Off-line test of the KISS gas cell

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Highlights

  • Construction of the KEK Isotope Separation System (KISS) at RIKEN.

  • Ionization scheme of an iron.

  • Measurement of transport time profile in a gas cell.

Abstract

The KEK Isotope Separation System (KISS) has been constructed at RIKEN to study the β-decay properties of neutron-rich isotopes with neutron numbers around N = 126 for application to astrophysics. A key component of KISS is a gas cell filled with argon gas at a pressure of 50 kPa to stop and collect the unstable nuclei, where the isotopes of interest will be selectively ionized using laser resonance ionization. We have performed off-line tests to study the basic properties of the gas cell and of KISS using nickel and iron filaments placed in the gas cell.

Introduction

The beta-decay properties of nuclei with N = 126, which act as progenitors in the r-process path forming the third peak (A 195) in the r-abundance element distribution, are considered critical for clearly understanding the production of heavy elements such as gold and platinum at astrophysical sites [1]. We have constructed the KEK Isotope Separation System (KISS) to produce pure low-energy beams of neutron-rich isotopes around N = 126 and to study their beta-decay properties, which are also of interest for astrophysics [2].

We plan to produce and study 200W, 201Re, 202Os and 203Ir (Z= 74–77, N = 126) by multi-nucleon transfer (MNT) reactions [3] between an energetically stable 136Xe beam at 10 MeV/nucleon and a 198Pt target. The recoil energies of nuclei with N = 126 produced as target-like fragments are as low as 1 MeV/nucleon and have a wide energy distribution. The emission angles for this recoil reaction calculated by the GRAZING code [4] vary widely around an average value of 65° in the laboratory frame. The first results from experiments on this reaction are reported in Ref. [5].

The characteristics of the MNT reaction products make it difficult to collect nuclei with N = 126 using an in-flight-type electromagnetic spectrometer. Therefore, we employ a gas catcher to efficiently collect all reaction products and use the laser resonance ionization technique to select nuclei with specific atomic numbers Z from the collected nuclei, and an electromagnetic separator (ISOL) to obtain nuclei with specific mass numbers A. This type of gas catcher system has been developed and applied effectively to the study of nuclear structure by the Leuven group [6], [7], [8], [9], [10], [11].

We use a gas cell filled with argon gas at a pressure of 50 kPa in conjunction with a laser resonance ionization technique for the selective ionization of the isotopes of interest. In this paper we report the results of off-line tests to investigate the performance of the KISS gas cell.

Section snippets

KISS setup

Fig. 1 shows a schematic layout of KISS, which was constructed at the RIBF facility in RIKEN at the beginning of 2011. It consists of a laser system, a mass-separator system, three decay measurement stations and a gas-cell system.

The laser system consists of two frequency-tunable dye lasers pumped by two excimer (XeCl, 308 nm) lasers and is installed in a separate room below the KISS gas cell system. A repetition rate of up to 200 Hz is used and the bandwidth of the dye laser is 0.15 cm−1. The

Off-line test

We have successfully extracted a stable nickel ion-beam, evaporated from a nickel filament placed in the gas cell and ionized using the laser resonance ionization technique, in an off-line test. The ionization scheme of 3d84s2 (J = 4)  3d84s4p (J = 5) (λ1 = 232.074 nm in vacuum) auto ionization state (λ2 = 537.960 nm in vacuum), as reported in Ref. [6], was employed in the present test. Using a nickel beam with an energy of 28 keV, we optimized the RF and DC voltages of the SPIG for cooling and

Summary

We constructed the KEK Isotope Separation System (KISS) at RIKEN to study the β-decay properties of neutron-rich isotopes with neutron numbers around N = 126 for applications in astrophysics. Using nickel and iron atoms evaporated from filaments, an off-line performance test of the gas cell system and the KISS was successfully performed. We established a new and efficient ionization scheme for iron for use in on-line tests. The extraction efficiency and the selectivity of KISS will be further

Acknowledgments

The authors acknowledge the staff of the RIKEN accelerator for their support. This work has been supported by Grant-in-Aids for Scientific Research (A) (S.C. Jeong, Grant No. 23244060) and for young scientists (B) (Y. Hirayama, Grant No. 24740180) from the Japan Society for the Promotion of Science (JSPS), by FWO-Vlaanderen (Belgium), by GOA/2010/010 (BOF KU Leuven), and by a grant from the European Research Council (ERC-2011-AdG-291561-HELIOS).

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