Objective: Advance the understanding of the high-energy environment through the development and deployment of advanced detectors, simulation of the environments and operations concepts, and interpretation and theoretical modeling of the observed phenomena, thereby address priority S&T goals of DoD, NASA and other civilian agencies.


S&T Status: Research in high-energy radiation detection and in the development of the science base for stand-off detection and for credible countermeasures. This research is advancing the understanding of the high energy environment through the deployment and development of advanced detectors in space, simulation of environments & operating concepts, interpretation and theoretical modeling of observed phenomena.
For more information, please contact nrl.ssd.code7600@nrl.navy.mil.

Figure: NRL’s major role in the Fermi Mission (launch 2008, upper left) has enabled broadly based astrophysical investigations including the gamma ray sky map (upper right) identifying over 1800 point sources and new insight into particle acceleration and radiations from pulsars, supernova remnants, active galactic nuclei, and many other topics. Research in detector design enabled by NRL’s NSI has resulted in three pending patents relating to “slim edge” detectors (middle left) and charge control using atomic layer deposition and three patents on deep reactive ion etching of detectors (lower left). The J-PEX EUV sounding rocket experiment (lower center) provided unprecedented spectral resolution on White Dwarf stars. Research in radiological/nuclear Weapons of Mass Destruction detection resulted in the dual container SuperMISTI detection system (middle right, in transport to Norfolk maritime testing) providing standoff detection and imaging of WMD. Image (lower right) shows SuperMISTI image of radiation source (blue block) hidden in the hold of the USS Cape Chalmers.

Selected Research

The gamma ray sky as seen by Fermi LAT is shown in galactic coordinates.  The bright horizontal line is the diffuse emission from cosmic rays interacting with the gas and dust in the galactic plane.  Fermi Gamma Ray Space Telescope

Objective
Advance the understanding of the high energy space environment and explore the most extreme environments in the universe, where nature accelerates particles to energies far beyond those achievable on Earth. Through its observations of gamma radiation and cosmic rays, Fermi is addressing long-standing questions in a range of topics, including solar flares, pulsars, gamma ray bursts, black holes and jet formation, the composition of dark matter, and the origin of cosmic rays.

The Fermi Gamma-ray Space Telescope has surveyed the sky in gamma-rays and revealed hundreds of unidentified gamma-ray sources. Here the Fermi newly discovered millisecond pulsars are shown overlaid on a Fermi map of the gamma-ray sky at energies above 1 GeV. Gamma Ray and Radio Pulsar Searches

Objective
Search for millisecond pulsars in the gamma-ray data from the Fermi Large Area Telescope and well as ground based data from the Green Bank Telescope in West Virginia. The computationally intensive searches are for pulsations from the gamma-ray sources to identify them as rapidly-spinning neutron stars, called ‘pulsars’.

Fermi-LAT g-ray spectrum of diffuse Galactic gas (Abdo et al. Astrophys. J. 703, 1249, 2009) fit with a model where the gas is bombarded by cosmic rays to make secondary pion decay g rays. The particle spectrum is a momentum power law with index s. Different nuclear production models and metallicity correction factors k are considered The Cosmic-Ray Spectrum in Interstellar Space

Objective
Understand the sources of cosmic rays, the extraterrestrial radiation discovered in Victor Hess’ pioneering balloon experiment, in which he discovered “a radiation of very high penetrating power [that] enters our atmosphere from above.” The idea of an origin of cosmic rays from supernovae—cataclysmic explosions taking place when a high-mass star exhausts its fuel, after which its iron core collapses to form a neutron star and a core-bounce-driven explosion—was made by Baade and Zwicky in 1934. Fermi himself conceived of the idea of statistical acceleration by magnetic clouds in 1949. Hard-and-fast evidence for the acceleration of cosmic-ray protons and ions in supernovae has been lacking because tangled interstellar magnetic fields misdirect the cosmic rays from their sources. But any cosmic-ray factory must be illuminated by the radiations formed when cosmic rays collide with target gas and dust nuclei.

A TGF launches gamma rays (magenta) and high-energy electrons (yellow) and positrons (green) into space.  Gamma rays emerge from the atmosphere in a broad beam. Electrons and positrons, moving at nearly the speed of light, travel into space along the Earth’s magnetic field. Calculations show that the high-field regions near a TGF may produce biologically significant radiation doses. Image Credit: NASA/GSFC & J. Dwyer/Florida Inst. of Technology. Terrestrial Gamma-ray Flashes (TGFs)

Objectives

  • Advance the understanding of particle acceleration and radiation transport in thunderstorms, which have only recently been understood to generate both intense flashes and continuous glows of ionizing radiation. Thunderstorms are the most powerful natural accelerators on Earth.
  • Address questions of the intensity distribution; the altitude range of the origin of the emission, the variations of TGF spectra at the source, the beaming characteristics of the radiation, and the type(s) of lightning that are associated with the production of ionizing radiation.
SWORD can model from detonation spectrum to input spectrum into silicon die SoftWare for Optimization of Radiation Detectors (SWORD)

Objective
Provide a vertically integrated radiation transport software tool for graphically setting up, running, and analyzing results from numerical simulation of high energy radiation detection systems and other systems that operate in a high energy radiation environment. Realistic radiation transport simulations provide a cost-effective means to investigate and optimize instruments and systems for defense, homeland security, and space science applications. SWORD enables developers and technical evaluators to assess instruments and systems in relevant radiation environments, without actual hardware, using a single software package that does not have a steep learning curve to implement.

Figure. Clockwise from upper left, MARS node configuration,  array of 4 nodes with varying shielding thickness, flight hardware, location of single nodes on GLADIS box. Miniature Array of Radiation Sensors (MARS)

Objectives

  • Provide an array of persistent, ubiquitous sensors that monitor the total dose radiation on the host spacecraft for 3-D rad modeling. The concept is to provide a radiation state-of-health measurement like that of a thermistor.
  • Validate SWORD modeling.
SWORD, applied to MARS data on the International Space Station (ISS)

Objective
SWORD (SoftWare for Optimization of Radiation Detectors) is a widely-used and trusted software capability that applies 3-D Monte Carlo methods to simulate the passage of high energy radiation through matter. The simulations provide an effective means to study radiation environments in maritime, urban, and space scenarios of interest. HPC systems are an efficient mechanism for performing the computationally-extensive SWORD studies in a timely manner.

Mobile Imaging & Spectroscopic Threat Identification (MISTI)

Objective
Provide a mobile system for the stand-off detection, identification, and localization of radioactive materials for the detection of hidden special nuclear materials.
The system was required to detect a 1 milliCurie source in 20 seconds at 100 meters and provide isotope identification and 3-D localization to 10 meters with at most one false positive for every 8 hours of observations.

SuperMISTI

Objective
The SuperMISTI instrument, a large gamma-ray imaging system built for the Office of Naval Research (ONR) under the auspices of the Maritime Weapons of Mass Destruction (WMD) Detection program, provides a deployable system for the detection and identification of special nuclear material from stand-off distances.
The detection system can be used both in passive detection mode and in active interrogation mode with interrogating beams.

Optical micrograph (cross section), laser-micromachined hole array in InP (hole diameter ~20 mm).  Nano-Fabrication Detector Development

Objective
Improve gamma-ray imaging for astrophysics research and ground based applications (shielded special nuclear material detection) by utilizing modern nano- and micro-fabrication techniques.
Modern radiation detectors are based on high-voltage semiconductor detectors. NRL is increasing their performance by increasing the detector size and thickness, developing novel detector designs, utilizing high atomic number semiconductors, and reducing "inactive" detector area.