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  • richardmitnick 1:24 pm on February 12, 2018 Permalink | Reply
    Tags: , ATLAS- Argonne Tandem Linac Accelerator System, LBNL Gammasphere, NEEC-Nuclear Excitation by Electron Capture   

    From ANL: “Captured electrons excite nuclei to higher energy states” 

    ANL Lab

    News from Argonne National Laboratory

    February 9, 2018
    Savannah Mitchem

    LBNL Gammosphere
    Argonne scientists and collaborators used the Gammasphere, this powerful gamma ray spectrometer, to help create the right conditions to cause and spot a long-theorized effect called nuclear excitation by electron capture. (Image by Argonne National Laboratory.)

    For the first time, physicists from the U.S. Department of Energy’s (DOE) Argonne National Laboratory and their collaborators, led by a team from the U.S. Army Research Laboratory, demonstrated a long-theorized nuclear effect. This advance tests theoretical models that describe how nuclear and atomic realms interact and may also provide new insights into how star elements are created.

    Physicists first predicted the effect, called nuclear excitation by electron capture (NEEC), over 40 years ago. But scientists had not seen it until now. Using the Argonne Tandem Linac Accelerator System (ATLAS), and Gammasphere, a powerful gamma ray spectrometer, the researchers created the right conditions to cause and spot the behavior.

    Argonne Tandem Linac Accelerator System (ATLAS)

    The NEEC effect occurs when a charged atom captures an electron, giving the atom’s nucleus enough energy to jump to a higher excited state.

    An excited nucleus stays in each energy state for a while before decaying into the state below it, shedding energy in the form of gamma rays. These excited states typically last for much less than a billionth of a second, but in some rare cases, they can live far longer, even for millions of times the age of the universe.

    The longer-lived energy states are called isomers, and to observe the NEEC effect, the researchers produced an isomer with a half-life of about seven hours. In other words, after seven hours of existing in the isomeric energy level, about half of the nuclei of this type will decay.

    The scientists chose to produce this nucleus, called 93Mo, an isotope of molybdenum, because of its unique arrangement of energy levels. “There is an allowed energy level not far above the isomer state,” said the Army Research Laboratory’s Chris Chiara, the study’s lead scientist. “Under normal circumstances, the isomer will decay naturally after about seven hours, but if NEEC occurs, the nucleus is excited out of the isomer to the slightly higher state. That state then quickly decays to a state below the isomer, emitting gamma rays that have distinct energies that we can look for.”

    To make 93Mo, the researchers used ATLAS, a DOE Office of Science User Facility, to accelerate a beam of ions towards the atoms in a target foil where the nuclei of the two fused together. These reactions formed 93Mo in a highly excited state at the center of Gammasphere, which waited to detect evidence of the effect in the form of gamma rays.

    As the 93Mo atoms move through the target material, they bump into atoms that slow them down and strip them of electrons, putting them in a high-charge state. Electrons from the target atoms then fill those vacancies in the 93Mo, and if the electrons have the right energy before the capture, they may excite the nucleus into the next highest state. When this state decays, the nucleus releases a gamma ray that can be traced back to the NEEC reaction.

    The target, made by ATLAS’s in-house target maker, John Greene, played a crucial role in the detection of NEEC. Greene was able to work on the fly, tweaking the target as the scientists learned more about the 93Mo nucleus. With everything in place, the team began to gather data.

    “We detected gamma rays from these reactions over the course of the three-day experiment, and we accumulated around eight billion events in total,” said Mike Carpenter, a group leader at Argonne in charge of Gammasphere. “From these events, we were able to identify around 500 gamma rays that were emitted during the decay of 93Mo that wouldn’t have been released if it weren’t for NEEC.”

    The power and sensitivity of Gammasphere was vital to the experiment’s success. “We made use of a new digital Gammasphere mode, which allowed us to run at a rate about five times higher than would have been possible with the older analog system,” said Chiara. But it was not only the hardware at ATLAS that was important. “As experts in the field of gamma-ray spectroscopy, the Argonne staff provided invaluable scientific and technical support,” he added.

    The team’s success may lead to advances in astronomy and cosmology as it could improve the accuracy of models scientists use to gauge how stars form. The quantities of elements in a star depend largely on the structure and behavior of nuclei. Over long periods, and with vast numbers of atoms interacting, the survival — or destruction — of specific isomers can have a cumulative influence. Taking the NEEC effect into account could improve our understanding of what stars are made of and how they evolve.

    Scientists at the Army Research Laboratory are also interested in possible future applications for the controlled release of nuclear energy from isomers via the NEEC effect. If scientists and engineers could harness this energy, it might help develop power sources with 100,000 times greater energy per unit mass than chemical batteries.

    The results of the experiment were published in a paper titled Isomer depletion as experimental evidence of nuclear excitation by electron capture, on February 8 in Nature.

    Other Argonne co-authors include physicists Robert Janssens (now at the University of North Carolina at Chapel Hill/Triangle Universities Nuclear Laboratory), Darek Seweryniak and Shaofei Zhu.

    The work was funded by DOE’s Office of Science, the U.S. Army Research Laboratory, the National Science Foundation, the Australian Research Council and the Polish National Science Centre.

    The U.S. Army Research Laboratory is part of the U.S. Army Research, Development and Engineering Command (RDECOM), which has the mission to provide innovative research, development and engineering to produce capabilities that provide decisive overmatch to the Army against the complexities of the current and future operating environments in support of the joint warfighter and the nation. RDECOM is a major subordinate command of the U.S. Army Materiel Command.

    See the full article here .

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  • richardmitnick 12:59 pm on February 9, 2018 Permalink | Reply
    Tags: , , , NEEC-Nuclear Excitation by Electron Capture, ,   

    From ANU via COSMOS: “40-year cosmic theory confirmed” 

    ANU Australian National University Bloc

    Australian National University


    09 February 2018
    Andrew Masterson

    A stellar reaction long predicted but never seen has been demonstrated in the lab.

    After four decades of research, a theory is finally confirmed. CONEYL JAY/SCIENCE PHOTO LIBRARY/Getty Images.

    An abundant new energy supply could be derived from controlling a quantum reaction that takes place in stars, according to research from the Australian National University (ANU).

    The possibility arises because the ANU scientists plus others from institutions including the US Army Research laboratory and Poland’s National Centre for Nuclear Research have succeeded in confirming the existence of a reaction first predicted four decades ago but unmeasured until now.

    In a paper published in the journal Nature, ANU physicist Greg Lane and colleagues report the confirmation of a phenomenon known as Nuclear Excitation by Electron Capture (NEEC). Confirming that NEEC actually happens supplies a key mechanism for understanding how evolving stars produce elements such as gold and platinum.

    NEEC can occur when an atom captures an electron. If the electron’s kinetic energy and the energy required to capture it add up to just the right amount, the atom’s nucleus is pushed to a higher state of excitation.

    The energy increase, however, comes at the cost of a shorter life. What was a long-lived stable nucleus must now decay, either through an electromagnetic process known as internal conversion which spits out an electron, or by emitting a photon.

    Although discussed since the 1970s, experimental proof for NEEC has remained elusive.

    The new work, however, has now provided the necessary evidence. The researchers did so by creating an exotic isotope – molybdenum-93 – by firing a beam of zirconium atoms at lithium targets, using the ANU’s Heavy Ion Accelerator and the ATLAS Accelerator at Argonne National Laboratory in the United States.

    ANU’s Heavy Ion Accelerator

    ATLAS Accelerator at Argonne National Laboratory

    The resulting molybdenum atoms zipped around at as much as 10% of the speed of light, smashing into the remaining lithium, stripping off electrons and leaving highly charged ions behind.

    As the interactions continued, the molybdenum ions lost kinetic energy until they reached a state where they could capture an electron with just the right energy to push the molybdenum nuclei from their long-duration “isomer” states into higher level but shorter-lived intermediate ones. These intermediate states decayed, giving off a unique gamma-ray signature that proved NEEC had occurred.

    The research now provides a model against which other theoretical calculations for the NEEC effect in different elements can be tested, illuminating further the process by which nuclear interactions in stars produce certain metals.

    “The abundance of the different elements in a star depends primarily on the structure and behaviour of atomic nuclei,” says Lane.

    “The NEEC phenomenon modifies the nucleus lifetime so that it survives for a shorter amount of time in a star.”

    As well cosmological implications, the confirmation of the NEEC effect opens the door to potentially accessing energy stored in longer-lived isomer nuclei. Lane suggests the technique could create energy sources 100,000 times more powerful than chemical batteries.

    It is a possible outcome that has not gone unnoticed by at least one of the ANU’s research partners.

    “Our study demonstrated a new way to release the energy stored in a long-lived nuclear state, which the US Army Research Laboratory is interested to explore further,” says Lane.

    See the full article here .

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