Periodic Reporting for period 3 - NEXT (Neutron-rich, EXotic, heavy nuclei produced in multi-nucleon Transfer reactions)
Reporting period: 2022-09-01 to 2024-02-29
Chemical elements are the building blocks of our world. So far, 118 elements have been discovered. According to the liquid drop model of a nucleus, the elements with a proton number of Z=104 and higher could not exist and should split instantaneously . Due to the influence of stabilizing nuclear shell effects, these so-called “superheavy elements” could be formed and studied in the laboratory. Production rates for these elements are low and they follow the general trend that their half-lives decrease with an increasing proton number.
For decades, scientist have been searching for the so-called Island of Stability. The island is formed by nuclear shell closures. It is expected that nuclides around the island are inherently stable against nuclear fission and have relatively long half-lives. Depending on the theoretical models, the island has been predicted around the neutron number N=182 and the proton numbers Z=114, Z=120 or Z=126. The NEXT project will extend the chart of known-nuclides to the neutron-rich side in the heavy element region.
The heaviest element which occurs naturally in macro amounts on our earth is uranium with a proton number Z=92. The formation of elements heavier than bismuth with a proton number Z=83 can be explained by the rapid neutron-capture (r-) process. The r-process requires an environment with a high-density neutron flux. In 2017, the “smoking gun” of the r-process has for the first time been observed by multi-messenger astronomy in a neutron star merger. The exact path of the r-process along the nuclear landscape is still not known, and depends on the nuclear properties of neutron-rich isotopes involved such as half-lives, decay modes, neutron capture cross sections and for heavier elements also on the fission barrier. Nuclear physics studies, theoretical simulations and astronomical observations are the key to explain the formation of elements in our universe and answer the questions if elements heavier than uranium have been formed.
In the NEXT project, we want to address two major questions in nuclear and astrophysics:
A. How can we access neutron-rich heavy nuclei?
B. Is it possible that superheavy elements have been formed in our universe?
To address these questions a setup dedicated to discover and study Neutron-rich, EXotic, heavy nuclei produced in multi-nucleon Transfer reactions (NEXT) will be built at the AGOR cyclotron facility in Groningen. These exotic nuclei are the key to answer the question of the origin of the chemical elements heavier than iron in our universe. Isotopes relevant for r-process will be discovered and their mass and decay properties will be determined. Mass measurements of these exotic nuclei are important benchmark data for nuclear- and nuclear astrophysics theory. Decay modes such as fission have significant influence on the formation of heavy elements in our universe. The proposed mass and decay studies of neutron-rich, exotic nuclei will therefore contribute to our knowledge of nuclear structure and of the element synthesis in astrophysical processes.
In the NEXT project, the world-wide first separator dedicated to multi-nucleon transfer reactions with heavy (actinide) targets will be constructed. The AGOR cyclotron is capable of delivering the required beam with significant intensities and thus, NEXT can provide unique access to exotic nuclei and that is complementary to existing rare-isotope beam facilities.
For decades, scientist have been searching for the so-called Island of Stability. The island is formed by nuclear shell closures. It is expected that nuclides around the island are inherently stable against nuclear fission and have relatively long half-lives. Depending on the theoretical models, the island has been predicted around the neutron number N=182 and the proton numbers Z=114, Z=120 or Z=126. The NEXT project will extend the chart of known-nuclides to the neutron-rich side in the heavy element region.
The heaviest element which occurs naturally in macro amounts on our earth is uranium with a proton number Z=92. The formation of elements heavier than bismuth with a proton number Z=83 can be explained by the rapid neutron-capture (r-) process. The r-process requires an environment with a high-density neutron flux. In 2017, the “smoking gun” of the r-process has for the first time been observed by multi-messenger astronomy in a neutron star merger. The exact path of the r-process along the nuclear landscape is still not known, and depends on the nuclear properties of neutron-rich isotopes involved such as half-lives, decay modes, neutron capture cross sections and for heavier elements also on the fission barrier. Nuclear physics studies, theoretical simulations and astronomical observations are the key to explain the formation of elements in our universe and answer the questions if elements heavier than uranium have been formed.
In the NEXT project, we want to address two major questions in nuclear and astrophysics:
A. How can we access neutron-rich heavy nuclei?
B. Is it possible that superheavy elements have been formed in our universe?
To address these questions a setup dedicated to discover and study Neutron-rich, EXotic, heavy nuclei produced in multi-nucleon Transfer reactions (NEXT) will be built at the AGOR cyclotron facility in Groningen. These exotic nuclei are the key to answer the question of the origin of the chemical elements heavier than iron in our universe. Isotopes relevant for r-process will be discovered and their mass and decay properties will be determined. Mass measurements of these exotic nuclei are important benchmark data for nuclear- and nuclear astrophysics theory. Decay modes such as fission have significant influence on the formation of heavy elements in our universe. The proposed mass and decay studies of neutron-rich, exotic nuclei will therefore contribute to our knowledge of nuclear structure and of the element synthesis in astrophysical processes.
In the NEXT project, the world-wide first separator dedicated to multi-nucleon transfer reactions with heavy (actinide) targets will be constructed. The AGOR cyclotron is capable of delivering the required beam with significant intensities and thus, NEXT can provide unique access to exotic nuclei and that is complementary to existing rare-isotope beam facilities.
In order to access the neutron-rich side of the nuclear chart through multinucleon transfer reactions, we are building a new setup which consists of a solenoid separator, a gas-catcher, an ion guide, and a MultiReflection Time-of-Flight MassSpectrometer (MR-ToF MS).
The solenoid separator is based on an old MRI magnet which will be used to separate the transfer products of interest from unwanted by-products by their magnetic rigidity. In order to find the optimum layout of the components of the separator, we developed a Python code to simulate the trajectories of multinucleon transfer products and by-products through the magnetic field. As model reactions we have chosen Xe-136+Pt-198 to produce nuclei around the N=126 shell closure and Ca-28+Cf-251 to produce nuclei in the transfermium region. Input data for the simulations containing the differential cross-section, kinetic energies, and the angular distribution of the transfer products were provided by theory. The calculation of the atomic charge state distribution is implemented in our Python code. We implemented a series expansion of an axially symmetric method to interpolate the static magnetic field of the solenoid magnet in cylindrical co-ordinates which provides a realistic magnetic field map including the fringe fields. The code allowed us to determine the optimum position of the production target as well as the position of the gas-catcher which was used for the conceptual design. The solenoid separator is in the technical design state.
The ions flying out of the solenoid are stopped and extracted from a gas-catcher and injected into an Multi Reflection Time-of-Flight MassSpectrometer (MR-ToF MS). The MR-ToF MS has been designed and all parts have been manufactured and need to be assembled. The MR-ToF MS will allow for precision mass measurements as well as the preparation for pure samples for decay spectroscopy. The gas-catcher and the MR-ToF MS are coupled through an ion guide. There are several requirements on the ion guide. It has to be able to capture a divergent and continuous beam from the gas-catcher, and inject it as focused ion bunches into the MR-ToF MS. Furthermore, the ion guide section has to function as a differential pumping section to connect the gas-catcher filled with 50 mbar helium to the MR-ToF MS which operates at a pressure of 1e-9 mbar. Therefore. we developed a novel stacked-ring ion guide for cooling and bunching. The design was optimized with the help of ion optical simulation using the SIMION software package. Currently, the new ion guide and an offline test setup are under construction.
The solenoid separator is based on an old MRI magnet which will be used to separate the transfer products of interest from unwanted by-products by their magnetic rigidity. In order to find the optimum layout of the components of the separator, we developed a Python code to simulate the trajectories of multinucleon transfer products and by-products through the magnetic field. As model reactions we have chosen Xe-136+Pt-198 to produce nuclei around the N=126 shell closure and Ca-28+Cf-251 to produce nuclei in the transfermium region. Input data for the simulations containing the differential cross-section, kinetic energies, and the angular distribution of the transfer products were provided by theory. The calculation of the atomic charge state distribution is implemented in our Python code. We implemented a series expansion of an axially symmetric method to interpolate the static magnetic field of the solenoid magnet in cylindrical co-ordinates which provides a realistic magnetic field map including the fringe fields. The code allowed us to determine the optimum position of the production target as well as the position of the gas-catcher which was used for the conceptual design. The solenoid separator is in the technical design state.
The ions flying out of the solenoid are stopped and extracted from a gas-catcher and injected into an Multi Reflection Time-of-Flight MassSpectrometer (MR-ToF MS). The MR-ToF MS has been designed and all parts have been manufactured and need to be assembled. The MR-ToF MS will allow for precision mass measurements as well as the preparation for pure samples for decay spectroscopy. The gas-catcher and the MR-ToF MS are coupled through an ion guide. There are several requirements on the ion guide. It has to be able to capture a divergent and continuous beam from the gas-catcher, and inject it as focused ion bunches into the MR-ToF MS. Furthermore, the ion guide section has to function as a differential pumping section to connect the gas-catcher filled with 50 mbar helium to the MR-ToF MS which operates at a pressure of 1e-9 mbar. Therefore. we developed a novel stacked-ring ion guide for cooling and bunching. The design was optimized with the help of ion optical simulation using the SIMION software package. Currently, the new ion guide and an offline test setup are under construction.
Within the NEXT project a novel spectrometer to overcome current limitation in the synthesis of heavy elements in multi-nucleon transfer reactions will be built. The spectrometer is a combination of a solenoid magnet which functions as an ion-optical lens and separator, and a Multi-Reflection-Time-of-flight Mass Spectrometer (MR-ToF MS). The new spectrometer will allow for the study of isotopes with a wide range of half-lives from a few milliseconds up to several hours and it will open the door for the discovery of new isotopes. The masses and the decay properties of neutron-rich isotopes will be determined with the MR-ToF MS and the detector system. The NEXT spectrometer will be located at the AGOR cyclotron facility in Groningen. It will be the first separator in the world dedicated to study multi-nucleon transfer reactions with heavy (actinide) targets and thus will provide unique access to neutron-rich isotopes of heavy and superheavy elements which is complementary to existing rare-isotope beam facilities.
It will open the door to the discovery of new neutron-rich nuclei in the fermium region. Furthermore, we will get access to the masses and decay properties of nuclei at the 3rd waiting point of the astrophysical r-process and in the heavy element region. Additionally, the aim is to study the fission half-lives in the fermium region as fission defines the end point of the r process.
It will open the door to the discovery of new neutron-rich nuclei in the fermium region. Furthermore, we will get access to the masses and decay properties of nuclei at the 3rd waiting point of the astrophysical r-process and in the heavy element region. Additionally, the aim is to study the fission half-lives in the fermium region as fission defines the end point of the r process.