Engineering topics

Cummings, A. C.

Publications and source records attributed to Cummings, A. C..

At least 19 records

NASA NTRS2016

Observation of the 60Fe Nucleosynthesis-Clock Isotope in Galactic Cosmic Rays

Iron-60 (60Fe) is a radioactive isotope in cosmic rays that serves as a clock to infer an upper limit on the time between nucleosynthesis and acceleration. We have used the ACE-CRIS instrument to collect 3.55 105 iron nuclei, with energies 195 to 500 megaelectron volts per nucleon, of which we identify 15 60Fe nuclei. The 60Fe56Fe source ratio is (7.5 2.9) 105. The detection of supernova-produced 60Fe in cosmic rays implies that the time required for acceleration and transport to Earth does not greatly exceed the 60Fe half-life of 2.6 million years and that the 60Fe source distance does not greatly exceed the distance cosmic rays can diffuse over this time, 1 kiloparsec. A natural place for 60Fe origin is in nearby clusters of massive stars.

Binns, W. R.↗

NASA NTRS2013

Constraints on Galactic Cosmic-Ray Origins from Elemental and Isotopic Composition Measurements

The most recent measurements by the Cosmic Ray Isotope Spectrometer (CRIS) aboard the Advanced Composition Explorer (ACE) satellite of ultra-heavy cosmic ray isotopic and elemental abundances will be presented. A range of isotope and element ratios, most importantly Ne-22/Ne-20, Fe-58/Fe-56, and Ga-31/Ge -32 show that the composition is consistent with source material that is a mix of approx 80% ISM (with Solar System abundances) and 20% outflow/ejecta from massive stars. In addition, our data show that the ordering of refractory and volatile elements with atomic mass is greatly improved when compared to an approx 80%/20% mix rather than pure ISM, that the refractory and volatile elements have similar slopes, and that refractory elements are preferentially accelerated by a factor of approx 4. We conclude that these data are consistent with an OB association origin of GCRs.

Galactic Cosmic Rays↗

NASA NTRS2013

Elemental GCR Observations during the 2009-2010 Solar Minimum Period

Using observations from the Cosmic Ray Isotope Spectrometer (CRIS) onboard the Advanced Composition Explorer (ACE), we present new measurements of the galactic cosmic ray (GCR) elemental composition and energy spectra for the species B through Ni in the energy range approx. 50-550 MeV/nucleon during the record setting 2009-2010 solar minimum period. These data are compared with our observations from the 1997-1998 solar minimum period, when solar modulation in the heliosphere was somewhat higher. For these species, we find that the intensities during the 2009-2010 solar minimum were approx. 20% higher than those in the previous solar minimum, and in fact were the highest GCR intensities recorded during the space age. Relative abundances for these species during the two solar minimum periods differed by small but statistically significant amounts, which are attributed to the combination of spectral shape differences between primary and secondary GCRs in the interstellar medium and differences between the levels of solar modulation in the two solar minima. We also present the secondary-to-primary ratios B/C and (Sc+Ti+V)/Fe for both solar minimum periods, and demonstrate that these ratios are reasonably well fit by a simple "leaky-box" galactic transport model that is combined with a spherically symmetric solar modulation model.

Solar Modulation↗

NASA NTRS2013

Solar Energetic Particle Anisotropies Observed by STEREO/LET

The Low Energy Telescopes (LETs) onboard the twin STEREO spacecraft can measure the anisotropies of energetic particles for protons through iron at energies of 1.8-12 MeV/nucleon, depending on species. A large variety of anisotropies are observed. Unidirectional beamed distributions often appear at the onset of magnetically well-connected solar energetic particle (SEP) events, while long-lasting bidirectional flows are seen within several interplanetary coronal mass ejections (ICMEs) due to either injection of particles at both footpoints of the CME or mirroring of a unidirectional beam. Several examples of a loss-cone distribution are clearly seen, in which particles with pitch angles far from the field direction are mirrored while those with smaller pitch angles are not, either because the magnetic field strength did not become large enough to turn the smaller pitch angle particles around, or more scattering occurred between the observer and the more distant mirror points of these particles. Distributions with pronounced depletions at 90 deg to the field, as well as those that instead have enhancements at 90 deg (i.e., trapped distributions) are also seen. The magnitude of the anisotropies often depends on particle energy and species, with lower energy particles typically more anisotropic than higher energy particles. We present some of the more interesting LET anisotropy observations throughout the STEREO mission to date and discuss the implications of these observations for SEP transport in the heliosphere.

coronal mass ejections↗

NASA NTRS2013

Galactic Cosmic-Ray Energy Spectra and Composition during the 2009-2010 Solar Minimum Period

We report new measurements of the elemental energy spectra and composition of galactic cosmic rays during the 2009-2010 solar minimum period using observations from the Cosmic Ray Isotope Spectrometer (CRIS) onboard the Advanced Composition Explorer. This period of time exhibited record-setting cosmic-ray intensities and very low levels of solar activity. Results are given for particles with nuclear charge 5 <= Z <= 28 in the energy range approx. 50-550 MeV / nucleon. Several recent improvements have been made to the earlier CRIS data analysis, and therefore updates of our previous observations for the 1997-1998 solar minimum and 2001-2003 solar maximum are also given here. For most species, the reported intensities changed by less than approx. 7%, and the relative abundances changed by less than approx. 4%. Compared with the 1997-1998 solar minimum relative abundances, the 2009-2010 abundances differ by less than 2sigma, with a trend of fewer secondary species observed in the more recent time period. The new 2009-2010 data are also compared with results of a simple "leaky-box" galactic transport model combined with a spherically symmetric solar modulation model. We demonstrate that this model is able to give reasonable fits to the energy spectra and the secondary-to-primary ratios B/C and (Sc+Ti+V)/Fe. These results are also shown to be comparable to a GALPROP numerical model that includes the effects of diffusive reacceleration in the interstellar medium.

Galactic Cosmic Rays↗

NASA NTRS2012

Large Proton Anisotropies in the 18 August 2010 Solar Particle Event

The solar particle event observed at STEREO Ahead on 18 August 2010 displayeda rich variety of behavior in the particle anisotropies. Sectored rates measured by theLow Energy Telescope (LET) on STEREO showed very large bidirectional anisotropies in4 6 MeV protons for the first 17 hours of the event while inside a magnetic cloud, withintensities along the field direction several hundred to nearly 1000 times greater than thoseperpendicular to the field. At the trailing end of the cloud, the protons became isotropic andtheir spectrum hardened slightly, while the HeH abundance ratio plunged by a factor of approximatelyfour for about four hours. Associated with the arrival of a shock on 20 Augustwas a series of brief (10 minute duration) intensity increases (commonly called shockspikes) with relatively narrow angular distributions (45 FWHM), followed by an abruptdecrease in particle intensities at the shock itself and a reversal of the proton flow to a directiontoward the Sun and away from the receding shock. We discuss the STEREOLETobservations of this interesting event in the context of other observations reported in theliterature

cosmic rays solar↗

NASA NTRS2012

Sudden Intensity Increases and Radial Gradient Changes of Cosmic Ray Mev Electrons and Protons Observed at Voyager 1 Beyond 111 AU in the Heliosheath

Voyager 1 has entered regions of different propagation conditions for energetic cosmic rays in the outer heliosheathat a distance of about 111 AU from the Sun. The low energy 614 MeV galactic electron intensity increased by 20over a time period 10 days and the electron radial intensity gradient abruptly decreased from 19AU to 8AU at2009.7 at a radial distance of 111.2 AU. At about 2011.2 at a distance of 116.6 AU a second abrupt intensity increase of25 was observed for electrons. After the second sudden electron increase the radial intensity gradient increased to18AU. This large positive gradient and the 13 day periodic variations of 200 MeV particles observed near theend of 2011 indicate that V1 is still within the overall heliospheric modulating region. The implications of these resultsregarding the proximity of the heliopause are discussed.

protons↗

NASA NTRS2011

The Integrated Science Investigation of the Sun (ISIS): Energetic Particle Measurements for the Solar Probe Plus Mission

One of the major goals of NASA's Solar Probe Plus (SPP) mission is to determine the mechanisms that accelerate and transport high-energy particles from the solar atmosphere out into the heliosphere. Processes such as coronal mass ejections and solar flares, which peak roughly every 11 years around solar maximum, release huge quantities of energized matter, magnetic fields and electromagnetic radiation into space. The high-energy particles, known as solar energetic particles or SEPs, present a serious radiation threat to human explorers living and working outside low-Earth orbit and to technological assets such as communications and scientific satellites in space. This talk describes the Integrated Science Investigation of the Sun (ISIS) - Energetic Particle Instrument suite. ISIS measures key properties such as intensities, energy spectra, composition, and angular distributions of the low-energy suprathermal source populations, as well as the more hazardous, higher energy particles ejected from the Sun. By making the first-ever direct measurements of the near-Sun regions where the acceleration takes place, ISIS will provide the critical measurements that, when integrated with other SPP instruments and with solar and interplanetary observations, will lead to a revolutionary new understanding of the Sun and major drivers of solar system space weather.

McComas, D. J.↗

NASA NTRS2009

The Energetic Trans-Iron Nuclei Experiment (ENTICE)

The ENTICE experiment is one of two instruments that comprise the "Orbiting Astrophysical Spectrometer in Space (OASIS)" which is presently undergoing a NASA "Astrophysics Strategic Mission Concept Study". ENTICE is designed to make high precision measurements of the abundances of individual elements from neon through the actinides and, in addition, will search for possible superheavy nuclei in the galactic cosmic rays. The ENTICE instrument utilizes silicon detectors, aerogel and acrylic Cherenkov counters, and a scintillating optical fiber hodoscope to measure the charge and energy of these ultra-heavy nuclei for energies greater than 0.3 GeV/nucleon. It is a large instrument consisting of four modules with a total effective geometrical factor of ~20 m2sr. Measurements made in space for a period of 3 years with ENTICE will enable us to determine if cosmic rays include a component of recently synthesized heavy elements (Pu and Cm), what the age of that component is, and test the model of the OB association origin of galactic cosmic rays. Additionally, it will enable us to study how diffusive shock acceleration of cosmic rays operates differently on interstellar grains and gas.

Binns, W. R.↗

NASA NTRS2009

The Energetic Trans-Iron Cosmic-ray Experiment (ENTICE)

The ENTICE experiment is one of two instruments that comprise the "Orbiting Astrophysical Spectrometer in Space (OASIS)", which is presently undergoing a NASA "Astrophysics Strategic Mission Concept Study". ENTICE is designed to make high precision measurements of the abundances of individual elements from neon through the actinides and, in addition, will search for possible superheavy nuclei in the galactic cosmic rays. The ENTICE instrument utilizes silicon detectors, aerogel and acrylic Cherenkov counters, and a scintillating optical fiber hodoscope to measure the charge and energy of these ultra-heavy nuclei for energies greater than 0.5 GeV/nucleon. It is a large instrument consisting of four modules with a total effective geometrical factor of approx.20 sq m sr. Measurements made in space for a period of three years with ENTICE will enable us to determine if cosmic rays include a component of recently synthesized transuranic elements (Pu-94 and Cm-96), to measure the age of that component, and to test the model of the OB association origin of galactic cosmic rays. Additionally, these observations will enable us to study how diffusive shock acceleration of cosmic rays operates differently on interstellar grains and gas. Keywords: cosmic rays Galaxy:abundances

Binns, W. R.↗

NASA NTRS2009

Observation and Interpretation of Energetic Neutral Hydrogen Atoms from the December 5, 2006 Solar Flare

We discuss observations of energetic neutral hydrogen atoms (ENAs) from a solar flare/coronal mass ejection event reported by Mewaldt et al. (2009). The observations were made during the 5 December 2006 X9 solar flare, located at E79, by the Low Energy Telescopes (LETs) on STEREO A and B. Prior to the arrival of the main solar energetic particle (SEP) event at Earth, both LETs observed a sudden burst of 1.6 to 15 MeV particles arriving from the Sun. The derived solar emission profile, arrival directions, and energy spectrum all show that the <5 MeV particles were due to energetic neutral hydrogen atoms produced by either flare or shock-accelerated protons. RHESSI measurements of the 2.2-MeV gamma-ray line provide an estimate of the number of interacting flare-accelerated protons in this event, which leads to an improved estimate of ENA production by flare-accelerated protons. CME-driven shock acceleration is also considered. Taking into account ENA losses, we conclude that the observed ENAs must have been produced in the high corona at heliocentric distances .2 solar radii.

Barghouty, A. F.↗

NASA NTRS2009

Observation and Interpretation of Energetic Neutral Hydrogen Atoms from the December 5, 2006 Solar Event

We report the first observations of energetic neutral atoms (ENAs) from a solar flare/coronal mass ejection event. The observations were made during the December 5, 2006 X9 solar flare, located at E79, by the Low Energy Telescopes (LETs) on the STEREO A and B spacecraft. Within 1-2 hours of the flare onset, both LETs observed a sudden burst of 1.6 to 15 MeV protons arriving hours before the onset of the main solar energetic particle (SEP) event at Earth. More than 70% of these particles arrived from a longitude within +-10 degrees of the Sun. The derived emission profile at the Sun lasted for more than an hour and had a profile remarkably similar to the GOES soft X-ray profile. The observed arrival directions and energy spectrum argue strongly that the particle events <5 MeV were due to energetic neutral hydrogen atoms that were stripped of their electrons upon entering the LET sensor. To our knowledge, this is the first reported observation of ENA emission from a solar flare/coronal mass ejection. We discuss possible origins for the production of ENAs in solar events, including charge-transfer reactions involving both flare and shock-accelerated protons. Assuming isotropic emission, we find that ~2 x 10E28 ENAs escaped from the Sun in the upper hemisphere. Based on the 2.2 MeV gamma-ray emission observed by RHESSI in this event, and using measured and theoretical cross sections, we estimate that ~3 x 10E31 ENAs with 1.8 - 5 MeV could be produced by protons accelerated in the flare. CME-driven shock acceleration is also a possible ENA source, but unfortunately there were no CME observations available from this event. Taking into account ENA losses, we conclude that the observed ENAs were most likely produced in the high corona at heliocentric distances 1.6 solar radii.

Mewaldt, R. A.↗

NASA NTRS2009

STEREO Observations of Energetic Neutral Hydrogen Atoms during the 5 December 2006 Solar Flare

We report the discovery of energetic neutral hydrogen atoms emitted during the X9 solar event of December 5, 2006. Beginning ~1 hour following the onset of this E79 flare, the Low Energy Telescopes (LETs) on both the STEREO A and B spacecraft observed a sudden burst of 1.6 to 15 MeV protons beginning hours before the onset of the main solar energetic particle (SEP) event at Earth. More than 70% of these particles arrived from a longitude within 10 of the Sun, consistent with the measurement resolution. The derived emission profile at the Sun had onset and peak times remarkably similar to the GOES soft X-ray profile and continued for more than an hour. The observed arrival directions and energy spectrum argue strongly that the particle events less than 5 MeV were due to energetic neutral hydrogen atoms (ENAs). To our knowledge, this is the first reported observation of ENA emission from a solar flare/coronal mass ejection. Possible origins for the production of ENAs in a large solar event are considered. We conclude that the observed ENAs were most likely produced in the high corona and that charge-transfer reactions between accelerated protons and partially-stripped coronal ions are an important source of ENAs in solar events.

Mewaldt, R. A.↗

NASA NTRS2008

The Solar Energetic Particle Event of December 14, 2006

We report on observations of a solar energetic particle event by instruments on five different spacecraft: the Advanced Composition Explorer (ACE), STEREO A and B, WIND, and GOES II. The event began with a class X1.5 .soft x-ray flare in AR930 on December 14 at 22:15 UT. At this time the two STEREO spacecraft were located outside the Earth's magnetosphere and were heading for their first lunar swing-by on December 15. The x-ray event was located on the sun at W46, a longitude which is nominally well-connected magnetically to the Earth. An interplanetary shock, associated with an earlier X3.4 event on December 13 (also from AR930), passed the Earth on December 14 at approx.13:56 (time at ACE). The corresponding magnetic cloud arrived at approx.22 UT on December 14, close to the time of the onset of the particle event associated with the X1.5 flare, and extended until approx.08 UT on December 15. The intensity of approx.14 MeV protons at STEREO A shows three dips by factors of approx.10 or more during the early stages of this event while the spacecraft was within the magnetic cloud. Similar dips are seen for protons to at least 100 MeV. In principle, these dips could have been caused by changes in the magnetic field direction with respect to the particle telescope's field of view while viewing a beamed particle distribution. However, this possibility can be ruled out because the magnetic field at the spacecraft shows no evidence of such directional variations, and similar particle intensity dips were seen by instruments on other spacecraft in the near-Earth solar wind. We shall present evidence that the dips were actually associated with varying magnetic connection to the Sun within the magnetic cloud. These dips were not observed at GOES II, suggesting they were somehow smoothed out by passage into the magnetosphere.

vonRosenvinge, T. T.↗

NASA NTRS2008

The High Energy Telescope for STEREO

The IMPACT investigation for the STEREO Mission includes a complement of Solar Energetic Particle instruments on each of the two STEREO spacecraft. Of these instruments, the High Energy Telescopes (HETs) provide the highest energy measurements. This paper describes the HETs in detail, including the scientific objectives, the sensors, the overall mechanical and electrical design, and the on-board software. The HETs are designed to measure the abundances and energy spectra of electrons, protons, He, and heavier nuclei up to Fe in interplanetary space. For protons and He that stop in the HET, the kinetic energy range corresponds to approx. 13 to 40 MeV/n. Protons that do not stop in the telescope (referred to as penetrating protons) are measured up to approx. 100 MeV/n, as are penetrating He. For stopping He, the individual isotopes He-3 and He-4 can be distinguished. Stopping electrons are measured in the energy range approx. 0.7 - 6 MeV.

vonRosenvinge, Tycho↗

NASA NTRS2007

Cosmic Ray Helium Intensities over the Solar Cycle from ACE

Observations of cosmic-ray helium energy spectra provide important constraints on cosmic ray origin and propagation. However, helium intensities measured at Earth are affected by solar modulation, especially below several GeV/nucleon. Observations of helium intensities over a solar cycle are important for understanding how solar modulation affects galactic cosmic ray intensities and for separating the contributions of anomalous and galactic cosmic rays. The Cosmic Ray Isotope Spectrometer (CRIS) on ACE has been measuring cosmic ray isotopes, including helium, since 1997 with high statistical precision. We present helium elemental intensities between approx. 10 to approx. 100 MeV/nucleon from the Solar Isotope Spectrometer (SIS) and CRIS observations over a solar cycle and compare these results with the observations from other satellite and balloon-borne instruments, and with GCR transport and solar modulation models.

DeNolfo, G. A.↗

NASA NTRS2007

Observations of the Li, Be, and B Isotopes and Constraints on Cosmic-ray Propagation

The abundance of Li, Be, and B isotopes in galactic cosmic rays (GCR) between E=50-200 MeV/nucleon has been observed by the Cosmic Ray Isotope Spectrometer (CRIS) on NASA's ACE mission since 1997 with high statistical accuracy. Precise observations of Li, Be, B can be used to constrain GCR propagation models. We find that a diffusive reacceleration model with parameters that best match CRIS results (e.g. B/C, Li/C, etc) are also consistent with other GCR observations. A approx. 15-20% overproduction of Li and Be in the model predictions is attributed to uncertainties in the production cross-section data. The latter becomes a significant limitation to the study of rare GCR species that are generated predominantly via spallation.

deNolfo, G. A.↗

NASA NTRS2004

Elemental Abundance Variations Observed in Solar Energetic Particle Events During Solar Cycle 23

We report on observations of the abundances of elements from Helium to Nickel in over 50 different solar energetic particle events using the Solar Isotope Spectrometer (SIS) on-board the Advanced Composition Explorer (ACE) spacecraft. It had originally been expected that the energy spectra of different elements would show spectral roll-overs at energies related to the Q/M ratio of each element. Due to the partial stripping of Fe and essentially complete stripping of O, it was expected that the Fe/O ratio would be observed to decrease with increasing energy. While many events show this pattern, others have Fe/O which is constant with energy, while for yet others Fe/O actually increases with energy. Events having constant Fe/O could simply have their spectral breaks outside of the observed energy range. However, events which show increasing Fe/O cannot be explained within the framework of spectral breaks. Possible explanations include injection of remnant heavy ions from earlier impulsive events, hybrid Events consisting of a combination of flare-accelerated and shock-accelerated particles from a single solar event, and some new physical process in shock acceleration. We will report on efforts to distinguish these possible explanations.

vonRosenvinge, T. T.↗