Dr. Steven Pain, Research and Development Associate

Dr. Steven Pain

Development of the Oak Ridge Rutgers University Barrel Array - a detector for studying the single-particle structure of exotic nuclei

Physics Division, Oak Ridge National Laboratory

*The organization and the title are those when awarded


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Exotic, unstable nuclei play a crucial role in many astrophysical sites, including massive stars and stellar explosions, which contribute to the formation many of the elements found in nature around us. Understanding the properties of these exotic nuclei is critical to understanding these astrophysical sites, and the processes in which elements are synthesized. For decades, one of the major tools for studying the properties of stable nuclei has been the measurement of transfer reactions. A new detector array (ORRUBA: the Oak Ridge Rutgers University Barrel Array) has been developed to perform measurements of transfer reactions using beams of short-lived unstable nuclei, to obtain detailed structure information exotic nuclei. ORRUBA uses a large cylindrical array of resistive-strip silicon detectors to measure transfer reactions with high precision in a cost-effective manner, and has been used for a number of ground-breaking measurements using exotic nuclear beams. By coupling ORRUBA to gamma ray detectors, future measurements will be possible with an order of magnitude greater sensitivity than before.

Research summary

Exotic nuclei with an excess of neutrons are unstable, but play a crucial role in the production of the stable elements found on Earth.  

However, due to their short lifetimes, it is difficult to study their structures and properties.  

Dr. Pain and colleagues in Oak Ridge National Laboratory and Rutgers University are taking up the challenge.  

In their method, the exotic heavy nuclei produced at an accelerator collides with deuterium, using the inverse kinematics technique.  

In the collision, protons are ejected with wide range of angles and energies, carrying information on the exotic heavy nucleus.  

Dr. Pain developed a unique barrel array detect or with large solid angular acceptance, which can successfully detect the proton ejectiles.  

Studying the properties of exotic nuclei is important for understanding the astrophysical production of elements heavier than iron, in exotic sites such as supernova and neutron-star mergers.