This document describes the full set of BARREL Balloon X-ray Instruments, XRIs and allows for search aggregation of XRI information from all balloons.

The BARREL Balloon XRIs measure the energy spectrum and flux of Bremsstrahlung X-rays over time. It consists of a cylindrical 7.5 cm diameter by 7.5 cm height scintillator NaI crystal, a photomultiplier tube, PMT, and a peak detect board. It has an energy response from 10 keV to 10 MeV with a spectral resolution of 5 keV. When X-rays from precipitating electrons enter the crystal, visible light photons are generated. The number of photons produced in the scintillator is proportional to the incident X-ray energy. These photons are detected by a PMT which converts the light pulse into charge pulses. The amplitude of each charge pulse is then determined by a pulse height analyzer. The charge pulse amplitudes can be plotted to show the X-ray spectrum, which can then be used to study the energies of the precipitating electrons. This paragraph was adapted in part from the Millan et al. (2013) Spase Sci. Rev. publication listed in the fifth Information URL below.

To fit within telemetry constraints, the X-ray data are binned into three different kinds of spectra that trade between energy resolution and time resolution. The highest time resolution data, important for detecting electron microbursts, are count rates in four energy bands (10 keV to 180 keV, 180 keV to 550 keV, 550 keV to 840 keV, and 840 keV to 1500 keV) every 50 ms, similar to those shown in Figure 1 of Millan et al. (2013). Higher energy resolution is necessary for inverting the X-ray observations to determine the energy and flux of precipitating electrons (e.g., Smith et al., 1995). This is provided with binned X-ray spectra, acquired every 4 s in 48 logarithmically spaced energy channels between 20 keV and 7 MeV. Finally, the highest energy resolution spectra, used for in-flight calibration, consist of 256 energy channels between 20 keV and 7 MeV acquired over 32 s. This paragraph was adapted in part from the Millan et al. (2013) J. Atmos. and Sol.-Terr. Phys. publication listed in the fourth Information URL below.