College Physics
posted by Angie .
An xray photon collides headon with an electron and is scattered directly back at 160◦ to
its original direction.
What is the shift in the wavelength of the incident xray?
do i need to figure out the "compton shift" in order to solve..can someone please show me how to do this problem? Please and thank you so much!

delta wavelength=.00243(1cos theta)

Yes, it is a Compton shift problem. The "theta" that you use is 160 degrees, which is the angle that the Xray photon is scattered. (The electron is scattered at a different angle).
Your 0.00243 constant is actually
h/(mc), where h is Planck's constant and m is the electron mass. You need to say what the units are.
h/mc = 2.43*10^10 cm according to my textbook. That would be 2.43*102 Angstroms or 2.43*10^3 nanometers (nm)
The equation you wrote down apparently uses nanometers.
The wavelength change is 1.94*2.43*10^3 = 4.7*10^3 nm, or 47 Angstroms
The scattered wavelength is longer by that amount. 
My 'nanometers' number is correct, but would be 4.7*10^2 Angstroms
Xray wavelengths are typically 0.01 to 10 nm, which is 0.1 to 100 Angstroms
The Angstroms unit of wavelength seems to be less fashionable, although most "wavelength tables" published in the past used Angstroms