The prompt gamma-ray spectrum
from a La[Cl.sub.3]:Ce detector was measured using the portable neutron generator-based PGNAA set up described earlier  and shown in Figure 1.
Hooper and his colleagues conclude that annihilations of dark matter particles with a mass between 31 and 40 GeV provide a remarkable fit for the excess based on its gamma-ray spectrum
, its symmetry around the galactic center, and its overall brightness.
The pion-decay gamma-ray spectrum
could ride on top of the continuum deriving from primary electron bremsstrahlung.
The bubbles seem to have sharp edges, perhaps marking expanding shock fronts from such an event, but the gamma-ray spectrum
recorded by Fermi is again too "hard" (dominated by especially high-energy emission).
There he worked with Dr Alice Harding, and they were the first to develop a relatively accurate procedure to predict the high-energy to very high-energy gamma-ray spectrum
of the Crab Nebula.
Since many materials, including SNM, emit gamma radiation, elevated levels of gamma radiation may or may not indicate the presence of SNM, but careful analysis of the total gamma-ray spectrum
, as discussed in Chapter 2 under GADRAS, may reveal the presence of SNM.
Because a gamma-ray spectrum
reveals how much of this high-energy radiation is absorbed, it provides a tally of the lower-energy photons generated by all the galaxies that lie between the distant blazar and Earth, says Romani.
As a result, a device using an inorganic crystal has a good ability to identify the radioactive material producing a gamma-ray spectrum
. There are several drawbacks.
Other observers found additional light echoes (135: 155; 136; 12) and unusual characteristics in the supernova's gamma-ray spectrum
To identify radioactive sources creating a gamma-ray spectrum
, GADRAS matches an entire gamma ray spectrum against one or more known spectra.
Furthermore, because the gamma-rays should be coming from a narrow shell of gas, the range of wavelengths would be small, producing a sharp line in the gamma-ray spectrum
. However, the researchers saw a wide spectral line and detected no shift to a shorter wavelength.
Finally, a terrorist group might conceivably place radioactive material in a shipment containing a weapon or SNM chosen so as to mask the unique gamma-ray spectrum
of SNM by presenting a spectrum of several known innocuous materials with peaks to interfere with those of SNM or that have an intensity much higher than SNM.