray photon of energy 1.02 MeV interacts with matter
_{+1}e^{0},_{-1}e^{0}pair will be produced. This is referred as pair production.

γ →_{+1}e^{0},_{-1}e^{0} - If E
_{γ}< 1.02 MeV then

1) Pair production is not possible. - Electron emission is possible by photo electric emission.
- If E
_{γ}> 1.02 MeV then

1) Pair - production is possible. - The extra energy will be shared equally by the pair of particles in the form of K.E.
- BREEDER REACTOR : It converts non fissionable materials into fissionable material and generates electric power.

\tt _{92}U^{238} + {_{0}N^{1}} \rightarrow {_{92}U^{239}} \ {\underrightarrow{2 \beta}} \ {_{94}U^{239}} - POWER REACTOR: Generates electric power P = nE/t
- \tt P = \left(\frac{x}{A}N\right) \frac{E}{t} x = nuclear fuel in grams, N = Avogadro number, A = mass number, E = energy released per fission.
- Breeder reactors are used to generate nuclear fuel.

Name | Quarks | Anti quarks | ||

Symbol | Charge | Symbol | Charge | |

Up | U | \tt + \frac{2}{3} e | \tt \overline{u} | \tt - \frac{2}{3} e |

Down | d | \tt - \frac{1}{3} e | \tt \overline{d} | \tt + \frac{1}{3} e |

Strange | S | \tt - \frac{1}{3} e | \tt \overline{S} | \tt + \frac{1}{3} e |

Charmed | C | \tt + \frac{2}{3} e | \tt \overline{C} | \tt - \frac{2}{3} e |

Top | t | \tt + \frac{2}{3} e | \tt \overline{t} | \tt - \frac{2}{3} e |

Bottom | b | \tt - \frac{1}{3} e | \tt \overline{b} | \tt + \frac{1}{3} e |

### Nuclear Force View the Topic in this video From 00;18 To 13;29

### View the Topic in this video From 00:26 To 5:03

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The chain reaction once started will either remains steady, accelerate or retard depending upon a factor called neutron reproduction or critical factor (k). If is defined as

\tt k = \frac{Rate \ of \ production \ of \ neutrons}{Rate \ of \ loss \ of \ neutrons}