This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Do cosmic radiation doses near the moon differ significantly from those received by astronauts in low Earth orbit? Experimental lithium fluoride detectors, installed aboard the Orion spacecraft during the Artemis I mission, have now made it possible to obtain preliminary estimates.
As the Orion capsule of the uncrewed Artemis I mission orbited the moon in late November and early December 2022, more than 10,000 small crystals, embedded within two human phantoms, were collecting data on cosmic radiation doses. Among them were several dozen experimental fluorescent lithium fluoride detectors, developed at the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN) in Cracow. A method for reading the information stored in these detectors, providing insights into radiation doses and the properties of the detectors themselves, has now been presented in the journal Radiation Measurements.
"The fluorescent radiation dose detectors based on lithium fluoride, developed at our institute, are passive in nature. In other words, they work like photographic film: once the crystals have been exposed to radiation, the tracks left by individual particles must be analyzed optically under a microscope," explains Pawel Bilski (IFJ PAN), one of the co-authors of the paper. The operating principle of passive radiation detectors based on lithium fluoride crystals is straightforward.
As particles of ionizing radiation pass through a detector, they produce defects in the material's crystal lattice, which begin to act as color centers. During laboratory readout, these centers are excited by blue light and, as a result, emit red fluorescence, which can be observed under a microscope. As part of the MARE (Matroshka AstroRad Radiation Experiment) experiment conducted during the Artemis I mission, several dozen experimental lithium fluoride detectors were installed in both human phantoms, some of them highly enriched in the lithium-7 isotope.
However, IFJ PAN's overall contribution to the experiment was considerably greater, as Cracow physicists also supplied nearly 600 crystalline detectors of another type, namely thermoluminescent detectors. Conventional passive track detectors made of plastic must undergo chemical etching before readout. Lithium fluoride crystals, by contrast, require no such cumbersome chemical treatment, and a standard fluorescence microscope is sufficient for observing the tracks.
Reading the particle tracks recorded in the vicinity of the moon was therefore quick and posed no difficulties for the researchers. Challenges arose when they attempted to extract quantitative information; this required the development of nontrivial methods for calibrating the results. The fundamental difficulty stemmed from the nature of cosmic radiation.
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