Entwicklung eines Neutronendosimeters und Messung schneller Neutronen in der Verkehrsluftfahrt

Das entwickelte NEUtronen DOSimeter (NEUDOS) besteht aus einem organischen Szintillationsdetektor aus gewebeäquivalentem Kunststoff. Um elektrisch neutrale Teilchen von geladenen Teilchen unterscheiden zu können, ist der Detektor komplett von sechs weiteren Szintillatoren umschlossen. Das Ansprechvermögen der Antikoinzidenz wurde mit relativistischen Myonen bestimmt, es beträgt 99,6%. Die mit dem NEUDOS gemessene Energiedosis wurde ebenfalls mit relativistischen Myonen kalibriert. Am Europäischen Referenzfeld für Dosimeter in der Luftfahrt („CERN EU High Energy Reference Field“) CERF wurde das NEUDOS für die Messung von Äquivalentdosen neutraler Teilchen kalibriert. Um den Neutronenanteil an der gesamten Äquivalentdosisleistung in Verkehrsflugzeugen zu bestimmen, wurden verschiedene Messflüge durchgeführt. So wurden Flüge in hohen Breiten, wie auch über den Äquator durchgeführt. Aus den Messungen ergeben sich für verschiedene Flugflächen in hohen und niedrigen magnetischen Breiten Äquivalentdosisleistungen zwischen 1,8±0,02 µSv/h in einer Flughöhe von ca. 28.000 Fuß in der Nähe des magnetischen Äquators und 5,9±0,06 µSv/h in einer Flughöhe von ca. 34.000 Fuß in der Nähe des magnetischen Nordpols. Der Anteil der Neutronen lag hierbei zwischen 0,6±0,01 µSv/h und 2,8±0,03 µSv/h. Für hohe magnetische Breiten wie auch für Flüge in Äquatornähe wurde die Höhenabhängigkeit der Äquivalentdosisleistung untersucht. Die durch neutrale Teilchen induzierte Äquivalentdosisrate steigt vom Äquator zu hohen Breiten um eine Faktor 3, während der Beitrag der geladenen Teilchen nur um einen Faktor von 1,7 steigt

Active radiation measurements over one solar cycle with two DOSTEL instruments in the Columbus laboratory of the International Space Station

Two DOSimetry TELescopes (DOSTELs) have been measuring the radiation environment in the Columbus module of the International Space Station (ISS) since 2009 in the frame of the DOSIS and DOSIS 3D projects. Both instruments have measured the charged particle flux rate and dose rates in a telescope geometry of two planar silicon detectors. The radiation environment in the ISS orbit is mostly composed by galactic cosmic radiation (GCR) and its secondary radiation and protons from the inner radiation belt in the South Atlantic Anomaly (SAA) with sporadic contributions of solar energetic particles at high latitudes. The data presented in this work cover two solar activity minima and corresponding GCR intensity maxima in 2009 and 2020 and the solar activity maximum and corresponding GCR intensity minimum in 2014/2015. Average dose rates measured in the Columbus laboratory in the ISS orbit from GCR and SAA are presented separately. The data is analyzed with respect to the effective magnetic shielding and grouped into different cut-off rigidity intervals. Using only measurements in magnetically unshielded regions at low cut-off rigidity and applying a factor for the geometrical shielding of the Earth, absorbed dose rates and dose equivalent rates in near-Earth interplanetary space are estimated for the years 2009 to 2022

Galactic Cosmic Ray induced absorbed dose rate in deep space – Accounting for detector size, shape, material, as well as for the solar modulation

Depending on the radiation field, the absorbed dose rate can depend significantly upon the size of the detectors or the phantom used in the models. In deep space (interplanetary medium) the radiation field is on avarage dominated by Galactic Cosmic Ray (GCR) nuclei. Here, the deep space dose rate that a typical small silicon slab detector measures is compared to a larger phantom corresponding to an ICRU sphere with a 15 cm radius composed of water. To separate and understand respective effects from the composition, size and shape differences in the detectors, this comparison is implemented in several steps. For each phantom, the absorbed dose rate due to GCR nuclei up to Z = 28, as a function of solar modulation conditions, is calculated. The main components of the GCR flux are protons, followed by helium nuclei and electrons, with Z > 2 nuclei accounting for approximately 1% of the total number of particles. Among the light nuclei with Z > 2, most abundant ones are C, N and O. In this study, we use the GEANT4 model to calculate the absorbed dose (energy deposited as ionization, divided by mass) due to the GCR flux provided by the Badhwar-O’Neill 2010 (BON-10) model. Furthermore, we investigate how the determined absorbed dose rate changes throughout the solar cycle by varying the GCR models from solar minimum to solar maximum conditions. The developed model is validated against the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) microdosimeter measurements. In our current approach, we do not consider the effects of shielding, which will always be present under realistic scenarios. A second goal of this study is to quantify the contribution of each Z = 1, …, 28 GCR nuclei to absorbed dose rate, in relation to the phantom characteristics. For each Z we determine the most relevant energy range in the GCR spectra for absorbed dose rate estimations. Furthermore, we calculate a solar modulation dependent conversion factor to convert absorbed dose rate measured in silicon to absorbed dose rate in water. This information will improve our understanding of the radiation environment due to GCR in the near-Earth deep space and also benefit further modeling efforts by limiting the number and energy range of primary particle species that have to be considered

The Lunar Lander Neutron and Dosimetry (LND) Experiment on Chang'E 4

Chang'E 4 is the first mission to the far side of the Moon and consists of a lander, a rover, and a relay spacecraft. Lander and rover were launched at 18:23 UTC on December 7, 2018 and landed in the von K\'arm\'an crater at 02:26 UTC on January 3, 2019. Here we describe the Lunar Lander Neutron \& Dosimetry experiment (LND) which is part of the Chang'E 4 Lander scientific payload. Its chief scientific goal is to obtain first active dosimetric measurements on the surface of the Moon. LND also provides observations of fast neutrons which are a result of the interaction of high-energy particle radiation with the lunar regolith and of their thermalized counterpart, thermal neutrons, which are a sensitive indicator of subsurface water content.Comment: 38 pages, submitted to Space Science Review

DOSTEL measurements as part of DOSIS/DOSIS3D: An update

In the frame of the DOSIS / DOSIS3D Experiments two DOSTEL units are utilized to measure the radiation environment inside the COLUMBUS module of the International Space Station. DOSIS and its successor DOSIS3D measure the radiation dose induced by Galactic Cosmic Rays, Radiation Belt Particles and Solar Energetic Particles. The instruments are operative for more than 13 years since 2009. This means more than one half of a 22-year solar cycle is covered by the experiment by now. The variation of the radiation field inside the station depends on this solar cycle as well as the geomagnetic shielding by the earth’s magnetosphere. The data gathered over this long period of time will be presented as well as the plans for the future. We are currently preparing DOSTEL3D, a three-axis-telescope for the station. DOSTEL3D shall replace the two DOSTEL instruments by modern electronics to increase the energy- and time resolution. It is planned to operate the current DOSTEL units simultaneously with the new system to have good inflight cross calibration to have a continuous comparable data set. The current status of DOSTEL 3D will be presented as well as its design

Update on DOSTEL measurements in COLUMBUS within the DOSIS/DOSIS3D projects

Two Silicon‐detector based DOSimetry TELescopes (DOSTELs) have been measuring the cosmic radiation in the COLUMBUS module of the International Space Station since 2009 and have now recorded data over more than one solar cycle covering the maxima of galactic cosmic ray intensity in 2009 and 2020 and the intensity minimum in between. Dose rates in the ISS orbit from galactic cosmic radiation and trapped particles from the radiation belt in the South Atlantic Anomaly over this time are presented. The variation of dose rates over the solar cycle and the dependency on the geomagnetic shielding quantified by the cut‐off rigidity are investigated. Using dose rates measured at low geomagnetic shielding and correcting for the altitude dependent shielding from Earth against cosmic radiation, the expected dose and dose equivalent rates from galactic cosmic radiation in near‐Earth interplanetary space are derived. In addition to the data as measured with the DOSTEL instruments a short update for the data as measured with the passive radiation detectors in the frame of the DOSIS and DOSIS 3D projects will be provided as well

The DOSIS 3D Project on-board the International Space Station – Analysis of the Solar particle Event in September 2017

The nominal radiation environment in Low Earth Orbit (LEO), especially for the International Space Station (ISS), is dominated by two sources. The first is galactic cosmic radiation (GCR) which is modulated by the interplanetary and the Earth’s magnetic fields and the second is trapped radiation in the form of the Van Allen Belts. The trapped radiation inside the ISS is mostly due to protons of the inner radiation belt. In addition to these sources sporadic Solar Particle Events (SPEs) can produce high doses inside and outside the ISS, depending on the intensity and energy spectrum of the event. Before 2017, the last SPE observed inside the ISS with relevant radiation detectors occurred in May 2012. Even though we are currently approaching the next solar minimum, an SPE was observed in September 2017, which was a) a Ground Level Enhancement (GLE 72); b) measured with various radiation detector systems on-board the ISS and c) observed on the surface of Mars. This presentation gives an overview of the 10 September 2017 SPE measured with the DOSIS 3DDOSTEL and the ISS-RAD (Radiation Assessment Detector) instruments, both located at this time in close proximity to each other in the Columbus Laboratory of the ISS. The additional dose received during the SPE, was 146.2 µGy in Si as measured by ISS-RAD and 67.8 µGy in Si as measured by the DOSIS 3D-DOSTEL instruments. In addition we will show first results of GEANT4 simulations for the 10 September 2017 event and also provide comparison with events observed with DOSTEL like instruments on space station MIR (1997) and on the ISS (2001)

A Small Active Dosimeter for Applications in Space

The radiation field in low Earth orbits (LEO) differs significantly from the radiation environment on Earth's surface. Exposures are by far higher and pose an additional health risk for astronauts. Continuous monitoring is therefore a necessary task in the frame of radiation protection measures. A small battery-driven active dosimeter telescope based on silicon detectors meeting the requirements for LEO applications has been developed. The instrument, the Mobile Dosimetric Telescope (MDT), is designed to measure the absorbed dose rate and the linear energy transfer (LET) spectra. From the latter the mean quality factor of the radiation field can be derived and hence an estimate of the dose equivalent as a measure of the exposure. The calibration of the device is done using radioactive isotopes and heavy ions. Fragmentation products of heavy ions are used to show the ability of the MDT to reliably detect energy depositions from high energetic nuclei. Radiation measurements inside aircraft during long distance flights, serving as field tests of the instrument, prove the good performance of the instrument

Materials and technologies for fabrication of three-dimensional microstructures with sub-100 nm feature sizes by two-photon polymerization

The fabrication of sub-100 nm feature sizes in large-scale three-dimensional (3D) geometries by two-photon polymerization requires a precise control of the polymeric reactions as well as of the intensity distribution of the ultrashort laser pulses. The authors, therefore, investigate the complex interplay of photoresist, processing parameters, and focusing optics. New types of inorganic- organic hybrid polymers are synthesized and characterized with respect to achievable structure sizes and their degree of crosslinking. For maintaining diffraction-limited focal conditions within the 3D processing region, a special hybrid optics is developed, where spatial and chromatic aberrations are compensated by a diffractive optical element. Feature sizes below 100 nm are demonstrated