Where did the energy for this come from? The nucleus.

Unstable nuclei … the beginnings of nuclear medicine.

Wilhelm Conrad Röntgen

E = mc2

+ energy

VI. Fission and Fusion

A. In nuclear reactions, the amount of mass and energy

must be conserved. In energy-producing reactions:

reactants: products:

1 or more 1 or more particles particles

more mass less mass

The total mass of the products is less. The “missing”

mass is called the mass defect. It is converted into

energy according to Einstein’s famous equation:

m = mass in kilogramsc = speed of light in a vacuum = 3 x 108 m/s

How were these things explained?

The energy appears as gamma radiation and as the

kinetic energy of the product particles, as they move off

at high speeds.

The energy produced by nuclear reactions is far

greater than that of ordinary chemical reactions.

Ex. chemical:

Burn 1 gram of methane: E = 55,600 J

nuclear:

Convert 1 gram of any matter into pure

energy by E= mc2 = (1 x10-3 kg)(3 x 108 m/s)2

=

Gram for gram, the nuclear reaction releases over a

billion times more energy.

9 x 1013 J

Electron powered aschemicals burn. Nucleus powered as

nuclei lose mass burn.

B Fission begins with the capture of a neutron by a

heavy element, making it unstable. It fissions (splits).

The products are middle-weight nuclei, n’s + energy.

Ex. A typical reaction is:

before: after:

mass:

U-235n

Ba-142

Kr-91

n

n

n

1 + 235 142 + 91 + 3(1)

charge: 0 +92 56 + 36 + 3(0)

=

=

U92

235n0

1+ Ba

56

142Kr

36

91+ n

0

1+ 3

Is charge conserved?

Is mass conserved?

YES: The # of nucleons (n and p) is __________________.

NO: The nucleons in Ba and Kr are ________________!!!

___________mass!_________mass!

The “missing” mass became ___________ ( E = mc2)

in the form of _______ of Ba, Kr, n and _________________.

This energy can be used to heat water into steam

in a ____________________ or 2/ ________________________

in an _______________________ .

Yes.

Yes and no.the same

smaller

lessmore

KE radiation

to kill people

energy

power plant

atomic bomb

U92

235n0

1+ Ba

56

142Kr

36

91+ n

0

1+ 3

The neutron is easily absorbed because it is neutral.

A moderator slows the neutrons to make capture easier.

A chain reaction occurs when the neutrons produced

in one reaction are used to start new

reactions.

________________– used to

____________the reaction

by ____________neutrons

absorbing

limit

control rods

n

U-235 or Pu-239

Design of a nuclear reactor:

First atomic bomb test: “Trinity” July 16, 1945, at Alamogordo, New Mexico was set off by imploding a subcritical mass of plutonium.

20 kilotonsof TNT

Today:

First military use of atomic weapons:Hiroshima, Japan, August 6, 1945.

Hiroshima

Little Boy use U-235

It contained 64 kg of uranium, of which less than a kilogram underwent nuclear fission, and of this mass only 0.6 g was transformed into energy

Nagasaki – 3 days laterReplica of Fat Man:

Yield: 21 kilotons of TNT

Method: implosion of Pu

Churchill = Fat ManRoosevelt = Thin Man Little Boy after design changeStalin = The Butcher Knife

Indian Point: 1970 MW

Nine Mile Point:1756 MW

2 plantsin Oswego

New York Nuclear Power Plants:

James Fitzpatrick:844 MW

near Oswego

R. E. Ginna:498 MW

on Lake Ontarioeast of Rochester

C. Fusion occurs when light nuclei combine to form

heavier ones. However, extremely high temperatures

and pressures are needed because the positive charges of

the nuclei repel each other. Fusion only occurs in stars.

Ex. A typical reaction:

charge

mass

before: after:

H-2

H-2

He-3

n

2 + 2 3 + 1 =

1 + 1 2 + 0 =

H1

2H

1

2 He2

3n

0

1+ +

lessmore

Is charge conserved?

Is mass conserved?

YES: The number of nucleons (n and p) is the same.

NO: The nucleons in He are smaller!!!

Yes.

Yes and no.

The “missing” mass became energy ( E = mc2)

in the form of KE of He and n and radiation.

____________mass!_________mass!

H1

2H

1

2 He2

3n

0

1+ +

How can both fission and fusion release energy?Both result in less mass.

Fission:

Big nuclei can be fissioned to produceenergy b/c the products have less mass.

Fusion:

Notice: In both fission and fusion, iron (Fe) is the lowest point on the curve. Its nucleons are smallest.

Small nuclei can be fusioned to produceenergy b/c the products have less mass.

Number of fission reactors in the world:

Number of fusion reactors in the world:

439 reactors in 31 countries150 naval vessels6% of world’s energy15% of world's electricity

In the US: 10% of fission energy is supplied by using old Soviet warheads.

Recognizing fission vs. fusion reactions:

fission: fusion:

BIG + n smallnuclei

BIGGERNUCLEI

smallernuclei

The products of fusion are much less radioactive

than the products of fission. Also, H is much more

abundant than U. Moreover, fusion yields more

energy per unit mass. This is why fusion power is

more desirable than fission. Alas, currently we have

no

fusion plants but many hydrogen bombs.

i splits u unites

First hydrogen bomb test

The Soviet Tsar bomb:57 megatons (largest ever)

A hydrogen bomb uses fusion, the sameprocess that powers the Sun.It is more powerful than a fission bomb.