FIVE YEARS OF RADIATION MEASURMENTS ON THE FAR SIDE OF THE MOON – RESULTS FROM THE LUNAR LANDER NEUTRON AND DOSIMETRY EXPERIMENT ON CHANG’E-4

Abstract

Human exploration of the Moon is associated with substantial risks to astronauts from space radiation. On the surface of the Moon, this consists of the chronic exposure to galactic cosmic rays and sporadic solar particle events. The interaction of this radiation field with the lunar soil leads to a third component that consists of neutral particles, i.e., neutrons and gamma radiation. We report on five years worth of radiation measurements acquired by the Lunar Lander Neutron and Dosimetry (LND) experiment aboard the Chinese lunar lander Chang’E 4 and describe the instrument. First results were reported by Wimmer-Schweingruber, R.F., et al. (2020), here we will provide an update to reflect rising solar activity. During the first two lunar days (Jan 3 – 10 and Jan 31 – Feb 10, 2019) after landing on the Moon, LND measured an average dose equivalent of 1369 Sv/day. For the same time period, the dose equivalent onboard the International Space Station (ISS) as measured with the DOSIS 3D DOSTEL instruments was 731 Sv/day with contributions only from galactic cosmic rays (GCRs) of 523 Sv/day. The additional 208 Sv/day is due to protons while crossing the South Atlantic Anomaly (SAA). Therefore, the daily GCR dose equivalent on the surface of the Moon is around a factor of 2.6 higher than the dose inside the ISS.After more than five years on the far side of the Moon, LND continues to measure dose rates from charged and neutral particles, and provides other critical dosimetric quantities such as LET spectra in preparation of human exploration of the Moon.