nuclear reactions

33
Nuclear reactions Physics 100 Chapt 25 part b Using the strong nuclear force to produce useful energy

Upload: imogene-ferguson

Post on 15-Mar-2016

25 views

Category:

Documents


2 download

DESCRIPTION

Nuclear reactions. Using the strong nuclear force to produce useful energy. Physics 100 Chapt 25 part b. Strong Nuclear Force. It is very strong It overcomes the electrical repulsion between positively charged protons that are only 10 -15 m apart. It acts over a very short range - PowerPoint PPT Presentation

TRANSCRIPT

Page 1: Nuclear reactions

Nuclear reactions

Physics 100Chapt 25 part b

Using the strong nuclear force to produce useful energy

Page 2: Nuclear reactions

Strong Nuclear Force• It is very strong

– It overcomes the electrical repulsion between positively charged protons that are only 10-15m apart.

• It acts over a very short range– It is not felt by nucleons when they

are more than 10-15m apart.• It is selective

– It is felt by neutrons & protons, but not by electrons

Page 3: Nuclear reactions

Nuclear “bullets”Protons are repelled by electrical the repulsion force of the positively nucleus. Only protons with KE ofa few MeV or more can get within the range of thestrong nuclear force & produce “nuclear reactions”

++

++++

+

++

++

++

++

++

++

+

vF

Producing nuclear reactionswith protons (or any other

charged nuclei) is a challenge

Page 4: Nuclear reactions

Neutron induced nuclear reactionsNeutrons don’t feel the electrical force so even very slow, low-energy neutrons can strike the nucleus & produce “nuclear reactions”

+++

++

+

++

++

++

++

++

++

+

v

Low energy neutrons areeffective nuclear “bullets”

Page 5: Nuclear reactions

Nuclear fission

n + 92U 56Ba + 36Kr + 2n235 142

92

Page 6: Nuclear reactions

Energy balance in a fission reaction

141Ba +92Kr + 2n

200 MeV KE heat 235U + n

Page 7: Nuclear reactions

Chain reaction

Use the neutrons produced by onefission to initiate another fissionEnrico Fermi

Page 8: Nuclear reactions

Requirements for A-bomb

• Fissionable material: 235U or 239Pu

• Critical mass

• Mechanism

Page 9: Nuclear reactions

Critical Mass

Enriched 235U 50kg

239Pu 10kg

Mcrit

Page 10: Nuclear reactions

Fissionable MaterialFortunately, only certain nuclear isotopes undergo the

fission process:

235U only 0.7% of naturally occurring U(99.3% is 238U, which doesn’t fission)

239Pu doesn’t occur naturally, but is produced in nuclear reactors

…. There are other fissionable isotopes, e.g. 233U &232Th, but they are very rare

Page 11: Nuclear reactions

Little boy (235U)

(doughnut-like)

Page 12: Nuclear reactions

Fat man (239Pu)

Page 13: Nuclear reactions

Devastation

Hiroshima Aug 6 1945 8:15AM

80,000 people killed immediately;

~100,000 people were exposed to lethal radiation & died painful slow deaths

Page 14: Nuclear reactions

Hiroshima aftermath

Page 15: Nuclear reactions

Devastation

Nagasaki Aug 9 1945 10:45AM

39,000 people killed immediately;

~70,000 people were exposed to lethal radiation & died painful slow deaths

Page 16: Nuclear reactions

Nagasaki aftermath

Page 17: Nuclear reactions

Nuclear fusion

2H + 3H 4He + n

Two light nuclei fuse togetherto form a heavier one

Here the nuclei have to start outwith large energy in order to

overcome the electrical repulsion

Page 18: Nuclear reactions

Energy balance in a fusion reaction

4He+n

12.3 MeV KE heat 2H +3H

Page 19: Nuclear reactions

Need to overcome electric repulsion

+

+Protons need ~2MeVenergy to get within10-15 m of each other(where strong nuclear force can be felt)

This requires super-hightemperatures (severalMillion degrees). Such hightemperatures exist in thecore of the Sun or in an Atomic-Bomb explosion

Page 20: Nuclear reactions

H-bomb: powered by nuclear fusion

Nuclear fission bomb “detonator”produces the high temperature

required to initiate fusion processes

Nuclear fusion bomb

Page 21: Nuclear reactions

Brighter than 1000 suns

1000 times the power of an A-bomb!!

Page 22: Nuclear reactions

Dangers of teaching nuclear physics

Oh, and I suppose it

was me who said ‘what

harm could it be to give the

chickens a book on nuclear

physics?’

Page 23: Nuclear reactions

Fusion in the Sun

The core temperatureis ~14 million degrees

Here a tiny fractionof the protons haveenough thermal energyto undergo fusion

Page 24: Nuclear reactions

Solar fusion

processes

+ 5.5 MeV

+ 1.4 MeV

+ 12.9 MeV

Page 25: Nuclear reactions

pp-cycle

6 protons 4He + 2 protons + 2 “positrons” + 2neutrinos

Page 26: Nuclear reactions

Energy balance in the pp-cycle

4He

25 MeV KE heat 4 protons

+ 2 neutrinos

Page 27: Nuclear reactions

How do we know what goes oninside the Sun?

Page 28: Nuclear reactions

Superkamiokande

Page 29: Nuclear reactions

Superkamiokande

Page 30: Nuclear reactions

Direction of neutrinosdetected in Superkamiokande

Page 31: Nuclear reactions

Sun as seen by a neutrino detector

Page 32: Nuclear reactions

Neutrinos come directly from solar core

Page 33: Nuclear reactions

Neutrinos are everywhere