Session DI: Instrumentation I

The New fIREBall

Measurement of conversion electrons in coincidence with gamma rays promises new information on nuclear structure specifically about distinguishing coexistence from vibrational excitations. The Internal Conversion Electron Ball (ICEBall) mini-orange array of SiLi detectors, now located at the Nuclear Science Laboratory of the University of Notre Dame,  is being upgraded to the fInternal ConveRsion Electron Ball (fIREBall) array. The upgrade includes improvements to the filters allowing more of the beam to make it to the Si detectors, new designs for the magnet filters with optimized designs to improve detection efficiency, and new detectors. A combination of FreeCAD, COMSOL, and Geant4 was used to develop a working simulation to test a wide variety of shapes. Using the simulations, we have discovered shapes that could more than double the efficiency of ICEBall. We have achieved good agreement between experimental tests of the new magnet shapes with the simulation predictions, establishing the reliability of using simulations to design future magnet shapes. With the designs finalized, we are preparing for fIREBall’s first commission run, a repeat of a previous ICEBall experiment, a ^152,154Sm(α,2n)^154,156Gd reaction, to confirm/determine the improvements achieved, specifically in coincidence measurements. Details about the magnet design process and the upcoming commission run will be presented.   

Progress on the development of a novel Energy Loss Optical Scintillation System for heavy-ion PID

The Energy Loss Optical Scintillation System (ELOSS) is a proposed high-scintillation gaseous detector used for atomic number identification of rare, short-lived atomic nuclei. ELOSS will function as part of the focal-plane detector system of the S800 spectrograph [1] for particle identification (PID) in nuclear physics experiments at the Facility for Rare Isotope Beams (FRIB). State-of-the-art experimental equipment like ELOSS will tap into FRIB’s unprecedented discovery potential by studying isotopes at high beam rate and with high performance, resulting in a broad impact on radiation-detection physics and technology. ELOSS also represents a prototype for the development of PID technologies of other planned and future spectrometers, such as the High Rigidity Spectrometer [2].

     This work will focus on the operational mechanism and performance of ELOSS, including the description of the optical readout based on photomultiplier tubes (PMTs), an expected energy/timing resolution (respectively 0.4% and <200 psec), and high rate capability (up to ~80 kHz limited only by the DAQ). We also discuss the work performed for a full characterization of the optical readout, including PMT gain calibration and gain matching, both of which are needed to achieve the optimal ELOSS performance.

    

Progress towards the EDM3 instrument at FRIB Part 1: Ionization and mass separation

The study of radioactive molecules receives increasing attention due to their enhanced sensitivity to fundamental symmetry violations and Beyond Standard Model physics. In  particular, ²²⁵RaF has been proposed as powerful probe due to its enhanced Schiff-moment. While the principle advantage of such systems is known for more than 30 years [1], the progress in the field relies on the development of novel instruments and the availability of suitable radioisotopes. At the Facility for Rare Isotope Beams (FRIB), the latter is being addressed by development of isotope harvesting techniques [2].

Within a series of two contributions, we introduce the in-design FRIB-EDM³ instrument. The first contribution covers ionization and mass-separation of harvested radioisotopes; the second contribution is focused on neutralization of molecular ions and their embedding in a solid noble gas matrix [3].

The efficient ionization of harvested radioisotopes from aqueous phase is pursued with a spray-ionization method [4]. Subsequently, the molecular ion beam is analyzed by mass-to-charge ratio by a quadrupole mass filter. Octupole ion guides serve to minimize losses during the differential pumping stages. We will report on the progress of the instrument’s construction and its simulation-aided design.   

The Neutron Irradiation Station at Notre Dame

The Neutron Irradiation Station (NIS) at the University of Notre Dame Nuclear Science Laboratory is a facility designed for the production of high-flux monoenergetic neutrons using the reaction ⁷Li(p,n). Available neutron energies will span from 100 keV to a few MeV and will be utilized for measurements of neutron-induced reaction cross sections, in particular neutron capture reactions with applications in nuclear security and nuclear energy. An overview of the facility will be presented in this talk and preliminary characterization of the neutron flux as a function of angle for various proton energies will be discussed.   

Looking to the Future: Upgrading the Low Energy Neutron Detector Array (LENDA)

LENDA consists of 24 BC-408 plastic-scintillator bars and was designed to detect low energy neutrons produced in (p,n) charge-exchange reactions in inverse kinematics using rare isotope beams. However, LENDA is unable to differentiate between neutron and γ-ray signals, making background subtractions much more challenging than it would be if signal differentiation were possible. Radiation Monitoring Devices, Inc. (RMD) and Sandia National Laboratory are developing novel organic glass scintillators (OGSs) that have pulse-shape discrimination (PSD) capabilities for separating neutrons and gammas. The research group at FRIB that uses LENDA in experiments tested several of these scintillators as they could be potential candidates to add PSD capabilities to LENDA. This talk will focus on the results of tests of six different OGS samples, which included determination of time and energy resolutions, gain, neutron-detection thresholds, and neutron efficiencies.   

Progress report on CHICO-X

CHICO spectrometer, designed to be an auxiliary charged-particle detector array for Gammasphere, consists of two identical hemispheres with 10 individual PPAC’s in each hemisphere. It requires modifications to be geometrically compatible to GRETA. The modified spectrometer, CHICO-X, has a smaller chamber diameter of 12.6 inches with built-in fixtures to hold PPAC’s. The new pixelated position-sensing board still is located at the original position with a flight path of 13 cm to maintain the same time and position resolutions as those of CHICO(2) but with smaller solid-angle coverage. The reduced angular coverage for θ is from 23^o to 77^o for the forward hemisphere and from 103^o to 157^o for the backward hemisphere. The φ range remains the same as that of CHICO2 covering 280^o out of 360^o. The fabrication of all the mechanical parts will be completed by September 2022 and the same schedule for the redesigned pixelated boards and transmission lines. The assembling of CHICO-X will begin in October 2022. Some detailed of those work will be presented.

    

Development of a Cryogenic Helium Gas Target for Direct Reaction Studies

Helium-3-induced reactions can be used as tools to study properties of nuclei by selectively populating states via (³He,d), (³He,p), (³He,a), (³He,n), etc. At Louisiana State University, a gas target has been developed with a cryogenic cooling system to enable studies of ³He-induced reactions. The target windows are 7.5 um-thick Kapton with a 0.5-inch diameter aperture. The linear thickness may be varied by changing the window flanges. An areal density of 134 ug/cm² can be achieved with a 5-mm thick target filled with 500 Torr of ³He at 90 K. One example of a ³He-induced reaction is ⁷Be(³He,p)⁹B that can be used to populate states of ⁹B. The first-excited state of ⁹B has been studied and modeled for decades with little agreement on the energy and width of the state. Test experiments using the gas target as a ³He target have been conducted with ⁷Li and ⁷Be beams at Texas A&M University. The gas target performance and preliminary results from these (³He,p) reactions will be presented.   

TriSol: Improving RIBs at the University of Natre Dame

TwinSol, a pair of coupled superconducting solenoids at the University of Notre Dame Nuclear Science Laboratory, has been a powerful tool for producing unstable beams. For the past couple of decades there was an abundance of work done to study the structure of nuclei, both stable and unstable. In order to meet the need for more precision nuclear data, the system has been upgraded with the addition of a 15 degree bending magnet, a third solenoid, and a set of variable slits. The improvements to beam quality that this upgraded system, TriSol, yields has been systematically studied. A variety of radioactive ion beams have been studied with TriSol, including ⁸B, ¹¹C, ¹⁴O, and ¹⁷F. The details of the new system will be presented and the enhancements discussed.   

Upgrading the BACoN liquid argon cryogenic system to study scintillation light

The study of liquid argon scintillation light is of interest for many nuclear and particle physics experiments. Doping with xenon significantly shifts the wavelength of scintillation light, changes the time profile, and increases the light yield. Measurements will be performed using the BACoN test stand on the campus of the University of New Mexico (UNM), consisting of a cryostat vacuum system for liquid argon with precision injection of xenon gas for doping. The BACoN system has already produced significant results and is currently being upgraded to enhance its capability. An array of silicon photomultipliers (SiPMs) will be deployed and to be complemented by a new photomultiplier Tube (PMT) to collect scintillation light. The upgrade plan also includes the deployment of germanium detector(s) in Xe-doped liquid argon. We will describe the current progress and future plan of the BACoN experiment. The project is supported by DOE via Los Alamos National Lab LDRD, by NSF via the University of South Dakota, and by UNM funds.