a few questions on nuclear fusion

[the guy]

i have a few questions about nuclear fusion....

 

by the way please keep your answers simple as, much as i would love to, i'm afraid i do not study physics

 

and please refer to the question you are answering in your reply

 

Q.1. 'The fusion of two nuclei with lower masses than iron generally releases energy while the fusion of nuclei heavier than iron absorbs energy' - does this mean that the lighter you get, the more energy is released? (and visa versa when heavier than iron)

 

Q.2. in the case of iron does it release or absorb energy?

 

Q.3. in hydrogen fusion, does it work if you use H-1?

 

Q.4. if 'yes' to question 3, does it release more, less or the same amount of energy? and does it release radiation?

 

Q.5. if 'yes' to question 3, what are the products?

 

Q.6. if 'no' to question 2, why not?

 

Q.7. does helium fusion work with He-4 and if so does this release radiation? and what are the products?

[Janus]

i have a few questions about nuclear fusion....

 

by the way please keep your answers simple as, much as i would love to, i'm afraid i do not study physics

 

and please refer to the question you are answering in your reply

 

Q.1. 'The fusion of two nuclei with lower masses than iron generally releases energy while the fusion of nuclei heavier than iron absorbs energy' - does this mean that the lighter you get, the more energy is released? (and visa versa when heavier than iron)

Roughly speaking, yes

 

Q.2. in the case of iron does it release or absorb energy?

Absorb

 

Q.3. in hydrogen fusion, does it work if you use H-1?

It can, but it is more difficult to do.

 

Q.4. if 'yes' to question 3, does it release more, less or the same amount of energy?

Than what? The H-H reaction releases 0.42 Mev as compared to the 17Mev released by the H2-H3 reaction used in thermonuclear weapons.

 

and does it release radiation?

yes

 

Q.5. if 'yes' to question 3, what are the products?

H2 + positron + neutrino

 

Q.7. does helium fusion work with He-4 and if so does this release radiation? and what are the products?

 

If you fuse two He-4 nuclei, you get beryllium-8, which is unstable and breaks back down into two He_4 nuclei very quickly. If however, another He-4 fuses with the Be-8 before it decays, then you can get C-12.

[the guy]

so would He-4 fusion not be very violent? or very violent? or a bit violent? or what? when i say violent i mean if it was an uncontrolled reaction, like it is in an h-bomb

[Moontanman]

so would He-4 fusion not be very violent? or very violent? or a bit violent? or what? when i say violent i mean if it was an uncontrolled reaction, like it is in an h-bomb

 

 

 

It would seem some stars do indeed go critical and a runaway nuclear fusion reaction disrupts the star completely.

 

 

http://en.wikipedia.org/wiki/Supernova

 

 

 

Type Ia

 

Formation of a type Ia supernovaMain article: Type Ia supernova

There are several means by which a supernova of this type can form, but they share a common underlying mechanism. If a carbon-oxygen[nb 2] white dwarf accreted enough matter to reach the Chandrasekhar limit of about 1.38 solar masses[4] (for a non-rotating star), it would no longer be able to support the bulk of its plasma through electron degeneracy pressure[39][40] and would begin to collapse. However, the current view is that this limit is not normally attained; increasing temperature and density inside the core ignite carbon fusion as the star approaches the limit (to within about 1%[41]), before collapse is initiated.[4] Within a few seconds, a substantial fraction of the matter in the white dwarf undergoes nuclear fusion, releasing enough energy (1–2 × 1044 joules)[42] to unbind the star in a supernova explosion.[43] An outwardly expanding shock wave is generated, with matter reaching velocities on the order of 5,000–20,000 km/s, or roughly 3% of the speed of light. There is also a significant increase in luminosity, reaching an absolute magnitude of -19.3 (or 5 billion times brighter than the Sun), with little variation.[44]

[Janus]

so would He-4 fusion not be very violent? or very violent? or a bit violent? or what? when i say violent i mean if it was an uncontrolled reaction, like it is in an h-bomb

 

The He-4 to Be-8 reaction is endothermic, that is it takes energy (92 Kev) to cause it to happen. It takes the third He-4 nuclei to fuse and form Carbon-12 before you get a net release of energy (7.37 MeV). It takes 3 He-4 nuclei fusing to liberate 7.37 Mev, while it takes 4 H-1 nuclei in the proton-proton chain (the major reaction of the Sun) to ultimately release ~19 Mev, so thats 2.46 Mev per nucleon for He-4 fusion and 4.75 Mev per nucleon for the proton-proton chain. Again, compare this to the 8.5 Mev per nucleon liberated by the H-3, H-4 reaction of a thermonuclear bomb.

[the guy]

if, somehow, only two hydrogen atoms fused in a bomb, would it release enough energy to set of the chain reaction of the other atoms?

 

also, if you had a hydrogen bomb, and next to it a hydrogen tank, would the hydrgogen in the tank undergo fusion aswell? or would it just combust?

[swansont]

if, somehow, only two hydrogen atoms fused in a bomb, would it release enough energy to set of the chain reaction of the other atoms?

 

also, if you had a hydrogen bomb, and next to it a hydrogen tank, would the hydrgogen in the tank undergo fusion aswell? or would it just combust?

 

 

The cross-section for proton-proton fusion is exceedingly small. In the sun, the reaction rate means the average proton fuses roughly once every billion years. (It has to be slow, or else the sun would have burned out long ago)

 

http://csep10.phys.utk.edu/astr162/lect/energy/ppchain.html

 

A billion years is 3 x 10^16 seconds, so the reaction rate (under those conditions) is the inverse of that. If you had a mole of hydrogen gas in the tank, and the bomb reaction was similar to the conditions of the sun and took a microsecond, you might expect to have ~100 p-p fusion reactions.

 

So it would mostly combust.

[the guy]

in a hydrogen bomb, do all the protons fuse? or are there some left unfused? if the latter then what percentage is left unfused?

[swansont]

in a hydrogen bomb, do all the protons fuse? or are there some left unfused? if the latter then what percentage is left unfused?

 

Hydrogen bombs use tritium. I don't know what the efficiency is, but the much larger cross section means that it will be a lot bigger than p-p reactions.

[mechaniker]

It is hard ! here is my thinks ! http://mecanicosaereos.blogspot.com/2011/11/nuclear-fusion-is-it.html