a)NASA studies cosmic radiation to protect high-altitude travelers
January 27, 2017 by Mara Johnson-Groh
RaD-X prepares to launch from Fort Sumner, New Mexico. Credit: NASA/Christopher Mertens
NASA scientists studying high-altitude radiation recently published new results on the effects of cosmic radiation in our atmosphere. Their research will help improve real-time radiation monitoring for aviation industry crew and passengers working in potentially higher radiation environments.
Imagine you’re sitting on an airplane. Cruising through the stratosphere at 36,000 feet, you’re well above the clouds and birds, and indeed, much of the atmosphere. But, despite its looks, this region is far from empty.
Just above you, high-energy particles, called cosmic rays, are zooming in from outer space. These speedy particles crash wildly into molecules in the atmosphere, causing a chain reaction of particle decays. While we are largely protected from this radiation on the ground, up in the thin atmosphere of the stratosphere, these particles can affect humans and electronics alike.
Launched in September 2015 near Fort Sumner, New Mexico, NASA’s Radiation Dosimetry Experiment, or RaD-X, used a giant helium-filled balloon to send instruments into the stratosphere to measure cosmic radiation coming from the sun and interstellar space. The results, presented in a special issue of the Space Weather Journal, showcase some of the first measurements of their kind at altitudes from 26,000 to over 120,000 feet above Earth.
“The measurements, for the first time, were taken at seven different altitudes, where the physics of dosimetry is very different,” said Chris Mertens, principal investigator of the RaD-X mission at NASA’s Langley Research Center in Hampton, Virginia. “By having the measurements at these seven altitudes we’re really able to test how well our models capture the physics of cosmic radiation.”
Cosmic radiation is caused by high-energy particles that continually shower down from space. Most of these energetic particles come from outside the solar system, though the sun is an important source during solar storms.
The RaD-X payload ascended into the stratosphere to measure cosmic radiation coming from the sun and interstellar space. Credit: NASA
Earth’s magnetosphere, which acts as a giant magnetic shield, blocks most of the radiation from ever reaching the planet. Particles with sufficient energy, however, can penetrate both Earth’s magnetosphere and atmosphere, where they collide with molecules of nitrogen and oxygen. These collisions cause the high-energy particles to decay into different particles through processes known as nucleonic and electromagnetic cascades.
If you could see the particles from the airplane window, you would notice them clustering in a region above the plane. The density of the atmosphere causes the decay to happen predominantly at a height of 60,000 feet, which creates a concentrated layer of radiation particles known as the Pfotzer maximum.
Radiation in the atmosphere can be measured in two ways—by how much is present or by how much it can harm biological tissue. The latter is known as the dose equivalent and is the standard for quantifying health risks. This quantity is notoriously hard to measure, as it requires knowing the both the type and energy of the particle that deposited the radiation, not simply how many particles there are.
These particles, both the primary high-energy particles and the secondary decay particles, can have adverse health effects on humans. Cosmic radiation breaks down DNA and produces free radicals, which can alter cell functions.
The RaD-X mission took high-altitude measurements, few of which previously existed, to better understand how cosmic radiation moves through Earth’s atmosphere. Measuring dose equivalent rate over a range of altitudes, they found a steady increase in the rate higher in the atmosphere, a finding seemingly contrary to the concentration of particles at the Pfotzer maximum. This can be explained by the complex interplay of primary and secondary particles at these altitudes, as the primary particles found higher up have a much more damaging effect on tissue than the secondary particles.
Because of their time spent in Earth’s upper atmosphere, aircrew in the aviation industry are exposed to nearly double the radiation levels of ground-based individuals. Exposure to cosmic radiation is also a concern for crew aboard the International Space Station and future astronauts journeying to Mars, which has a radiation environment similar to Earth’s upper atmosphere. Learning how to protect humans from radiation exposure is a key step in future space exploration.
Radiation dose rates, seen in this NAIRAS model, increase with altitude and latitude and can vary from hour to hour. Rates for Nov. 14, 2012, 20:00-21:00 GMT are shown above. Warmer colors indicate higher amounts of radiation. Credit: NASA/NAIRAS
The results from RaD-X will be used to improve space weather models, like the Nowcast of Atmospheric Ionizing Radiation for Aviation Safety, or NAIRAS, model, which predicts radiation events. These predictions are used by commercial pilots to know when and where radiation levels are unsafe, allowing rerouting of aircraft in the affected region when necessary.
While balloon flights like RaD-X are essential for modelling the radiation environment, they cannot provide real-time radiation monitoring, which NAIRAS requires for forecasting. NASA’s Automated Radiation Measurements for Aerospace Safety program works in conjunction with RaD-X to develop and test instruments that can be flown aboard commercial aircraft for real-time monitoring at high altitudes.
Currently, an instrument called a TEPC – short for tissue equivalent proportional counter – is the standard instrument for measuring cosmic radiation. This instrument is large, expensive and cannot be commercial built – making it less than ideal for wide-scale distribution.
“We need small, compact, solid-state based instruments calibrated against the TEPC that can reliably measure the dose equivalents and can be integrated into aircraft cheaply and compactly,” Mertens said.
The flight mission tested two new instruments – the RaySure detector and the Teledyne TID detector – in hope that they can be installed on commercial aircraft in the future. These new instruments offer the advantage of being compact and easily produced. During RaD-X mission testing, both instruments were found to be promising candidates for future real-time, in situ monitoring.
Provided by: NASA’s Goddard Space Flight Center
b)Random radiation clouds found in atmosphere at flight altitudes
A large team of researchers with members from several institutions in the U.S., Korea, and the U.K. has found evidence of random radiation clouds in the Earth’s atmosphere at elevations used by aircraft. In their paper published in the journal Space Weather, the team describes how they discovered the clouds and offers a theory for their existence.
For several years, NASA has been conducting a project called Automated Radiation Measurements for Aerospace Safety (ARMAS)—devices are placed aboard aircraft that measure radiation levels during flights; readings are recorded in a database for study. In this new effort, the researchers accessed the database and examined data from 265 flights during the period 2013 to 2017. In so doing, they found mostly what was expected—higher than ground levels of radiation. But they also found unusual readings—six instances of high altitude and high latitude flights during which radiation levels rose to twice the normal level for several minutes. The researchers described the events as flying through a radiation cloud.
Increased radiation exposure is, of course, the norm for people aboard an airplane due to their closer proximity to outer space. But the risk from such flights is considered small—equivalent to a chest X-ray for longer flights, or a dental X-ray for shorter flights. Such radiation comes from space courtesy of the solar wind or from other sources in outer space. Our atmosphere and magnetic poles filter enough of it to enable Earth. But we do experience geomagnetic storms sometimes, during which electrons escape from the Van Allen radiation belts (zones of charged particles surrounding the planet that have been captured by the Earth’s magnetic field) and rain down to the surface. Data from the ARMAS devices indicated that the radiation clouds might be linked to such storms.
The discovery of such clouds suggests that frequent flying at high altitudes (above 55,000 feet) may be slightly more hazardous than has been thought. The researchers suggest that sensor networks could be used to create a grid for pinpointing such clouds to allow rerouting of airplanes around them.
More information: W. Kent Tobiska et al. Global real-time dose measurements using the Automated Radiation Measurements for Aerospace Safety (ARMAS) system, Space Weather (2016). DOI: 10.1002/2016SW001419 , (PDF)
The Automated Radiation Measurements for Aerospace Safety (ARMAS) program has successfully deployed a fleet of six instruments measuring the ambient radiation environment at commercial aircraft altitudes. ARMAS transmits real-time data to the ground and provides quality, tissue-relevant ambient dose equivalent rates with 5 min latency for dose rates on 213 flights up to 17.3 km (56,700 ft). We show five cases from different aircraft; the source particles are dominated by galactic cosmic rays but include particle fluxes for minor radiation periods and geomagnetically disturbed conditions. The measurements from 2013 to 2016 do not cover a period of time to quantify galactic cosmic rays’ dependence on solar cycle variation and their effect on aviation radiation. However, we report on small radiation “clouds” in specific magnetic latitude regions and note that active geomagnetic, variable space weather conditions may sufficiently modify the magnetospheric magnetic field that can enhance the radiation environment, particularly at high altitudes and middle to high latitudes. When there is no significant space weather, high-latitude flights produce a dose rate analogous to a chest X-ray every 12.5 h, every 25 h for midlatitudes, and every 100 h for equatorial latitudes at typical commercial flight altitudes of 37,000 ft (~11 km). The dose rate doubles every 2 km altitude increase, suggesting a radiation event management strategy for pilots or air traffic control; i.e., where event-driven radiation regions can be identified, they can be treated like volcanic ash clouds to achieve radiation safety goals with slightly lower flight altitudes or more equatorial flight paths.
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