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  • richardmitnick 1:17 pm on November 28, 2018 Permalink | Reply
    Tags: , , LBNL FIONA, , Superheavy elements man made elements   

    From Lawrence Berkeley National Lab: “FIONA Measures the Mass Number of 2 Superheavy Elements: Moscovium and Nihonium” 

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    From Lawrence Berkeley National Lab

    November 28, 2018

    First results from Berkeley Lab’s new tool confirm predicted measurements.


    FIONA is a new system at Berkeley Lab’s 88-Inch-Cyclotron that enables direct mass number measurements of superheavy elements. (Credit: Marilyn Chung/Berkeley Lab)

    A team led by nuclear physicists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has reported the first direct measurements of the mass numbers for the nuclei of two superheavy elements: moscovium, which is element 115, and nihonium, element 113.

    They obtained the results using FIONA, a new tool at Berkeley Lab that is designed to resolve the nuclear and atomic properties of the heaviest elements. The results are detailed in the Nov. 28 edition of the Physical Review Letters journal.

    FIONA is an acronym that means: “For the Identification Of Nuclide A,” with “A” representing the scientific symbol for an element’s mass number – the total number of protons and neutrons in an atom’s nucleus. Protons are positively charged and the proton count is also known as the atomic number; neutrons have a neutral charge. Superheavy elements are human-made and have a higher atomic number than those found in naturally occurring elements.

    The global rush for mass numbers

    Gathering and validating this first data from FIONA had been a top priority for the Lab’s 88-Inch Cyclotron and Nuclear Science Division since FIONA’s commissioning wrapped up in early 2018. Cyclotron staff worked with visiting and in-house scientists to conduct FIONA’s first experimental run, which spanned five weeks.

    “It is very exciting to see FIONA come online, as it is extremely important to pin down the masses of superheavy elements,” said Barbara Jacak, Nuclear Science Division director. “Until now the mass assignments have been made with circumstantial evidence rather than by direct measurement.”

    Jackie Gates, a staff scientist in Berkeley Lab’s Nuclear Science Division who played a leading role in the conception, construction, and testing of FIONA, and who leads FIONA’s mass-number-determination efforts, said, “There has been a lot of interest in making an experimental measurement of superheavy mass numbers.”

    Gates added that this effort to measure superheavy elements’ mass numbers is of global interest, with teams from Argonne National Laboratory and Japan’s nuclear research program among those also making mass measurements of superheavy elements using slightly different approaches or tools.

    Guy Savard, a senior scientist at Argonne National Laboratory, designed, built, and contributed several components for FIONA. He also aided in the commissioning of FIONA and in its first scientific campaign.

    Roderick Clark, a senior scientist in Berkeley Lab’s Nuclear Science Division, said, “Everyone is coming together in this grand race. This can open up a whole range of physics of these heavy and superheavy samples,” as well as new studies of the structure and chemistry of these exotic elements, and a deeper understanding of how they bond with other elements.

    “If we can measure the mass of one of these superheavy elements, you can nail down the entire region,” Clark said.

    A new chapter in heavy element research

    The mass number and atomic number (or “Z”) – a measure of the total number of protons in an atom’s nucleus – of superheavy elements have relied on the accuracy of nuclear mass models. So it’s important to have a reliable way to measure these numbers with experiments in case there is a problem with models, noted Ken Gregorich, a recently retired senior scientist in Berkeley Lab’s Nuclear Science Division who worked closely with Gates to build and commission FIONA.

    For example, superheavy elements could possibly exhibit unexpected nuclear shapes or densities of protons and neutrons that aren’t accounted for in the models, he said.

    Berkeley Lab has made enormous contributions to the field of heavy-element research: Lab scientists have played a role in the discovery of 16 elements on the periodic table, dating back to the synthesis of neptunium in 1940, and have also supplied hundreds of isotope identifications. Isotopes are different forms of elements that share the same number of protons but have a different number of neutrons in their nuclei.

    FIONA (see related article) is an add-on to the Berkeley Gas-filled Separator (BGS). For decades, the BGS has separated heavy elements from other types of charged particles that can act as unwanted “noise” in experiments. FIONA is designed to trap and cool individual atoms, separate them based on their mass and charge properties, and deliver them to a low-noise detector station on a timescale of 20 milliseconds, or 20 thousandths of a second.

    ‘One atom a day’

    “We can make one atom a day, give or take,” of a desired superheavy element, Gregorich noted. In its early operation, FIONA was specifically tasked with trapping individual moscovium atoms. “We have about a 14 percent chance of trapping each atom,” he added. So researchers had hoped to capture a single measurement of moscovium’s mass number per week.

    Moscovium was discovered in 2015 in Russia by a joint U.S.-Russian team that included scientists from Lawrence Livermore National Laboratory, and the discovery of nihonium is credited to a team in Japan in 2004. The element names were formally approved in 2016.

    To produce moscovium, scientists at the 88-Inch Cyclotron bombarded a target composed of americium, an isotope of an element discovered by Berkeley Lab’s Glenn T. Seaborg and others in 1944, with a particle beam produced from the rare isotope calcium-48. The needed half-gram of calcium-48 was provided by the DOE Isotope Program.

    There is a distinct looping signature for each atom trapped and measured by FIONA – a bit like watching a fixed point on a bicycle tire as the bicycle rolls forward. The trajectory of this looping behavior is related to the atomic “mass-to-charge ratio” – the timing and position of the energy signal measured in the detector tells scientists the mass number.

    Ideally, the measurement includes several steps in the particle’s decay chain: Moscovium has a half-life of about 160 milliseconds, meaning an atom has a 50 percent chance to decay to another element known as a “daughter” element in the decay chain every 160 milliseconds. Capturing its energy signature at several steps in this decay chain can confirm which parent atom began this cascade.

    “We have been trying to establish the mass number and the proton number here for many years now,” said Paul Fallon, a senior scientist in Berkeley Lab’s Nuclear Science Division who leads the division’s low-energy program. Detector sensitivity has steadily improved, as has the ability to isolate individual atoms from other noise, he noted. “Now, we have our first definitive measurements.”

    Confirming the mass numbers of element 113 and element 115

    In FIONA’s first scientific run, researchers identified one moscovium atom and its related decay daughters, and one nihonium atom and its decay daughters. The measurements of the atoms and the decay chains confirm the predicted mass numbers for both elements.

    While researchers had been seeking only to create and measure the properties of a moscovium atom, they were also able to confirm a measurement for nihonium after a moscovium atom decayed into nihonium before reaching FIONA.

    “The success of this first measurement is incredibly exciting,” said Jennifer Pore, a postdoctoral fellow who was involved in FIONA’s commissioning experiments. “The unique capabilities of FIONA have sparked a new renaissance of superheavy element research at the 88-Inch Cyclotron.”

    Gregorich credited the efforts of staff at the 88-Inch Cyclotron – including mechanical, electrical, operations, and control systems experts – for maximizing FIONA experimental time during its initial five-week scientific run.

    He noted particular contributions from other BGS and FIONA group members, including Greg Pang, a former project scientist who was involved in FIONA’s construction and testing; Jeff Kwarsick, a graduate student whose Ph.D. thesis is focused on FIONA results; and Nick Esker, a former graduate student whose Ph.D. work focused on the mass separator technique incorporated by FIONA.

    Plans for new measurements and the addition of ‘SHEDevil’

    Fallon said that another scientific run is planned for FIONA within the next six months, during which nuclear physics researchers may pursue a new round of measurements for moscovium and nihonium, or for other superheavy elements.

    There are also plans to install and test a new tool, dubbed “SHEDevil” (for Super Heavy Element Detector for Extreme Ventures In Low statistics) that will help scientists learn the shape of superheavy atoms’ nuclei by detecting gamma rays produced in their decay. These gamma rays will provide clues to the arrangement of neutrons and protons in the nuclei.

    Researchers from Berkeley Lab, UC Berkeley, Argonne National Laboratory, Lawrence Livermore National Laboratory, the University of Chicago, and TRIUMF in Canada participated in this work, which was supported by the U.S. Department of Energy’s Office of Science.

    See the full article here .


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  • richardmitnick 4:22 pm on May 3, 2017 Permalink | Reply
    Tags: , , LBNL FIONA,   

    From LBNL: “FIONA to Take on the Periodic Table’s Heavyweights” 

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    Berkeley Lab

    May 3, 2017
    Glenn Roberts Jr
    (510) 486-5582

    Berkeley Lab Scientists Jackie Gates, left, and Kenneth Gregorich work on FIONA, a new device at the Lab’s 88-Inch Cyclotron. FIONA is designed to precisely measure the mass number of the periodic table’s superheavy elements, and could also be useful for other types of explorations of superheavy elements. (Credit: Marilyn Chung/Berkeley Lab)

    A new tool at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) will be taking on some of the periodic table’s latest heavyweight champions to see how their masses measure up to predictions.

    Dubbed FIONA, the device is designed to measure the mass numbers of individual atoms of superheavy elements, which have higher masses than uranium.

    “Once we have determined those mass numbers, we will use FIONA to learn about the shape and structure of heavy nuclei, guide the search for new elements, and to give us better measurements for nuclear fission and related processes in nuclear physics and nuclear chemistry research,” said Kenneth Gregorich, a senior scientist in Berkeley Lab’s Nuclear Science Division who has been involved in building and testing FIONA.

    Jackie Gates, a Berkeley Lab staff scientist, points to a branching region of the periodic table that is populated by isotopes of superheavy elements. (Credit: Marilyn Chung/Berkeley Lab)

    FIONA’s full name is “For the Identification Of Nuclide A.” The “A” is a scientific symbol representing the mass number—the sum of protons, which are positively charged, and neutrons, which do not have an electric charge— in the nucleus of an atom. The proton count, also known as the atomic number, is unique for each element and is the basis for the arrangement of elements in the periodic table.

    FIONA builds on a long history of expertise in heavy element discoveries and nuclear physics research at Berkeley Lab. The Lab’s scientists have been involved in the discovery of 16 elements and also various forms of elements, known as isotopes, which have different numbers of neutrons.

    VIDEO: Chemistry World magazine visited Berkeley Lab’s 88-Inch Cyclotron to discuss how superheavy elements are made and studied. (Credit: © Chemistry World)

    Nuclear physicists have used the known masses of radioactive decay “daughter atoms” as a framework for determining the masses for these heavier “parent” elements.

    Previous experiments have also helped to home in on the masses of some of the superheavy elements. But determining the mass number of some of the heaviest elements has remained out of reach because it is challenging to produce isolated atoms and to measure them before they rapidly decay.

    FIONA’s measurements are expected to provide a better fundamental understanding of the makeup of these manufactured superheavy atomic nuclei.

    “We will be exploring the limits of nuclear stability, answering basic questions such as how many protons you can put in a nucleus,” Gregorich said.

    A holy grail in this field is to reach the so-called “island of stability,” an as-yet unexplored realm in the chart of nuclei where human-made isotopes are theorized to be long-lived.

    “We will perhaps be probing the edge of this ‘island’ — informing theories that predict such things so they can be refined,” Gregorich said.

    FIONA was installed in November 2016 at Berkeley Lab’s 88-Inch Cyclotron, which produces intense particle beams for nuclear physics experiments and to test the radiation-hardness of computer chips for use in satellites, and has since undergone a range of tests to prepare it for a first round of experiments this summer. FIONA is an enhancement to a long-running machine called the Berkeley Gas-filled Separator (BGS) that separates atoms of superheavy elements from other types of charged particles.

    Jeffrey Kwarsick, a graduate student, works on the installation of FIONA at Berkeley Lab’s 88-Inch Cyclotron. (Credit: Marilyn Chung/Berkeley Lab)

    The separator’s job is to separate the heavy elements of interest from the beam and other unwanted reaction products,” Gregorich said, and FIONA is designed to move the desired atoms away from this “noisy” environment and to quickly measure them within about 10 thousandths of a second.

    This is important because the human-made superheavy elements discovered so far have very short half-lives, in some cases decaying down to lighter elements on scales measured in thousandths of a second.

    FIONA components include a new shielding wall that is designed to reduce background noise from other charged particles, a specialized trapping mechanism for atoms, and a sensitive silicon-based detector array that can measure the energy, position, and timing of the decay of radioactive atoms.

    Several components of FIONA were constructed under contract with Argonne National Laboratory, and the mass analyzer was designed and built at Berkeley Lab.

    “The design for FIONA is practical, flexible, and unique,” Gregorich said. “We were looking at different ways to perform mass separation, and everything else was either more expensive or more difficult.”

    A view of FIONA’s detector components. (Credit: Marilyn Chung/Berkeley Lab)

    The initial beams that will be produced at the 88-Inch Cyclotron for the early FIONA experiments will use an isotope of calcium that is accelerated to strike a target containing a heavy element—typically human-made americium, which is heavier than plutonium. This bombardment fuses some of the atomic nuclei to produce even heavier atoms.

    Jackie Gates, a staff scientist in the Nuclear Science Division and a leader of the FIONA team, said, “Some other devices have a much higher mass resolution but a lower efficiency—FIONA will have the highest efficiency.” This higher efficiency means that FIONA can isolate and measure more atoms of a specific superheavy element in a given time than comparable devices.

    Even so, the creation of the heaviest atoms yet discovered is challenging: Of all the particles pouring through the separator, perhaps one in a quintillion (one followed by 18 zeros) reaching the experiment will form a superheavy element of interest.

    That translates into the production of possibly one atom of interest per day, and several detections will be needed to determine the mass number, Gates said.

    After separation in the Berkeley Gas-filled Separator, atoms of interest are trapped, bunched, and cooled in a device known as a radiofrequency quadrupole trap.

    They are then sent through the FIONA mass separator, which contains crossed electric and magnetic fields. In the separator, the ions take on a looping trajectory, sending them to the detector with positions determined by their mass-to-charge ratio. The position in the detector at which the superheavy element radioactive decay is detected gives the mass number.

    A view of FIONA in Cave 2 at Berkeley Lab’s 88-Inch Cyclotron. (Credit: Marilyn Chung/Berkeley Lab)

    FIONA’s commissioning should wrap up this spring, Gates said, and one of the headline experiments for the new device will be to study decay processes associated with element 115, recently named moscovium (its periodic table symbol is “Mc”).

    “The Berkeley Gas-filled Separator gave us 20 years of science,” Gates said, “and now we are looking at extending this another 10 to 20 years with FIONA.”

    This work is supported by the Department of Energy’s Office of Nuclear Physics.

    See the full article here .

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