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  4. /Bragg's Law Calculator

Bragg's Law Calculator

Calculator

Results

Wavelength

154.1106

pm

Wavelength

1.5411

angstrom

Bragg Angle theta

15.8

deg

2-theta

31.6

deg

d-spacing

283

pm

d-spacing

2.83

angstrom

Bragg Ratio λ/(2d)

0.27228

sin(theta)

0.27228

Results

Wavelength

154.1106

pm

Wavelength

1.5411

angstrom

Bragg Angle theta

15.8

deg

2-theta

31.6

deg

d-spacing

283

pm

d-spacing

2.83

angstrom

Bragg Ratio λ/(2d)

0.27228

sin(theta)

0.27228

Bragg's Law Calculator computes the relationship between X-ray wavelength, crystal plane spacing, and diffraction angle using Bragg's law: n*lambda = 2*d*sin(theta). This fundamental equation in crystallography, derived by William Lawrence Bragg and his father William Henry Bragg in 1913 (Nobel Prize in Physics 1915), is the basis for X-ray crystallography — the most powerful method for determining molecular and crystal structures.

When X-rays strike a crystal, the regularly spaced atomic planes act as diffraction gratings. Constructive interference (and therefore a detectable diffracted beam) occurs only when the path difference between waves reflected from adjacent planes equals an integer multiple of the wavelength: n*lambda = 2*d*sin(theta), where d is the interplanar spacing, theta is the angle between the incident beam and the crystal plane (the Bragg angle), and n is the order of diffraction.

By measuring the angles at which diffracted beams occur (using a diffractometer or exposing film/detector), the d-spacings of crystal planes can be calculated. Combined with knowledge of the crystal symmetry, the full three-dimensional arrangement of atoms can be determined. X-ray crystallography has solved the structures of over 170,000 proteins, DNA, thousands of drugs, minerals, and nanomaterials.

In X-ray powder diffraction (XRD), a finely ground polycrystalline sample is used. The resulting diffraction pattern (a plot of intensity vs 2*theta) is a fingerprint of the crystalline phase composition, used for phase identification, crystallite size analysis (Scherrer equation), and residual stress measurement in materials science and engineering.

Common X-ray sources: Cu K-alpha radiation at 154.2 pm (1.542 angstrom), Mo K-alpha at 71.1 pm (0.711 angstrom), used for different applications depending on required penetration depth and angular range.

Visual Analysis

How It Works

Bragg's law: n*lambda = 2*d*sin(theta). To find wavelength: lambda = 2*d*sin(theta)/n. To find d-spacing: d = n*lambda/(2*sin(theta)). To find angle: theta = arcsin(n*lambda/(2*d)). The detector measures 2*theta (twice the Bragg angle). Convert pm to angstrom by dividing by 100.

Understanding Your Results

d-spacings in crystals range from ~100 pm (tight atomic planes) to >1000 pm (protein unit cells). Cu K-alpha (154.2 pm) gives Bragg peaks at theta between 5 and 70 degrees for most common minerals and metals. Small d gives large theta (high-angle peaks). Each peak in an XRD pattern corresponds to a specific set of crystal planes (hkl Miller indices).

Worked Examples

NaCl (200) planes with Cu K-alpha

Inputs

n order1
d spacing pm282.8
theta deg15.8
solve forlambda

Results

wavelength pm154.1
two theta deg31.6
wavelength angstrom1.541
d calc pm282.8

The (200) planes of NaCl (d = 282.8 pm) give a first-order Bragg peak at theta = 15.8 degrees with Cu K-alpha radiation (154.2 pm). The powder diffractogram shows the peak at 2-theta = 31.6 degrees.

Protein Crystal, Large d-spacing

Inputs

n order1
d spacing pm3000
theta deg1.48
solve forlambda

Results

wavelength pm154.5
two theta deg2.96
wavelength angstrom1.545
d calc pm3000

Protein crystals have large unit cells with d-spacings of nanometers. At d = 3000 pm (3 nm), the first Bragg peak occurs at only 1.48 degrees (2-theta ~ 3 degrees), requiring small-angle X-ray equipment.

Frequently Asked Questions

n*lambda = 2*d*sin(theta): constructive interference of X-rays occurs when the path difference between rays reflected from adjacent crystal planes equals n wavelengths. It relates X-ray wavelength, crystal plane spacing, and diffraction angle.

The perpendicular distance between parallel crystal planes with the same Miller indices (hkl). For a cubic crystal with lattice parameter a: d_hkl = a/sqrt(h^2+k^2+l^2). Measuring d-spacings from XRD gives the lattice parameters.

In X-ray diffractometry, the detector moves to twice the Bragg angle (2*theta) from the incident beam direction to collect the diffracted beam. XRD patterns are plotted as intensity vs 2-theta, typically from 5 to 80 degrees for powder diffraction.

Crystal plane spacings are 0.1-1 nm, comparable to X-ray wavelengths (0.05-0.25 nm). Visible light wavelengths (400-700 nm) are far too large to be diffracted by atomic planes.

Phase identification (mineral/drug analysis), crystal structure refinement (Rietveld method), crystallite size from peak broadening (Scherrer equation), residual stress analysis, and thin film characterization in materials science and pharmaceuticals.

John Kendrew and Max Perutz solved the first protein structures (myoglobin and hemoglobin, respectively) in 1958-1960, earning the 1962 Nobel Prize in Chemistry. Watson and Crick used X-ray data from Rosalind Franklin to propose the DNA double helix structure in 1953.

Tau = K*lambda/(beta*cos(theta)), where tau is the crystallite size, K is a shape factor (~0.9), lambda is the X-ray wavelength, and beta is the full width at half maximum of the diffraction peak. Broad peaks indicate small crystallites.

Neutrons (with wavelengths of 50-300 pm, similar to X-rays) are diffracted by crystals following Bragg's law. Neutrons interact with atomic nuclei (not electrons), making them sensitive to light atoms (H, Li) invisible to X-rays and to magnetic ordering in materials.

Yes. Electrons accelerated through kilovolt potentials have de Broglie wavelengths of 1-100 pm and are diffracted by crystal planes. Electron diffraction patterns (LEED, RHEED, TEM) also follow Bragg's law and are used to study surface structures and thin films.

The structure factor F_hkl is a complex number whose magnitude determines the intensity of the Bragg reflection (hkl). It depends on atom positions within the unit cell and atomic scattering factors. Some reflections may have F=0 (systematic absences) due to crystal symmetry.

Sources & Methodology

Bragg, W. L. (1913). The Diffraction of Short Electromagnetic Waves by a Crystal. Proceedings of the Cambridge Philosophical Society, 17, 43. Hammond, C. The Basics of Crystallography and Diffraction, 4th ed. Cullity, B. D. Elements of X-Ray Diffraction.
R

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