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Origin of the Isotopes

The  Origin of the Isotopes SAG will explore the scientific potential of a next-generation mission optimized to enable transformative studies of nuclear processes in explosive transients and compact objects.

About Isotopes SAG

Enabling Studies of Nucleosynthesis and Explosion Physics Inaccessible by Other Means

The Isotopes SAG will explore the scientific potential of a next-generation gamma-ray mission optimized for narrow line sensitivity to point sources.

Such a mission could prioritize detection sensitivity with spectral resolution, potentially at the expense of field of view or imaging performance, in order to enable transformative studies of nuclear processes in explosive transients and compact objects that will test the laws of physics and trace the origin and evolution of matter in the universe, from the production of the elements to the expansion history of cosmic space-time.

The spatial distribution of 44 Ti in Cas A compared with the other bright X-ray features. The NuSTAR 65-70 keV background subtracted image covering the 68 keV 44 Sc line tracing the 44 Ti-rich ejecta is shown in blue. The NuSTAR image has been adaptively smoothed for clarity. The 4-6 keV continuum observed by Chandra image is shown in gold, the ratio in the Si/Mg band highlighting the NE/SW jet is shown in green (data courtesy NASA/CXC, Si/Mg ratio image J. Vink), while the distribution of X-ray emitting iron is shown in red (Fe distribution courtesy U. Hwang).
Image credit: Robert Hurt, NASA/JPL-Caltech, with label inspiration from Grefenstette et al. ApJ 834, 19 (2016).

Nuclear gamma rays and positron annihilation radiation are among the most powerful diagnostics in astrophysics. Whereas atomic lines reveal elemental abundances and plasma conditions, and molecular lines probe gas dynamics and chemistry, nuclear lines provide direct measurements tied to specific radioactive isotopes. Further, their known decay lifetimes serve as intrinsic chronometers. These properties enable studies of nucleosynthesis, explosion physics, and matter transport that are inaccessible by other means. Observations of radioactive isotopes uniquely probe the creation, distribution, and annihilation of matter in the universe, connecting stellar explosions, compact objects, and Galactic ecosystems.

The principal objectives of this science interest group are to: 

  1. Astrophysical Sources and Discovery Space
    Which transient and persistent sources can be studied through nuclear gamma rays and positron annihilation? What unique insights would such observations provide? Candidate targets include thermonuclear supernovae, novae, core-collapse supernovae, kilonovae, rapidly accreting white dwarfs, and other explosive or accretion-powered systems. Are there additional source classes that would benefit from enhanced sensitivity?
  1. Measurement Requirements
    What detection sensitivity is required to observe these sources to meaningful distances? What spectral resolution is needed to measure line profiles and kinematics? What are the scientific gains as a function of field of view or spatial resolution? What mission or instrument requirements are driven by these science goals?
  1. Mission Concepts and Pathways
    What mission architectures or detector technologies could achieve the required performance? What mission classes (e.g., Probe, MIDEX, or strategic missions) are necessary to reach these capabilities? How do existing or proposed concepts compare with the science requirements identified by this group?

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SAG Leadership

NameInstitution
Eric BurnsLSU
Carolyn KieransNASA/GSFC
Chris FryerLANL

News & Events

Meetings, conferences, seminars, workshops, and other events for Isotopes SAG

Isotopes SAG Kickoff Meeting, 5 June 2026

Kickoff Meeting As we are now unraveling the origin of the heaviest elements, we begin exploring the Origin of the Isotopes. In this area of interest, we have initiated a new Science Analysis Group to explore what a next-generation nuclear…

May 7, 2026
Origin of the Isotopes Science Analysis Group (Isotopes SAG)

Nuclear gamma rays and positron annihilation radiation are among the most powerful diagnostics in astrophysics. Whereas atomic lines reveal elemental abundances and plasma conditions, and molecular lines probe gas dynamics and chemistry, nuclear lines provide direct measurements tied to specific…

May 6, 2026

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This cropped horizontal image has layers of semi-opaque rusty red colored gas and dust that starts at the bottom right and goes toward the top left. There are three prominent pillars rising toward the top left. The left pillar is the largest and widest. The peaks of the second and third pillars are set off in darker shades of brown and have red outlines.