
 The radioisotope 26Al is a key observable for nucleosynthesis in the Galaxy and the environment of the early Solar System. To properly interpret the large variety of astronomical and meteoritic data, it is crucial to understand both the nuclear reactions involved in the production of 26Al in the relevant stellar sites and the physics of such sites. These range from the winds of low- and intermediate-mass asymptotic giant branch (AGB) stars; to massive and very massive stars, both their Wolf-Rayet (WR) winds and their final core-collapse supernovae (CCSN); and the ejecta from novae, the explosions that occur on the surface of a white dwarf accreting material from a stellar companion. Several reactions affect the production of 26Al in these astrophysical objects, including (but not limited to) 25Mg(p,γ)26Al, 26Al(p,γ)27Si, and 26Al(n,p/α). Extensive experimental effort has been spent during recent years to improve our understanding of such key reactions. Here we present a summary of the astrophysical motivation for the study of 26Al, a review of its production in the different stellar sites, and a timely evaluation of the currently available nuclear data. We also provide recommendations for the nuclear input into stellar models and suggest relevant, future experimental work.

https://iopscience.iop.org/article/10.1088/1361-6471/ac9cf8/pdf

Progress on nuclear reaction rates affecting the stellar production of 26Al

Compton telescopes rely on the dominant interaction mechanism in the MeV gamma-ray energy range: Compton scattering. By precisely recording the position and energy of multiple Compton-scattering interactions in a detector volume, a photon’s original direction and energy can be recovered. These powerful survey instruments can have wide fields of view, good spectroscopy, and polarization capabilities and can address many of the open science questions in the MeV range and, in particular, from multimessenger astrophysics. The first space-based Compton telescope was launched in 1991, and progress in the field continues with advancements in detector technology. This chapter will give an overview of the physics of Compton scattering and the basic principles of operation of Compton telescopes; electron-tracking and polarization capabilities will be discussed. A brief introduction to Compton event reconstruction and imaging reconstruction is given. The point spread function for Compton telescopes and standard performance parameters are described, and notable instrument designs are introduced. 

Compton Telescopes for Gamma-ray Astrophysics

The spare detectors from NASA's Compton Gamma-Ray Observatory COMPTEL instrument have been reconfigured to demonstrate the capability at ground level to remotely locate and identify sources of gamma radiation. The Gamma-Ray Experimental Telescope Assembly (GRETA) employs two 28 cm diameter scintillation detectors separated by 81 cm: one 8.5 cm thick liquid scintillator detector and one 7.5 cm thick Nal(Tl) detector. The assembly electronics and real-time data acquisition system measures the energy deposits and time-of-flight for each coincident detection and compiles histograms of total energy and incident angle as computed using the kinematics of Compton scattering. GRETA's field of view is a cone with full angle approximately 120deg. The sensitive energy range is 0.3 to 2.6 MeV. Energy resolution is ~10% FWHM. The angular resolution, ~15deg in the simplified configuration tested, will improve to better than 5deg with well-defined enhancements to the data acquisition hardware and data analysis routines. We conducted a series of laboratory demonstrations to characterize the performance of the GRETA detector. Following detector characterization, we demonstrate GRETA 's ability to locate and identify an unknown source and position within its field of view. In this scenario, the location and isotope-identifying energy spectrum of an 800 muCi137 Cs source 10 meters from the instrument with two intervening walls was determined in less than one minute. We will present further details of the instrument design and the measurements.

/pdf/a-compton-telescope-for-remote-location-and-identification-29npqk8j1t.pdf

A Compton Telescope for Remote Location and Identification of Radioactive Material

Many astronomers have discussed the property of BL Lacertae objects, including the variation of spectrum, the correlation of multi-wave bands and the property of polarization, which could give good information for studying intrinsic correlation of components and position of BL Lacertae objects. In the paper, we investigated the properties of RBLs and XBLs and RBLs/XBLs (these objects can also be found by radio survey as by X-ray survey). Firstly, we collected the light curve of 28 BL Lacertae objects, and gained their short timescales by Structure Function (SF). Secondly, we analyzed the distribution of the short timescales of some BL Lacertae objects, including 28 objects’ timescales calculated by SF, as well as the distribution of the redshift and the black hole mass and the flux densities of the multi-wavebands (radio, near-infrared, optical and Gamma-ray). Based on statistical analysis, the result of the paper support the unification model of RBLs and XBLs.

The unification of RBLs with XBLs

The spare detectors from NASA Compton Gamma-Ray Observatory COMPTEL instrument have been reconfigured to
demonstrate the capability at ground level to remotely locate and identify sources of g radiation or the movement of
material that might shield γ-ray sources. The Gamma-Ray Experimental Telescope Assembly (GRETA) employs two 28
cm diameter scintillation detectors separated by 81 cm: one 8.5 cm thick liquid scintillator detector and one 7.5 cm thick
NaI(Tl) detector. The assembly electronics and real-time data acquisition system measures the energy deposits and time-of-
flight for each coincident detection and compiles histograms of total energy and incident angle as computed using the
kinematics of Compton scattering. The GRETA field of view is a cone with full angle approximately 120°. The
sensitive energy range is 0.3 to 2.6 MeV. Energy resolution is ~10% FWHM. The angular resolution, ~19° in the
simplified configuration tested, will improve to better than 5° with well-defined enhancements to the data acquisition
hardware and data analysis routines. When operated in the mode that was used in space, the instrument is capable of
measuring and imaging up to 30 MeV with an angular resolution of 1.5°.
The response of the instrument was mapped in the laboratory with 14 Ci 22 Na source 3 m from the instrument. Later,
we conducted demonstrations under two measurement scenarios. In one, the remotely located instrument observed an
increase of background radiation counts at 1.4 MeV when a large amount of lead was removed from a building and a
corresponding decrease when the lead was replaced. In the other scenario, the location and isotope-identifying energy
spectrum of a 500 μCi 137 Cs source 3-5 m from the instrument with two intervening walls was determined in less than
one minute. We report details of the instrument design and these measurements.

/pdf/a-compton-telescope-for-remote-location-and-identification-2ep0obyx69.pdf

A Compton telescope for remote location and identification of radioactive material

The Compton imaging telescope (COMPTEL) on the Gamma Ray Observatory (GRO) is a wide field of view instrument. The coincidence measurement technique in two scintillation detector layers requires specific analysis methods. Straightforward event projection into the sky is impossible. Therefore, detector events are analyzed in a multi-dimensional dataspace using a gamma ray sky hypothesis convolved with the point spread function of the instrument in this dataspace. Background suppression and analysis techniques have important implications on the gamma ray source results for this background limited telescope. The COMPTEL collaboration applies a software system of analysis utilities, organized around a database management system. The use of this system for the assistance of guest investigators at the various collaboration sites and external sites is foreseen and allows different detail levels of cooperation with the COMPTEL institutes, dependent on the type of data to be studied.

/pdf/data-analysis-of-the-comptel-instrument-on-the-nasa-gamma-y9pr8sxdto.pdf

Data analysis of the COMPTEL instrument on the NASA gamma ray observatory

COMPTEL Observations of GRB 930131

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Data analysis of the COMPTEL instrument on the NASA gamma ray observatory

COMPTEL Observations of GRB 930131

COMPTEL Observations of GRB 930131