Experiment 12: bragg diffraction, Equipment needed, Introduction – PASCO WA-9316A Complete Microwave Optics System User Manual

Page 31: Purpose, Procedure, Equipment needed: introduction

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Experiment 12: Bragg Diffraction

Experiment 12: Bragg Diffraction

Equipment Needed:

Introduction

Bragg’s Law provides a powerful tool for investigating crystal structure by relating the interplanar spacings in the crystal to the
scattering angles of incident x-rays. In this experiment, Bragg’s Law is demonstrated on a macroscopic scale using a cubic
“crystal” consisting of 10-mm metal spheres embedded in an ethafoam cube.

Before performing this experiment, you should understand the theory behind Bragg Diffraction. In particular, you should
understand the two criteria that must be met for a wave to be diffracted from a crystal into a particular angle. Namely, there is
a plane of atoms in the crystal oriented with respect to the incident wave, such that:

1. The angle of incidence equals the angle of reflection, and

2. Bragg's equation, 2dsin

 = n, is satisfied; where d is the spacing between the diffracting planes,  is the grazing angle of

the incident wave, n is an integer, and

 is the wavelength of the radiation.

Purpose

In this experiment you will investigate Bragg Diffraction.

Procedure

1. Arrange the equipment as shown in Figure 12.1.

2. Notice the three families of planes indicated in Figure 12.2. (The designations (100), (110), and (210) are the Miller indi-

ces for these sets of planes.) Adjust the Transmitter and Receiver so that they directly face each other. Align the crystal so
that the (100) planes are parallel to the incident microwave beam. Adjust the Receiver controls to provide a readable sig-
nal. Record the meter reading.

Item

Transmitter

Goniometer

Receiver

Rotating Table

Cubic Lattice

Rotating Table

(210)

(110)

(100)

Figure 12.1: Equipment Setup

: Figure 12.2: “Atomic” Planes of the

Bragg Crystal