The main emphasis of Nuclear Data Research is on nuclear structure and decay data, and their applications in nuclear physics research, and in applied nuclear technologies. Compiled and evaluated data are made available to the National Nuclear Data Center (NNDC) for inclusion into the Evaluated Nuclear Structure Data File (ENSDF) database or the results are published directly in peer-reviewed scientific journals. Contributions are also made to various specialized databases that serve specific needs in the fields of nuclear structure, nuclear astrophysics and applied nuclear physics. This effort includes evaluations of atomic masses and complementary nuclear structure data for the Atomic Mass Evaluation (AME) and NUBASE databases, and compilations of recently published nuclear structure data for the Unevaluated Nuclear Data List (XUNDL) database. Measurements aimed at providing answers to specific questions and at improving the quality of existing databases in specific areas are also carried out.
Nuclear Data Capabilities
The Argonne Tandem Linac Accelerator System (ATLAS), developed and operated by Argonne National Laboratory’s (ANL) PHY Division as a national user research facility for the Department of Energy, Office of Science, Nuclear Physics, is a world-class superconducting accelerator complex. It can provide beams above the Coulomb barrier for all stable isotopes from protons through uranium, as well as beams of long-lived nuclides, including minor actinides beyond uranium. In conjunction with the Californium Rare Ion Breeder Upgrade (CARIBU), which adds pure, neutron-rich fission products (FP) to the array of available ion beams, ATLAS provides a broad and unique suite of isotopes for various ND studies. In order to maximally benefit from this resource, PHY develops and maintains an inventory of state-of-the-art detector systems and support facilities that provide unique capabilities in multiple ND areas that are critical to studies of not only nuclear astrophysics and fundamental nuclear structure, but also to national security and nuclear energy missions, including but not limited to, nuclear forensics and safeguards, nuclear energy and associated fuel cycle operations, materials analysis, medical diagnosis and radiotherapy, and passive and active interrogation applications.
Neutron-induced capture and fission cross-sections: In addition to ATLAS’s already demonstrated capabilities in Accelerator Mass Spectrometry (AMS), the HELIOS solenoidal spectrometer is a unique instrument that can provide both improved precision on existing cross-section data as well as unique ND for neutron-induced capture and fission reactions on long-lived actinide isotopes. Additionally, a planned upgrade of CARIBU will allow for indirect (surrogate) measurements of neutron-induced capture cross-sections previously inaccessible to the research community on short-lived isotopes in the FP region.
Measurements of prompt and delayed gamma-rays and neutrons from fission: PHY has the capability to conduct precise measurements of prompt and delayed gamma-rays and neutrons for all FP. Using the Gammasphere spectrometer such fission signatures can be measured with unprecedented energy resolution and resolving power. In addition, prompt and delayed neutrons can also be measured by means of the neutron-shell detector array. Capabilities exist for dedicated beta-delayed neutron measurements as well.
Fission product yields (FPY): PHY maintains and operates a dedicated Penning Trap spectrometer that can be used to directly measure the independent and commutative fission product yields with part per million resolution for all FP. The CARIBU upgrade will enable further neutron-induced direct FPY measurements with unprecedented accuracy to be carried out for a number of fissile nuclides and it would also allow energy-dependence of neutron-induced FPY to be studied. In addition, PHY also operates the X-Array and SATURN moving-tape detector system, which can be used to measure FPY of short-lived radionuclides by means of beta and gamma detection.
Below are more technical details on the detectors and facilities at PHY involved in ND research, as well as planned upgrades and additional capabilities:
- Gammasphere is one of the world’s most powerful spectrometers for γ-ray coincidence data research. It consists of up to 110 high-purity, Compton-suppressed germanium detectors in a spherical arrangement, allowing for both discrete γ-ray spectroscopy and calorimetric total absorption spectroscopic approaches to be carried out simultaneously. Additionally, up to 35 forward modules on Gammasphere can be replaced with liquid-scintillator Neutron Shell modules for neutron detection.
- X-array is a highly-efficient array of high-purity germanium clover detectors for γ-ray detection, and SATURN (Scintillator And Tape Using Radioactive Nuclei) is a plastic scintillator detector combined with a tape-transport system for detection of beta particles and removal of long-lived isobaric decay activities produced in the decay of FP. When coupled together, the decay properties of neutron-rich isotopes from CARIBU such as half-lives and branching ratios can be measured with high precision.
- The Canadian Penning Trap (CPT) is used to conduct precise mass measurements on products from CARIBU by using their precession frequency. Due to its incredible mass resolving power, it can even separate isomers and measure their fission yield branches down to the 10-6 level.
- HELIOS (Helical Orbit Spectrometer) is a charged-particle spectrometer designed for the study of nuclear reactions in inverse kinematics. Inverse kinematic reactions are a necessity for studying ND with radioactive beams, but measurements of these reactions often result in poor resolution when using conventional detector techniques. HELIOS’s solenoidal design, pioneered by PHY, overcomes these difficulties to provide high-resolution measurements that can be used to study (n, γ) and (n, f) reactions that were previously difficult or impossible to probe precisely.
PHY operates the Center for Accelerator Target Science (CATS), which provides ATLAS targets via physical vapor deposition, mechanical rolling for isotopic foils and actinides, and other methods. CATS additionally performs research and development for target-making techniques and technologies, maintains an ND counting lab with two high-precision γ-ray spectrometers, and hosts the Argonne Target Library, which compiles and houses decades worth of target collections from around the nuclear physics complex. PHY also runs the Trace Radioisotope Analysis Center (TRACER) for the study and detection of rare, long-lived, noble gas radioisotopes. TRACER can detect these nuclides with isotopic abundances as low as 10-16.
Beyond these current capabilities, PHY plans two substantial upgrades of the ATLAS facility that will expand its ND capabilities: the neutron generator upgrade to CARIBU (nuCARIBU), which will add neutron-induced fission products from any actinide target to the already incredible range of ion beams ATLAS can deliver, and the multi-user upgrade (MUU), which will allow for simultaneous use of both stable and radioactive accelerated ion beams through ATLAS in order to substantially increase available beam time at the facility.
Critical to all of its current and potential ND research, PHY has extensive expertise and capabilities in performing nuclear data evaluations for the broader science and applied community. Additionally, PHY has advanced Monte Carlo computing and simulation capabilities, as well as access to ANL’s supercomputing facilities. A condensed summary of how PHY’s capabilities impact the various ND topics is shown in the table below.
Funding provided by: Office of Nuclear Physics, Office of Science, U.S. DOE