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The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on the Lunar Reconnaissance Orbiter (LRO) characterizes the radiation environment to be experienced by humans during future lunar missions. CRaTER measures the effects of ionizing energy loss in matter due to penetrating solar energetic protons (SEP) and galactic cosmic rays (GCR), specifically in silicon solid-state detectors and after interactions with tissue-equivalent plastic (TEP), a synthetic analog of human tissue. The CRaTER investigation quantifies the linear energy transfer (LET) spectrum in these materials through direct measurements with the lunar space radiation environment, particularly the interactions of ions with energies above 10 MeV, which penetrate and are detected by CRaTER. Combined with models of radiation transport through materials, CRaTER LET measurements constrain models of the biological effects of ionizing radiation in the lunar environment as well as provide valuable information on radiation effects on electronic systems in deep space. In addition to these human exploration goals, CRaTER measurements also provide new insights on the spatial and temporal variability of the SEP and GCR populations and their interactions with the lunar surface. We present here an overview of the CRaTER science goals and investigation, including: an instrument description; observation strategies; instrument testing, characterization, and calibration; and data analysis, interpretation, and modeling plans., United States. National Aeronautics and Space Administration (contract NNG05EB92C)

The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on the Lunar Reconnaissance Orbiter (LRO) characterizes the radiation environment to be experienced by humans during future lunar missions. CRaTER measures the effects of ionizing energy loss in matter due to penetrating solar energetic protons (SEP) and galactic cosmic rays (GCR), specifically in silicon solid-state detectors and after interactions with tissue-equivalent plastic (TEP), a synthetic analog of human tissue. The CRaTER investigation quantifies the linear energy transfer (LET) spectrum in these materials through direct measurements with the lunar space radiation environment, particularly the interactions of ions with energies above 10 MeV, which penetrate and are detected by CRaTER. Combined with models of radiation transport through materials, CRaTER LET measurements constrain models of the biological effects of ionizing radiation in the lunar environment as well as provide valuable information on radiation effects on electronic systems in deep space. In addition to these human exploration goals, CRaTER measurements also provide new insights on the spatial and temporal variability of the SEP and GCR populations and their interactions with the lunar surface. We present here an overview of the CRaTER science goals and investigation, including: an instrument description; observation strategies; instrument testing, characterization, and calibration; and data analysis, interpretation, and modeling plans., United States. National Aeronautics and Space Administration (contract NNG05EB92C)

We report spacecraft measurements of the energy spectra of solar protons and other solar particle properties during the 16 Ground Level Events (GLEs) of Solar Cycle 23. The measurements were made by seven instruments on the ACE, GOES, SAMPEX, and STEREO spacecraft and extend from »0.1 to »700 MeV. All of the proton spectra exhibit spectral breaks at energies ranging from »2.4 to »33 MeV and all are well fit by a double power-law shape. A comparison of GLE events with a sample of other SEP events shows that GLEs typically have harder spectra, with a mean slope of -3.17 at >40 MeV/nuc. On average, GLE events are enriched in species associated with impulsive _3He-rich SEP events, including enrichments in Ne/O, Fe/O, ^(22)Ne/^(20)Ne, and elevated mean charge states of Fe. This paper discusses these and other properties of particles measured in situ in GLE events.

Measurements of the energy spectra of SEP events over a broad energy range (~0.1 to 100 MeV/nuc) show that all large SEP events have spectral beaks organized by the charge-to-mass ratio (Q/M) of the ions. In this paper we present preliminary results of a multi-spacecraft study of the Q/M-dependence of spectral breaks in 11 SEP events and investigate whether the deduced Q/M dependence is correlated with other characteristics of the events.

The largest solar energetic particle (SEP) events are thought to be due to particle acceleration at a shock driven by a fast coronal mass ejection (CME). We investigate the efficiency of this process by comparing the total energy content of energetic particles with the kinetic energy of the associated CMEs. The energy content of 23 large SEP events from 1998 through 2003 is estimated based on data from ACE, GOES, and SAMPEX, and interpreted using the results of particle transport simulations and inferred longitude distributions. CME data for these events are obtained from SOHO. When compared to the estimated kinetic energy of the associated coronal mass ejections (CMEs), it is found that large SEP events can extract ~10% or more of the CME kinetic energy. The largest SEP events appear to require massive, very energetic CMEs.

Prior to 2003, there are two known cases where ultrarelativistic (>or~ 10MeV) electrons appeared in the Earth's inner zone radiation belts in association with high speed interplanetary shocks: the 24 March 1991 and the less well-studied 21 February 1994 storms. During the March 1991 event electrons were injected well into the inner zone on a timescale of minutes, producing a new stably trapped radiation belt population that persisted for ~10 years. More recently, at the end of solar cycle 23, a number of violent geomagnetic disturbances resulted in large variations in ultrarelativistic electrons in the inner zone, indicating that these events are less rare than previously thought. Here we present results from a numerical study of shock-induced transport and energization of outer zone electrons in the 1-7 MeV range, resulting in a newly formed 10-20 MeV electron belt near L~3. Test particle trajectories are followed in time-dependent fields from an MHD magnetospheric model simulation of the 29 October storm sudden commencement., Published in Journal of Geophysical Research, v112 nA09215, 2007. Prepared in collaboration with Dartmouth College, Hanover, NH; Aerospace Corp., Los Angeles, CA; and Boston University, Boston, MA.

The largest solar energetic particle (SEP) events are thought to be accelerated by shocks driven by fast coronal mass ejections (CMEs). We compare measurements of the energy content of large SEP events from 1998 to 2003 to the kinetic energy of the associated CMEs to study the efficiency of this process. Using CME data from SOHO and SEP data from ACE, SAMPEX, and GOES for a total of 17 events, we find that the ratio of the SEP to CME kinetic energies ranges from-0.1% to-20%, with the largest SEP events giving an average SEP/CME kinetic-energy ratio of -10%. Evidently shock acceleration is a relatively efficient process in these events. It is interesting that a similar efficiency is derived for cosmic-ray acceleration by supernova shocks.

From the end of 1997 to early 1998, the relatively steady-state solar-minimum conditions provided an ideal period to study the solar modulation of anomalous cosmic rays (ACRs) and galactic cosmic rays (GCRs). Using observations of the energy spectra of the most abundant elements (H, He, C, N, 0, and Ne) from an array of spacecraft and instruments, we calculate the radial gradients for ACRs and GCRs over a wide range of rigidity. The GCR radial gradient is near zero for all rigidities, out to 70 AU. The ACR radial gradient shows a strong rigidity dependence in the middle heliosphere, which is expected, but the rigidity dependence is not present in the outer heliosphere, and is not obvious in the inner heliosphere.

Quartz crystal resonators were systematically irradiated with 65 MeV protons to characterize low dose rate radiation-induced degradation. Results indicate: (1) test samples that exhibit large frequency shifts during testing tend to show large frequency shifts prior to irradiation, or during off-irradiation periods; (2) for radiation-sensitive samples, short-term effects seem to decrease after each irradiation on/off cycle (moreover, those devices in which radiation effects do not decrease after a few cycles are not very sensitive); (3) the fabrication process may be an important determinant of susceptibility to low dose radiation-induced degradation; and (4) total-dose effects may be sublinear., Prepared in collaboration with Naval Research Lab., Washington, DC.

It is well known that electrons, protons, and heavier ions can be accelerated to high energies (≳1 MeV) throughout the solar system by a variety of mechanisms. We review several of the sources of energetic ions and electrons that can produce enhanced fluxes of particles near the Earth's orbit. Solar energetic particles and particles accelerated at interplanetary shock waves are considered. We also review the properties and potential terrestrial influence of Jovian electrons. Recent measurements from the SAMPEX spacecraft in low-Earth orbit are examined to look for extraterrestrial sources of electrons and ions. We find clear evidence of both solar and Jovian electrons at high latitudes and at high altitudes around the Earth, but the durably trapped outer zone electron population seems best and most completely explained by an internal acceleration mechanism.

Energy spectra from three instruments on SAMPEX of geomagnetically trapped anomalous cosmic ray 0 and Ne with ~1 to 50 Me V /nucleon are peaked near the local western geomagnetic cutoff energy, sharply decreasing above and gradually decreasing below this energy. They are in reasonable agreement with model spectra based on the trapping theory.