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EXPERIMENT INFORMATION

Bonner Ball Neutron Detector (BBND)

Principal Investigator

+ Goka, Tateo

Bioastronautics Roadmap

+ Radiation

Species Studied

Homo sapiens (Human)

Experiment Description

OBJECTIVES:
Space travel is inherently dangerous for humans due to the large amounts of radiation present beyond Earth's atmosphere. The danger is even greater during times of extreme solar flare activity and during long duration crewed missions such as those proposed for Mars or other planets. High doses of radiation can kill cells and damage tissue, leading to cancer, cataracts, and even injury to the central nervous system.

In an effort to learn more about how to protect crewmembers from the effects of radiation, monitoring devices have flown on several Space Shuttle missions and the Russian space station Mir. These measurements yielded valuable information, but were limited to radiation doses on the external part of the body.

The Bonner Ball Neutron Detector (BBND) measures neutron radiation. Neutrons are uncharged atomic particles that have the ability to penetrate living tissues. Neutrons, especially those with energies exceeding 1MeV, are a major cause of astronaut exposure mainly because of their high radiation quality factor. Neutron radiation can affect the blood-forming marrow in the bones of human beings and other animals. By operating the Bonner Ball in space, neutron radiation information can be collected and used for the development of safety measures to protect crewmembers during long duration space flights.

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APPROACH:
The BBND hardware was launched on March 8, 2001 by STS-102 and was placed aboard the US Laboratory Module of the International Space Station (ISS) on March 18, 2001. The BBND continuously collected neutron radiation data from the inside of the ISS for over eight months, from March 23 through November 14, 2001, corresponding to the maximum solar-activity period. Useful data was acquired for 219 days 4 hours and 36 minutes with a temporal resolution of 1 minute. On August 9, 2001, the BBND hardware was relocated from the starboard side to the deck in the US Laboratory. BBND operations performed on-orbit consisted of daily hardware clock checks, weekly status checks with calibrations, and weekly neutron radiation data downlinks. The BBND experiment did not have data collection measurements pre- or postflight.

RESULTS:
During the Increment 2 mission, crewmembers were unable to perform the weekly data downlink of the on-orbit recordings due to unforeseen hardware problems. However, a plan was developed late in the increment to return the first two Small Computer System Interface (SCSI) drives filled with data to Earth. The data was returned to Earth by STS-104 and STS-108, and was forwarded to the investigator for analysis.

The investigator compared the neutron energy spectrum averaged for the entire investigation period to the results of a previous investigation on STS-89 in 1998. The neutron flux obtained during the ISS investigation was consistently lower than that in the previous investigation (shield thickness for the ISS and the STS-89 are not known). Galactic cosmic rays were the major cause of secondary neutrons measured inside the ISS by the BBND, and were inversely correlated with the 11-year solar activity.

The investigator also examined the variation of the dose-equivalent rate observed throughout the investigation period. The average dose-equivalent rate was calculated at 3.9 micro Sievert (Sv)/hour. The highest rate was 96 micro Sv/hour and appeared in the South Atlantic Anomaly (SAA) region. The characteristics of the distribution of the dose-equivalent rate averaged for the entire investigation period are a result of the geomagnetic rigidity cut off for galactic cosmic rays at the ISS orbital altitude, except in the SAA region where trapped protons caused a high rate.

Experiment Publications

Koshiishi H, Matsumoto H, Koga K, Goka T. Evaluation of Low-Energy Neutron Environment inside the International Space Station. Technical Report of Institute of Electronics, Information, and Communications Engineers. 2003; SANE2003-79:11-14 (Japanese)

Keywords :
• Elementary particle interactions
• Fast neutrons
• Gadolinium
• Neutrons
• Polyethylene

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• Protons
• Radiation dosage
• Radiation monitoring
• Solar activity

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