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FACILITY DESCRIPTION
NASA Space Radiation Laboratory
The NSRL comprises an extraction system, dedicated beam line, fully outfitted
experimental hall and counting rooms. The extraction system and beam line deliver
heavy ion beams from the AGS Booster synchrotron. The AGS Booster is an ideal
accelerator for space radiation studies due to the good overlap between the available ion
masses and energies with those encountered in space. A variety of heavy high energy
(HZE) particles are available with energies ranging from a maximum of 1.3 GeV/amu for
the lightest ions, to approximately 1.1 GeV/amu for iron and approximately 300
MeV/amu for gold, down to a minimum of less than 100 MeV/amu.
The experimental facilities include a well-shielded target area and a support building
containing the counting rooms, ready-rooms, laboratories, and offices. Beam
characterization is done using silicon solid state detectors using methods developed over
a number of years at the LBNL Bevalac and BNL AGS [Zeitlin (1998)].
Instruments to be exposed to beam are mounted on a simple and stable rail system with
adjustable attachments to which instrument holders can be readily adapted. Positioning is
done by means of a laser system. The beam is steered, focused and shaped using dipole,
quadrupole and octupole magnets. Spot sizes from 20x20 cm down to 1x1 cm have been
achieved. Particle intensities can be varied from 102 to 108 per spill. Signal and high
voltage cables run between the target area and counting rooms, and experimenters have
the option of using either their own data acquisition system or a local data acquisition
system provided by the LBNL and BNL groups.
Several beam opportunities per year are offered.
[Zeitlin (1998)] Detailed Characterization of the 1087 MeV/nucleon 56Fe Beam Used for
Radiobiology at the AGS. C. Zeitlin, L. Heilbronn, J. Miller, Radiat. Res. 149 560
(1998).
NSRL Beam Characterization
A typical setup for making bean characterization measurements is shown in Fig. 1. In
this case, the targets were different materials and thicknesses of spacecraft shielding.
(The bare beam is characterized with no target in place.) Charge and energy spectra are
obtained using a particle spectrometer, the major components of which are solid state
(silicon) detectors of several different thicknesses. The number and type of detectors is
adjusted according to the beam ion and energy. The detector system illustrated here was
used for with 1087 MeV/nucleon 56Fe ions at the BNL AGS, but a virtually identical
system is in use at the NSRL.
Target
PSD1
PSD2
d5mm1-2
PSD3
d3mm1-4
T1
&
T2
TOF1
scint
2.4 m
flight path
from T1 (start)
Beam direction
Not to scale
Fig. 1. Charged particle spectrometer used for beam characterization.
Solid state detectors record the energy deposited by charged particles traversing them.
Deconvoluting the energy losses in two or more detectors makes it possible to calculate
the particle’s charge and energy. The solid state detector stack was augmented in this
case by plastic scintillation counters to measure the time of flight between two points.
This information is needed to supplement the energy loss information in the case of the
lighter charged particles.
Each individual particle event seen by the detector system is recorded during the
accelerator run and offline computer analysis is used to extract information about the
charge and energy of the transmitted particles. Some correction to the data is required to
account for multiple scattering effects for which particles are lost from the detector
system.
Taking into account energy loss in the beamline and upstream detectors, the energy at the
target entrance was 1053 ± 5 MeV/nucleon. Figure 2 shows some results for fragment
fluence spectra produced by 56Fe in aluminum and two different thicknesses of graphite-
epoxy, one possible new shielding material. The primary iron beam produces the large
peak at the right in each spectrum, and discrete peaks for charges from the primary
( Z  26 ) down to at least Z  4 can be identified by eye. This simple example shows the
similarity in the fragmentation properties of 2.54 cm aluminum and 5 cm graphite-epoxy,
and the effects of doubling the thickness of graphite-epoxy from 5 to 10 cm: note the
increased energy loss at 10 cm (due to the slowing of the beam) and the increased
fragmentation, evidenced in the increased height of the fragment peaks relative to the
primary iron. The data can be readily converted into separate energy spectra for each
fragment, and analytical techniques using the information from additional detectors have
extended the range to Z  2 and in some cases Z=1.
Fig. 2. Energy loss spectra from 1.05 GeV/nucleon 56Fe fragmenting in three different shielding material
targets.
a) 10 cm graphite-epoxy; b) 5 cm graphite-epoxy; c) 2.54 cm aluminum. The ordinate is number of
counts (unnormalized). The abscissa is the summed energy loss (in MeV) in two 3 mm thick silicon
detectors.