Space Station sends back first radiation data

The first series of radiation data collected inside the International Space
Station (ISS) has been transmitted from space to scientists on Earth eager
to assess its potential biomedical impacts and implications for future
research.

The data were collected in May by radiation detectors on the ISS known as
thermoluminescent detectors (TLDs). An onboard electronic reader read the
data earlier this month and ISS astronaut James Voss transmitted it to
scientists on Earth. The TLDs are part of a set of radiation-monitoring
hardware known as the Passive Dosimeter System (PDS), which was developed by
the Space Station Biological Research Project at NASA Ames Research Center
and the Hungarian Space Office. The ability to accurately measure and
monitor radiation exposure is important both to crew health and to future
scientific research on the ISS.

“This is very good news,” exulted project science lead Kristofer Vogelsong
of Lockheed Martin Engineering and Sciences at NASA Ames, in the heart of
California’s Silicon Valley. “The quality of the data indicates that the
reader is functioning normally.” Space Shuttle Discovery ferried the TLDs to
the ISS in March.

The Passive Dosimeter System is a flexible, easy-to-use radiation monitoring
system that is available for use by researchers from the U.S. or ISS partner
nations. It complements existing dosimeters used in routine ISS operations.
The dosimeters can be placed anywhere in the ISS to provide an accurate
measurement of the radiation levels at their locations.

Vogelsong said the data indicate that all 12 TLDs currently in use are in
perfect condition. The detectors are a third-generation version of
dosimeters that flew on the Russian space stations Salyut 7 and Mir, and on
the space shuttle.

NASA scientists expect to receive a preliminary interpretation soon of the
radiation dose onboard the ISS from the Hungarian Space Office. A complete
picture of the space station’s radiation environment will not be available
until a second type of dosimeter, known as Plastic Nuclear Track Detectors
(PNTDs), is returned to Earth on an August space shuttle flight. The data
from the TLDs will be combined with the data from the PNTDs and other
radiation monitors as part of the Dosimetric Mapping Experiment (DOSMAP) to
characterize the space radiation environment on board the space station. The
DOSMAP experiment is being conducted by Dr. Guenther Reitz and is managed by
the Space and Life Sciences Directorate at NASA’s Johnson Space Center,
Houston.

The PNTDs — thin sheets of plastic similar to the material used for some
eyeglass lenses — were delivered to the ISS last April. The PNTD surface
becomes pitted with tiny craters as heavy charged ions pass through it.
After the detectors are returned to Earth, the plastic will be etched to
enlarge the craters, which will be counted and their shapes and sizes
analyzed using a microscope. This information is used to improve the
accuracy of the radiation dose the TLDs have recorded and to improve the
estimate of the biological effects of the radiation. Eril Research, San
Rafael, CA, developed and will analyze the PNTDs.

Each TLD, which resembles a fat fountain pen, contains calcium sulfate
crystals inside an evacuated glass bulb. The crystals absorb energy from
incident ionizing radiation (protons, neutrons, electrons, heavy charged
particles, gamma rays and x-rays) as the radiation passes through them. This
process results in a steady increase in the energy level of the electrons in
the crystal.

“We are happy the Passive Dosimeter System appears to be working well,” said
PDS payload manager Robert Jackson of Ames. “We expect that support to the
DOSMAP experiment will be followed in future years by continued use for many
experiments on the space station.”

Images of the TLDs are available at:
http://amesnews.arc.nasa.gov:8080/releases/2001/01images/thermolum/thermolum.html