Transcript Nuclear Changes

Nuclear Changes
Mr. Bean
Astronomy
1
7/21/2015
Key terms- What is Radioactivity?




2
Radioactivity– process by which an unstable nucleus
emits one or more particles or energy in the form of
electromagnetic radiation
Nuclear radiation- charged particles or energy emitted
by an unstable nucleus
Alpha Particle- A positively charged particle, emitted by
some radioactive nuclei, that consists of two protons
and two neutrons
video
7/21/2015
Key terms (continued)



3
Beta Particle- an electron emitted during the
radioactive decay of a neutron in an unstable
nucleus
Gamma Ray- High- energy electromagnetic
radiation emitted by a nucleus during
radioactive decay
Neutron Emission – The release of a highenergy neutron by some neutron-rich nuclei
during radioactive decay
7/21/2015
Positron
4
Neutrino
7/21/2015
Radioactive decay


Radioactive decay is the
spontaneous release of energy in
the form of radioactive particles
or waves.
This decay results in a decrease
over time of the original amount
of radioactive material.
A
Z
X
A=
Z=
X=
5
7/21/2015
Nuclear Decay: a- decay

Nucleus gives up two protons and two neutrons
A
Z
226
88
Ra Rn He
222
86
217
89
225
89
221
83
6
X
4
2
Ac X  He
A
Z
4
2
Ac X  Fr
A
Z
221
87
Bi X  He
A
Z
4
2
7/21/2015
Nuclear Decay: b-particle



Nucleus gains a proton and loses a neutron
For convenience, an electron has an atomic # = -1
b-particle essentially has no mass
14
6
12
5
B C X
63
28
7
C147 N  10e
12
6
A
Z
Ni X  e
A
Z
0
1
7/21/2015
Positron
23
12𝑀𝑔
→ 𝐴𝑍𝑋 + 01𝑒
What is the unknown?
8
7/21/2015
Nuclear Fission and Fusion



9
Strong Nuclear force- the interaction that binds
protons and neutrons together in a nucleus
Fission- the process by which a nucleus splits
into two or more smaller fragments, releasing
neutrons and energy
Neutrons released by fission can start a chain
reaction
7/21/2015
Nuclear Chain Reaction




10
A series of fission processes in which the
neutrons emitted by a dividing nucleus cause
the division of other nuclei
The chain reaction principle is used in the
nuclear bomb. Two or more masses of
uranium-235 are contained in the bomb.
Masses are surrounded by a powerful chemical
explosive.
Critical mass is created
7/21/2015
Critical mass



11
Refers to the minimum amount of a substance
that can not only undergo a fission reaction but
also sustain a chain reaction.
If the amount of fissionable substance is less
than the critical mass, a chain reaction will not
continue.
Nuclear bomb, a chain reaction is started and
proceeds very quickly.
7/21/2015
Fission: Nuclear Chain Reaction
12
7/21/2015
Nuclear Fusion



13
The process in which light nuclei combine at
extremely high temperatures, forming heavier
nuclei and releasing energy
Stars- energy is primarily produced when
hydrogen nuclei combine, or fuse together, and
release tremendous amounts of energy.
Temperature provide the energy needed to
bring hydrogen nuclei together.
7/21/2015
Fusion vs. Fission


14
Nuclear fission* is the splitting of one
atom into more than one.
Nuclear fusion* is the combining of two
or more atoms into one.
7/21/2015


15
Nuclear fission produces radioactive*
waste
Nuclear fusion is a source of tremendous
energy*.

Nuclear fusion produces so much heat
that we cannot contain the reaction.

It turns out that fusion yields energy for
low mass elements while fission releases
energy for high mass elements.
7/21/2015
Energy is released during fission




16
One mole of trinitrotoluene (TNT) is about
4.8 x 10-18 J of energy
Einstein, E = mc2, m = mass, c = speed of light
c = 3.0 x 108 m/s or 186,000 mi/s
1 kg of matter is 9 x 1016 J of energy, which is
more chemical energy than 8 million tons of
TNT
7/21/2015
Four Fundamental Forces of Nature





17
Force
Gravity
Electromagnetic
Weak Nuclear
Strong Nuclear
Strength
1
1042
1038
1044
Range
Infinite
Infinite
Subatomic
Subatomic
7/21/2015
Four Fundamental Forces of Nature




18
Gravity is one of 4 fundamental forces of nature.
By fundamental we mean that so far, we've never seen
any phenomenon that couldn't be explained by one of
these 4 forces.
The energy released by fusion in the form of light is
due to another fundamental force, the electromagnetic
force.
The process of fusion requires the other 2-fundamental
forces which work only in the subatomic realm, the
weak nuclear force and the strong nuclear force.
7/21/2015
Electromagnetic Force

19
ELECTROMAGNETIC FORCE 1042
=1,000,000,000,000,000,000,000,000,000,000,000,000,000,000 times
STRONGER than Gravity!!
7/21/2015
Fusion in the stars





20
In the fusion reaction, a little bit of the star's mass is sacrificed by
being turned into pure energy.
Here's how it works. Protons normally don't get very close
together since their positive charges cause the electromagnetic
force to repel them.
The electromagnetic force is 1042 times stronger than the force of
gravity between them!
It takes very high temperatures and pressures for protons to be
“near” each other.
At a temperature of at least 20 million degrees, protons achieve a
speed of just over 1 million miles per hour. If they collide at this
speed, they can get as close to each other as one trillionth of a
centimeter.
7/21/2015
Fusion in the stars
21
7/21/2015
Fusion in the stars



22
The strong force, once it turns
on, is 100 times stronger than the
electric force keeping the protons
apart.
If the protons get within one
trillionth of a centimeter of each
other, the strong force suddenly
kicks in and slams them together.
All in all, 4 protons have to be
“rammed” together by the strong
force in order to make one
helium atom.
7/21/2015