help w/ physics gre problem: radiation spectra

yxgao

64. Electromagnetic radiation provides a means to probe aspects of the physical universe. Which of the following statements regarding radiation spectra is NOT correct?

a. lines in the infaret, visible, and ultraviolet regions of the spectrum reveal primarily the nuclear structure of the sample.
b. the wavelengths identified in an absorption spectrum of an element are among those in its emission spectrum.
c. absorption spectra can be used to determine which elements are present in distant stars.
d. spectral analysis can be used to identify the composition of galactic dust.
e. band spectra are due to molecules.

The answer is a. This makes sense to me, but I'm not sure exactly why it must be the correct answer, and the others answers are false. Can someone explain each one in some detail?

Thanks!!

Nylex

According to the question, if a is the answer then it must be false and the others are true.

dextercioby

Yes,Nylex is right,answer a) is the false one.According to the shell model of the nucleus,nucleons are disposed in enery levels,similar to electrons in the entire atom,but the main difference is that the gaps between successive energy levels is huge,in the order of MeV,so that should take the emission/absorbtion spectrum to the lower (wavelength) X rays and definitely gamma.

Daniel.

PS.And beside,all of the other answers are true...

Astronuc

The key to why answer 'a' is wrong is found in " infared, visible, and ultraviolet regions of the spectrum" and "nuclear structure ".

The electromagnetic spectrum in this range is due to emission from 'atoms', or more specifically the change of state of 'electrons', which orbit the nucleus. They tell nothing of the nuclear structure.

b. is true - An atom will absorb light that is characteristic of its emission spectrum.

c. is true - since b is true.

d. is true - follows from 'c' and 'b'.

e. is true - band spectra
The combination of many different spectral lines resulting from vibrational, rotational and electronic transitions. Unresolved band spectra may appear as a spectral continuum. (from IIUPAC Compendium of Chemical Terminology)

yxgao

Thanks a lot guys! I suppose that this was a rather simple question, looking back on it.