Synchrotron Workshops for Students in September

3:15Australian Synchrotron: Its physics and technology: Synchrotron speaker (Banquet Room 1, 1st floor, UnionBuilding, MonashUniversity)

4:15Group 1: Site tourGroup 2: Practical activities (Banquet Room 3)

5:15Group 1: Practical activitiesGroup 2: Site tour

6:15Dinner (Banquet Room 2)

6:50Synchrotron radiation: Its properties and uses: Synchrotron speaker (Banquet Room 1)

7:30Finish

Practical activities: 10 groups of 3: A, B, C, D, E, F, G, H, I, J

0 - 10 min / 11 - 20 min / 21 - 30 min / 31 - 40 min / 41 - 50 min / 51 - 60 min
A / Microwave Bragg Diffraction Experiment: Station 1 / Modelling Bragg diffraction: Station 6 / CD Line Spacing: Station 8 / Laser diffraction activities: Station 10
B / Microwave Bragg Diffraction Experiment : Station 2 / Laser diffraction activities: Station 10 / Modelling Bragg diffraction Station 6 / CD Line Spacing: Station 8
C / Microwave Bragg Diffraction Experiment: Station 3 / CD Line Spacing: Station 8 / Laser diffraction activities: Station 10 / Modelling Bragg diffraction Station 6
D / Microwave Bragg Diffraction Experiment: Station 4 / Modelling Bragg diffraction Station 7 / CD Line Spacing: Station 9 / Laser diffraction activities: Station 11
E / Microwave Bragg Diffraction Experiment: Station 5 / Laser diffraction activities: Station 11 / Modelling Bragg diffraction Station 7 / CD Line Spacing: Station 9
F / Modelling Bragg diffraction Station 6 / CD Line Spacing: Station 8 / Laser diffraction activities: Station 10 / Microwave Bragg Diffraction Experiment: Station 1
G / Laser diffraction activities: Station 10 / Modelling Bragg diffraction Station 6 / CD Line Spacing: Station 8 / Microwave Bragg Diffraction Experiment: Station 2
H / CD Line Spacing: Station 8 / Laser diffraction activities: Station 10 / Modelling Bragg diffraction Station 6 / Microwave Bragg Diffraction Experiment: Station 3
I / Modelling Bragg diffraction Station 7 / CD Line Spacing: Station 9 / Laser diffraction activities: Station 11 / Microwave Bragg Diffraction Experiment: Station 4
J / Laser diffraction activities: Station 11 / Modelling Bragg diffraction Station 7 / CD Line Spacing: Station 9 / Microwave Bragg Diffraction Experiment: Station 5

Bragg Microwave Diffraction Experiment: Stations: 1 - 5

Background Theory

Bragg’s Law derived in 1913 by the English physicists Sir W.H. Bragg and his son Sir W.L. Bragg to explain why crystals appear to reflect X-ray beams at certain angles of incidence.

Bragg's Law:n = 2d sin

Where d is the distance between atomic layers in a crystal,

 is the wavelength in metres of the incident beam,

 is the angle of incidence; and

n is an integer representing the number of wavelengths required for constructive interference to occur. At the smallest angle of incidence () for a maxima n = 1, at the next smallest angle n = 2, etc.

Bragg’s Law is an example of X-ray wave interference or X-ray diffraction (XRD), and is used to determine the atomic structure of crystals.

The Braggs were awarded the Nobel Prize in physics in 1915 for their work in determining crystal structures (NaCl, ZnS and diamond).

Although Bragg's law was used to explain the interference pattern of X-rays scattered by crystals, diffraction has been developed to study the structure of all kinds of matter with a beam, as long as the wavelength used is comparable to the spacing of the molecules (or atoms) within the object under investigation.

In this experiment microwaves will be used with a frequency roughly 1/50,000th lower than the X-rays the Bragg’s used. This will allow the measurement of crystal spacings 50,000 times greater than those found in compounds such as diamond or sodium chloride (NaCl).

APPARATUS

Microwave transmitter and receiver, wavelength = 2.85 cm (freq = 10.525 GHz)

‘Foam Crystal’

Multimeter

Large Protractor

2  1 metre ruler

Aluminium barrier

METHOD

  1. Align one straight edge of the ‘foam crystal’ along the base of the large protractor as shown in figure 1 below. Record the number of the face towards the transmitter.
  2. Place the aluminium sheet barrier on the 90o line of the protractor so that the cones of the transmitter and receiver can ‘see’ the ‘foam crystal’, but that any direction radiation from transmitter to receiver is blocked.
  3. Place the microwave transmitter and receiver on the small blocks provided to raise them off the desk surface.
  4. Point the microwave transmitter toward the face of the ‘foam crystal’ at an initial angle of ~30o. Similarly align the receiver at 30o to the face of the ‘foam crystal’ to detect the reflected beam. See figure 1. (Hint: using 1 metre rulers to align the receiver and transmitter can save considerable time in setting up)
  5. Switch on the power to the transmitter and receiver and set the multimeter to a 0 – 20 V range.

CAUTION: Never allow the transmitter to be directed towards a person’s eyes at any time. Damage to the retinas is possible!

  1. Gradually move both the transmitter and receiver around on the angle. Ensure both devices are at the same angle at the same time and pointing directing to the centre of the protractor.
  2. Record the multimeter reading in the table over the page.
  3. Now decrease the angle of both the transmitter and receiver by two or five degrees and record the data in the table. Continue this down to about 5 degrees. The data in the table will give you an indication of where the maxima are.
  4. Reset the apparatus as in step 4 and repeat step 5 - 7 but gradually increase the angle.
  5. Take extra measurements to precisely locate the angles for various maxima.
  6. Each maxima represents a value for n. The smallest angle at which a maximum occurs will have a value of n= 1, with subsequent angles n =2, etc. Use Bragg’s Law to determine the spacing of the molecules in the ‘foam crystal’ for each angle.

RESULTS

Station No: ______

Record the angle () at which maximum readings were recorded.

Angle / Average
Value of n / Spacing
Spacing
(cm)

a)What is the uncertainty in the average spacing due to the different calculated values? ______

CONCLUSION The spacing for face no: ____ is ______+/- ______cm.

Angle / Reading / Angle / Reading

Modelling Bragg Diffraction with Microwave Apparatus: Stations 6 & 7

Equipment:A microwave transmitter and receiver, a multimeter, two strips of foam about 10 – 15 cm long, each with three equally spaces flat metal objects such as thumb tacks, coins, metal washers, one foam mount and one large protractor.

Procedure

  1. Place the foam mount at the centre of the protractor and the transmitter and the receiver at angles of 45 degrees,
  2. Place one of the foam strips on the top of the foam mount near the edge closest to the transmitter and receiver. The reflected beam from the metal objects on the foam strip should be picked up by the receiver and shows a strong signal.
  3. Place the second foam strip above and behind the first strip, but parallel to it and positioned so that it will also receive the signal. Now two signals, each travelling a different path will be arriving at the receiver.
  4. Set the spacing between the two rows of flat metal objects to be as small as possible. Now very slowly pull the second foam strip back. You should observe that the signal drops. This is due to cancellation because of the path difference.
  5. Continuepulling the foam strip back very slowly. You should observe that the signal begins to increase. Find the position where the signal is a maximum. At this spacing between the two rows, then path difference will be a full wavelength, because the waves are reinforcing each other.
  6. As you continue to pull the foam strip back the signal will move between maximum and minimum values, as the path difference moves between odd and even multiples of the wavelength.
  7. Record the spacing of the two rows for a series of successive maxima. The average distance between readings will give you a value for ‘d’ to substitute into the Bragg’s Law to find the wavelength  = 2d sin

Angle = 450

Results:

Successive spacings: ______, ______, ______, ______, ______

Distance between 1st and 2nd =

Distance between 2nd and 3rd =

Distance between 3rd and 4th =

Average distance = ______Wavelength = ______

Line Spacing on a CD: Stations 8 and 9

Aim: To measure the line spacing on a CD

Equipment:Laser (lab or pointer, wavelength must be known), CD, DVD, tape measure, ruler, retort stands & clamps, room which can be darkened.

Method:

  1. Clamp the CD in a vertical position and clamp laser to produce a horizontal beam onto a left or right edge of the CD.
  2. Reflect the light to a suitable screen (white board etc). If set up correctly, there should be a line of red dots on the screen, where the diffraction pattern has formed.
  3. Measure accurately the distances: CD to screen and the dot spacing.
  4. The spacing is calculated from / D = x/L, where D = CD groove spacing, x = dot spacing on the screen , laser wavelength
  5. Repeat the experiment with a DVD and observe the difference in the diffraction effect due to the different groove spacing.

Data: Wavelength of laser light = ______+/- ______= ____ +/- ____ cm

Measurements: L = ____ +/- ____ cm, x = ____ +/- ____ cm

Calculated value of D = = ______+/- ______cm

Laser diffraction activities: Stations 10 and 11

Modelling synchrotron radiation using visible light

Student investigations: Diffraction effects

Warning

Keep direct laser light out of your eyes. Point the laser away from you and from other people. Look away from bright reflections. Keep lasers at waist height and don’t sit at benches.

A.Fibres and wires

Use laser light to observe the diffraction pattern formed by different fibres. Sketch each pattern and take any measurements that you could use to calculate the diameter of each fibre.

  1. Put the objects in order of fibre diameter from thickest to thinnest. Sketch the diffraction patterns relative to the first fibre that you test or measure the dimensions of the pattern that you observe.

Object / Diffraction pattern : sketch or measurements / Relative diameter of one fibre
Paint brush
Feather
hair
Single strand of insect screen wire

Order:

  1. Two Dimensional Grids

Use laser light to observe the diffraction pattern formed by different materials. Sketch each pattern and take any measurements that you could use to calculate the spacing of strands in the material.

Object / Observations
Top bend of a needle threader
Insect screen mesh
Gauze ribbon 1
Gauze ribbon 2
Artificial flower petal
Tea strainer
Other: …….
  1. What is the effect of turning the material or object in front of the laser?

______

  1. What is the effect of two layers of the material?

______

  1. For each material, what conclusions can you make about
  • the structure of the material? ______
  • the size of the fibres in the material? ______

C. Two dimensional helix model

Use a pair of bolts or screws as in the diagram below. The laser beam must line up with the gap between the threads.

Object / Observations
Pair of bolts or screws

5.What does the pattern remind you of? ______