Large-acceptance Multipurpose Spectrometer Research Articles

Status of LAMPS at RAON

A new radioactive ion-beam accelerator facility, RAON, is under construction in Korea. Among the seven experimental systems being built, the Large Acceptance Multi-Purpose Spectrometer (LAMPS) in the high-energy experimental hall is the versatile detector system for nuclear physics. Its primary goal is to study the nuclear equation of state (EoS) and the symmetry energy of the compressed nuclear matter, which should be essential to understand the effective nuclear interactions and structure of the astrophysical objects like neutron stars. The basic LAMPS system consists of the beam diagnostic elements such as the starting counters and beam drift chambers, the time-projection chamber, the barrel and forward time-of-flight systems, the forward neutron detector array, and the superconducting solenoid magnet. In this paper the overview of the present status of each detector component for LAMPS will be given with some prospects.

Current status of experimental facilities at RAON

The Rare Isotope Science Project (RISP) was established in December 2011 for the construction of the accelerator complex RAON (Rare isotope Accelerator complex for ON-line experiments) which will be used for the rare isotope science in Korea. The rare isotope accelerator at RAON will provide both stable and rare isotope (RI) beams with an energy range from a few keV to a few hundreds of MeV per nucleon for research in the fields of basic and applied sciences.At the moment, there are 7 experimental facilities considered at RAON: KOrea Broad acceptance Recoil spectrometer and Apparatus (KOBRA) and Large Acceptance Multi-Purpose Spectrometer (LAMPS) for nuclear physics, High Precision Mass Measurement System (HPMMS) with Multi-Reflection Time-of-Flight (MR-ToF) and Collinear Laser Spectroscopy (CLS) for nuclear physics using atomic physics techniques, Nuclear Data Production System (NDPS) for nuclear reaction data, Muon Spin Rotation/Relaxation/Resonance (μSR) for material science, and Beam Irradiation System (BIS) for bio-medical science.In this paper, the current status including detail design and research goal of 7 experimental facilities at RAON will be discussed.

Performance of prototype neutron detectors for Large Acceptance Multi-Purpose Spectrometer at RAON

Abstract The performance of the prototype modules of neutron detectors for the Large Acceptance Multi-Purpose Spectrometer (LAMPS) was investigated, using cosmic muons and neutron beams at 65 and 392 MeV, provided by the Research Center for Nuclear Physics (RCNP). The timing and position resolutions were estimated using cosmic muons as 309 ps and 4.8 cm, respectively. The energy resolution depended on the incident energy of neutrons: 1.3% at 65 MeV and 3.1% at 392 MeV. The neutron-detection efficiency also showed weak energy dependence as it decreased from (9.0 ± 1.6)% at 65 MeV to (6.3 ± 1.0)% at 392 MeV.

Development of large acceptance multi-purpose spectrometer in Korea for symmetry energy

The Rare Isotope Accelerator complex for ON-line experiments (RAON) is a new radioactive ion beam accelerator facility under construction in Korea. The large acceptance multi-purpose spectrometer (LAMPS) is one of the experimental devices for nuclear physics at RAON. It focuses on the nuclear symmetry energy at supra-saturation densities. The LAMPS Collaboration has developed and constructed various detector elements, including a time projection chamber (TPC) and a forward neutron detector array. From the positron beam test, the drift velocity of the secondary electrons in the TPC is $$5.3 \pm 0.2$$ cm/ $$\upmu $$ s with P10 gas mixture, and the position resolution for pads with dimensions of 4 $$\times $$ 15 mm $$^{2}$$ is in the range of $$\sim $$ 0.6–0.8 mm, depending on the beam position. From the neutron beam test, the energy resolution of the prototype neutron detector module is determined to be 3.4%, and the position resolution is estimated to be better than 5.28 cm. At present, the construction of the LAMPS neutron detector system is in progress.

Design of a Solenoid Magnet for the Large Acceptance Multi-Purpose Spectrometer for the Rate Isotope Science

The Large Acceptance Multi-Purpose Spectrometer (LAMPS) is one of the experimental facilities for the Rare Isotope Science Project (RISP). It will be located downstream of the Ion-flight fragment (IF) separator. The LAMPS consists of a solenoid spectrometer and a neutron detector. A time projection chamber (TPC) in the solenoid spectrometer reconstructs tracks of charged particles from nucleus-nucleus collisions under a uniform magnetic field. The size of the LAMPS solenoid magnet is about 3 × 3 × 3.5 m3, and magnetic field is ~ 0.5 T. A field uniformity (ΔB/B) of ±1% is required in the TPC region for more accurate detection of particles.

Prospects of nuclear physics research using rare isotope beams at RAON in Korea

Korea plans to build a new radioactive ion-beam accelerator RAON together with various experimental facilities. In particular, KOBRA(the Korea Broad Acceptance Recoil Spectrometer & Apparatus) and LAMPS(the Large-Acceptance Multi-Purpose Spectrometer) will be constructed for the nuclear physics experiments.The primary goal of KOBRA is to study the structure of exotic nuclei near drip lines and various astrophysical processes at low energies. On the other hand, LAMPS will investigate the density dependence of the nuclear symmetry energy in wide beam energy range up to 2 times normal nuclear densities. This paper provides an overview of RAON and the experimental setup for the nuclear physics program.

Simulation of the time-projection chamber with triple GEMs for the LAMPS at RAON

The time-projection chamber (TPC) with triple gas-electron multipliers (GEMs) is designed for the large-acceptance multipurpose spectrometer (LAMPS) at the new radioactive ion-beam facility RAON, a pure Korean term for the accelerator complex, in Korea. The simulation environment has been set up to test the performance of the designed chamber, and the software package for analysis has been developed. Particle identification has been demonstrated to be possible up to 2 GeV/c in momentum for particles with the charge number 1 and 2 by using the simulated heavy-ion events. The transverse-momentum resolutions are expected to be about 2% for protons and about 1.3% for pions in the relatively high-momentum region. The total reconstruction efficiencies are estimated to be about 90 and 80% for charged pions and protons, respectively.

Back-thinning process research and characteristics measurement of thin sensor

It is important to develop a thin silicon detector using a large silicon wafer to reduce multiple Coulomb scattering and the material budget. A Si-CsI detector in a large acceptance multi-purpose spectrometer (LAMPS) is considered to identify isotopes. The thickness of the first of three silicon sensors in front of the CsI(Tl) crystal is 100 μm. We aim to establish a manufacturing process for thinning using a 6-inch silicon wafer that provides the characteristics of a photodiode. In this paper, we present a back-thinning process of the photodiode, and comparisons of its electrical characteristics and signal-to-noise ratios before and after the thinning process.

Study of the design optimization of AC-coupled single-sided silicon strip sensors

The high-intensity rare-isotope accelerator, RAON, will be constructed for nuclear physics research in Korea. AC-coupled single-sided silicon strip detectors (SSSDs) are being investigated for use in the Si-CsI detector of a large acceptance multi-purpose spectrometer to measure the energies of various isotopes. To determine the optimal design, four SSSD design parameters were examined in this study, namely the ratio of p+ implant width to strip pitch (I/P), the width of the metal layer, the presence of an n+-edge field shaper (FS), and the distance between the guard-ring and sensor edge (DGS). The designed detectors were fabricated on high resistivity n-type silicon wafers of 500 μm thickness. The SSSDs had the strip pitch of 730 μm and 32 readout strips in each, and the size of the sensors was 40.0 × 25.5 mm2. In terms of the leakage current and production yield, the noise improved by up to 30%when the I/P ratio was 0.4, the metal layer was wider than the p+ implantation, and the DGS with n+-edge FS was twice the sensor thickness. The signal-to-noise ratio of the SSSD with the design parameters that provided the optimal leakage current and coupling capacitance was measured to be 29.1 using a 90Sr radioactive source and commercial electronics.

Performance of a real-size prototype neutron detector for the LAMPS at RAON

A neutron detector array is one of the essential detector components for measuring the nuclear symmetry energy in the large-acceptance multipurpose spectrometer (LAMPS) to be built at the new radioactive ion-beam facility, RAON, in Korea. We have designed and built a real-size prototype neutron detector for the LAMPS and investigated its performance with radiation sources. The intrinsic time resolution of the prototype modules estimated by using 60Co is about 1 ns. The neutrons and the gammas from 252Cf are clearly separated in the time spectra. The kinetic energy spectrum of the fission neutrons from 252Cf has been reconstructed and compared to the empirical Watt function. The result demonstrates that the current prototypes can detect neutrons with kinetic energies larger than about 6 MeV.

Plan for nuclear symmetry energy experiments using the LAMPS system at the RIB facility RAON in Korea

A new rare isotope beam accelerator RAON and user facilities will be built in Korea. The Korea broad acceptance recoil spectrometer and apparatus (KOBRA) and the large-acceptance multipurpose spectrometer (LAMPS) will be ready from the beginning of the accelerator operation, and will be used to perform the nuclear physics experiments. We plan to use both spectrometers to investigate the density dependence of the nuclear symmetry energy in a wide range of beam energies. In particular, the high-energy setup of LAMPS, which is a combination of a solenoid and dipole spectrometers with neutron detector array, will be primarily used to study the symmetry energy of dense nuclear matter. This paper provides an overview of the RAON and the user facilities for the nuclear physics program with an emphasis on LAMPS.

Source test of the prototype neutron detector for the large-acceptance multipurpose spectrometer at RAON

A neutron detector array will be essential for the study of the nuclear symmetry energy in the large-acceptance multipurpose spectrometer (LAMPS) at the planned rare-isotope beam facility RAON in Korea. We have built the prototype neutron detector for LAMPS and examined its performance by using radiation sources. For data taking, we tested the voltage-threshold discriminator (VTD) and the constant-fraction discriminator (CFD) modules for the pulse process. The intrinsic time resolution of the prototype detector is estimated to be 723 ps for VTD and 488 ps for CFD. The fission neutrons and gammas emitted from 252Cf can be clearly separated in the time distribution. We reconstruct the energy spectrum of the spontaneous fission neutrons from 252Cf, which can be described well by using the empirical Watt spectrum.

Design of a Si-CsI detector for cluster measurements in the large-acceptance multipurpose spectrometer at RAON

We have designed a Si-CsI detector for measuring clusters from nuclear collisions in the forward region of the large-acceptance multipurpose spectrometer at RAON. The detector consists of two inclined annular rings, and covers the pseudorapidity from 1.6 to 2.1. Each ring comprises eight modules, and each module has three silicon layers and one CsI crystal bar. A realistic simulation demonstrates that the current design can identify isotopes at least up to Z = 9. The maximum measurable kinetic-energy range is distributed from 100 MeV to 1 GeV depending on the mass and Z. The Si-CsI detector will be useful for the study of the nuclear symmetry energy at RAON.