Data Set Information
DATA_SET_NAME DAWN GRAND MAP CERES IRON 7.6MEV GAMMA COUNTS V1.0
DATA_SET_ID DAWN-A-GRAND-5-CERES-IRON-COUNTS_V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : A global map of 7.6 MeV gamma rays produced by neutron capture with Fe within Ceres' regolith is provided as an ASCII table. The data were acquired by GRaND while the Dawn spacecraft was in a low altitude mapping orbit (LAMO) around Ceres. The map data are given for twenty-degree, quasi-equal-area pixels. The data reduction and analysis methods are presented in the Supplement of PRETTYMANETAL2017. The map of 7.6 MeV counting data given here appears in Fig. 1 of the main text of PRETTYMANETAL2017. The full-energy interaction rate of 7.6 MeV gamma rays produced by neutron capture with Fe within Ceres' regolith with GRaND's large-volume bismuth germanate scintillator produces a peak in the spectrum. The net peak area of this peak was determined as a function of time while Dawn was in LAMO. The time series was corrected for variations in the intensity of galactic cosmic rays and the solid angle subtended by Ceres at the spacecraft. Bad data and data not meeting pointing requirements were excluded from the analysis. The data were binned at the subsatellite point on 20-degree quasi-equal area pixels. For each pixel, the mean counting rate and the statistical uncertainty in the mean is reported along with the number of times the pixel was sampled. Parameters : Each row of the table gives 7.6 MeV counting rate for a single rectangular pixel. The format for each row is '(I10,4(F7.1),2(E14.4),I10)'. East longitude convention is used (-180 to 180 degrees). Each pixel spans a separate and unique portion of Vesta's surface, and together, the pixels provide full global coverage. The BROWSE directory displays the data as a global map. The column descriptions follow: COLUMN NAME FORMAT DESCRIPTION UNITS 0 PIXEL_INDEX (I10) N/A 1 MIN_LAT (F7.1) Pixel latitude lower boundary deg 2 MAX_LAT (F7.1) Pixel latitude upper boundary deg 3 MIN_LON (F7.1) Pixel longitude lower boundary deg 4 MAX_LON (F7.1) Pixel longitude upper boundary deg 5 TPE_COUNTING_RATE (E14.4) Mean 7.6 MeV counting rate counts/s 6 SIG_TPE_COUNTING_RATE (E14.4) Uncertainty in the mean counts/s 7 TPE_SAMPLES (I10) Number of samples
DATA_SET_RELEASE_DATE 2017-09-25T00:00:00.000Z
START_TIME 2015-12-16T12:00:00.000Z
STOP_TIME 2016-05-11T12:00:00.000Z
MISSION_NAME DAWN MISSION TO VESTA AND CERES
MISSION_START_DATE 2007-09-27T12:00:00.000Z
MISSION_STOP_DATE 2017-06-30T12:00:00.000Z
TARGET_NAME 1 CERES
TARGET_TYPE ASTEROID
INSTRUMENT_HOST_ID DAWN
INSTRUMENT_NAME GAMMA-RAY AND NEUTRON DETECTOR
INSTRUMENT_ID GRAND
INSTRUMENT_TYPE GAMMA RAY SPECTROMETER
NEUTRON SPECTROMETER
NODE_NAME Small Bodies
ARCHIVE_STATUS
CONFIDENCE_LEVEL_NOTE Confidence Level Overview : The data set is an intermediate data product from which Fe concentrations were determined [PRETTYMANETAL2017]. Review : This data set is in review by NASA Planetary Data System. Data Coverage and Quality : The data set contains a global map of 7.6 MeV neutron capture gamma ray counting rates. There are no gaps in coverage. Thermal+epithermal neutrons are sensitive to the composition of Ceres' regolith to depths up to a few decimeters (for example, see PRETTYMANETAL2011). Coordinate System : The prime meridian is anchored by a small crater called Kait at 2 degrees South [RUSSELLETAL2016]. East longitude convention is used. Limitations : A complete description of data reduction and mapping methods used to create this data set is presented by PRETTYMANETAL2017 (Supplement).
CITATION_DESCRIPTION Prettyman, T.H., Dawn GRaND hydrogen map, DAWN-A-GRAND-5-CERES-TPE-COUNTS-V1.0, NASA Planetary Data System, 2017.
ABSTRACT_TEXT A global map of gamma ray counting rates binned on twenty-degree quasi-equal-area pixels is provided. The map was determined from a time series of net counting rates for the 7.6 MeV gamma ray peak produced by neutron capture with Fe within Ceres' regolith. The data were acquired by Dawn's Gamma Ray and Neutron Detector (GRaND) while in low altitude mapping orbit, about 385 km from Ceres' surface (about 0.8 body radii altitude). Prior to mapping, the time series counting data were subjected to corrections for variations in the flux of galactic cosmic rays and measurement geometry, as described by PRETTYMANETAL2017.
PRODUCER_FULL_NAME THOMAS H. PRETTYMAN
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