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RIKEN Accel. Próg. Rep. 24 (1990)

111-5-9. Test Experiment of the GARIS/IGISOL

K. Morita, T. Nomura, A. Yoshida, T. Inamura, M. Koizumi, M. Fujioka, T. Shinozuka, H. Miyatake, K. Sueki, H. Kudo, Y. Nagai, K. Yoshimura, and T. Toriyama

We constructed an isotope separator on-line (ISOL) at the El experimental hall of the RIKEN Ring Cyclotron (RRC) facility. Since the ISOL consists of a gas-filled recoil isotope separator (GARIS) and an ion-guide type isotope separator on-line (IGISOL), we cali the system as GARIS/ IGISOL. The GARIS/IGISOL will provide us with short-lived isotopes which will be produced by nuclear reactions with high-energy heavy-ion beams from RRC for the study of spectroscopic features of these isotopes. The construction and the generał specifications of the system were reported in Ref. 1.

The GARIS consists of three magnets of a D-Q-Q configuration. The shape of the pole piece of a D-magnet and the geometrical setup of magnets are shown in Fig. 1 together with a beam trajectory obtained by first order calcula-tion. The characteristics of the system as a

D C Q3

Fig. 1. Geometrical setup of GARIS. A trajectory calcu-lated is shown.

Table 1. Characteristics of GARIS as a spectrograph.

	Model	Modę 11
Target posidon	Pole boundary	Center of the scattcring chamber
Totai length of the trajectory	4.07 m	4.77 m
Trajectory length in the magnedc field	1.94 ni	1.94 m
Dtspersion	0.20 cmJ%	0.78 cm/%
Angular acceptance (horizoltal)	±87.5 mrad	±81.3 mrad
Angular acceptance (vertical)	±78.5 mrad	±68.5 mrad
Solid angle (design value)	12 8 msr	11.2 msr
(measured value)	16.3 msr	12.1 msr
Magnificadon (horizonial)	0.57	0.74
Magnificadon (vcrtical)	1.47	1.51

magnetic spectrograph are listed in Table 1. Solid angular acceptances were measured with use of ²⁴¹ Am a-source, and their values are listed also in Table 1.

The efficiency of GARIS was measured by comparing the activity yields on a catcher detec-tor at the focal piane of the GARIS with those on catcher foils at about 5 cm behind targets. Abso-lute efficiencies (in the entire energy-range of the reaction products) were found to be 15 ±1% for the ¹⁶⁹Tm (⁴⁰Ar, xn) (E(⁴⁰Ar) = 5 MeV/u) reaction (fusion reaction), 5.3±0.4% for the ^,81Ta (⁴⁰Ar, tfxn) (E(⁴⁰Ar) = 6 MeV/u) reaction, and 0.5± 0.1% for the ^natW(¹⁴N, X)^,69Hf(E(^l4N) = 35 MeV/ u) reaction (target fragmentation). The efficiencies strongly depend not only on the angular distributions of the reactions but also the energy distributions of the recoiled products. The efficiencies of GARIS for recoiled products of morę than 18 MeV were found to be 30 ±3% for the fusion reaction, and 12±2% for the (HI, ^xn) reaction.

The parameters of the ion optics of IGISOL were tuned with an ⁴⁰Ar^l+ ion beam and i28-i36^_ei+ j_on 5_eams produced by discharge

between needles set inside a thermalization chamber which contains helium added with a smali amount of argon or xenon gas. The mass resolving power [A! A A) obtained by these timing were found to be about 120 for Ar-ion and about 250 for Xe-ions when the helium gas pres-sure was 100 mbar.

The efficiency of IGISOL was measured by ^l41Pr(⁴⁰Ar, xn)¹⁸¹~^xIr reactions under various experimental conditions. Recoiled Ir isotopes were collected with GARIS, then injected into the thermalization chamber of IGISOL, and then stopped there. The isotopes passed through the exit hole of the chamber with a helium gas-flow and were separated from helium atoms with a skimmer, ions were then accelerated to 30 keV with an electrostatic field. The accelerated ions were then collected on the surface of a Silicon surface barrier detector set inside a beam tubę just before an analyzer magnet of IGISOL. (3-Rays and a-particles emitted from the Ir isotopes were detected with the detector, and the effi-