Acronyms and Abbreviations  :   BGO Bismuth Germanate  CDP Claudia Double Prime coordinate system  EDR Experimental data records (Level 1A)  EPG Spacecraft Ephemerides, Pointing, and measurement Geometry  GCR Galactic Cosmic Ray  HED Howardite, Eucrite, and Diogenite meteorites  PDS Planetary Data System  RDR Reduced data records (Level 1B)  SBN Small Bodies Node of the Planetary Data System  SCLK Spacecraft Clock   Overview  :   This data set contains Reduced Data Records (RDR) from the Dawn  mission's Gamma Ray and Neutron Detector (GRaND). A description of GRaND  can be found in the instrument catalog (included in the archive) and in  the literature [PRETTYMANETAL2003, PRETTYMANETAL2011]. The archive  includes data from all phases of Dawn's encounter with Vesta. GRaND  data were used to study Vesta's geochemistry [PRETTYMANETAL2012,  LAWRENCEETAL2013, PEPLOWSKIETAL2013, PRETTYMANETAL2013,  YAMASHITAETAL2013]. Maps developed by these studies are available from  the PDS Small Bodies Node (SBN) as Level 2 data products for hydrogen,  iron, neutron counting products, and high energy gamma rays.   The RDR includes calibrated, time-series spectra and counting rates  along with information needed for analysis and mapping. Improved  reduction and analyses of gamma ray spectra has enabled the  identification of additional elements [Yamashita et al., 2014, 45th  Lunar and Planetary Science conference, Abstract 2674] and  quantification of global concentrations of K and Th ; Prettyman et al.,  2014, 45th Lunar and Planetary Science conference, Abstract 2565].  Energy-calibrated and corrected gamma ray spectra included in this  volume support studies of Vesta's geochemistry. The RDR data set  includes position, pointing, and measurement geometry data that can be  used with both the RDR and Experimental Data Records (EDR) for studies  with neutron and gamma ray data.   Parameters  :   The RDR are a time-ordered collection of corrected and calibrated pulse  height spectra and counting rates acquired by GRaND at Vesta.  Spacecraft ephemerides, pointing, and measurement geometry (EPG)  accompanies the counting data. The RDR were derived from a subset of the  EDR (Level 1A) data archived at the PDS SBN. Portions of the EDR data  set have not been subjected to energy calibration and, therefore, are  not included in the RDR. For example, spectral data for the boron-loaded  plastic (BLP) and lithium-loaded glass (LiG) phoswiches do not vary  appreciably in gain and are free of digitization artifacts. For this  data set, peak areas can be reliably extracted from the EDR within  selected epochs for which instrument settings are constant  [PRETTYMANETAL2012]. In contrast, spectra acquired by the bismuth  germanate (BGO) scintillator contain pronounced digitization artifacts  and must be subjected to gain-offset corrections in order to achieve the  highest possible resolution for gamma ray elemental analysis.   EPG data and selected scaler counting products are included in a single  file, which contains an entry for every record found in the EDR for  Vesta encounter (from 3-May-2011 to 9-Aug-2012):   GRD-L1B-110503-120809_YCMCDC-EPG.TAB   where YCMCDC is the creation date of the data file. Each record of the  EPG file includes data for a single science accumulation interval.  Entries include the time of acquisition, mission phase, instrument  setting and live time, the spacecraft position at the midpoint of the  data acquisition interval, the solid angle subtended by Vesta at the  spacecraft, and the triple coincidence counting rate. The latter can be  used as a proxy for the galactic cosmic ray flux. Example uses of the  EPG data include binning counts in longitude and latitude (mapping),  correcting counting rates for variations in geometry (solid angle) and  fluctuations in the galactic cosmic ray flux [e.g. see  PRETTYMANETAL2011, PRETTYMANETAL2012].   Corrected and energy-calibrated gamma ray spectra are provided in  separate files for each phase of Vesta encounter. The files have the  following naming convention:   GRD-L1B-Y0M0D0-Y1M1D1_YCMCDC-PHS-BGOC.TAB   where PHS is the three-letter mission phase identifier (e.g. VSL is  Vesta Science LAMO; see the mission catalog for a complete list), Y0M0D0  is the date on which the first science record was acquired during the  mission phase and Y1M1D1 is the date for the last science data record.  YCMCDC is the creation date of the data file. Each record contains the  spacecraft ephemeris time (SCET) in UTC format and the spacecraft clock  (SCLK) ticks (seconds) followed by counts/channel for each of 1024  channels. Each spectrum has been subjected to a linear energy  calibration and rebinned to a common energy scale. The midpoint of each  channel can be obtained by multiplying the channel index (0 to 1023) by  8.9 keV/channel. Digitization artifacts caused by the differential  nonlinearity of the analog-digital converter have been removed.   ***Cross-referencing with SCLK***  :   Every GRaND EPG science data record and RDR record is labeled with  spacecraft clock (SCLK) ticks, represented as a 9-digit integer. The  value of SCLK is unique for each record. Thus, SCLK can be used as a  serial code to identify the same science data record within other data  files. Each record of the EPG file includes SCLK. This allows  instrument settings, live time, position, pointing, solid angle, and GCR  corrections to be reliably matched with data in any EDR or RDR file.   Processing  :   Processing steps and validation of the ephemeris, pointing and geometry  data are described in GRD_L1B_Ephemeris_Pointing_Geometry_v1.pdf. A  description of the BGO data processing can be found in  GRD_L1B_BGO_Data_Processing_v4.pdf. The data processing documents can be  found in the DOCUMENTS directory.   Ancillary Data  :   Spacecraft ephemerides and pointing data were determined using NASA's  Navigation and Ancillary Information Facility (NAIF) SPICE Toolkit for  IDL (version N65). SPICE kernels for Vesta encounter were downloaded  from the NASA Planetary Data System (dawnsp_1000). The planetary  constants kernel for Vesta (dawn_vesta_v04.tpc) for the Claudia  coordinate system was modified with the latest pole position, per  private communication by R. Gaskell. The modified PCK file  (dawn_vesta_v04b.tpc) can be found in the EXTRAS directory.   Coordinate System  :   Longitudes are given in the International Astronomical Union (IAU)  Claudia Double Prime (CDP) coordinate system. A method to convert from  CDP to the Claudia coordinate system, used by the Dawn mission, can be  found in the EPG label file and data processing document.   The instrument coordinate system (Fig. 1) determines the naming  convention of the sensors and orientation of the instrument relative to  the spacecraft. The use of MZ indicates a sensor on the -Z (zenith-  facing during mapping) side of GRaND; PZ indicates the sensor is on the  +Z (spacecraft) side; MY indicates the sensor is on the -Y side  (inboard) side of the instrument; and PY indicates the sensor is on the  +Y side (outboard, towards the +Y solar panel) side of the instrument.  The phototube assembly, marked 'P' on the diagram in Fig. 1 points along  the +X axis (towards the high gain antenna).   The RDR/EPG contains pointing information. Direction cosines found in  each EPG record specify the direction of Vesta body center in the  instrument coordinate system. The cosines DIR_U, DIR_V, DIR_W are  measured relative to the X-, Y-, and Z-axes, respectively.   .................  . ooooooooooooo .  . o o .  . o o .  . o +Z o .  . o (PZ) o .  . o o .---> +Y (PY)  . ooo ooo .  . P P .  . P P .  . PPPPPPPPP .  . .  .................  |  v  +X (PX)   Figure 1. The coordinate system for GRaND is the same as that of the  S/C. For the diagram above, the observer is looking in the -Z (MZ)  direction and can see the outline of the phoswich assembly (o) on the +Z  side of GRaND. The phototubes are on the +X side and the scintillators  are on the -X side. During mapping at Vesta and Ceres, the planetary  surface is in the +Z direction.   Software  :   No software is provided with the archived data.   Media/Format  :   The RDR files are delivered by electronic transmission to the PDS. The  RDR consists of ASCII tables with separate labels containing the format  specification.

Review  :   The RDR were reviewed internally by the Dawn Science Team prior to  submission to the PDS. The EPG and BGO data have been used in studies  carried out by the Dawn Geochemistry team [PRETTYMANETAL2012,  LAWRENCEETAL2013, PEPLOWSKIETAL2013, PRETTYMANETAL2013,  YAMASHITAETAL2013]. The PDS will conduct an external peer review of the  EDR prior to releasing the data to the general public.   Data Coverage/Quality  :   The RDR were derived from the archived EDR data set, which includes all  of the data acquired during flight. Nonetheless, the EDR contained gaps  associated with instrument and spacecraft operations as well as  corrupted data. A complete description of the EDR data coverage can be  found in the CONFIDENCE_LEVEL_NOTE for the EDR data set.   The EPG data file contains spacecraft position and pointing for each and  every EDR record. Thus, the EPG data can be used in the analysis of any  GRaND time-series data product (EDR or RDR). Position and geometry data  are available for all records; however, for a small portion of the  records triples counts, live time, and information regarding instrument  configuration are unavailable and are flagged by MISSING_CONSTANT. In  addition, the counting data may occasionally contain anomalies, such as  spikes in live time or the triples rate. In some cases these may result  from corrupt data (e.g. data for which the master frame contained an  invalid checksum, which cannot be identified by the GRaND team). In  others, the fluctuations may be due to natural, short-term variations in  the energetic particle flux.   Solid angles were calculated from a shape model as described in the RDR  data processing document (GRD_L1B_Ephemeris_Pointing_Geometry_v1.pdf).  Solid angles are accurate to better than 0.5% over the entire range of  positions reported in the EPG file.   Live time determination is described in detail in the EPG data reduction  document (GRD_L1B_Ephemeris_Pointing_Geometry_v1.pdf). Live times  reported in the EPG file are valid only for quiet Sun conditions.  During solar energetic particle (SEP) events, the dead time counter can  roll an indeterminate number of times, resulting in inaccurate  determination of live time. SEP intervals can be identified by  examining the triples counting rate. During SEP events, the triples rate  is elevated. No attempt has been made to flag these intervals in the  EPG file; however, records within periods of elevated SEP flux have been  excluded from the BGO RDR data file. Additional exclusion rules to weed  out invalid data from the BGO time series are described in  GRD_L1B_BGO_Data_Processing_v4.pdf. These include out of range scaler  values, records with abnormal spectral shape (due to anomaly or  incomplete instrument configuration), and large accumulation times  during which instrument settings were adjusted.   Neither the EPG nor the BGO RDR contain replicate records. This is in  contrast to the EDR, for which some records are repeated at the  beginning and end of downlink intervals.   Limitations  :   The RDR gamma ray spectra can be used in the analysis of elemental  composition and mapping studies. Standard methods for gamma ray peak  fitting can be applied to extract counting rates. However, care must be  taken when subtracting spectra accumulated during different mission  phases. Background subtraction can introduce artifacts that can be  misinterpreted as gamma ray peaks. A spectrum of gamma rays originating  from Vesta can be obtained by subtracting a spectrum accumulated during  approach (VSA) from one accumulated in low altitude mapping orbit (VSL).  This approach to remove background contributions from the spacecraft  will result in the introduction of artifacts due to variations in the  energy resolution of the BGO sensor over large periods of time. To  avoid introduction of artifacts, both spectra must be appropriately  adjusted (by convolution) so that they have the same energy resolution  prior to subtraction. The RDR time series is properly calibrated;  however, no attempt has been made to adjust energy resolution on a  spectrum-by-spectrum basis.   The linear model used for energy calibration of BGO pulse height spectra  produces relatively large absolute residuals in comparison to a  quadratic model (see Fig. 5B, GRD_L1B_BGO_Data_Processing_v4.pdf). The  observed deviations are likely due to a combination of the  nonproportionality of BGO and the nonlinearity of the pulse processing  electronics chain (from the photomultiplier tube through the analog-to-  digital-converter). The linear calibration was selected for archive for  the following reasons:  - The linear model does a better job at predicting channel for the 7.6  MeV Fe neutron-capture peak than the quadratic model;  - Users of the data set can re-calibrate the spectra without knowledge  of the original calibration constants.  As our understanding of nonlinear effects matures, the GRaND team will  distribute improved versions of the calibrated spectra.