1. بسم الله الرحمن الرحيم
Compositional Study of Different Currency Coins Using Non-Destructive Laser Induced Breakdown Spectroscopy
2nd SASC
Muharram, 1425
Jeddah, KSA
Zain Yamani, Ph.D.
Physics Department
KFUPM

2. Presentation plan Introduction: What is LIBS?
Different physical methods for material analysis.
What is special about LIBS?
Compositional determination of coins using LIBS:
a- Experimental set-up
b- Results
c- Conclusions
Concluding remarks

3. LIBS: Laser Induced Breakdown Spectroscopy
Introduction
LIBS: Laser Induced Breakdown Spectroscopy
LIBS is an analytical method by which one can determine (qualitatively and quantitatively) the elemental composition of solid, liquid or gas samples.
LIBS
focused laser pulses
vaporize, atomize and excite the sample
plasma emission
collect, disperse and analyze light
atomic spectral lines determine the elemental composition

4. What other methods are used for elemental analysis

6. How does LIBS compare with other analytical methods?
Micro-LIBS
Portability
Rapid
NDT
Different types of samples
Little sample preparation
No (chemical) waste
This is not to say that there are no complications in LIBS.
Of course, there are!

7. (applications, from the literature)
What is LIBS used for?
(applications, from the literature)
Environmental monitoring to measure soil contamination (Zolotovitskaya et al., 1997)
Detect toxic metals (Yamamoto et al., 1996; Buckley et al., 2000)
Study the chemical compositions in liquids (Yueh et al., 2002; Samek et al., 2000)
Study the chemical compositions in polymers (Sattmann et al., 1998)
In forensics and military applications (Kincade, 2003)
Biomedical studies of bones and teeth
Art restoration (or conservation), by analyzing pigments and/or precious and ancient metals (Anzano et al., 2002)

8. LIBS for coin compositional determination
Experimental set-up
Nd-YAG
3rd harmonic
prism
dichroic mirror
personal computer
monochromator
mirror
collecting lens
Rotating sample holder
sample
PDA
Movie
Figure 1 shows a schematic of the experimental setup. The third harmonic of a Nd-YAG [Spectra Physics, Model GCR 250] emits 355 nm laser radiation at a repetition rate of 10 Hz, and the pulse duration is ~8 nsec.
The laser beam is focused on the sample under study which creates fluorescing plasma. A 5-cm converging lens collects the laser-induced plasma fluorescence onto a monochromator [500 M Spex]. A Jobin Yvon ISA Photo-detector Array (PDA) [model: spectraview-1D] detects the dispersed fluorescence with its 1024 array of diodes. The Spectra Max software controls the monochromator grating motor and collects data that is stored on a personal computer for further analysis.
Deliberately, low laser power (~2 mJ per pulse) was used and the sample was mounted on a rotating sample holder in order to reduce the damage suffered by the sample. The integration time was 30 seconds. This, however, was sometimes found to be too long and occasionally caused saturation of the PDA.
Two regions were studied: Å, and Å. The PDA was calibrated against well-known Hg lines emitted by the room fluorescent bulbs. Fe lines from iron pellets were also made use of.

9. grating
mirror
1024 diodes
PDA ~ optical multi-channel analyzer
With a Photo-Diode Array (PDA), one can simultaneously detect the intensity of many “different” wavelengths.

10. LIBS for coin compositional determination
Experimental Results
PDA Calibration
Apply LIBS to coins
Check repeatability
Look for coin signatures
Reliability (same results in different regions!!)
NDT

11. LIBS for coin compositional determination
Fe I
4045.8
4000
4063.6
1500
4071.7
1200
4143.9
800
Br II
4223.9
1000
4260.5
4271.8
4282.4
4307.9
4325.8
Br I
4365.1
2000
4365.6
4375.9
4383.5
3000
4404.8
4425.1
10% iron in KBr (calibration pellet)
Data: Å

12. Notice how the spectra are almost identical!!
LIBS spectra for (solid) one side of a 25 Fils Bahrain coin and (dashed) the other side of the same coin.
Notice how the spectra are almost identical!!

13. The game token does not contain copper (e.g. @ 4180, 4275 & 4377 Å).
There are similarities between the three spectra; for example, all have Fe peaks 4228 Å.
The game token does not contain copper 4180, 4275 & 4377 Å).
The real currencies do contain copper!!
Nickel has been limited, in the Euro currencies, to the two highest denominations of 1€ and 2€ Euro coins due to concerns that nickel possibly contribute to skin allergy (Fournier, 2003).
LIBS spectra for (solid) a 10-Hallalah Saudi coin, (dashed) 20 cent Euro coin and (dotted) a game token, in the Å region.
The Euro coin does not have the 4201 & 4401Å Ni peaks.
The game token has more iron and nickel than the other (real) currencies.

14. Common iron peaks (e.g. 5270 Å).
The game token does not contain copper. The real currencies do contain copper!! (e.g Å).
The Euro coin does not have the Ni peaks. (e.g Å).
LIBS spectra for (solid) a 10-Hallalah Saudi coin, (dashed) 20 cent Euro coin and (dotted) a game token, in the Å region.
The results are consistent with that of the Å region.
It is difficult to distinguish between Saudi and Bahrani coins. They probably have very similar elemental composition.

15. (a)
(b)
Photographs of the four coins used in the experiments (a) before and (b) after 30 seconds of laser irradiation. The coins show no apparent destruction due to LIBS.

16. LIBS as NDT?
Is LIBS absolutely NDT?

17. LIBS for coin compositional determination
Conclusions
LIBS spectra are repeatable.
LIBS gives consistent/ reliable results in different regions.
Coins have iron.
Game token has no copper.
20 cent Euro coin is nickel-free.
We can distinguish between “different” currencies using LIBS.
The spectra of the Saudi 10-Hallalah and the Bahrain 25 Fils are very similar.
At the macroscopic level, LIBS procedure can be NDT.

18. Good general references on LIBS
Also, check Applied Optics vol 42 (30), Oct (theme issue)

19. Concluding Remarks
LIBS is a very useful technique for the elemental analysis of material.
LIBS can be used for fast, precise, on-line, non- destructive testing of coins.
LIBS can be beneficial for the identification of currency and also for quality control in coins production.
LIBS applies to different types of material and is conducive to interdisciplinary research, a concept very beneficial for academic research in Saudi Arabia.

20. Further study:
both qualitative and quantitative.
different photon energy and laser pulse energy.
effect of optical alignment of beam with the sample, and optical alignment of beam with the detection system.
increase sensitivity by using gated ICCD.
study the effects of delayed time.
I would be happy to work with collaborators.

21. Acknowledgement
The support of King Fahd University of Petroleum and Minerals is gratefully acknowledged.
The encouragement of professor M.A. Gondal, as well as the assistance of Mr. Abdullah Baziyad and Mr. Abdullah Al-Zahrani, is deeply appreciated.
I am thankful to Mr. Fuad Enaya for his help in preparing the presentation.
Thank you for your attention

25. Complications in Using LIBS
Sample matrix
Morphology
Power [energy per pulse & pulse width] dependence
Atmosphere type and pressure
Shot to shot energy fluctuation
Depends on photon energy [esp. plasma absorption]