# Effective neutron multiplication factor

1. Apr 13, 2008

### Physicsissuef

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

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

2. Apr 13, 2008

### Physicsissuef

3. Apr 13, 2008

### 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

4. Apr 13, 2008

### Physicsissuef

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

5. Apr 13, 2008

### malawi_glenn

I dont understand what you dont 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??"

6. Apr 13, 2008

### 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....

7. Apr 13, 2008

### malawi_glenn

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

8. Apr 13, 2008

### Physicsissuef

9. Apr 13, 2008

### 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

10. Apr 13, 2008

### Physicsissuef

Ok, I understand now.
And look at this formula here:

To have constant chain reaction, lets say the k_eff will be (by using this picture):

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

11. Apr 14, 2008

### 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?

12. Apr 14, 2008

### malawi_glenn

its 2/(1+1)

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

13. Apr 14, 2008

### Physicsissuef

In the preceding one is lost...