As of today, the sun has been without sunspots for 100 days in 2018
As of today, the sun has been without sunspots for 100 days in 2018. If current trends continue, 2018 will end with a 10-year low in sunspot counts. This is a sign that Solar Minimum is approaching--even more rapidly than forecasters expected. What does this mean for us on Earth? Ironically, low solar activity boosts cosmic rays. Read on...
COSMIC RAYS IN AIRPLANES: Last month, flight attendants got some bad news. According to a new study from researchers at Harvard University, the crews of commercial airlines face an elevated risk of cancer compared to members of the general population. A likely reason: cosmic rays. High energy particles from space hitting the top of Earth's atmosphere create a spray of secondary radiation that penetrates the walls of airplanes flying above ~20,000 feet.
On June 19th, Spaceweather.com and students of Earth to Sky Calculus flew from California to New Zealand to launch a series of space weather balloons--part of our ongoing program to map cosmic rays around the globe. Naturally, we took our radiation sensors onboard the airplane. Here is what we measured:
Within minutes after takeoff from Los Angeles, radiation in the passenger compartment increased 25-fold and remained high until we landed again in Brisbane, Australia, 13 hours later. Peak dose rates were almost 40 times greater than on the ground below. In total, we absorbed a whole body dose approximately equal to a panoramic dental X-ray.
Our sensors measure three types of radiation: neutrons, X-rays, and gamma-rays. Using bubble chambers, we found that about 1/3rd of our exposure came from neutrons:
Each bubble pictured above is formed by an energetic neutron (200 keV – 15 MeV) passing through the chamber. Counting bubbles yield the total dose, about 8 uGy (micro-Gray) of neutrons during the entire flight. These measurements are important because neutrons are a biologically effective form of radiation of interest to cancer researchers.
The remaining 2/3rd of our exposure came from X-rays and gamma-rays, measured using Geiger tube devices:
These are the same sensors that we have been flying to the stratosphere on space weather balloons since 2015.
Adding it all together, we detected about 24.3 uGy of neutrons + X-rays + gamma rays during the Los Angeles to Brisbane leg of our flight. For comparison, a panoramic dental X-ray yields between 14 uGy and 24 uGy.
This is just the tip of the iceberg. Cosmic rays at aviation altitudes are a cocktail of different things: e.g., neutrons, protons, pions, electrons, X-rays, and gamma rays spanning a wide range of energies. Our sensors sample only three ingredients of that cocktail (neutrons, X-rays, gamma-rays) at relatively low energies typical of medical X-rays and airport security devices. This means flight crews and passengers absorb even more radiation than we can detect. It's something to think about the next time you board a plane...
Stay tuned for updates as we continue to process our haul of data from 5 airplane flights and 3 balloon flights over New Zealand.
Reference: Tobiska, W. K., et al. (2015), Advances in Atmospheric Radiation Measurements and Modeling Needed to Improve Air Safety, Space Weather, 13, doi:10.1002/ 2015SW001169.