The NASA Space Radiation Facility at BNL
By Michael Sivertz
So you want to be an astronaut? Space flight can be dangerous, but not all dangers come in the form of large hungry aliens with a bad attitude. NASA is concerned about the amount of radiation that astronauts are exposed to in routine space flights. Radiation from cosmic rays can represent a significant risk to astronauts, depending on the duration of the flight and other factors. Lack of understanding of this risk limits NASA space flight currently. Because of this, NASA decided to build the NASA Space Radiation Facility (NSRL) at BNL.
Although NASA has been conducting studies at BNL AGS since 1995, it was in 1997 that NASA first began the collaboration with BNL in the construction of the NASA Space Radiation Facility (NSRL) at BNL, which opened in 2003. NSRL makes use of a dedicated beam line fed by the Booster to deliver beams of protons and heavy ions to a target room where samples are exposed to simulated cosmic ray radiation to study the effects in great detail.
NASA’s approach has been three pronged: - to reduce the uncertainties in cancer formation by cosmic rays, - to develop the best possible shielding, - to study possible cancer mitigation efforts.
Cosmic Rays Although the overwhelming majority of all cosmic rays are protons, the risk from cosmic rays depends not just on the flux of particles, but also upon the damage done by those particles. Iron nuclei make up a small fraction of all cosmic rays, yet the energy delivered by an iron nucleus is nearly a thousand times greater than that from protons. More importantly, since life on earth evolved in the presence of singly charged cosmic ray particles, we have developed mechanisms for repairing most of the cellular damage that is done by singly charged cosmic rays. Our atmosphere protects us from exposure to iron or any other heavy ions from cosmic rays. So when astronauts are traveling outside of the earth’s protective atmospheric and magnetic shields, they encounter a whole new level of radiation damage.
Cosmic rays are classified into two categories: galactic cosmic rays (GCRs) that appear to come continuously from all points in the sky uniformly, and solar cosmic rays originating in the sun. The solar cosmic rays are almost exclusively protons, and tend to have energy distributions that are somewhat softer than the galactic cosmic rays. GCRs are the source for almost all of the heavy ion components in cosmic rays. Solar cosmic rays can be produced in events called solar storms during which the intensity of protons from the sun increases by many orders of magnitude. Radiation doses delivered by solar storms could be fatal to unprotected astronauts.
Although cosmic rays extend to extremely high energies, the distribution peaks between 100 and 300 MeV per nucleon, more or less independent of ion species.
NSRL Beamline and Users The beam used for most NSRL experiments is large, typically 20 cm square, in order to expose a large number of biological samples all at the same time. The beam also needs to be uniform, and an ingenious series of magnets is used to produce a large beam with a very flat intensity profile across the core of the beam.
Dosimetry is controlled by measuring the ionization produced in a series of ion chambers.
Experimenters place samples in the target room, select a dose rate and total dose to deliver, and the ion chambers record the dose and cut off the beam when the desired dose is reached. Typical exposures last one minute. Experimenters may do 50 or more exposures in a single experiment, and several experiments can be conducted each day.
In addition to biological samples, physics experiments are conducted at NSRL with the goal of developing a comprehensive simulation of cosmic ray radiation throughout its interaction with matter to its deposition of energy at the microscopic level. Studies of the effectiveness of shielding have taught us that rather than trying to stop all cosmic rays, it is often helpful to just break up the heavy ions into lighter fragments that are not so heavily ionizing. Modest thicknesses (10cm) of polyethylene or water could prove to be very helpful in reducing the radiation dose of cosmic radiation.
Factors that influence cellular repair are also under study at NSRL. Since most of the damage that is done to cells by cosmic rays is repaired, experimenters are trying to better understand the ways the repair mechanism fails and how it might be improved. Antioxidants and other agents that scavenge free radicals appear to be very beneficial to cells exposed to cosmic radiation.
Running Schedule NSRL conducts experiments during three running periods throughout the year. There is usually a fall run in September-October, a spring run in March-April, and a summer run in June. A typical run will be comprised of 30-40 experiments participated in by over 100 scientists from 20-30 national and international research groups. NASA conducts a summer school during the June run during which time a small group of radiobiology students are trained in the techniques of experiments with lectures and lab work at the facility.
Additional information can be found here.