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The Facility for Rare Isotope Beams will be completed in late 2021. We report here on the current efforts to commission the first stages of the 200-MeV/u superconducting, continuous wave heavy-ion linac. The statuses of the cryogenic plant and its distribution system, the accelerator cryomodule commissioning and operations, the ion source and front end transport development, the radio-frequency quadrupole commissioning, and thenbeam dynamics development to support high-power operation are reviewed. Plans for commissioning the remainder of the linac systems are presented.

Many neutron star (NS) properties, such as the proton fraction within a NS, reflect the symmetry energy contributions to the Equation of State that dominate when neutron and proton densities differ strongly. To constrain these contributions at supra-saturation densities, we measure the spectra of charged pions produced by colliding rare isotope tin (Sn) beams with isotopically enriched Sn targets. Using ratios of the charged pion spectra measured at high transverse momenta, we deduce the slope of the symmetry energy to be $42 < L < 117$ MeV. This value is slightly lower but consistent with the $L$ values deduced from a recent measurement of the neutron skin thickness of $^{208}$Pb.

Physics letters / B 822, 136681 (2021). doi:10.1016/j.physletb.2021.136681, Published by North-Holland Publ., Amsterdam

In this paper, we present a software framework, S$\pi$RITROOT, which is capable of track reconstruction and analysis of heavy-ion collision events recorded with the S$\pi$RIT time projection chamber. The track-fitting toolkit GENFIT and the vertex reconstruction toolkit RAVE are applied to a box-type detector system. A pattern recognition algorithm which performs helix track finding and handles overlapping pulses is described. The performance of the software is investigated using experimental data obtained at the Radioactive Isotope Beam Facility (RIBF) at RIKEN. This work focuses on data from $^{132}$Sn + $^{124}$Sn collision events with beam energy of 270 AMeV. Particle identification is established using $\left$ and magnetic rigidity, with pions, hydrogen isotopes, and helium isotopes., Comment: 10 pages, 17 figures

Excited states in $^{14}$O have been investigated both experimentally and theoretically. Experimentally, these states were produced via neutron-knockout reactions with a fast $^{15}$O beam and the invariant-mass technique was employed to isolate the 1$p$ and 2$p$ decay channels and determine their branching ratios. The spectrum of excited states was also calculated with the Shell Model Embedded in the Continuum that treats bound and scattering states in a unified model. By comparing energies, widths and decay branching patterns, spin and parity assignments for all experimentally observed levels below 8 MeV are made. This includes the location of the second 2$^{+}$ state that we find is in near degeneracy with the third 0$^{+}$ state. An interesting case of sequential 2$p$ decay through a pair of degenerate $^{13}$N excited states with opposite parities was found where the interference between the two sequential decay pathways produces an unusual relative-angle distribution between the emitted protons., 19 pages, 20 figures

Neutron-transfer reactions with fast secondary beams of $^{17}\mathrm{Ne}, ^{15}\mathrm{O}$, and $^{9}\mathrm{C}$ have been studied with the HiRA and CAESAR arrays. Excited states of $^{18}\mathrm{Ne}, ^{16}\mathrm{O}$, and $^{10}\mathrm{C}$ in the continuum have been identified using invariant-mass spectroscopy. The best experimental resolution of these states is achieved by selecting events where the decay fragments are emitted transverse to the beam direction. We have confirmed a number of spin assignments made in previous works for the negative-parity states of $^{18}\mathrm{Ne}$. In addition we have found new higher-lying excited states in $^{16}\mathrm{O}$ and $^{18}\mathrm{Ne}$, some of which fission into two ground-state $^{8}\mathrm{Be}$ fragments. Finally for $^{10}\mathrm{C}$, a new excited state was observed. These transfer reactions were found to leave the remnant of the $^{9}\mathrm{Be}$ target nuclei at very high excitation energies and may be associated with the pickup of a deeply bound $^{9}\mathrm{Be}$ neutron.

The SπRIT Time Projection Chamber (TPC) was constructed at Michigan State University in the U.S.A. and transported to the Radioactive Isotope Beam Factory at RIKEN in Japan. In October 2015, the SπRIT TPC was commissioned with 200 AMeV 79Se beams outside the SAMURAI dipole magnet. The experimental setup consists of the SπRIT TPC, a Multiplicity Trigger Array, a KATANA array, and a Active Veto array. The TPC is fully equipped with a newly-developed read-out electronics system, GET electronics. The trigger logic to select events of the TPC based on the ancillary detectors was tested. The analysis software, SpiRITROOT, was developed to analyze the SπRIT TPC data to determine the best trigger logic for upcoming experiments.

The sequential two-proton decay of the second excited state in $^{17}\mathrm{Ne}$, produced by inelastic excitation at intermediate energy, is studied. This state is found to be highly spin aligned, providing another example of a recently discovered alignment mechanism. The fortuitous condition that the second decay step is slightly more energetic than the first, permits the lifetime of the one-proton daughter, the ground state of $^{16}\mathrm{F}$, to be determined from the magnitude of the final-state interactions between the protons. This new method gave a result [$\mathrm{\ensuremath{\Gamma}}=20.6(57)$ keV] consistent with that obtained by directly measuring the width of the state [$\mathrm{\ensuremath{\Gamma}}=21.3(51)$ keV]. This width allows one to determine the continuum coupling constant in this mass region. Real-energy continuum-shell-model studies yield a satisfactory description of both spectra and widths of low-energy resonances in $^{16}\mathrm{F}$ and suggest an unusual large ratio of proton-proton to proton-neutron continuum couplings in the vicinity of the proton drip line.

A Time-Projection Chamber (TPC) called the SAMURAI Pion-Reconstruction and Ion-Tracker (S$\pi$RIT) has recently been constructed at Michigan State University as part of an international effort to constrain the symmetry-energy term in the nuclear Equation of State (EoS). The S$\pi$RIT TPC will be used in conjunction with the SAMURAI spectrometer at the Radioactive Isotope Beam Factory (RIBF) at RIKEN to measure yield ratios for pions and other light isospin multiplets produced in central collisions of neutron-rich heavy ions, such as $^{132}$Sn + $^{124}$Sn. The S$\pi$RIT TPC can function both as a TPC detector and as an active target. It has a vertical drift length of 50 cm, parallel to the magnetic field. Gas multiplication is achieved through the use of a multi-wire anode. Image charges are produced in the 12096 pads, and are read out with the recently developed Generic Electronics for TPCs., Comment: 7 pages, 3 figures, 2 tables. Submitted to NIM A Proceedings

Pion energy spectra are presented for central collisions of neutron-rich $^{132}\mathrm{Sn}+^{124}\mathrm{Sn}$ and neutron-deficient $^{108}\mathrm{Sn}+^{112}\mathrm{Sn}$ systems using simulations with the Boltzmann-Uehling-Uhlenbeck transport model. These calculations, which incorporate isospin-dependent mean-field potentials for relevant baryons and mesons, display a sensitivity to the pion spectra that could allow significant constraints on the density dependence of the symmetry energy and its mean-field potential at suprasaturation densities. The predicted sensitivity increases with the isospin asymmetry of the total system and decreases with incident energy.

A simple but novel driver system has been developed to operate the wire gating grid of a Time Projection Chamber (TPC). This system connects the wires of the gating grid to its driver via low impedance transmission lines. When the gating grid is open, all wires have the same voltage allowing drift electrons, produced by the ionization of the detector gas molecules, to pass through to the anode wires. When the grid is closed, the wires have alternating higher and lower voltages causing the drift electrons to terminate at the more positive wires. Rapid opening of the gating grid with low pickup noise is achieved by quickly shorting the positive and negative wires to attain the average bias potential with N-type and P-type MOSFET switches. The circuit analysis and simulation software SPICE shows that the driver restores the gating grid voltage to 90% of the opening voltage in less than 0.20 $\mu$s. When tested in the experimental environment of a time projection chamber larger termination resistors were chosen so that the driver opens the gating grid in 0.35 $\mu$s. In each case, opening time is basically characterized by the RC constant given by the resistance of the switches and terminating resistors and the capacitance of the gating grid and its transmission line. By adding a second pair of N-type and P-type MOSFET switches, the gating grid is closed by restoring 99% of the original charges to the wires within 3 $\mu$s., Comment: 18 pages, 10 figures, 2 tables. Submitted to Nuclear Instruments & Methods in Physics Resarch A

When Time Projection Chambers (TPCs) are used in low to intermediate heavy ion collisions, the mass and momentum range of the emitted particles cover a wide range in energy losses. Many TPC readout electronics currently only have a single gain output with a fixed dynamic range. In a recent set of experiments using the SAMURAI Pion-Reconstruction and Ion-Tracker (S π RIT) TPC, it was important to simultaneously measure relativistic pions and heavy ion tracks from the same collisions. As the ionization from a track’s energy loss is collected and multiplied by the anode wires, a distribution of image charges is induced on the TPC read-out pads. If the avalanche on a wire is large enough, the charge collected by pads directly underneath will saturate the readout electronics; pads farther away in the distribution will not be saturated. Using these unsaturated pads and the known pad distribution function, we can estimate the charge on saturated pads, increasing the dynamic range by a factor of 5.

This study examines the full process of how paintings originate, and how they proceed from creation to the final stage of their sale. In it, we shall see that there are a few parties, which are involved from beginning to end. We observe in this that the artist is not the supreme being, but a cog in the wheels of the creation and distribution of art.

The difference in neutron total cross section between 40 Ca and 48 Ca is sensitive to the n/p asymmetry dependence of the surface imaginary potential in a dispersive optical model analysis, from which spectroscopic information can be extracted. The measured cross sections imply that the strength of neutron correlations changes little as neutron number increases in neutron-rich isotopes. In contrast, for the light-nucleus-induced knockout of the valence neutron in 36 Ca, the small experimental knockout cross section (as compared to an eikonal reaction theory) implies a very small spectroscopic factor (and a strong trend in correlations with asymmetry). If this type of knockout analysis is correct, it implies that standard shellmodel calculations miss spectroscopic strength as the Fermi energy nears the continuum. If this is not the case, it may be that there is a problem with the application of the eikonal theory to very deeply bound nucleons at these intermediate energies. The term correlations refers to interactions between nucleons that go beyond the mean field considered in an independent-particle-model (IPM) approach. The effect of these correlations is that in real nuclei, the spectroscopic strength of a singleparticle orbital is fragmented over energy. The spectroscopic factor (SF) quantifies the strength found at a discrete energy, and the sum of spectroscopic strength over all energies below the Fermi energy EF gives the occupation of the orbital. Correlations reduce the occupation of a single-particle state relative to its IPM value, since some of the fragmented spectroscopic strength is shifted above EF . The nuclear shell model (SM) can account for some of these correlations by including mixing between single-particle states (within a finite basis set). But due to the finite model space, the presence of the hard-core of the N-N interaction, and the tensor interaction (which further reduce the occupancies by shifting strength to high-momentum states), standard SM calculations still overestimate the occupancies of bound states. The reduction in occupancy due to correlations is not a direct experimental observable, but it will affect particle removal cross sections. By comparing experimental cross sections to calculated single-particle cross sections, one can learn about the strength of correlations. Electron-induced proton knockout (e,e’p) experiments have indicated a roughly constant 30% reduction in spectroscopic strength for valence protons in beta-stable nuclei. For unstable nuclei, light-nucleus-induced knockout experiments in inverse kinematics suggest that the affect of correlations is weaker for weakly-bound nucleons and much stronger for very deeply-bound nucleons (e.g.

A digital-signal-processing method was developed and used to measure the total neutron cross-sections of 48 Ca from 15 to 300 MeV. This technique allows for cross-sections to be obtained with high statistical accuracy even for samples that are an order of magnitude smaller than those used with conventional (non-digital) techniques. The isotopic and energy dependence of rare-isotope total neutron cross-sections are of considerable value for extracting the n/p asymmetry dependence of optical-model potentials.

This paper presents the design and test results of an eight-channel prototype integrated circuit chip intended to greatly simplify the pulse-processing electronics needed for large arrays of scintillation detectors. Because the chip design employs (user-controlled) multi-region charge integration, particle identification is incorporated into the basic design. Each channel on the chip also contains a time-to-voltage converter which provides relative time information. The pulse-height integrals and the relative time are all stored on capacitors and are either reset, after a user controlled time, or sequentially read out if acquisition of the event is desired. Each of the three pulse-height sub-channels consists of a gated integrator with eight programmable charging rates and an externally programmable gate generator that defines the start (with four time ranges) and width (with four time ranges) of the gate relative to an external discriminator signal. The chip supports three triggering modes, two time ranges, two power modes, and produces four sparsified analog pulse trains (three for the integrators and another for the time) with synchronized addresses for off-chip digitization with a pipelined ADC. The eight-channel prototype chip occupies an area of 2.8 mm×5.7 mm, dissipates 60 mW (low-power mode), and was fabricated in the AMI 0.5-μm process (C5N).

The complete three-body correlation pictures are experimentally reconstructed for the two-proton decays of the Be-6 and (45)e ground states. We are able to see qualitative similarities and differences between these decays. They demonstrate very good agreement with the predictions of a theoretical three-body cluster model. Validity of the theoretical methods for treatment of the three-body Coulombic decays of this class is thus established by the broad range of lifetimes and nuclear masses spanned by these cases. Implementations for decay dynamics and nuclear structure of 2p emitters are discussed. (C) 2009 Elsevier B.V. All rights reserved.

The sequential breakup of $E/A=65.5\text{-MeV}\phantom{\rule{4pt}{0ex}}^{7}\mathrm{Be}$ and $E/A=36.6\text{-MeV}\phantom{\rule{4pt}{0ex}}^{6}\mathrm{Li}$ projectiles excited through inelastic interactions with $^{9}\mathrm{Be}$ target nuclei has been studied. For events where the target nucleus remained in its ground state, significant alignment of the excited projectile's spin axis parallel or antiparallel to the beam direction was observed. This unusual spin alignment was found to be largely independent of the projectile's scattering angle and it was deduced that the target nucleus has a significant probability of changing its spin orientation during the interaction. It is proposed that the unusual spin alignment is a consequence of the molecular structure of the $^{9}\mathrm{Be}$ nucleus.

The interaction of an E/A = 57.6-MeV Ne-17 beam with a Be target is used to populate levels in Ne-16 following neutron knockout reactions. The decay of 16Ne states into the three-body O-14 + p + p continuum is observed in the High Resolution Array (HiRA). For the first time for a 2p emitter, correlations between the momenta of the three decay products are measured with sufficient resolution and statistics to allow for an unambiguous demonstration of their dependence on the long-range nature of the Coulomb interaction. Contrary to previous measurements, our measured limit Gamma < 80 keV for the intrinsic decay width of the ground state is not in contradiction to the small values (of the order of keV) predicted theoretically.

The interaction of an E/A=70 - MeV 7Be beam with a Be target was used to populate levels in 6Be following neutron knockout reactions. The three-body decay of the ground and first excited states into the alpha+p+p exit channel were detected in the High Resolution Array. Precise three-body correlations extracted from the experimental data allowed us to obtain insight into the mechanism of the three-body democratic decay. The correlation data are in a good agreement with a three-cluster-model calculation and thus validate this theoretical approach over a broad energy range., 5 pages, 7 figures; Corrected typos

The cross sections for single-nucleon knockout from Ca-36 on a Be-9 target at 70 MeV/nucleon were measured to be sigma(exp)(-p) = 51.1 +/- 2.6 mb for proton knockout and sigma(exp)(-n) = 5.03 +/- 0.46 mb for neutron knockout. The spectroscopic factors and orbital angular momenta of the neutrons and protons removed from Ca-36, leading to bound A = 35 residues, were deduced by comparison of the experimental cross sections and longitudinal- momentum distributions to those calculated in an eikonal reaction theory, and found to be S(p, 1d(3/2)) = 0.79 +/- 0.04 and S(n, 2s(1/2)) = 0.23 +/- 0.02 (relative to independent-particle-model values and only including experimental contributions to the uncertainties). As found in previous knockout studies, the spectroscopic factor deduced for the deeply bound neutron was significantly reduced relative to shell-model calculations, a result at variance with dispersive optical model (DOM) extrapolations, which suggest a spectroscopic factor closer to 60% of the independent-particle-model value.

High-resolution triple-$\ensuremath{\alpha}$ coincidence data were used to reconstruct the decay of the excited states in ${}^{12}$C at 7.65 MeV (${J}^{\ensuremath{\pi}}={0}^{+}$) and 9.64 MeV $({J}^{\ensuremath{\pi}}={3}^{\ensuremath{-}})$. These data are consistent with the $\ensuremath{\alpha}$-particle decay of both levels proceeding exclusively through ${}^{8}$Be${}_{g.s.}$. In the first of these cases, the Hoyle state, an upper limit of 0.45% (at the 99.75% confidence level) is set for a component producing three nearly equal-energy $\ensuremath{\alpha}$ particles.

Deviations from the isobaric multiplet mass equation are presented and discussed for the $A=7$, $T=3/2$ quartet and the $A=8$, $T=2$ quintet.

The interactions of an E/A=70-MeV {sup 9}C beam with a Be target was used to populate levels in Be, B, and C isotopes, which undergo decay into many-particle exit channels. The decay products were detected in the HiRA array and the level energies were identified from their invariant mass. Correlations between the decay products were examined to deduce the nature of the decays, specifically to what extent all the fragments were created in one prompt step or whether the disintegration proceeded in a sequential fashion through long-lived intermediate states. In the latter case, information on the spin of the level was also obtained. Of particular interest is the five-body decay of the {sup 8}C ground state, which was found to disintegrate in two steps of two-proton decay passing through the {sup 6}Be{sub g.s.} intermediate state. The isobaric analog of {sup 8}C{sub g.s.} in {sup 8}B was also found to undergo two-proton decay to the isobaric analog of {sup 6}Be{sub g.s.} in {sup 6}Li. A 9.69-MeV state in {sup 10}C was found to undergo prompt four-body decay to the 2p + 2{alpha} exit channel. The two protons were found to have a strong enhancement in the diproton region and the relativemore » energies of all four p-{alpha} pairs were consistent with the {sup 5}Li{sub g.s.} resonance.« less

Neutron elastic-scattering angular distributions were measured at beam energies of 11.9 and 16.9 MeV on 40,48 Ca targets. These data plus other elastic-scattering measurements, total and reaction cross-sections measurements, (e, ep) data, and single-particle energies for magic and doubly magic nuclei have been analyzed in the dispersive optical-model (DOM), generating nucleon self-energies (optical-model potentials) that can be related, via the many-body Dyson equation, to spectroscopic factors and occupation probabilities. It is found that, for stable nuclei with N Z, the imaginary surface potential for protons exhibits a strong dependence on the neutron-proton asymmetry. This result leads to a more modest dependence of the spectroscopic factors on asymmetry. The measured data and the DOM analysis of all considered nuclei clearly demonstrate that the neutron imaginary surface potential displays very little dependence on the neutron-proton asymmetry for nuclei near stability (N Z).

$^{8}\mathrm{C}$ is found to decay to four protons and an $\ensuremath{\alpha}$ particle in two $2p$ emission steps. The correlations between the protons in the first step ($^{8}\mathrm{C}$ to $^{6}\mathrm{Be}$) exhibit a significant enhancement in the region of the decay phase space where the two protons have small relative energy, a region sometimes called the diproton region. The decay of the isobaric analog of $^{8}\mathrm{C}$ in $^{8}\mathrm{B}$ is also found to decay by $2p$ emission. This is the first case of isospin-allowed $2p$ decay between isobaric analog states.

Three-body correlations for the ground-state decay of the lightest two-proton emitter Be-6 are studied both theoretically and experimentally. Theoretical studies are performed in a three-body hyperspherical-harmonics cluster model. In the experimental studies, the ground state of Be-6 was formed following the alpha decay of a C-10 beam inelastically excited through interactions with Be and C targets. Excellent agreement between theory and experiment is obtained demonstrating the existence of complicated correlation patterns that can elucidate the structure of Be-6 and, possibly, of the A = 6 isobars.

Resonance-decay spectroscopy is used to study particle-unbound excited states produced in interactions of $E/A=10.7 \mathrm{MeV}$ $^{10}\mathrm{C}$ on Be and C targets. After inelastic scattering, structures associated with excited states in $^{10}\mathrm{C}$ were observed at 5.22, 5.29, 6.55, 6.56, 6.57, and 8.4 MeV which decay into the $2p+2\ensuremath{\alpha}$ final state. This final state is created via a number of different decay paths, which include prompt and sequential two-proton decay to the ground state of $^{8}\mathrm{Be}$, $\ensuremath{\alpha}$ decay to $^{6}\mathrm{Be}{}_{\mathrm{g}.\mathrm{s}.}$, and proton decay to the 2.345-MeV state of $^{9}\mathrm{B}$. For the sequential two-proton decay states (5.22 and 6.55 MeV), angular correlations between the first two decay axes indicate that the spin of these states are nonzero. For the prompt two-proton decay of the 5.29-MeV state, the three-body correlations between the two protons and the core are intermediate between those measured for ground-state $^{6}\mathrm{Be}$ and $^{45}\mathrm{Fe}$ decays. The 6.55- and 6.57-MeV structures are most probably associated with the same level, which has a 14% two-proton decay branch with a strong ``diproton'' character and a 86% sequential two-proton decay branch. Correlations between the fragments following the three-body decay of the 2.345-MeV state of $^{9}\mathrm{B}$ can be approximately described by sequential $\ensuremath{\alpha}$ decay to the $^{5}\mathrm{Li}$ intermediate state. The 8.06- and 9.61-MeV $^{10}\mathrm{B}$ states that decay into the $d+^{6}\mathrm{Li}{}_{2.186}$ channel are confirmed. Evidence for cluster structure in $^{13}\mathrm{N}$ is obtained from a number of excited states that decay into the $p+3\ensuremath{\alpha}$ exit channel.

The decay of {sup 10}C excited states to the 2p+2{alpha} exit channel has been studied using inelastic excitation of a secondary {sup 10}C beam. The decay sequences leading to the 2p+2{alpha} final state are determined for the previously known levels and for a newly found level at E*=8.4 MeV. A state at E*=6.57 MeV is shown to undergo two-proton decay to {sup 8}Be{sub g.s.} with strong p-p correlations consistent with the {sup 1}S phase shift. Based on the lack of such correlations for other two-proton decays, this indicates that the correlations are associated with structure of the parent level.

Two-proton decay is discussed in a number of light isobaric multiplets. For the lightest two-proton emitter, 6Be, the momentum correlations between the three decay products were measured and found to be consistent with quantum-mechanical three-cluster-model calculations. Two-proton decay was also found for two members of the A=8 and A=11 quintets. Finally, a third member of the A=11 sextet, the double isobaric analog of the halo nucleus 11Li in 11B was observed by its two-proton decay.

The asymmetric unit of the title compound, [(CH(3))(2)NH(CH(2))(2)NH(CH(3))(2)][CoCl(4)], contains a tetra-chlorido-cobalt-ate(II) dianion and two halves of two centrosymmetric, crystallographically-independent, dications. One independent dication is disordered between two conformations in a 0.784 (13):0.216 (13) ratio. In the crystal, inter-molecular N-H⋯Cl hydrogen bonds link cations and anions into chains propagated in [01]. These hydrogen bonds contribute to the distorted tetra-hedral geometry at the Co(II) atom.