However, the number of particles measured per second per square cm per MeV obtained by
BBND is consistently lower than that of the previous investigations. The average dose-
equivalent rate observed through the investigation was 3.9 micro Sv/hour or about 10 times
the rate of radiological exposure to the average U.S. citizen. In general, radiation damage to the
human body is indicated by the amount of energy deposited in living tissue, modified by the
type of radiation causing the damage; this is measured in units of Sieverts (Sv). The background
radiation dose received by an average person in the United States is approximately 3.5 milli
Sv/year. Conversely, an exposure of 1 Sv can result in radiation poisoning and a dose of 5 Sv will
result in death in 50% of exposed individuals. The average dose-equivalent rate observed
through the BBND investigation is 3.9 micro Sv/hour, or about 10 times the average U.S. surface
rate. The highest rate, 96 micro Sv/hour was observed in the SAA region.
On November 4, 2001, a solar flare and the associated geomagnetic activity caused the most
severe radiation environment inside the ISS during the BBND experiment. The increase of
neutron dose-equivalent due to those events was evaluated to be 0.19mSv, which is less than
1% of the measured neutron dose-equivalent measured over the entire 8-month period.
Although this experiment did not characterize the neutron radiation environment outside of
Earth's magnetic field, the BBND sampling equipment provided results without return of
equipment to Earth and proved that similar measurement systems could be used on missions to
the moon and Mars to monitor real-time radiation risks (Expedition 2 and 3 One Year Postflight
Report).
PUBLICATION(S)
Yajima K, Yasuda H, Takada M, et al. Measurements of cosmic-ray neutron energy spectra from
thermal to 15 MeV with Bonner Ball Neutron Detector in aircraft. Journal of Nuclear Science
and Technology. January 2010;47(1):31-39. doi: 10.1080/18811248.2010.9711934.
Koshiishi H, Matsumoto H, Chishiki A, Goka T, Omodaka T. Evaluation of the neutron radiation
environment inside the International Space Station based on the Bonner Ball Neutron Detector
experiment. Radiation Measurements. October 2007;42(9):1510-1520. doi:
10.1016/j.radmeas.2007.02.072.
Sato T, Niita K, Iwase H, Nakashima H, Yamaguchi Y, Sihver L. Applicability of particle and heavy
ion transport code PHITS to the shielding design of spacecrafts. Radiation Measurements.
October 2006;41(9-10):1142-1146. doi: 10.1016/j.radmeas.2006.07.014.
Koshiishi H, Matsumoto H, Goka T, Koga K. Evaluation of low-energy neutron environment
inside the International Space Station. Technical Report of Institute of Electronics, Information,
and Communications Engineers. 2003;103(486):11-14. [Japanese]
This investigation is complete and all results are published.