One of the problems with having Humans in space and living there is how to deal with cosmic radiation. When we start talking about having habitats in Space, for example on the Moon or on Mars, dangers of cosmic radiation is one of the risks that we have to address. We don’t have to worry about it in our daily life because on Earth we are protected by its magnetic shield from the cosmic radiation, however once we get outside the atmosphere & magnetic shield it becomes an issue. Unprotected humans living on the Space Station are at significant risk for radiation sickness, increased risk of cancer and degenerative diseases. Dangers of Cosmic radiation are long known however there has never been any accurate measurement of how much stronger the Cosmic radiation is on the Moon since it doesn’t have an atmosphere or magnetic field to block the dangerous radiation and knowing the strength of the radiation would be crucial in designing habitats on the Moon to protect the astronauts living there.
Now thanks to an International collaborative effort we finally have an answer to the question “How much higher is the Radiation on the moon, as compared to Earth & the ISS”. Using the Lunar Lander Neutron and Dosimetry (LND) which was part of the payload on China’s Chang’e-4 lunar probe (which landed on the far side of the moon early last year) the researchers were able to measure the radiation it was exposed to. Basically the LND measured the total amount of radiation it was exposed to over the 2 week period of its operation and sent that data back to earth where the researchers divided the total radiation dose by the amount of time tool operated to calculate the daily total.
This gives us the first concrete measurement of the Cosmic radiation on the surface of the moon. Unfortunately the numbers are not pretty, the base Radiation level on the surface of the Moon is approximately 200 times more than the base Radiation level on the surface of the Earth. Even when we compare it to the level on the ISS, it turns out that the moon has over 2.6 times higher radiation levels than the ISS making it very risky for unshielded humans to stay there for a long duration.
The only way to protect the astronauts is to shield their habitats and spacesuits. For the spacesuits there is ongoing research to identify the best material for shielding (lead works great but is heavy) and for the habitats the cheapest and most effective option would be to just build the whole thing underground. The lunar soil would act as a shield to protect the interior and best of all it doesn’t require us to lift heavy shielding material into orbit reducing the cost of the missions. As per the team’s calculations burying the habitat under ~30 inches of lunar soil would give it protection equivalent to ground level on Earth.
For the assessment of the radiation exposure, the relevant quantities have to be measured by the detector systems: The absorbed dose, D, is the ratio of the energy (E; usually measured in keV) deposited in a detector and the mass, m, of the detector and is expressed in units of Gray (Gy = J/kg). Division by the accumulation time results in the measured dose rate (expressed in Gy/hour). Using a combination of two detectors in coincidence, one measures the distribution of energies deposited in a detector to obtain the linear energy transfer (LET) spectrum [usually in units of keV per micrometer (keV/μm)]. This spectrum is integrated with so-called quality factors, Q, used as biological weights to obtain the dose equivalent, H, which is expressed in units of Sievert (Sv = J/kg). The exact procedures are defined by the International Commission on Radiation Protection (17). Because the human body is not made of silicon, and to make dose, dose rate, and LET measurements more easily comparable to others, one normally converts the values measured in Si to the corresponding quantities in water using a constant dose conversion factor of 1.30 (18).
The Lunar Lander Neutrons and Dosimetry (LND) experiment is described in more detail in the literature (19), but we summarize the pertinent information here for convenience. The LND is mounted in the payload compartment of the Chang’E 4 lander. The red arrow in Fig. 1 points at the reclosable door that protects LND from the cold lunar nights but is open during lunar daytime. The LND consists of a stack of 10 dual-segment silicon solid-state detectors (SSDs), A to J, as shown in the main part of Fig. 2. Total absorbed dose and dose rate are measured in detector B, and the absorbed dose (rate) from neutral particles is measured in the inner segment of the C detector, C1, with the closely spaced detectors B and D as well as the outer segment of C, C2, serving as anticoincidence to discriminate against charged particles. The LET is then determined as discussed above from the dE/dx measured using three different combinations of detector pairs with different counting rates and average path lengths. Penetrating particles are measured by requiring signals in all 10 detectors.
More details of the research are available on the paper published in the journal Science Advances late last month. Check it out if you are interested in learning more technical details about the project.
– Suramya