Prototype for SONTRAC: a scintillating plastic fiber detector for solar neutron spectroscopy

We report the scientific motivation for and performance measurements of a prototype detector system for SONTRAC, a solar neutron tracking experiment designed to study high- energy solar flare processes. The full SONTRAC instrument will measure the energy and direction of 20 to 200 MeV neutrons by imaging the ionization tracks of the recoil protons in a densely packed bundle of scintillating plastic fibers. The prototype detector consists of a 12.7 mm square bundle of 250 micrometer scintillating plastic fibers, 10 cm long. A photomultiplier detects scintillation light from one end of the fiber bundle and provides a detection trigger to an image intensifier/CCD camera system at the opposite end. The image of the scintillation light is recorded. By tracking the recoil protons from individual neutrons the kinematics of the scattering are determined, providing a high signal to noise measurement. The predicted energy resolution is 10% at 20 MeV, improving with energy. This energy resolution translates into an uncertainty in the production time of the neutron at the Sun of 30 s for a 20 MeV neutron, also improving with energy. A SONTRAC instrument will also be capable of detecting and measuring high-energy gamma rays greater than 20 MeV as a \u27solid-state spark chamber.\u27 The self-triggering and track imaging features of the prototype are demonstrated with cosmic ray muons and 14 MeV neutrons. Design considerations for a space flight instrument are presented

SONTRAC—A low background, large area solar neutron spectrometer

SONTRAC is a scintillating fiber neutron detector designed to measure solar flare neutrons from a balloon or spacecraft platform. The instrument is comprised of alternating orthogonal planes of scintillator fibers viewed by photomultiplier tubes and image intensifier/CCD camera optics. It operates by tracking the paths of recoil protons from the double scatter of 20 to 200 MeV neutrons off hydrogen in the plastic scintillator, thereby providing the necessary information to determine the incident neutron direction and energy. SONTRAC is also capable of detecting and measuring high-energy gamma rays \u3e20 MeV as a “solid-state spark chamber.” The self-triggering and track imaging features of a prototype for tracking in two dimensions have been demonstrated in calibrations with cosmic-ray muons, 14 to ∼65 MeV neutrons and ∼20 MeV protons

A prototype for SONTRAC, a scintillating plastic fiber tracking detector for neutron imaging and spectroscopy

We report on tests of a prototype detector system designed to perform imaging and spectroscopy on 20 to 250 MeV neutrons. Although developed for the study of high-energy solar flare processes, the detection techniques employed for SONTRAC, the SOlar Neutron TRACking experiment, can be applied to measurements in a variety of disciplines including atmospheric physics, radiation therapy and nuclear materials monitoring. The SONTRAC instrument measures the energy and direction ofneutrons by detecting double neutron-proton scatters and recording images of the ionization tracks of the recoil protons in a densely packed bundle of scintillating plastic fibers stacked in orthogonal layers. By tracking the recoil protons from individual neutrons, the kinematics of the scatter are determined. This directional information results in a high signal to noise measurement. SONTRAC is also capable of detecting and measuring high-energy gamma rays \u3e20 MeV as a “solid-state spark chamber”. The self-triggering and track imaging features of a prototype for tracking in two dimensions are demonstrated in calibrations with cosmic-ray muons, 14 to ~65 MeV neutrons and ~20 MeV protons

SPI Measurements of Galactic 26Al

The precision measurement of the 1809 keV gamma-ray line from Galactic $^{26}$Al is one of the goals of the SPI spectrometer on INTEGRAL with its Ge detector camera. We aim for determination of the detailed shape of this gamma-ray line, and its variation for different source regions along the plane of the Galaxy. Data from the first part of the core program observations of the first mission year have been inspected. A clear detection of the \Al line at about 5--7 $\sigma$ significance demonstrates that SPI will deepen \Al studies. The line intensity is consistent with expectations from previous experiments, and the line appears narrower than the 5.4 keV FWHM reported by GRIS, more consistent with RHESSI's recent value. Only preliminary statements can be made at this time, however, due to the multi-component background underlying the signal at \about 40 times higher intensity than the signal from Galactic $^{26}$Al.Comment: 5 pages, 8 figures; accepted for publication in A&A (special INTEGRAL volume

SPI/INTEGRAL observation of the Cygnus region

We present the analysis of the first observations of the Cygnus region by the SPI spectrometer onboard the Integral Gamma Ray Observatory, encompassing ${\sim}$ 600 ks of data. Three sources namely Cyg X-1, Cyg X-3 and EXO 2030+375 were clearly detected. Our data illustrate the temporal variability of Cyg X-1 in the energy range from 20 keV to 300 keV. The spectral analysis shows a remarkable stability of the Cyg X-1 spectra when averaged over one day timescale. The other goal of these observations is SPI inflight calibration and performance verification. The latest objective has been achieved as demonstrated by the results presented in this paper.Comment: 6 pages, 10 figures, accepted for publication in A&A (special INTEGRAL volume

Radioactive 26Al and massive stars in the Galaxy

Gamma-rays from radioactive 26Al (half life ~7.2 10^5 yr) provide a 'snapshot' view of ongoing nucleosynthesis in the Galaxy. The Galaxy is relatively transparent to such gamma-rays, and emission has been found concentrated along the plane of the Galaxy. This led to the conclusion1 that massive stars throughout the Galaxy dominate the production of 26Al. On the other hand, meteoritic data show locally-produced 26Al, perhaps from spallation reactions in the protosolar disk. Furthermore, prominent gamma-ray emission from the Cygnus region suggests that a substantial fraction of Galactic 26Al could originate in localized star-forming regions. Here we report high spectral resolution measurements of 26Al emission at 1808.65 keV, which demonstrate that the 26Al source regions corotate with the Galaxy, supporting its Galaxy-wide origin. We determine a present-day equilibrium mass of 2.8 (+/-0.8) M_sol of 26Al. We use this to estimate that the frequency of core collapse (i.e. type Ib/c and type II) supernovae to be 1.9(+/- 1.1) events per century.Comment: accepted for publication in Nature, 24 pages including Online Supplements, 11 figures, 1 tabl