Effective neutron multiplication factor

[Physicsissuef]

Can somebody please explain effective neutron multiplication factor, with example? So when k=1, k>1, k<1 , please give me some example.

$$k=\frac{N_2}{N_1}=\frac{N_3}{N_2}=...=\frac{N_i}{N_i_-_1}$$

 

[Physicsissuef]

malawi, somebody helppp please?

 

[malawi_glenn]

but hey you asked just 4h ago! Remember that the majority of PF-users are from the states and they sleeping at the moment..

Also, again, if this is course work post at approriate subforum. Otherwise, why is this (and other questions that you ask here) urgent??


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

 

[Physicsissuef]

I read that but still can't understand what does it mean to keep constant the neutrons number. Please give me any example.

 

[malawi_glenn]

I read that but still can't understand what does it mean to keep constant the neutrons number. Please give me any example.

I don't understand what you don't understand, please clarify.

Why is it so hard to understand that in order to retain a ciritical chain reaction, k must be equal to 1.

Why should I construct an example for you if you can't even answer my questions:

"Also, again, if this is course work post at approriate subforum. Otherwise, why is this (and other questions that you ask here) urgent??"

 

[Physicsissuef]

So in the first generation must be there 1 neutron, and in the second generation must have 1 neutron.

$$\frac{1}{1}=\frac{2}{2}=\frac{3}{3}=\frac{4}{4}...$$, like this?

But as I know chain reaction goes with 1 neutron, then 3 neutrons, 9, 27...

 

[malawi_glenn]

yes an over-critical chain reaction does that, but an exactly critical has k=1

 

[Physicsissuef]

In my book have same picture like this, and it says, this is http://media.wiley.com/assets/83/12/fg0-7645-5430-1_0503.jpg"

 

[malawi_glenn]

yes, but they have not specidied what KIND of chain reaction it is..

there exists 3kinds of chain reactions:
under critical, cirical & over critical

 

[Physicsissuef]

Ok, I understand now.
And look at this formula http://www.tpub.com/content/doe/h1019v2/css/h1019v2_32.htm":

To have constant chain reaction, let's say the k_eff will be (by using http://dtirp.dtra.mil/Products/products/images/941p-fig9.jpg" :

$$\frac{2}{1+1}$$, or what?

 

[Physicsissuef]

or maybe $$\frac{1}{1+0}$$? Probably "neutron production from fission in one generation" means the neutron which is not absorbed nor lost to the system, right?

 

[malawi_glenn]

its 2/(1+1)

2 neutrons are produced, one is absorbed, one is lost in the system.

 

[Physicsissuef]

In the preceding one is lost...