H. Kawakami

Slow RI-beams from projectile fragment separators

Abstract The projectile fragment separator provides a wide variety of short-lived RI-ions with less restrictions on their chemical property or lifetime limit. The beam energy and quality is, however, not adequate for low-energy beam experiments, in particular for trapping experiments. Recently, one has proposed to obtain a low-energy beam from an energetic RI-beam leaving a projectile fragment separator by using a large gas-catcher and an rf ion-guide system. In off-line and in on-line test experiments, the principle of the rf ion-guide was proven. An overall efficiency of 0.2% for 70 MeV/u 8 Li from the RIKEN projectile fragment separator (RIPS) was obtained so far.

A new cooling and focusing device for ion guide

Abstract A highly efficient focusing device which uses a RF multipole field (sextupole-ion-beam guide (SPIG)) has been developed for the ion guide isotope separator on-line (IGISOL). The SPIG, placed after the nozzle, consists of six circular rods uniformly distributed on a circle in the plane perpendicular to the axis of symmetry. Under the combined action of the sextupole RF electric field produced by the rods and helium gas flow, well focused ion beams with low energy spread can be transmitted efficiently by use of the SPIG. The experimental results, using a discharge ion source, show that almost nearly 90% of the ions which leave the nozzle can be transported through the SPIG, and that the width of the kinetic energy distribution after the SPIG is about 0.8 eV (FWHM). These experimental results agree with the results of Monte Carlo simulations; the simulation studies also indicate that the size of the spatial distribution in the plane perpendicular to the symmetry axis is less than 1 mm in diameter at the end of the SPIG.

New upper bound on the electron anti-neutrino mass☆

A new upper bound ofmv < 13 eV at 95% CL has been obtained on the electron anti-neutrino mass. Thus results is based on a more than tenfold improvement in data relative to our previous measurements of the β-spectrum in 3H decay, and its in conflict with the finite mass of 17 <mv< 40 eV reported by an ITEP group

Accumulation of ions from a recoil mass separator in a new type of linear ion trap

Abstract A new type of linear ion trap system in combination with a sextupole ion beam guide (SPIG) has been developed for the accumulation of a continuous ion beam. An axial trapping potential is generated by three cylindrical electrodes mounted outside, but concentric to, the SPIG. The ions in a continuous beam are trapped in the potential well via collisions with He gas. This linear ion trap is called the “SPIG-trap”. The properties of the SPIG-trap were tested off-line with a discharge ion source in a gas cell. Up to 106 ions were trapped and extracted as a bunch with an efficiency of 10% for 10 ms of accumulation. The SPIG-trap system was then connected to a gas filled recoil mass separator (GARIS) and tested with an energetic primary beam from a cyclotron (16O, 107 MeV). The overall efficiency of the SPIG-trap including ion losses in an energy degrader, which was placed in front of the He cell, was measured to be of the order of 10−5 for 10 ms accumulation.

Quasi-gamma bands in even-mass Xe AND Ba nuclei

Abstract Low-lying excited states of 124,126 Xe and 132 Ba have been studied by means of in-beam γ-ray spectroscopy in (p, x n y ) reactions. Excitation functions, angular distributions and γ-γ coincidence spectra were obtained. The 2 2 + , 3 + , 4 2 + and 5 + levels were observed at the following excitation energies in keV: 846.4(2 2 + ), 1247.5(3 + ), 1437.3 (4 2 + ), 1836.6(5 + ) in 124 Xe, 879.7(2 2 + ), 1317.3(3 + ), 1488.2(4 2 + ), 1903.1(5 + ) in 126 Xe and 1032.1(2 2 + ), 1511.3(3 + ), 1729.9(4 2 + ) in 132 Ba. The 2214.3 and 2561.7 keV levels in 126 Xe were tentatively assigned as the 6 2 + and 7 + levels, respectively. These 2 2 + , 3 + , 4 2 + , 5 + , 6 2 + and 7 + levels are interpreted as members of a quasi-γ band. The E2/M1 mixing ratios of the 2 2 + → 2 1 + transitions in 124,126 Xe and 132 Ba were obtained as + 6.3 +5.3 −2.0 + 10.8 7.8 −3.2 and + 8.3 +4.9 −2.2 , respectively.

Lifetime measurements on E2 isomers in N = 48 nuclei and E2 effective charges of 1g92 nucleons

Abstract New E2 isomeric 8 + → 6 + transitions have been identified in three N = 48 nuclei, 86 Sr, 88 Zr and 90 Mo. The half-lives have been determined to be 0.46, 1.75 and 1.05 νs, respectively. The comparison of the B ( E 2, 8 + → 6 + ) values in 86 Sr and 90 Zr indicates that the E2 polarization charge for the neutron is fairly larger than that for the proton.

High sensitivity search for a 17 keV neutrino. Negative indication with an upper limit of 0.095

Abstract We have performed a search for a 17 keV neutrino by looking for a kink in the 63 Ni β-spectrum near the expected energy threshold. Using a large number of events (2.4 × 10 9 ) accumulated in a narrow energy region with the INS iron-free π √2 β -spectrometer, we obtain a mixing strength of [1.8±3.3(stat.)±3.3(syst.)]×10 −4 , and no indication of the presence of a 17 keV neutrino with the order of 1% mixing. We set an upper limit of 0.095% for the admixture of a neutrino with a mass of 17 keV and of 0.1% with a mass range of 10–24 keV, at the 95% confidence level.

INS gas-filled recoil isotope separator

Abstract The characteristics and performance of a small sized gas-filled recoil isotope separator recently made at INS are described. The total efficiency and the ΔBρ / Bρ values have been measured using low velocity 16 O, 40 Ar and 68 As ions and found to be 10 and 5%, respectively. The Z -dependence of the mean charge is discussed.

Cyclotron ion guide for energetic radioactive nuclear ions

A new ion guide, with an additional function having an infinite gas thickness by using a strong magnetic field, is proposed, which enables us to stop energetic radioactive nuclear ions in He gas. The stopped singly charged ions, guided in a dc field with a focusing force generated by an rf field in the gas, are extracted with a SPIG (sextupole rf ion guide) of a focusing device for a spectroscopic study of radioactive nuclei.

Development of thick, long-lived carbon stripper foils for PSR of LANL

Abstract Thick carbon stripper foils (multi-layer thickness ≈ 200 μg/cm 2 ) have been developed for use with 800 MeV, H + ion beam in the Proton Storage Ring (PSR) at Los Alamos National Laboratory. Foils were prepared by means of the modified controlled ACDC arc discharge method (mCADAD). The lifetime measurements of the foils made by different methods were performed using an 800 MeV proton beam of up to 85 μA in the PSR, and a 3.2 MeV Ne + ion beam of 3 μA at Tokyo Institute of Technology. The foils made by the mCADAD method showed very long lifetimes, as compared to other foils tested, for both 800 MeV p and 3.2 MeV Ne + beam bombardments.