RI Beam Research Articles

Development of long-life carbon stripper foils for uranium ion beams

Carbon foils (C-foils) are extensively used as charge strippers for heavy-ion beams at the RIKEN RI beam factory. Multi-layer polymer coated C-foils (PCC-foils) of 300 μg/cm 2 carbon thickness were irradiated by a 11 MeV/nucleon 238U 35+ beam and their lifetimes were measured. Using an atomic force microscope (AFM) and an electron probe microanalyzer (EPMA), it was observed that the surface property and cross-sectional image of the PCC-foils had changed after the irradiation. A rotating-cylinder stripper device, which was developed to further increase the lifetime of C-foils, was also tested.

PRESENT STATUS OF RARE-RI RING PROJECT IN RIKEN RIBF

We are going to construct a precise mass-measurement apparatus; "Rare-RI Ring" at RIKEN RI Beam Factory and measure masses of exotic neutron-rich nuclei far from the stability line with the assistance of high intensity primary beam from the cyclotrons at RIBF. The present status of our project and the progress of some parts of Rare-RI Ring will be presented.

Low-lying non-normal parity states in 8B measured by proton elastic scattering on 7Be

A new measurement of proton resonance scattering on 7Be was performed up to the center-of-mass energy of 6.7 MeV using the low-energy RI beam facility CRIB (CNS Radioactive Ion Beam separator) at the Center for Nuclear Study of the University of Tokyo. The excitation function of Be7+p elastic scattering above 3.5 MeV was measured successfully for the first time, providing important information about the resonance structure of the 8B nucleus. The resonances are related to the reaction rate of 7Be(p,γ)8B, which is the key reaction in solar 8B neutrino production. Evidence for the presence of two negative parity states is presented. One of them is a 2− state observed as a broad s-wave resonance, the existence of which had been questionable. Its possible effects on the determination of the astrophysical S-factor of 7Be(p,γ)8B at solar energy are discussed. The other state had not been observed in previous measurements, and its spin and parity were determined as 1−.

Experimental Approach to Explosive Nucloeosynthesis with RI Beams

Experimental e orts to investigate stellar reactions under high-temperature and high density conditions have been made as a major program using the RI beams from the Center for Nuclear Study (CNS) low-energy inight RI beam separator (CRIB) at University of Tokyo in order to understand the evolution of the universe, as well as various stellar phenomena. Speci cally, two subjects of hydrogen burning are discussed here. One is a reaction study of the pp-chain and the second is of the explosive hydrogen burning, the rp-process. Some s-wave resonances have been identi ed by the thick target method in the crucial reaction processes in the hydrogen burning. The resonant scattering with the thick target method also succeeded in identifying inelastic resonant scattering, giving proton widths for the rst excited state of the target nucleus. This provided very e ciently the reaction rate estimate for the process under high-temperature equilibrium conditions. Possibilities of the CRIB facility in near future are also brie y discussed.

Identification of New Isotopes 125Pd and 126Pd Produced by In-Flight Fission of 345 MeV/nucleon 238U: First Results from the RIKEN RI Beam Factory

A search for new isotopes using in-flight fission of a 345 MeV/nucleon 238 U beam has been carried out in the commissioning experiment of the next-generation in-flight radioactive isotope beam separator BigRIPS at the RI Beam Factory at the RIKEN Nishina Center. Two neutron-rich palladium isotopes 125 Pd and 126 Pd were observed for the first time, which demonstrates the great potential of the RIKEN RI beam factory.

RI beam facility project at RIKEN and physics programs

In the Radioactive-Isotope Beam Factory (RIBF) project in RIKEN, intense primary beams can be provided at the energies E = 350−400MeV over the whole range of atomic number in the cascade-cyclotron acceleration scheme, for which three cyclotrons, fRC, IRC, and SRC, have been newly constructed. The project proceeds through two phases. In the phase-I program, the superconducting in-flight radioactive-isotope beam separator BigRIPS and the following ZeroDegree spectrometer have been installed as well as the three cyclotrons. In the commissioning, after the successful extraction of a 238U beam from SRC at E = 345 A MeV in the cascade-acceleration scheme, radioactive-isotope beams were produced and isotope-separated with BigRIPS as designed. The RIBF project is fully capitalized in the phase-II program, in which the construction of several experimental key devices has been proposed. The upgrade of the former fragment separator RIPS is also included there. It allow for a scheme to use intense primary beams at the intermediate energy E = 115 A MeV with RIPS. Remarkably, the produced radioactive-isotope beams at this energy can be spin-polarized taking the advantage of the fragmentation-induced spin orientation phenomena.

Development of a time-of-flight detector for the Rare-RI Ring project at RIKEN

We have tested the timing properties of several thin plastic scintillators (10–500μm) designed for the Rare-RI Ring project at the RI beam factory. The experiments were performed at the heavy-ion synchrotron facility, HIMAC (Heavy Ion Medical Accelerator in Chiba), using a Xe beam with an energy of 200MeV/nucleon. The scintillation light was read out by fast-timing photomultipliers through standard fishtail-shaped light guides. The resultant timing resolutions reached a few tens of picoseconds, which satisfied our requirement for the project. We also measured charge-state distributions for Xe42+ and Fe20+ ions penetrating carbon foils of 10–500μg/cm2 thickness. The results were compared with a theoretical model calculation for charge-state evolution.

Rare-RI ring project at RIKEN RI beam factory

A new apparatus named “Rare-RI Ring”, for precisely measuring the masses of short-lived rare nuclei including the r-process region is proposed. The Rare-RI Ring is one of the major experimental installations at the RIKEN RI beam factory. It consists of three main parts: a long injection beam line, a fast kicker system and a cyclotron-like storage ring. The combination of a long injection beam line and a fast kicker system enables us to inject short-lived rare nuclei into the ring one by one. The revolution time of each nucleus in the ring is measured with an accuracy of better than 10-6. Overall, the masses of short-lived rare nuclei including the r-process region can be determined with an order of 10-6 precision.

An Air-Core Type Superconducting Quadrupole Triplet for the BigRIPS Separator at RIKEN

The BigRIPS fragment separator in the RIKEN RI beam factory has an air-core type superconducting quadrupole triplet as the first focusing element. The quadrupole triplet consists of three air-core superconducting coils having effective lengths of 500 mm, 800 mm, and 500 mm, and the maximum field gradients of 24 T/m, 20 T/m, and 20 T/m. All three quadrupoles are assembled into a single cryostat and cooled by liquid-helium bath cooling using a cryogenic plant. The coils have a flat racetrack shape and their warm bore radii are 90 mm, 120 mm, and 120 mm. Its cryostat characterized by gas-cooled current leads with multiple electrodes is also discussed.

Commissioning of the Superconducting Ring Cyclotron for the RIKEN RI Beam Factory

Since 1997, RIKEN Nishina Center has been constructing the Radioactive Isotope Beam Factory (RIBF) and succeeded in beam commissioning of its accelerator complex at the end of 2006. The world's first superconducting ring cyclotron (SRC) is the final booster in the RIBF accelerator complex which is able to accelerate all-element heavy ions to a speed of about 70% of the velocity of light. Assembling of the superconducting sector magnets was completed in August 2005. The superconducting coils were successfully cooled down and excited for tests on many operational aspects: magnetic force, coil protection and quality of magnetic field, showing that they work as designed. After a series of tests the other components were installed and tested under stray fields from the sector magnets. Local magnetic shields were put to the components which could not work under the stray fields. After setups of beam vacuum and radio frequency, beam commissioning started. The first beam was extracted at the end of 2006 and the first uranium beam was extracted in March 2007.

Magnets for the Beam Transport Line in the RIKEN RI Beam Factory

In the RI beam factory project, heavy ion beams are transported from the K 2500 MeV superconducting ring cyclotron (SRC) to the superconducting fragment separator, called BigRIPS. Magnets for the beam transport line from the SRC to the BigRIPS are reported. All the magnets are resistive type and the beam line consists of two kinds of dipoles and three kinds of quadrupoles. One of the dipole, having the maximum field strength of 2.0 T, a gap height of 60 mm, and a core length of 3.51 m is discussed in detail.

Development of a cryogenic gas target for intense RI beam production at CRIB

Nuclear reactions of astrophysical interest, especially those under high-temperature and high-density conditions, require high-intensity low-energy radioactive ion beams, because the cross-sections are very small for the direct method study. Production of high-intensity radioactive ion beams is, therefore, one of the key developments for RI beam facilities. We report the development of a new cryogenic RI beam production gas target, along with its characteristics and performance. Some of its advantages are the increased stability against high-current primary beams and the increased thickness due to the cooling by liquid nitrogen. The target is being tested with heavy-ion beams. Measures by energy loss of the beam indicate that a thickness of about 2.4 mg/cm 2 of H 2 gas has been attained and a secondary beam of 7Be 4+ at 4.0 MeV/ u of more than 2×10 8 pps was produced.

23aZH-9 RCNPにおける不安定核ビームによる核融合反応を用いた高スピン状態の研究(不安定核・核モーメント・高スピン・核融合,実験核物理領域)

23aZH-9 RCNPにおける不安定核ビームによる核融合反応を用いた高スピン状態の研究(不安定核・核モーメント・高スピン・核融合,実験核物理領域)

New superconducting electron cyclotron resonance ion source for RIKEN RI beam factory project

For RIKEN radio isotope beam project, we started to construct the new superconducting electron cyclotron resonance ion source (SC-ECRIS), which has an operational frequency of 28 GHz, in 2007. The main feature of this ion source is that we can produce large size of resonance zone with six sets of solenoid coils. Before starting, we intensively studied the effect of several key parameters of ECRIS (magnetic field configuration, microwave power density, negatively biased disk) on the plasma. In this article, we describe the effect of key parameters on the plasma and detailed structure of the new SC-ECRIS.

II. Radiation Safety and Management at RIKEN RI Beam Factory(RIBF)

II. Radiation Safety and Management at RIKEN RI Beam Factory(RIBF)

Radioactive Isotope Beam Factory at RIKEN (RIBF)1

The RIKEN RI Beam Factory (RIBF) has started its operation after ten years of construction [1]. It is designed to provide beams of various kinds of unstable nuclei with the world's highest intensities. The institute RIKEN was founded in 1917, and covers a variety of research fields such as physics, chemistry, medical science, biology, and engineering. RIKEN has a long history of constructing accelerators. The first cyclotron in Japan was built in 1937 by Yoshio Nishina in the former RIKEN campus, and the RIKEN's 4th cyclotron completed in 1966 was the first heavy-ion cyclotron in Japan, which accelerated light nuclei to the energy around 7 MeV/nucleon.

Physics opportunities with the RI Beam Factory at RIKEN

Physics opportunities with the RI Beam Factory at RIKEN

Polarized proton target for RI Beam experiments

We have constructed a polarized proton solid target system for radioactive nuclear beam experiments at the Center for Nuclear Study, the University of Tokyo. The proton polarization is based on an electron population difference in a photo-excited triplet state of pentacene molecule. The target system was completed in 2003 and applied to a RI beam experiment in 2003 and 2005 by using the projectile fragment separator, RIPS at RIKEN. The maximum polarization reached 20% under the condition of T=100 K and B=0.09 T. Overview of the polarized target and its application in physics experiments at RIPS and RIBF of RIKEN are presented.

The Superconducting Ring Cyclotron in RIKEN

RIKEN Nishina Center for accelerator-based science in RIKEN is constructing the radioactive isotope beam factory (RIBF), which is capable of providing the world's most intense RI beams over the whole range of atomic masses. The world's first superconducting ring cyclotron (SRC) is the final booster in the RIBF accelerator complex which is able to accelerate all-element heavy ions to a speed of about 70% of the velocity of light. Assembling of six superconducting sector magnets in the SRC vault was completed in August 2005. This paper describes results of their cool-down and excitation tests, which were performed to check the magnet system from the various points of views: magnetic force, coil protection, magnetic field and operation of their cryogenic cooling system.

The radioactive ion beam project at VECC, Kolkata – Its present status and future plans

A project to build an ISOL type radioactive ion beam facility has been undertaken at Variable Energy Cyclotron Centre, Kolkata. The status of RIB facility being built at VECC is presented. Stable ion beams of 30keV/u have already been accelerated with very high efficiency through the RFQ. The completion of the accelerator system to 400keV/u is expected in 2007. A second phase for production of neutron-rich RIB through photo-fission route and further acceleration of RI beams using Linacs up to about 6–7MeV/u is under consideration.