# Bragg angles

1. Apr 13, 2007

### debwaldy

1. The problem statement, all variables and given/known data
Diamond crystallises with a cubic unit cell and the lattice is face centred.Calculate the respective angles(in degrees) at which the lowest first four reflections are allowed from a polycrystalline specimen of diamond(given (wavelength)^2/4a^2 = 0.0467,where a = unit cell parameter)

2. Relevant equations
n*wavelength = 2dsin(theta)
d^2 = a^2/(h^2+k^2+l^2)

3. The attempt at a solution
I tried working backwards and used the fact that i knew that 0.0467 is the HCF of the equation: sin^2(theta) = ((wavelength)^2/4a^2)*(h^2+k^2+l^2)
because it is fcc it means that 4r = (2^0.5)*a

I took the square root of 0.0467 = and then the inverse sin of this in order to obtain one angle,:

(0.0467)^0.5 = 0.2161
sin^-1(0.2161) = 12.48degrees
The problem is i dont know how to calculate the other three angles?
should i multiply 0.0467 by 2,then repeat the process to get the next angle or?any help would be much appreciated
thanks debs