A search for the heaviest isotopes of fluorine, neon, and sodium was conducted by fragmentation of an intense ^{48}Ca beam at 345 MeV/nucleon with a 20-mm-thick beryllium target and identification ...of isotopes in the large-acceptance separator BigRIPS at the RIKEN Radioactive Isotope Beam Factory. No events were observed for ^{32,33}F, ^{35,36}Ne, and ^{38}Na and only one event for ^{39}Na after extensive running. Comparison with predicted yields excludes the existence of bound states of these unobserved isotopes with high confidence levels. The present work indicates that ^{31}F and ^{34}Ne are the heaviest bound isotopes of fluorine and neon, respectively. The neutron dripline has thus been experimentally confirmed up to neon for the first time since ^{24}O was confirmed to be the dripline nucleus nearly 20 years ago. These data provide new keys to understanding the nuclear stability at extremely neutron-rich conditions.
•In-flight particle identification of RI beams developed for BigRIPS separator.•Atomic number Z and mass-to-charge ratio A/Q are deduced by the TOF-Bρ-ΔE.•Precise determinations of Bρ and TOF with ...trajectory reconstruction and slew correction, respectively.•The achieved A/Q resolution is high enough to clearly identify the charge state.•Thorough removal of background events improves the reliability of identification.
We have developed a method for achieving excellent resolving power in in-flight particle identification of radioactive isotope (RI) beams at the BigRIPS fragment separator at the RIKEN Nishina Center RI Beam Factory (RIBF). In the BigRIPS separator, RI beams are identified by their atomic number Z and mass-to-charge ratio A/Q which are deduced from the measurements of time of flight (TOF), magnetic rigidity (Bρ) and energy loss (ΔE), and delivered as tagged RI beams to a variety of experiments including secondary reaction measurements. High A/Q resolution is an essential requirement for this scheme, because the charge state Q of RI beams has to be identified at RIBF energies such as 200–300MeV/nucleon. By precisely determining the Bρ and TOF values, we have achieved relative A/Q resolution as good as 0.034% (root-mean-square value). The achieved A/Q resolution is high enough to clearly identify the charge state Q in the Z versus A/Q particle identification plot, where fully-stripped and hydrogen-like peaks are very closely located. The precise Bρ determination is achieved by refined particle trajectory reconstruction, while a slew correction is performed to precisely determine the TOF value. Furthermore background events are thoroughly removed to improve reliability of the particle identification. In the present paper we present the details of the particle identification scheme in the BigRIPS separator. The isotope separation in the BigRIPS separator is also briefly introduced.
Unbound states in C17 were investigated via one-neutron removal from a C18 beam at an energy of 245 MeV/nucleon on a carbon target. The energy spectrum of C17, above the single-neutron decay ...threshold, was reconstructed using invariant mass spectroscopy from the measured momenta of the C16 fragment and neutron, and was found to exhibit resonances at Er=0.52(2), 0.77(2), 1.36(1), 1.91(1), 2.22(3) and 3.20(1) MeV. The resonance at Er=0.77(2) MeV Ex=1.51(3) MeV was provisionally assigned as the second 5/2+ state. The two resonances at Er=1.91(1) and 3.20(1) MeV Ex=2.65(2) and 3.94(2) MeV were identified, through comparison of the energies, cross sections and momentum distributions with shell-model and eikonal reaction calculations, as p-shell hole states with spin-parities 1/21− and 3/21−, respectively. A detailed comparison was made with the results obtained using a range of shell-model interactions. The YSOX shell-model Hamiltonian, the cross-shell part of which is based on the monopole-based universal interaction, was found to provide a very good description of the present results and those for the neighbouring odd-A carbon isotopes – in particular for the negative parity cross-shell states.
•Large-area Parallel Plate Avalanche Counter (PPAC) developed for position measurement.•A specially developed delay line is utilized to obtain the position information.•Excellent performance in ...sensitivity uniformity as well as position measurement.•Double-PPAC structure enables to obtain high detection efficiency.•A signal transmission system using optical fiber cables has been developed for PPACs.
We have developed a position-sensitive Parallel Plate Avalanche Counter (PPAC), which has been used as a focal plane detector in the BigRIPS fragment separator and the subsequent RI-beam delivery lines at the RIKEN Nishina Center RI Beam Factory. The PPAC detector plays an important role not only in the tuning of the separator and delivery lines but also in the particle identification of rare isotope (RI) beams. The PPAC detector has a sensitive area of 240mm×150mm, and the position information is obtained by a delay-line readout method. Being called double PPAC, it is composed of two full PPACs, each measuring the particle locus in two dimensions. High detection efficiency has been made possible by the twofold measurement using the double PPAC detector. The sensitivity uniformity is also found to be excellent. The root-mean-square position resolution is measured to be 0.25mm using an α source, while the position linearity is as good as ±0.1mm for the detector size of 240mm. Characteristics, operating principles, specifications, performance and issues of the PPAC detector are presented, including its signal transmission system using optical fiber cables.
BigRIPS is a powerful two-stage in-flight separator for the research with exotic nuclei studied in frontier experiments since more than a decade. The ion-optical system is very versatile due to the ...multi-stage structure of BigRIPS combined with the ZeroDegree spectrometer or the Superconducting Ring Cyclotron (SRC). Various optical modes can be flexibly realized according to the purpose of experiments. Two categories of developments are presented here. One is a new operating mode of BigRIPS aiming at higher ion-optical resolving power. BigRIPS itself has a two-stage structure. Spatial isotope separation is made at both the first and second stages. In the standard operating mode of BigRIPS, at the second stage the two spatial separations with energy degraders are subtractive in their resolving powers. Here, we present the additive mode. With the resulting increased spatial separation power, the isotopic background can be substantially reduced. Higher ion-optical resolving powers of the first and second BigRIPS degrader stages are also investigated with the goals to reduce further the background and to yield access to new isotopes of heavier elements. The other development is a dispersion-matched system with BigRIPS for high-resolution spectrometer experiments. The BigRIPS and ZeroDegree spectrometer are presently two independent, coupled achromatic systems. A new dispersion-matched mode of BigRIPS and ZeroDegree will enable novel experiments. For high-resolution spectroscopy experiments with high-intensity light projectiles, SRC and BigRIPS can be operated as a dispersion-matched system. The described different ion-optical developments are a base for a new category of experiments exploring exotic nuclei and mesic atoms. Characteristic future experiments with these new ion-optical developments are exemplified in this report.
The results of measurements of the production of neutron-rich nuclei by the fragmentation of a 76Ge beam are presented. The cross sections were measured for a large range of nuclei including 15 new ...isotopes that are the most neutron-rich nuclides of the elements chlorine to manganese (50Cl, 53Ar, ;{55,56}K, ;{57,58}Ca, ;{59,60,61}Sc, ;{62,63}Ti, ;{65,66}V, 68Cr, 70Mn). The enhanced cross sections of several new nuclei relative to a simple thermal evaporation framework, previously shown to describe similar production cross sections, indicates that nuclei in the region around 62Ti might be more stable than predicted by current mass models and could be an indication of a new island of inversion similar to that centered on 31Na.
•High power beam dump for BigRIPS separator has been developed to cope with 238U beam of 82kW. Sophisticated water cooling tubes such as swirl tubes and screw tubes were utilized. Detailed thermal ...model calculation was performed to evaluate the cooling power od the beam dump.
The high-power beam dump system for the BigRIPS fragment separator at the RIKEN Nishina Center RI Beam Factory was designed to handle ion beams up to 238U at 345MeV/nucleon and intensity of 1 particle μA. A water-cooled stationary beam dump system utilizing screw or swirl tubes as water cooling channels was developed based on detailed thermal simulation. Since March 2007, the system has been successfully operated with the various beams at the RI Beam Factory (RIBF), although the available beam power remains less than one-tenth of the goal. Temperatures of beam spots at the beam dump were measured and compared with the thermal simulations to evaluate the cooling capacity of the systems.
•We measured the production cross sections for a variety of radioactive isotopes.•They were produced from 124Xe, 48Ca, and 238U beams at 345MeV/nucleon using BigRIPS.•The measured production cross ...sections were compared with the EPAX formulae.•We discovered four new isotopes 85,86Ru and 81,82Mo produced by 124Xe+Be.•103Sb is particle unbound with an upper limit of 49ns for the half-life.
We have measured the production rates and production cross sections for a variety of radioactive isotopes which were produced from 124Xe, 48Ca, and 238U beams at an energy of 345MeV/nucleon using the BigRIPS separator at the RIKEN Nishina Center RI Beam Factory (RIBF). Proton-rich isotopes with atomic numbers Z=40–52 and neutron-rich isotopes with Z=5–16 were produced by projectile fragmentation of the 124Xe and 48Ca beam on Be targets, respectively. Neutron-rich isotopes with Z=20–59 were produced by in-flight fission of the 238U beam, in which both Be and Pb were used as production targets. The measured production rates and production cross sections were compared with those of the LISE++ calculations, and overall fairly good agreement has been obtained. Furthermore, in the measurements with the 124Xe beam, we have discovered four new isotopes on the proton-drip line, 85,86Ru and 81,82Mo, and obtained the clear evidence that 103Sb is particle unbound with an upper limit of 49ns for the half-life. The measurements of projectile-fragment momentum distributions have been also performed with the 124Xe beam, in which the low-momentum tails of the distributions have been measured for the first time at the energy of 345MeV/nucleon.
Pillow seal system at the BigRIPS separator Tanaka, K.; Inabe, N.; Yoshida, K. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
12/2013, Letnik:
317
Journal Article
Recenzirano
•Pillow seal system has been installed for a high-intensity RI-beam facility at RIKEN.•It is aimed at facilitating remote maintenance under high residual radiation.•Local radiation shields are ...integrated with one of the pillow seals.•Pillow seals have been aligned to the beam axis within 1mm accuracy.•A leakage rate of 10–9Pam3/s has been achieved with our pillow seal system.
We have designed and installed a pillow seal system for the BigRIPS fragment separator at the RIKEN Radioactive Isotope Beam Factory (RIBF) to facilitate remote maintenance in a radioactive environment. The pillow seal system is a device to connect a vacuum chamber and a beam tube. It allows quick attachment and detachment of vacuum connections in the BigRIPS separator and consists of a double diaphragm with a differential pumping system. The leakage rate achieved with this system is as low as 10–9Pam3/s. We have also designed and installed a local radiation-shielding system, integrated with the pillow seal system, to protect the superconducting magnets and to reduce the heat load on the cryogenic system. We present an overview of the pillow seal and the local shielding systems.
The 82Ge beam has been produced by the in-flight fission reaction of the 238U primary beam with 345MeV/u at the RIKEN RI beam factory, and slowed down to about 15MeV/u using the energy degraders. The ...momentum-compression mode was applied to the second stage of the BigRIPS separator to reduce the momentum spread. The energy was successfully reduced down to 13±2.5MeV/u as expected. The focus was not optimized at the end of the second stage, therefore the beam size was larger than the expectation. The transmission of the second stage was half of the simulated value mainly due to out of focus. The two-stage separation worked very well for the slowed-down beam with the momentum-compression mode.
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