Y. Togano

DALI2: A NaI(Tl) detector array for measurements of

A NaI(Tl) detector array called DALI2 (Detector Array for Lo w Intensity radiation 2) has been constructed for in-beam γ-ray spectroscopy experiments with fast radioactive isotope (R I) beams. It consists typically of 186 NaI(Tl) scintillator s covering polar angles from∼15◦ to ∼160◦ with an average angular resolution of 6 ◦ in full width at half maximum. Its high granularity (good angular resolution) enables Doppler-shift correcti ons that result in, for example, 10% energy resolution and 20 % full-energy photopeak e fficiency for 1-MeVγ rays emitted from fast-moving nuclei (velocities of v/c ≃ 0.6). DALI2 has been employed successfully in numerous experiments using fast RI beams wi th velocities ofv/c = 0.3 − 0.6 provided by the RIKEN RI Beam Factory.

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A superconducting dipole magnet for a large-acceptance spectrometer named SAMURAI has been constructed and installed at the RIKEN RI Beam Factory. The important features of the SAMURAI superconducting dipole magnet are a large pole gap, a wide horizontal opening, and a large momentum bite. The magnet is an H-type dipole, having circular superconducting coils and cylindrical pole pieces with a diameter of 2 m and a pole gap of 880 mm. The coils are orderly wound by the wet winding method developed by Toshiba using a Nb/Ti superconducting wire. The upper and lower coils are installed in two separate cryostats and cooled by the liquid helium bath cooling method. Each cryostat has six cryocoolers: one for a coil vessel at 4 K, four for thermal shields, and one for high- TC superconducting power leads. The size of the iron yoke is 6.7 m wide, 3.5 m deep, 4.64 m tall, and the total weight of the magnet is about 650 tons. The maximum magnetic field is 3.08 T at 563 A (1.922 MA turns/coil), which gives a bending power (field integral) of 7.05 Tm. The maximum stored energy amounts to 27.4 MJ and the inductance varies from 396 H to 150 H as the magnetic field increases. The fringe fields are smaller than 5 mT at 0.5 m from the magnet. The construction of the SAMURAI magnet started in 2008 and was completed in June 2011. The commissioning of the SAMURAI spectrometer was successfully performed using RI beams in March 2012.

rays from fast nuclei

Abstract First experimental evidence of the population of the first 2 − state in 16 C above the neutron threshold is obtained by neutron knockout from 17 C on a hydrogen target. The invariant mass method combined with in-beam γ -ray detection is used to locate the state at 5.45(1) MeV. Comparison of its populating cross section and parallel momentum distribution with a Glauber model calculation utilizing the shell-model spectroscopic factor confirms the core-neutron removal nature of this state. Additionally, a previously known unbound state at 6.11 MeV and a new state at 6.28(2) MeV are observed. The position of the first 2 − state, which belongs to a member of the lowest-lying p – sd cross shell transition, is reasonably well described by the shell-model calculation using the WBT interaction.

Superconducting Dipole Magnet for SAMURAI Spectrometer

The neutron-rich, even-even 122,124,126Pd isotopes has been studied via in-beam gamma-ray spectroscopy at the RIKEN Radioactive Isotope Beam Factory. Excited states at 499(9), 590(11), and 686(17) keV were found in the three isotopes, which we assign to the respective 2+ -> 0+ decays. In addition, a candidate for the 4+ state at 1164(20) keV was observed in 122Pd. The resulting Ex(2+) systematics are essentially similar to those of the Xe (Z=54) isotopic chain and theoretical prediction by IBM-2, suggesting no serious shell quenching in the Pd isotopes in the vicinity of N=82.

One-neutron knockout reaction of 17C on a hydrogen target at 70 MeV/nucleon

Abstract One-neutron knockout from 24O leading to the first excited state in 23O has been measured for a proton target at a beam energy of 62 MeV/nucleon. The decay energy spectrum of the neutron unbound state of 23O was reconstructed from the measured four momenta of the 22O fragment and emitted neutron. A sharp peak was found at E decay = 50 ± 3 keV , corresponding to an excited state in 23O at 2.78 ± 0.11 MeV , as observed in previous measurements. The longitudinal momentum distribution for this state was consistent with d-wave neutron knockout, providing support for a J π assignment of 5 / 2 + . The associated spectroscopic factor was deduced to be C 2 S ( 0 d 5 / 2 ) = 4.1 ± 0.4 by comparing the measured cross section ( σ − 1 n exp = 61 ± 6 mb ) with a distorted wave impulse approximation calculation. Such a large occupancy for the neutron 0 d 5 / 2 orbital is in line with the N = 16 shell closure in 24O.

Collectivity evolution in the neutron-rich Pd isotopes toward the N=82 shell closure

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Neutron occupancy of the 0d5/2 orbital and the N = 16 shell closure in 24O

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The 18Ne(α,p)21Na breakout reaction in x-ray bursts: Experimental determination of spin-parities for α resonances in 22Mg via resonant elastic scattering of 21Na+p

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Reaction Cross Section Of The Two-neutron Halo Nucleus 22C At 235 MeV/nucleon

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Halo structure of the island of inversion nucleus 31Ne.

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