An Introduction To Thermonuclear Fusion

Front 1

Relationship between mass and energy

Back 1

Einstein:
E=mc^2
matter is frozen energy

Front 2

Modern Conservation Law

Back 2

sum total of mass and energy is conserved

Front 3

How much energy can a tiny mass of sun produce?

Back 3

LOTS OF ENERGY, the sun can remain hot and unchanging for billions of years

Front 4

How does the conversion of mass to energy occur?

Back 4

1. spontaneously, energy released in the radioactive breakdown of naturally occurring elements like Uranium

Front 5

Another way of conversion of mass to energy?

Back 5

happens in great effectiveness due to simply because it is HOT there, allows serious of
THERMONUCLEAR REACTIONS

Front 6

How is helium produced in the sun?

Back 6

hydrogen atoms are fused together to make helium, a lump of helium less massive than four hydrogens that were joined together, and the loss in mass appears in energy

Front 7

HYDROGEN --> HELIUM, cannot happen unless very hot environment? why?

Back 7

hydrogen nuclei, which are protons, repel each other since have same positive electrical charge, PROTONS WILL ONLY FUSE TOGETHER IF THEY CAN BE MADE TO RACE ABOUT AT HIGH SPPED AND SLAM INTO ONE ANOTHER, once they get very close, then another force takes over

Front 8

Where were the heavier elements created?

Back 8

in stars

Front 9

Why is the sun SO stable?

Back 9

squeezing makes it hotter in the middle, which increases the sustaining pressure, it also increases the thermonuclear reactions, which releases more energy

Front 10

Why are the thermonuclear reactions taking place between the nuclei?

Back 10

since the material in the centre of the sun is completely ionized plasma (hot gas where the electrons are stripped off)

Front 11

What happens in fission?

Back 11

-a big nucleus breaks into two or more smaller pieces
-the sum of the masses of the pieces is less than the original, with the difference showing up in the form of energy

Front 12

What happens in fusion?

Back 12

-two or more small lumps are merged together to form a heavier nucleus
-the new lumps weighs less than the sum of the small pieces, and energy is released

Front 13

Binding energy curve

Back 13

critical point: shape
steepness @ low-atomic number end tell us that merging little pieces (hydrogen to for helium) you get out ALOT of energy
-breaking a lump, like uranium into smaller pieces yields less energy but still a lot (atomic bomb)

Front 14

fission occurs...

Back 14

-stay neutron hits the uranium nucleus and makes it unstable
uranium breaks into two big nuclei (Krypton and Barium) and releases two or more neutrons, then sparks another fission

Front 15

What happens if uranium atoms are close together?

Back 15

CHAIN REACTION, release LOTS of energy

Front 16

What happens if TOO many uraniums in close proximity (more than the critical mass)?

Back 16

reaction is uncontrollable and you have an atomic bomb

Front 17

Do hydrogen bombs rely on chain reactions?

Back 17

NO.
you have to have ultra-hot material, with colossal release of energy

Front 18

What is the difference between atomic and hydrogen bomb?

Back 18

atomic: accumulate the fuel into a lump that exceeds the critical mass
hydrogen: fuel needs to be heated to millions of degrees before the reaction will start, in fact, the "fuse" in hydrogen bomb is a atomic bomb

Front 19

FUSION products vs. FISSION products?

Back 19

fusion: essentially limitless energy and not produce dirty waste products
fission: dirty waste products since hard to confine gas which is temperature of millions of degrees

Front 20

pp/ proton-proton cycle

Back 20

cycle produces positrons ("ant-matter") and neutrinos

Front 21

What are positrons?

Back 21

carry off positive charge of two of the original protons
-positrons short lived
-promptly run into electrons and annihilate completely, forming gamma rays (radiant energy)

Front 22

What are the medical application of positrons?

Back 22

PET (positron emission tomography)
-created by decay of trace elements of radioactive elements introduced into the body

Front 23

Law of the Conservation of Mass and Energy

Back 23

if mass vanishes, an exactly equivalent amount of energy must appear

Front 24

How much percentage does the sun convert it's mass to energy?

Back 24

less than one percent

Front 25

How do we know the relative abundance of hydrogen atoms?

Back 25

1. spectrum of the sun
2. composition of things like comets and meteorites
3. composition of the planets Jupiter and Saturn
4. relative abundances of at least the heavier element from moon rocks and earth rocks
5. spectra of other stars and gas clouds

Front 26

Ratio of lithium to hydrogen atoms?

Back 26

10^10 hydrogen atoms for one lithium atom

Front 27

What elements are rare?

Back 27

heavier elements

Front 28

"odd-even" effect

Back 28

-carbon is abundant (6) and oxygen (8) BUT nitrogen (7) is less abundant


can be explained: as a consequence of nuclear reaction in stars

Front 29

Where in the sun is the energy generated by nuclear reactions most?

Back 29

91% of energy generated by nuclear reactions occurs within the innermost twenty percent of the sun's radius

Front 30

How does the energy in the innermost core diffuse out?

Back 30

radiative transport: photons make their way through the material, without the material itself moving much)

Front 31

How does the energy in outermost parts of the sun diffuse out?

Back 31

convective transport: large churning motions in the material itself, just as in a pot boiling soup

Front 32

What sort of radiation (light) does it emit?

Back 32

sun emits yellow (visible) light because of its high temperature, whereas your much cooler human body emits infrared radiation

Front 33

What happens if energy is put into the material? (heat it)

Back 33

1. moderate temperatures: breaking of the inter-atomic or intermolecular bonds , still held together but not in a rigid structured way
2. @500K: molecules and atoms can escape liquids so that the particles are now moving freely as a gas
3. @5000K: temperatures like that at the sun, many atoms are therefore ionized, free moving charged particles
typically motions of charged particles give rise to magnetic fields called plasma

Front 34

@ 10million K, where is this temperature found?

Back 34

CORE OF A STAR
all atoms are completely ionized: all electrons are torn off from positively charged nuclei by virtue of vigorous collisions
-thermonuclear reactions can take place and a new source of energy can be tapped, the energy source of the stars

Front 35

What is a deuterium?

Back 35

"HEAVY WATER", a hydrogen with an extra neutron

Front 36

Sun's energy-generation going..

Back 36

keeps a little bit to sustain itself against continuing gravitational contraction

Front 37

what happens in an atomic bomb

Back 37

1.-lump of fuel, one nuclei spontaneously fissions and large amounts of energy released +couple of neutrons
2. new neutrons individually run into yet another uranium nucleus, chain reaction
3.moderators that control speed of the neutrons to not explode
4.if want explosion, fissionable material which exceeds the so-called critical mass

Front 38

What happens in an hydrogen bomb?

Back 38

-need to heat hydrogen fuel to force hydrogen nuclei together
-atomic bomb is used as a fuse for hydrogen bomb
-in the sun: the reaction rates are steady and indeed rather slow

Front 39

What happens in a pp chain?

Back 39

1. two protons combine
2. third one comes in
-parallel sequence occurs somewhere else so six protons altogether are processed
3. lumps of light helium merge to liberate two protons so the net effect is FOUR PROTONS --> ONE HELIUM

Front 40

Positron..

Back 40

-anti-matter
-'mirror particle' of an electron
-when meets electron their mass converted ti pure radiant energy (gamma rays)