A great deal of the information known about radiation levels in LEO was obtained from measurements made on the Russian MIR station and on U.S. Space Shuttle missions. 

Three radiation  experiments will soon be operating on ISS:

1) From the U.S.A., Johnson Spacecraft Center (JSC) will fly a "phantom torso". The Principal Investigator is Gautam Badhwar

Background: The primary radiation risk to astronauts arises due to induced cancer for which organ level dose equivalent measurements are required.  The issue in assessing radiation risk in manned spaceflight is related to the estimation of organ level dose-equivalent.  Currently, both experimental and operational methods are limited to the measurement of surface (skin) dose.  Organ level dose is conservatively estimated by calculations using the radiation environment model and the appropriate radiation transport models. If the accuracy of these models were refined, the more experienced astronauts would be less flight limited by measured, accrued skin dose.
Purpose: The overall goal of the Torso experiment is to develop the capability to accurately calculate organ-absorbed dose and dose equivalent in humans exposed to ionizing space radiation.  This experiment proposes using a fully instrumented phantom torso (with head) to provide the necessary depth-dose-equivalent measurements.  Depth-dose-equivalent measurements will be taken as a function of spacecraft altitude, attitude, location and time.  Measurements internal to the phantom torso will be supported by other radiation measurements from the Tissue Equivalent Proportional Counter and the Charged Particle Direction Spectrometer.

The hardware for this experiment consists of three major pieces Similar equipment was flown on earlier shuttle missions.

a) The Phantom Torso itself is a tissue-muscle plastic equivalent anatomical model of a male head and torso comprised of 35 sliced "sections" housed in a Nomex suit.  Each section is connected via a system of pins and holes.  Voids within the phantom are used for active and passive radiation detectors.  The five small active dosimeters are located at strategic radiobiological points of interest (head, neck, heart, stomach and colon) within the phantom and will provide real time measurements. 

b) A Tissue Equivalent Proportional Counter (TEPC) will be placed near the phantom to measure external dose.  This instrument provides an efficient method of determining radiation dose and dose-equivalent in complex (mixed) radiation fields.  It records the linear energy spectra for determining dose-equivalent exposures.

c) A Charged Particle Direction Spectrometer (CPDS) will be placed near the phantom to measure particle energy and direction in the same general environment as the TEPC.  Since the interactions of heavy ions and their secondaries with tissue are not at all well understood, proton and heavy ion spectra both incident upon and inside the spacecraft will be measured.

The CPDS and TEPC units together

The Phantom Torso will be deployed in the US lab of the ISS in a location that will not interfere with the daily activities of the crew.  Photo in mockup.  Data collection occurs without crew intervention.  Every 7-10 days a crewmember downloads data from all three hardware components to the HRF PC.  These data are then downlinked to the Telescience Center at JSC in Houston.

2) A package called Dosimetric Mapping (DOSMAP) is provided by the Deutsches Zentrum fur Luft und Raumfahrt (DLR) in Germany. The Principal Investigator is Guenther Reitz.

Radiation constitutes one of the most important hazards for a human during long-term space missions.  Leaving the Earth’s surface exposes man to a wide spectrum of radiation particles and energies.  The International Space Station provides shielding, but some radiation gets through.  This experiment attempts to map the different types of radiation that gets inside the space station, which could cause harm to humans by using devices called dosimeters that detect radiation. Due to the variety of particles and energies that make up radiation, no single type of dosimeter is capable of providing sufficient information.  Several different types of dosimeters are used in this experiment.

Nuclear Track DetectorPackages (NTDP) will provide an integral measurement of energy and charge of the heavy ion component.  These small packages will be placed around the station to monitor incoming radiation. Each package contains 3 strips of CR39 plastic, one for each of 3 perpendicular axes. The graphic at left shows a typical track in this plastic due to the passage of a high energy particle. These films are returned to the ground where the tracks are analyzed.

The DOSimetry TELescopes (DOSTEL) containing two thin silicon detectors will be used to measure the flux (and the LET distribution) of charged particles.Two of these will be placed near each other in an empty rack space in the U.S. Lab.

  Several small mobile dosimetry units (MDU) can be used by crewmembers as a personal dosimeter or placed throughout the station.  Twelve thermoluminescence dosimeters (TLD) will measure the neutron dose of the incoming radiation and the mission average absorbed dose. 
Picture of MDU plugged into the Control and Interface unit :

The dosimeters, placed in various locations throughout the space station, will absorb radiation during a three-month period.  Some of the dosimeters will be gathered up every two weeks and taken to a device that will record the radiation information and allow it to be saved on one of the station computers.  Other dosimeters will simply record all the radiation absorbed and be brought back to Earth for analysis.  The radiation gathered by the various dosimeters will provide scientists information on the nature and distribution of radiation inside the space station.

Dosimetric Mapping experiments carried out on previous Space Shuttle missions.
 

3) The Japanese space agency  NASDA will contribute a radiation detector called the "Bonner ball". The Principal Investigator is Ted Goka.

The Bonner Ball Neutron Detector (BBND) is a piece of equipment developed by the National Aeronautics/Space Development Agency of Japan (NASDA) as part of a set of experiments to study the environmental and biological effects of space radiation.

In January of 1998, the Bonner Ball Neutron Detector first flew aboard the Space Shuttle Endeavor to perform neutron radiation measurements inside the vehicle during the penultimate U.S. mission to the Russian Space Station Mir (STS-89). In fact, this was the first time that neutron radiation was ever measured with an "active" detector inside the Space Shuttle. (Previous neutron measurements were made using emulsions and foils. These passive techniques require that the detection media be returned to the Earth for analysis. BBND allows one to see how the neutron flux varies with time during a mission.) The BBND was able to differentiate between neutron and proton radiation which up to that point was considered to be very difficult to carry out.

A Japanese web site about this neutron detector

The Bonner Ball Neutron Detector will fly again aboard the International Space Station to collect continuous neutron measurements for approximately six months. The BBND will consist of two units permanently attached to each another: The BBND Control Unit (not flown during the STS-89 mission) and the BBND Detector Unit. The control unit will feature a removable computer drive where the measurements will be stored; also, the BBND Control Unit (BBND-CU) will be able to control the quality of the data recorded by performing system calibrations, making adjustments, and using a time stamp on the recorded neutron measurements. The Detector Unit (BBND-DU) is composed of six detector spheres that contain a form of the gas Helium (3He) where the neutron radiation is measured.

Neutrons are uncharged atomic particles that have the ability to penetrate living tissues. Particularly, neutron radiation can affect the blood-forming marrow in the mineral bones of humans and other animals. By operating the BBND in space, neutron radiation information can be used for the development of safety measures to protect Astronauts during long missions aboard the International Space Station.

Click to learn how the Bonner Ball detector works