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**1. The problem statement, all variables and given/known data**

Aluminium metal is FCC with lattice parameter a=0.405nm. suppose that n Al crystal is illuminated by a beam of neutrons with wavelength [tex]\lambda[/tex]= 1.078 angstrom

(a) determine the first 10 allowed reflections, in order of increasing scattering vector, counting (101),(110),(1bar01) as one reflection.

(b) tabulate the scattering vector, kappa, the scattering angle (2theta), the miller indices and the quantity h^2+k^2+l^2.

**2. Relevant equations**

2d

_{hkl}sin(theta)=lambda

bragg's law: 2dsin(theta)=N*lambda

d

_{hkl}= a/sqrt(h^2+k^2+l^2)

kappa = 4*pi*sin(theta)/lambda

3. The attempt at a solution[/b]

i found the structure factor to be S

_{basis}= f(1+exp(-i*pi(h+k))+exp(-i*pi(l+k))+exp(-i*pi(h+l))

and if h,k,l re all odd or all even then S

_{basis}=4f otherwise S

_{basis}= 0

how do i find the first 10 allowed reflections??

and how do i do it in order of increasing scattering vector if i havent found those values yet??

really stuck....PLEASE HELP!