ANALYTICAL SPECTROSCOPY Old (2000) Exam #2 - Numerical Answers
Spring 2003
#1.
alpha = 10.5 degrees
#2.
31 micrometers
#3.
Cross-dispersed Echelle. Uses an echelle grating for efficent high-order operation and a prism for order sorting, to eliminate order overlap. Gives a 2-D "echellogram". Get large dispersion due to: high order operation and large beta. These also need to compensate for dispersive power lost due to decreased number of facets on the echelle grating.
Rowland-Circle. Uses a concave grating to both focus light and disperse it. Large dispersion is due to use of very large values for beta.
#4.
Since the entire spectral distribution is contained within the effective bandwidth of the monochromator, line radiant power will vary linearly with slitwidth (with the changing area of the aperture).
Continuum background radiant power, however, will vary as the square of the slitwidth due to the dependence on both the aperture area as well as the change in spectral area.
As slitwidth decreases, both line and background radiant powers decrease, but background decreases faster (as the square of the slitwidth), so L/B will INCREASE.
#5.
Sample intro: torroidal shape of plasma enables sample to enter plasma instead of going around it.
Atomization: sample is exposed to very high temps inside plasma (6000 -10000 K) and so is efficiently atomized, with few atomization interferences
Excitation: high excitation temps ensure high population of excited states for significant emission for even harder to excite elements. Torroidal shape minimizes self-absorption (assuming observation is radial and not axial), giving a LDR of more than 6 decades.
Key to ICP's success: torroidal shape (due to high freq RF power and tangential gas flows in torch).
#6.
S/N = 370
Thermal Noise of detector is major noise source (with signal noise a close second!).
#7.
a. If limiting noise was thermal noise or detector shot noise
b. No chromatic abberations with mirrors
c. High precision/accuracy in wavelength calibration and high light throughput with high resolution
d. CCD is best for low light level measurements
e. Increase travel of the moving mirror.
Created and copyright by Joel M. Goldberg. Last updated: April 11, 2003