Coupled Cyclotron Facility Research Articles

The new Batch Mode Ion Source for stand-alone operation at the Facility for Rare Isotope Beams (FRIB)

Gas stoppers have been used for a long-standing successful science program at Michigan State University with stopped and rare-isotope beams produced by projectile fragmentation. The National Superconducting Cyclotron Laboratory’s Coupled Cyclotron Facility has recently transitioned into the Facility for Rare Isotope Beams (FRIB) laboratory to provide rare isotopes using a high-power superconducting linear accelerator and new production facilities. To allow the science program with stopped and reaccelerated beams to continue during the transition period, a stand-alone capability was added. The Batch Mode Ion Source (BMIS) was built and has been providing beams of long-lived and stable isotopes of a variety of elements for successful user experiments. The BMIS system is described and results from the production of various beams are presented.

An isotope harvesting beam blocker for the National Superconducting Cyclotron Laboratory

Harvesting isotopes from beam stops and other activated materials at accelerator facilities is a promising source of environmentally, scientifically and socially important radionuclides. At the Facility for Rare Isotope Beams (FRIB), a multitude of short- and long-lived radionuclides will be collected in a synergistic manner by dumping unused beams into a flowing-water beam stop. Ongoing exploratory research at the National Superconducting Cyclotron Laboratory (NSCL) with an analogous beam blocker aims towards obtaining the necessary radiochemical expertise for this endeavor.Herein we present a beam blocker and an isotope harvesting system which allows collection of a wide variety of aqueous and gaseous radionuclides. The water which flows through the beam blocker functions as an isotope production target and concurrently transports the newly formed radionuclides to collection sites. The system includes analytical instruments for online measurements of conductivity, dissolved oxygen, temperature, pressure and for detection of radiolytic products. To limit the levels of radiolytically produced hydrogen peroxide, a stainless-steel based degradation system was designed and implemented. The suitability of the constructed system for the anticipated radionuclide harvesting project was demonstrated by offline tests and under irradiation with 140 MeV/u 48Ca20＋ ions at the NSCL Coupled Cyclotron Facility.

Mass measurement of Fe51 for the determination of the Fe51(p,γ)Co52 reaction rate

Background: The $^{51}\mathrm{Fe}(p,\ensuremath{\gamma})^{52}\mathrm{Co}$ reaction lies along the main rp-process path leading up to the $^{56}\mathrm{Ni}$ waiting point. The uncertainty in the reaction $Q$ value, which determines the equilibrium between the forward proton-capture and reverse photodisintegration $^{52}\mathrm{Co}(\ensuremath{\gamma},p)^{51}\mathrm{Fe}$ reaction, contributes to considerable uncertainty in the reaction rate in the temperature range of interest for Type I x-ray bursts and thus to an $\ensuremath{\approx}10%$ uncertainty in burst ashes lighter than $A=56$.Purpose: With a recent Penning trap mass measurement of $^{52}\mathrm{Co}$ reducing the uncertainty on its mass to 6.6 keV [Nesterenko et al., J. Phys. G 44, 065103 (2017)], the dominant source of uncertainty in the reaction $Q$ value is now the mass of $^{51}\mathrm{Fe}$, reported in the 2016 atomic mass evaluation to a precision of 9 keV [Wang et al., Chin. Phys. C 41, 030003 (2017)]. A new, high-precision Penning trap mass measurement of $^{51}\mathrm{Fe}$ was performed to allow the determination of an improved precision $Q$ value and thus new reaction rates.Method: $^{51}\mathrm{Fe}$ was produced using projectile fragmentation at the Coupled Cyclotron Facility at the National Superconducting Cyclotron Laboratory, and separated using the A1900 fragment separator. The resulting secondary beam was then thermalized in the beam stopping area before a mass measurement was performed using the LEBIT 9.4T Penning trap mass spectrometer.Results: The new mass excess, $\mathrm{ME}=\ensuremath{-}40189.2(1.6)$ keV, is sixfold more precise than the current AME value, and $1.6\ensuremath{\sigma}$ less negative. This value was used to calculate a new proton separation energy for $^{52}\mathrm{Co}$ of 1431(7) keV. New excitation levels were then calculated for $^{52}\mathrm{Co}$ using the nushellx code with the GXPF1A interaction, and a new reaction rate and burst ash composition was calculated.Conclusions: With a new measured $Q$ value, the uncertainty on the $^{51}\mathrm{Fe}(p,\ensuremath{\gamma})$ reaction rate is dominated by the poorly measured $^{52}\mathrm{Co}$ level structure. Reducing this uncertainty would allow a more precise rate calculation and a better determination of the mass abundances in the burst ashes.

Observation of the Isovector Giant Monopole Resonance via the ^{28}Si(^{10}Be,^{10}B^{*}[1.74 MeV]) Reaction at 100 AMeV.

The (^{10}Be,^{10}B^{*}[1.74 MeV]) charge-exchange reaction at 100 AMeV is presented as a new probe for isolating the isovector (ΔT=1) nonspin-transfer (ΔS=0) response of nuclei, with ^{28}Si being the first nucleus studied. By using a secondary ^{10}Be beam produced by fast fragmentation of ^{18}O nuclei at the NSCL Coupled Cyclotron Facility, applying the dispersion-matching technique with the S800 magnetic spectrometer to determine the excitation energy in ^{28}Al, and performing high-resolution γ-ray tracking with the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) to identify the 1022-keV γ ray associated with the decay from the 1.74-MeV T=1 isobaric analog state in ^{10}B, a ΔS=0 excitation-energy spectrum in ^{28}Al was extracted. Monopole and dipole contributions were determined through a multipole-decomposition analysis, and the isovector giant dipole resonance and isovector giant monopole resonance (IVGMR) were identified. The results show that this probe is a powerful tool for studying the elusive IVGMR, which is of interest for performing stringent tests of modern density functional theories at high excitation energies and for constraining the bulk properties of nuclei and nuclear matter. The extracted distributions were compared with theoretical calculations based on the normal-modes formalism and the proton-neutron relativistic time-blocking approximation. Calculated cross sections based on these strengths underestimate the data by about a factor of 2, which likely indicates deficiencies in the reaction calculations based on the distorted wave Born approximation.

Accelerator test of an improved Angle Detecting Inclined Sensor (ADIS) prototype with beams of 78Kr and fragments

The measurement of cosmic rays and Solar energetic particles in space is basic to our understanding of the Galaxy, the Sun, phenomena in the heliosphere and the emerging field of space weather. For these reasons, cosmic ray instruments are common on both scientific spacecraft and operational spacecraft such as weather satellites.Cosmic rays and Solar energetic particles include ions over the full range of elements found in the Solar System. High-resolution measurements of the elemental and isotopic composition require the angle of incidence of these energetic ions be determined to correct for pathlength variation in detectors within an instrument. The Angle Detecting Inclined Sensor (ADIS) system is a simple detector configuration used to determine the angle of incidence of heavy ions in space instruments. ADIS replaces complex position sensing detectors (PSDs) with a system of simple, reliable and robust detectors inclined at an angle to the instrument axis. An ADIS instrument thus offers significant advantages in mass, power, telemetry and cost.In February 2008 an improved ADIS prototype was tested with a 150MeV/u 78Kr beam at the National Superconducting Cyclotron Laboratory's (NSCL) Coupled Cyclotron Facility (CCF). This demonstrated a charge resolution of σ~0.3 e at Kr (Z=36), an exceptional charge resolution for such a simple instrument system.

Opportunities for isotope discoveries at FRIB

Expected production yields of the Facility for Rare Isotope Beams (FRIB) were calculated for a wide range of rare isotopes using the code LISE++ and planned performance parameters (Tarasov and Bazin, 2008; Bollen et al., 2011 [2]). A comparison between isotope discoveries of the last decade and expected particle yields indicates the range of isotopes that can likely be detected at FRIB. This paper will highlight recent isotope discoveries at NSCL’s Coupled Cyclotron Facility and deduce how far the limits could be pushed with the Facility for Rare Isotope Beams.

Nuclear Data Sheets for A = 87

The evaluated experimental data are presented for 14 known nuclides of mass 87 (Ga, Ge, As, Se, Br, Kr, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru). New datasets have been added for 87Ga, 87Se, 87Kr, 87Rb, 87Sr, 87Nb, and 87Tc. The observation of and new lifetime measurements for 87As at the NSCL Coupled Cyclotron Facility and the Oak Ridge Isochronous Cyclotron at the HRIBF–ORNL Facility are included in the adopted levels for this isotope. The new evaluation also includes an isomeric level at unknown energy for 87Tc, changes to the adopted levels for 87Nb based on newly published data including an extension of the high spin levels and new lifetime measurements, and new heavy ion data for 87Kr. New high spin levels for 87Rb were observed, indicating possible neutron core excitations. In addition, the ground state lifetime of 87Rb has been revised and a new lifetime measurement for an excited level in 87Rb indicates a possible proton spin flip. New excitation levels have been observed for the first time in 87Se. New direct and precise measurement of atomic masses of 87Tc, 87Mo, 87Nb, 87Zr, 87Mo and 87Tc have greatly improved the Q value landscape in this mass region. This work supersedes the previous A=87 evaluation published in 2002He09, and Q values for all isotopes were updated to incorporate the mass evaluation in 2012Wa38.

Unbound excited states of theN=16closed shell nucleusO24

Two low-lying neutron-unbound excited states of $^{24}\mathrm{O}$, populated by proton-knockout reactions on $^{26}\mathrm{F}$, have been measured using the MoNA and LISA arrays in combination with the Sweeper Magnet at the Coupled Cyclotron Facility at the NSCL using invariant mass spectroscopy. The current measurement confirms the separate identity of two states with decay energies 0.51(5) MeV and 1.20(7) MeV, and provides support for theoretical model calculations, which predict a ${2}^{+}$ first excited state and a ${1}^{+}$ higher-energy state. The measured excitation energies for these states, 4.70(15) MeV for the ${2}^{+}$ level and 5.39(16) MeV for the ${1}^{+}$ level, are consistent with previous lower-resolution measurements, and are compared with five recent model predictions.

Henry Gabriel Blosser

Henry Gabriel Blosser

Commissioning of the collinear laser spectroscopy system in the BECOLA facility at NSCL

A collinear laser-spectroscopy (CLS) system in the BEam COoler and LAser spectroscopy (BECOLA) facility was constructed at National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. The BECOLA facility will be used to advance measurements of nuclear properties of low-energy rare isotope beams generated via in-flight reactions and subsequent beam thermalization in a buffer gas. The CLS studies at BECOLA will complement laser spectroscopy studies of charge radii and nuclear moments mostly obtained so far at Isotope SeOn Line (ISOL) facilities. Commissioning tests of the CLS system have been performed using an offline ion source to produce stable-ion beams. The tests set the ground work for experiments at the future Facility for Rare Isotope Beams (FRIB) as well as experiments at the current Coupled Cyclotron Facility at NSCL.

A simulation tool for Recoil Distance Method lifetime measurements at NSCL

A detailed, universal simulation tool for the Recoil Distance Method lifetime measurements at the National Superconducting Cyclotron Laboratory (NSCL) is presented. The measurements are made with the Köln-NSCL plunger-SeGA setup and utilize fast, secondary beams of exotic nuclei provided by the Coupled Cyclotron Facility and the A1900 fragment separator. The simulation tool, built upon GEANT4 and Root toolkits, incorporates all relevant aspects of a plunger experiment. The tool is applied in two ways. First, to aid in the design of new experiments by facilitating the choice of optimal experimental conditions. Second, to aid in off-line analysis of the experimental data and in particular to deduce the lifetime by comparison of experimental and simulated peak shapes in the γ -ray energy spectra. All the important features of the simulation tool are described, followed by examples of the application of the tool in the cases of real experiments completed or proposed at NSCL.

Development of an 18GHz superconducting electron cyclotron resonance ion source at RCNP

An 18 GHz superconducting electron cyclotron resonance ion source has recently been developed and installed in order to extend the variety and the intensity of ions at the RCNP coupled cyclotron facility. Production of several ions such as O, N, Ar, Kr, etc., is now under development and some of them have already been used for user experiments. For example, highly charged heavy ion beams like (86)Kr(21+,23+) and intense (16)O(5+,6+) and (15)N(6+) ion beams have been provided for experiments. The metal ion from volatile compounds method for boron ions has been developed as well.

Neutrons cross the line

For most atomic nuclei, the maximum number of neutrons that can be bound is unknown. The discovery of two neutron-rich nuclei — and the confirmed absence of others — might help solve this conundrum. The limit of how many neutrons can be bound by a given number of protons — called the neutron drip line — is of fundamental importance in nuclear physics. It is unknown for all but the lightest elements, because of the complex interplay between single particle and collective quantum effects, but the detection of two new neutron-rich isotopes of magnesium and aluminium is a significant step towards establishing this limit. 40Mg and 42Al, predicted to be 'drip-line' nuclei on the edge of stability, were produced at the coupled cyclotron facility of the US National Superconducting Cyclotron Laboratory. The debut of 42Al is the first experimental indication that the stability of very neutron-rich aluminium isotopes is enhanced relative to magnesium, and indicates that the neutron drip line may be farther from stable isotopes than expected. The findings suggest that the drip line may be beyond the reach of most current and projected nuclear science facilities for nuclei with atomic numbers over 12.

High-precision Penning trap mass measurements ofCa37,38and their contributions to conserved vector current and isobaric mass multiplet equation

Penning trap mass measurements of the super-allowed \ensuremath{\beta} emitter $^{38}\mathrm{Ca}$ and of $^{37}\mathrm{Ca}$ have been performed using the low-energy beam and ion trap facility at the coupled cyclotron facility of the National Superconducting Cyclotron Laboratory. Both isotopes were produced by fast-beam fragmentation and in-flight separation. The mass of $^{38}\mathrm{Ca}$ (${T}_{1/2}=440$ ms) was determined with a precision of $\ensuremath{\delta}m=280$ eV, corresponding to a relative mass uncertainty of $\ensuremath{\delta}m/m\ensuremath{\approx}8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$. A mass excess value of ME $=\ensuremath{-}22508.52(28)$ was obtained. $^{38}\mathrm{Ca}$ is a ${0}^{+}\ensuremath{\rightarrow}{0}^{+}$ emitter, and the improved mass value makes it a new candidate for testing the conserved vector current hypothesis. For $^{37}\mathrm{Ca}$ (${T}_{1/2}=180$ ms), a mass excess value of ME $=\ensuremath{-}13135.7(1.4)$ was measured. Using the quadratic form of the isobaric mass multiplet equation and the improved $^{37}\mathrm{Ca}$ mass value, a precise prediction of the excitation energy of the $^{37}\mathrm{Ar}$ isobaric analog state was obtained.

Accelerator test of an angle detecting inclined sensor (ADIS) prototype with beams of 48Ca and fragments

The measurement of cosmic rays and Solar energetic particles in space is basic to our understanding of the Galaxy, the Sun, phenomena in the Heliosphere and what has come to be known broadly as “space weather”. For these reasons, cosmic ray instruments are common on both scientific spacecraft and operational spacecraft such as weather satellites. The resource constraints on spacecraft generally mean that instruments that measure cosmic rays and Solar energetic particles must have low mass (a few kg) and low power (a few W), be robust and reliable yet still highly capable. Such instruments must identify ionic species (at least by element, preferably by isotope) from protons through the iron group. The charge and mass resolution of heavy ion instruments in space depends upon determining ions’ angles of incidence. The Angle Detecting Inclined Sensor (ADIS) system is a highly innovative and uniquely simple detector configuration used to determine the angle of incidence of heavy ions in space instruments. ADIS replaces complex position sensing detectors (PSDs) with a system of simple, reliable and robust Si detectors inclined at an angle to the instrument axis. In August 2004, we tested ADIS prototypes with a 48Ca beam at the National Superconducting Cyclotron Laboratory's (NSCL) Coupled Cyclotron Facility (CCF). Among the analyses performed on the data taken at the NSCL, we demonstrate that our prototype design with an ADIS system has a charge resolution of less than 0.25 e. We also present a more generalized analytic derivation of instrument response and report on the corresponding analysis of Monte-Carlo modeling data.

Nuclear Astrophysics with Fast Radioactive Beams

Simultaneous progress in astronomical observations and nuclear physics experiments with radioactive beams offers new opportunities in nuclear astrophysics, in particular concerning the r-process and the rp-process. I review some of the open questions and recent developments, and present two recent experimental results from the new Coupled Cyclotron Facility at MSU. These are the measurement of the half-life of 78Ni relevant for the r-process and the measurement of excited states in 33Ar that reduce the uncertainties in the 32Cl(p, γ)33Ar reaction rate in the rp-process by several orders of magnitude.

Heteroepitaxial diamond detectors for heavy ion beam tracking

Heteroepitaxy has been shown to produce uniform crystals of single crystal diamond. An advantage of heteroepitaxy is its potential for creating materials suitable for energetic particle detectors that require large-area plates. At this point, there is little information on the electronic properties of heteroepitaxial material and its suitability for detector use is an open question. To address this issue, a heteroepitaxially grown single crystal was used for high-temperature DC transport measurements and for evaluation as a heavy ion particle detector. Using a transverse geometry with an as-grown Ir film as one electrode and a diffused Ti–Au top electrode, the sample showed no detectable current leakage at room temperature up to 100 V bias. At temperatures between 250 and 600 °C, the DC electrical conductivity exhibited thermally activated behavior with an activation energy of 1.4 eV. A 76Ge beam with an energy of 100 MeV/u produced at the Coupled Cyclotron Facility at Michigan State University was used to test detector performance. At typical beam fluences, single events were recorded with instrumentally limited rise times of 0.5 ns and pulse width 1 ns. Single pulses corresponded to an energy loss Δ E = 46 MeV. A pulse-height resolution of the energy loss signal of Δ E / E = 18% was measured. Of particular importance is the fast performance at high beam intensities. No degradation of timing properties and energy resolution could be observed with count rates up to 10 6 particles/s. These measurements reflect the properties of the as-grown heteroepitaxial diamond crystal to which no subsequent processing was applied. It is anticipated that by using thicker crystals that allow the defective initial growth region to be removed mechanically, greatly improved energy resolution can be observed.

Nuclear astrophysics with fast radioactive beams

Simultaneous progress in astronomical observations and nuclear physics experiments with radioactive beams offers new opportunities in nuclear astrophysics, in particular concerning the r-process and the rp-process. I review some of the open questions and recent developments, and present two recent experimental results from the new Coupled Cyclotron Facility at MSU. These are the measurement of the half-life of 78Ni relevant for the r-process and the measurement of excited states in 33Ar that reduce the uncertainties in the 32Cl(p, γ)33Ar reaction rate in the rp-process by several orders of magnitude.

The LEBIT 9.4 T Penning trap system

The initial experimental program with the Low-Energy Beam and Ion Trap Facility, or LEBIT, will concentrate on Penning trap mass measurements of rare isotopes, delivered by the Coupled Cyclotron Facility (CCF) of the NSCL. The LEBIT Penning trap system has been optimized for high-accuracy mass measurements of very short-lived isotopes.

Experiments with radioactive beams of r-process nuclei

Despite a lot of experimental and theoretical progress the question of the r-process site and the origin of the heavy elements in nature remains one of the biggest open questions in nuclear astrophysics. I discuss the need for experimental nuclear data and review recent progress made at rare isotope beam facilities. In particular, I summarize some recent experiments performed at the NSCL Coupled Cyclotron Facility at MSU with beams of r-process nuclei, including the measurement of the half-life of 78 Ni.