A specimen of nickel powder is studied by X—ray di

正确答案：Ni is FCCso the next plane in the sequence of reflections is(311)．Let’s use Bragg’s Lawλ＝2d_hklsinθ to determine the angle of reflection for(311)． d₃₁₁＝a／ λ＝2_hklsinθ θ＝sin^-1(λ／2d_hkl)＝sin^-1(1．08)＝undefined Thusthe only way to measure reflections from planes of higher Miller index than(220)is to change the target in the X-ray generator to a heavier element in order to decrease the wavelength of the radiation．In this wayit is possible to satisfy Bragg’s Law．
NiisFCC,sothenextplaneinthesequenceofreflectionsis(311)．Let’suseBragg’sLaw,λ＝2dhklsinθtodeterminetheangleofreflectionfor(311)．d311＝a／λ＝2hklsinθθ＝sin-1(λ／2dhkl)＝sin-1(1．08)＝undefinedThus,theonlywaytomeasurereflectionsfromplanesofhigherMillerindexthan(220)istochangethetargetintheX-raygeneratortoaheavierelementinordertodecreasethewavelengthoftheradiation．Inthisway,itispossibletosatisfyBragg’sLaw．