# Find Number of Neutrons in a Copper Bar given volume of bar?

1. Oct 4, 2009

### viper2308

The problem statement, all variables and given/known data

A bar of copper has dimensions 0.5605 ft. x 3.545 in x 5.722 cm. The density of copper is 8.921 g / cm3. Copper contains 2 isotopes, 63Cu (69.09% abundant) and 65Cu (30.91% abundant). How many neutrons are in the bar of copper?

The attempt at a solution

I took the volume: 11.37cm^3 x 8.921g/cm^3 x 6.022E23 neutrons/63.546g Cu = 9.612E23 neutrons.

Is this right? I think I need to use the isotope information somewhere but I don't know where or how.

2. Oct 4, 2009

### mgb_phys

You have already used the isotope information, 63.546g is the weighted average of the two isotopes

3. Oct 4, 2009

### viper2308

Ok I just got the from the periodic table. So the isotope information is unnecessary?

4. Oct 4, 2009

### mgb_phys

>63Cu (69.09% abundant) and 65Cu (30.91% abundant)
Means that a sample = 63 * 69.09/100 + 65 * 30.91/100 = 63.618
You should probably use this value in your calcs.