Nuclear Science Laboratory Research Articles

The use of second foil stripping in tandem accelerators

The 10 MV FN Tandem at the University of Notre Dame’s Nuclear Science Laboratory has the option for a second foil stripper halfway down its high energy column. With its utilization, users are able to produce beams with higher energies and/or transmission than single foil stripping alone would be capable of achieving. A discussion of the Schiwietz–Grande, Nikolaev–Dmitriev, and Baudinet-Robinet semi-empirical models used to determine the resulting charge state abundances, as well as how they compare to measured charge state distributions is presented. The advantages of a second foil stripper are discussed alongside measurements of the charge state abundances produced. The potential for more interfering beam species of similar magnetic rigidity is also discussed. It was found that for most of the beams tested, second foil stripping allowed higher energies with higher yields than the single terminal foil stripping alone could achieve which can enhance the capabilities of other laboratories using similar accelerator systems.

IAEA fostering of the development and applications of nuclear analytical techniques for Heritage Science

The IAEA Physics Section is strongly involved in the development and utilization of accelerator-based analytical techniques, which are powerful tools for the characterization of cultural and natural heritage objects and materials. Various activities are carried out with the purpose to build capacity, strengthen capabilities, transfer knowledge and foster networking in the field of heritage science. In addition, access to different X-ray fluorescence spectrometers and other analytical techniques is provided at the Nuclear Science and Instrumentation Laboratory (part of the IAEA Physics Section), and access to ion beam accelerators and synchrotron light is facilitated thanks to collaborations with Ruđer Bošković Institute (RBI) in Croatia and the Elettra Sincrotrone facility in Italy, respectively. Member States are also supported on their Research and Development programmes, as well as through the technical cooperation projects. This paper aims to provide a broad overview about how the IAEA Physics Section is engaged in the field of heritage science, promoting the safe, reliable, and effective use of ion beam, X-ray and neutron-based techniques for the characterization and preservation of cultural and natural heritage through its global networks and partners.

Monte Carlo modelling of cyclotron and radioisotope center (CYRIC) at Tohoku University: a radiation protection study

Protection against ionizing radiations is important in laboratories with radioactive materials and high energy cyclotron beams. The Cyclotron and Radioisotope Center (CYRIC) located in Tohoku University in Miyagi prefecture, Japan and is a well-known nuclear science laboratory with cyclotron beams and substantial number of high activity radioactive materials. Considering this, it is important to perform complete radiation transport computations to ensure the safety of non-occupational and occupational workers. In the present work, we have developed a complete 3-dimensional model of the main cyclotron building and radiation labs using Monte Carlo method. We have found that the dispersed photons and neutrons inside and in the surrounding of the CYRIC building pose no significant risk to occupational and non-occupational workers. The present work and the developed models would be useful in the field of radiation protection.

Cooling the atmosphere

AbstractThis is a paper on experimental studies performed in the 1940s at the University of Notre Dame accelerator laboratory to investigate radiation effects on materials and also to probe the efficiency of atmospheric cooling of the fireball created by a nuclear fission device. This was a critical question to be addressed during the early phases in the development of the Manhattan project, which was again raised in the film Oppenheimer, posing the question whether “a bomb can set the atmosphere on fire.” This paper brings forth the formerly classified reaction studies performed at Notre Dame's Nuclear Science Laboratory to answer this question.

The Enge Split-Pole Spectrograph at the University of Notre Dame

Nuclear reactions play a crucial role in determining the nucleosynthesis that occurs in astrophysical events. The rates of many reactions that significantly impact certain nucleosynthesis processes can not be currently measured via direct means. These reactions must be constrained in another manner, such as determining the level energies and other structure properties of the compound nuclei. In order to measure level energies of nuclei relevant to nuclear astrophysics, the Enge split-pole spectrograph has been installed and commissioned at the University of Notre Dame’s Nuclear Science Laboratory. The first scientific measurement has also been performed. Structure properties of 58Cu were measured via the reaction 58Ni(3He,t)58Cu to provide the first experimental constraint of the 57Ni(p,γ)58Cu reaction rate, which impacts the production of of 44Ti, 57Fe, and 59Ni in core-collapse supernovae. Preliminary analysis of this measurement confirms the level energies of states in 58Cu that could lead to significant resonances in the 57Ni(p,γ)58Cu reaction rate, while suggesting the presence of additional states that have not been previously observed but could also lead to significant resonances.

On-line installation of the Superallowed Transition Beta-Neutrino Decay Ion Coincidence Trap

The Cabibbo-Kobayashi-Maskawa quark mixing matrix currently does not satisfy unitarity at the 2σ-level. This could be the result of an inaccurate value of one or both of its largest matrix elements Vus and Vud. In the case of Vud, the most precise measurement is obtained from the f t-value measurements of superallowed beta-transitions between 0+ states. The accuracy of this determination can, in turn, be tested by extracting Vud in other transitions including superallowed transitions between mirror nuclei. The Superallowed Transition Beta-Neutrino Decay Ion Coincidence Trap (St. Benedict) is currently under construction at the Nuclear Science Laboratory of the University of Notre Dame to perform such a determination, with the goal of shedding more light on this tension with unitarity. St. Benedict will take a radioactive ion beam produced by TwinSol, thermalize it in a large volume gas catcher, then transport it in two separate differentially-pumped volumes using a radio-frequency (RF) carpet and a radio-frequency quadrupole (RFQ) ion guide before injecting it in an RFQ trap to create cool ion bunches for injection in the measurement Paul trap. In this paper, we detail the installation of the beam preparation components of St. Benedict, and present the results of the first RIBs successfully stopped and extracted from its gas catcher.

Experimental study of 6He Coulomb breakup as an indirect measurement of 4He(2n,γ)6He reaction rate for the astrophysical r-process

In this work, we report the measurement of elastic and Coulomb break-up channels in 6He+208Pb collisions at Elab = 19.3 MeV, close to the Coulomb barrier of this system ∼ 19 MeV. In the context of the astrophysical r-process, the reaction 4He(2n,γ)6He has been proposed to be a key reaction in the path of synthesizing seed nuclei for the r-process, as 12C, in an environment composed mainly of alpha particles and neutrons. Based on a theoretical approach for treating three body reactions by means of which its reaction rate can be inferred, our experimental approach aims to obtain an indirect measurement of the reaction rate of 4He(2n,γ)6He by measuring the Coulomb breakup of 6He under the intense electric field produced by a 208Pb target nucleus. The experiment was carried out at the TriSol facility operated in the Nuclear Science Laboratory of the University of Notre Dame, USA, which delivered a 6He beam together with other contaminants. Particular care must be taken for the alpha particles produced in the production reaction.

The St. Benedict Facility: Probing Fundamental Symmetries through Mixed Mirror β-Decays

Precise measurements of nuclear beta decays provide a unique insight into the Standard Model due to their connection to the electroweak interaction. These decays help constrain the unitarity or non-unitarity of the Cabibbo–Kobayashi–Maskawa (CKM) quark mixing matrix, and can uniquely probe the existence of exotic scalar or tensor currents. Of these decays, superallowed mixed mirror transitions have been the least well-studied, in part due to the absence of data on their Fermi to Gamow-Teller mixing ratios (ρ). At the Nuclear Science Laboratory (NSL) at the University of Notre Dame, the Superallowed Transition Beta-Neutrino Decay Ion Coincidence Trap (St. Benedict) is being constructed to determine the ρ for various mirror decays via a measurement of the beta–neutrino angular correlation parameter (aβν) to a relative precision of 0.5%. In this work, we present an overview of the St. Benedict facility and the impact it will have on various Beyond the Standard Model studies, including an expanded sensitivity study of ρ for various mirror nuclei accessible to the facility. A feasibility evaluation is also presented that indicates the measurement goals for many mirror nuclei, which are currently attainable in a week of radioactive beam delivery at the NSL.

Improvements for heavy-ion accelerator mass spectrometry at the university of Notre Dame’s nuclear science laboratory

The detection of heavy (A > 127), long-lived trace radionuclides using accelerator mass spectrometry requires accelerator systems with high mass resolution and detectors with high efficiency, timing and energy resolution, and resistance to degradation. At the University of Notre Dame’s Nuclear Science Laboratory, a two-anode gas ionization detector, similar to others employed at ETH Zurich, Vienna, and the Australia National University, has been built to be used with a time-of-flight system. This new detector is more robust than the existing Si detector, with two high resolution ΔE segments. This work describes the detector design and modifications to the time-of-flight system, summarizes the observed performance, and provides comparisons to a Geant4 model. The energy resolution (9% for 44 MeV 238U beams) was found to be better than the existing Si detector and its larger acceptance contributed a factor of five improvement (from 4% to 20%) in transmission through the detection system for uranium beams.

Construction of St. Benedict

The Superallowed Transition Beta-Neutrino Decay Ion Coincidence Trap (St. Benedict) is currently under construction at the University of Notre Dame Nuclear Science Laboratory. It is designed to measure the beta-neutrino angular correlation parameter in superallowed mixed beta-decay transitions between mirror nuclei in order to extract the Fermi-to-Gamow Teller mixing ratio and test theoretical corrections entering in the determination of the Vud element of the Cabibbo–Kobayashi–Maskawa quark mixing matrix. St. Benedict includes a large volume gas catcher to thermalize the radioactive ion beam from TwinSol, a differentially-pumped extraction system, a radiofrequency quadrupole ion cooler and buncher, and a Paul trap for the observation and detection of the β decay products. The status of each of these components will be presented.

Development towards 53Mn Accelerator Mass Spectrometry capabilities at the University of Notre Dame

Accelerator Mass Spectrometry (AMS) with 53Mn has geological applications as a chronometer for exposure and burial times for discontinuously deposited sediments. It has also been used to search for evidence of recent supernovae events, and proposed as a proxy to monitor the variation in the galactic cosmic ray spectrum over time. The current sensitivity limit amongst active facilities is 53Mn/ 55Mn = 3×10−13 while a sensitivity of 53Mn/ 55Mn = 1×10−13 is necessary to fully exploit 53Mn’s capabilities. At the University of Notre Dame’s Nuclear Science Laboratory (NSL), a 10 MV tandem accelerator and a Browne–Buechner Spectrograph operated as a gas-filled magnet were used to separate 53Mn from 53Cr. Samples covering ranges of 53Mn/ 55Mn = 10−10−10−8 were measured for the first time at the NSL using various settings resulting in a background level of 53Mn/ 55Mn =6.2(3)×10−11. Analysis of the results, descriptions of experimental settings, and further explorations will be presented in this paper.

A novel activation technique for integrated cross section measurements using accelerator mass spectrometry

41Ca (t1/2 = 9.94 × 104 yrs) is an important stellar radionuclide and its production in the Early Solar System from various irradiation scenarios can help determine the viability of models of early stellar processes. A novel reaction technique has been under development and recently tested at the Nuclear Science Laboratory at the University of Notre Dame. This technique utilizes an “in-cathode” reaction method, where natural CaF2 material is packed into an ion source sample holder (cathode) and then irradiated and subsequently measured using Accelerator Mass Spectrometry (AMS) without the need for chemical processing afterward. The setup for the irradiation was performed using a 3He beam to measure the reaction natCa(3He,x)41Ca. Initial AMS results suggest additional complexity due to ion source sputtering rates and geometry, which will need to be explored further.

Initial tests of Accelerator Mass Spectrometry with the Argonne Gas-Filled Analyzer and the commissioning of the MONICA detector

As the scope of Accelerator Mass Spectrometry (AMS) expands, there is an increased need to extend the capability of isobaric separation to the medium-heavy mass region. Existing AMS facilities are limited in their ability to separate radioactive nuclei in the A = 100–200 range of interest from their neighboring stable isobars, as such measurements require higher energies than available in most facilities. ATLAS is one of the highest energy system used for AMS based experiments and has enabled isobaric discrimination for medium to heavy nuclides, notably via the Gas-Filled Magnet technique. A preparatory experiment performed in November, 2019, successfully demonstrated isobaric separation of 92Zr-92Mo using the Argonne Gas-Filled Analyzer (AGFA) with high magnetic rigidity. Since that time, MONICA, an eight-anode ionization chamber that measures both energy loss and position with two sets of split anodes, has been developed to aid in AMS experiments at AGFA and has undergone four commissioning runs at the Nuclear Science Laboratory at the University of Notre Dame utilizing Si, Fe/Ni, and Mn beams. This report presents the AGFA AMS run (November 2019) and the subsequent commissioning runs of the MONICA detector, including preliminary measurements on the long-lived isotopes 39Ar (268 y) and for the first time on 42Ar (33 y).

Commissioning of the St. Benedict RF carpet

The Superallowed Transition BEta NEutrino Decay Ion Coincidence Trap (St. Benedict) aims to measure the beta-neutrino angular correlation parameter for superallowed mixed beta decay transitions between mirror nuclei in order to conduct precision tests of the Standard Model. St. Benedict will include a gas catcher, a differentially pumped extraction system, a radio-frequency quadrupole (RFQ) cooler and buncher, and a Paul trap to utilize radioactive ion beams produced at the Nuclear Science Laboratory of the University of Notre Dame. The two-part differentially pumped extraction system contains a RF carpet at a helium gas pressure of around 3 mbar, and a radio-frequency quadrupole (RFQ) ion guide at a pressure of around 2×10−3 mbar. Transport efficiency of potassium ions in the first part of the extraction system using the RF carpet in the presence of gas flow was determined to be near 100% in the 0.75 to 5 mbar pressure range using the ion surfing transport method.

Investigation of the B10(p,α)Be7 reaction from 0.8 to 2.0 MeV

Background: A multitude of broad interfering resonances characterize the B10(p,α)Be7 cross section at low energies. The complexity of the reaction mechanism, as well as conflicting experimental measurements, have so far prevented a reliable prediction of the cross section over the energy ranges pertinent for a boron-proton fusion reactor environment. Purpose: To improve the evaluated cross section of the B10(p,α)Be7 reaction, this study targets the proton energy region from 0.8 to 2.0 MeV, where kinematic overlap of the scattered protons and reaction α particles have made past measurements very challenging. Method: New detailed studies of the reaction have been performed at the Edwards Accelerator Laboratory at Ohio University and the Nuclear Science Laboratory at the University of Notre Dame using time-of-flight and degrader foil techniques, respectively. Results: Proton and α-particle signals were clearly resolved using both techniques, and 16 point differential cross sections were measured over an angular range of θlab=45∘ and 157.5∘. A comprehensive R-matrix analysis of the experimental data, including data from previous low-energy studies of the B10(p,α)Be7, B10(p,p)B10, and B10(p,γ)C11 reactions, was achieved over the region of measurement. Using a representative set of previous data, the fit was extended to very low energies. Conclusions: On the basis of this data and R-matrix analysis, a more reliable and consistent description of the B10(p,α)Be7 cross section has been established. The uncertainty over the energy range of this study has been reduced from ≈20% to ≈10%, and the level structure over this region has been clarified considerably.8 MoreReceived 18 January 2022Accepted 26 April 2022DOI:https://doi.org/10.1103/PhysRevC.105.055802©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDirect reactionsNuclear astrophysicsNuclear fusionNuclear powerNuclear reactionsNuclear reactorsNuclear structure & decaysRadiative captureResonance reactionsProperties6 ≤ A ≤ 19Nuclear PhysicsPlasma Physics

Heavy-ion production of 77Br and 76Br

Many radioisotopes with potential medical applications are difficult to produce routinely, especially those on the proton-rich side of the valley of stability. Current production methods typically use light-ion (protons or deuteron) reactions on materials of similar mass to the target radioisotope, which limits the elemental target material available and may require the use of targets with poor thermal properties (as is the case for the production of radiobromine). These reactions may also create significant amounts of proton-rich decay products which require chemical separation from the desired product in a highly radioactive environment. A promising alternative method using heavy-ion fusion-evaporation reactions for the production of the medically relevant bromine radioisotopes 76Br (t1/2 = 16.2 h) and 77Br (t1/2 = 57.0 h) is presented. Heavy-ion beams of 28Si and 16O were used to bombard natural chromium and copper targets just above the Coulomb barrier at the University of Notre Dame's Nuclear Science Laboratory to produce these bromine and precursor radioisotopes by fusion-evaporation reactions. Production yields for these reactions were measured and compared to PACE4 calculations. In addition to using more robust targets for irradiation, a simple physical–chemical separation method is proposed that will lead to very high radiopurity yields. A summary of accelerator facility requirements needed for routine production of these radioisotopes is also presented.

Investigation of secondary γ -ray angular distributions using the N15(p,α1γ)C*12 reaction

The observation of secondary $\ensuremath{\gamma}$-rays provides an alternative method of measuring cross sections that populate excited final states in nuclear reactions. The angular distributions of these $\ensuremath{\gamma}$-rays also provide information on the underlying reaction mechanism. Despite the large number of data of this type in the literature, publicly available $R$-matrix codes do not have the ability to calculate these types of angular distributions. In this paper, the mathematical formalism derived by C. R. Brune and R. J. deBoer [Phys. Rev. C 102, 024628 (2020)] is implemented in the $R$-matrix code azure2 and calculations are compared with previous data from the literature for the $^{15}\mathrm{N}(p,{\ensuremath{\alpha}}_{1}\ensuremath{\gamma})^{12}\mathrm{C}^{*}$ reaction. In addition, new measurements, made at the University of Notre Dame Nuclear Science Laboratory using the Hybrid Array of Gamma Ray Detectors (HAGRiD), are reported that span the energy range from ${E}_{p}=0.88$ MeV to ${E}_{p}=4.0\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$. Excellent agreement between the data and the phenomenological fit is obtained up to the limit of the previous fit at ${E}_{p}=2.0\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ and the $R$-matrix fit is extended from ${E}_{x}\ensuremath{\approx}13.5$ MeV up to ${E}_{x}\ensuremath{\approx}15.3$ MeV, where $^{15}\mathrm{N}+p$ and $^{12}\mathrm{C}+\ensuremath{\alpha}$ reactions are fit simultaneously for the first time. An excellent reproduction of the $^{15}\mathrm{N}(p,{\ensuremath{\alpha}}_{1}\ensuremath{\gamma})^{12}\mathrm{C}^{*}$ and $^{12}\mathrm{C}(\ensuremath{\alpha},\ensuremath{\alpha})^{12}\mathrm{C}$ data is achieved, but inconsistencies and difficulty in fitting other data are encountered and discussed.

Recent developments in the AMS system at the Nuclear Science Laboratory: Impacts on radionuclide sensitivities and current capabilities

In recent years, the AMS system at the Nuclear Science Laboratory of the University of Notre Dame has introduced a series of upgrades which have dramatically increased the capabilities for the measurement of trace radionuclides. These upgrades have solved issues with isotopic selectivity in the injection system, allowed for the measurement of heavier radionuclides, and improved the quality of both ion beams and the data obtained with them. The specifics of the installed equipment, as well as preliminary results on isotopic sensitivities for previously measured and newly-developed radionuclides, are discussed. Finally, the impacts on the development of planned radionuclide measurements in the future, including measurements of the actinides, will be mentioned.

IAEA activities in support of nuclear physics research and applications

Facilitation of development and promotion of nuclear applications for peaceful purposes and related capacity building are among the IAEA missions where Physics Section contributes most. The relevant activities fall under the IAEA’s program ‘nuclear science’ and cover four main thematic areas: applications of particle accelerators, sustainable utilization of research reactors, controlled fusion research and technology, and nuclear instrumentation. The Section also operates the Nuclear Science and Instrumentation Laboratory (NSIL) at Seibersdorf, located approximately 40 km south of Vienna. NSIL’s primary mission is to assist IAEA Member States to establish, operate and maintain various nuclear instrumentation and spectrometry-based techniques in support of a wide range of applications such as materials This paper will illustrate through a number of selected examples how the IAEA supports nuclear physics research and diverse applications in order to address key development priorities in many areas of societal importance and economic growth of the developing countries. In addition, some future plans on enhancing capabilities of the Nuclear Science and Instrumentation Laboratory as part of Physics Section will be highlighted, in particular by establishment of the neutron science facility and considerations for a compact ion beam accelerator.

Precise half-life determination of the mixed-mirror β -decaying O15

The half-life of $^{15}\mathrm{O}$ was measured using the $\ensuremath{\beta}$-Counting Station at the University of Notre Dame's Nuclear Science Laboratory. Our new result, ${t}_{1/2}=122.308(49)$ s, is the most precise determination to date for $^{15}\mathrm{O}$, and improves the world average by a factor of 4, yielding ${t}_{1/2}^{\text{world}}=122.27(6)$ s. This more precise value will be important for future determinations of ${V}_{\text{ud}}$ using superallowed $T=1/2$ mirror transitions.