2.2.2 spase://SMWG/Instrument/VenusExpress/ASPERA4/NPD Venus Express ASPERA-4 Neutral Particle Detector 2012-06-13T00:00:00Z The Neutral Particle Detector (NPD) of the ASPERA-4 package flown on Venus Express provides measurements of the ENA differential flux over the energy range 100 eV - 10 keV resolving H and O with a coarse 5 deg x 30 deg angular resolution. The sensor consists of two identical detectors each with a 9 deg x 90 deg intrinsic field of view. The measurement technique is based on a principle similar to the Neutral Particle Imager. ENAs incident on a surface at a grazing angle of 15 deg are reflected and cause secondary electron emission. The secondary electrons are transported to an MCP assembly, which gives the START signal. The reflected ENAs hit the second surface and again produce the secondary electrons used to generate the STOP signal. The time-of-flight (TOF) electronics give the ENA velocity. The pulse-height distribution analysis of the STOP signals is used to provide a rough determination of the ENA mass. spase://SMWG/Person/Stas.Barabash PrincipalInvestigator PSA ASPERA web page ftp://psa.esac.esa.int/pub/mirror/VENUS-EXPRESS/ASPERA4/VEX-V-SW-ASPERA-2-ELS-V1.0/CATALOG/INST.CAT NeutralAtomImager ASPERA4_NPD spase://SMWG/Observatory/VenusExpress