Large amounts of money are being applied to the construction of the next generation of spallation sources for neutron scattering. Neutron powder diffraction instruments will be an important element of these facilities and the incorporation of detectors into these instruments with a high neutron capture efficiency is desirable. A new detector design named the Flexible Embedded Fiber Detector (FEFD) has been developed and tested for this thesis. This detector is based on wavelength shifting fibers embedded in a zinc-sulfide lithium-fluoride based scintillator. The virtue of this design is that the detecting surface can be curved around the Debye-Scherrer rings. This virtue is lacking in other detector designs, making them more complex and poorer in performance than our FEFD detectors. Monte Carlo calculations were performed to determine the neutron capture efficiencies of our FEFD detectors, which proved to be much higher than those of the proposed powder diffractometer design for the Spallation Neutron Source and about equal with the efficiency for the ISIS powder diffractometer design. Four FEFD detector prototypes were then fabricated and tested at the Intense Pulsed Neutron Source at Argonne National Laboratory. We find that our measured and calculated relative efficiencies are in good agreement.