Yasushi Kino

Gaussian expansion method for few-body systems

Abstract We review our method of calculation, Gaussian Expansion Method (GEM), for bound and scattering states of few-body systems. The method was proposed in 1988 and has been applied to a variety of few-body systems. The understanding on the structure and the mechanisms of reactions of those systems obtained from such applications is discussed together with some useful techniques for the calculations. A well-chosen set of Gaussian basis functions forms an approximate complete set in a finite coordinate space so that it can describe accurately short-range corielations and long-range asymptotic behavior as well as highly oscillatory character of wave functions in the bound and the scattering states of the systems. Examples of applications of GEM include i) the latest determination of antiproton mass by the analysis of laser spectroscopic data for antiprotonic helium atoms, ii) predictions and experimental verifications on the structure of hypernuclei and hyperon-nucleon interactions, iii) Coulomb three-body calculations of bound and resonant states of muonic molecules as well as muon transfer reactions in muon catalyzed fusion cycles, iv) a new treatment of CDCC (continuum-discretized coupled channels) method for three- and four-body breakup processes, and v) benchmark test calculations for three- and four-nucleon bound states using realistic interactions.

Stau-catalyzed 6Li production in big-bang nucleosynthesis

Abstract If the gravitino mass is in the region from a few GeV to a few 10s GeV, the scalar lepton X such as stau is most likely the next lightest supersymmetry particle. The negatively charged and long-lived X − may form a Coulomb bound state ( A X − ) with a nucleus A and may affect the big-bang nucleosynthesis through catalyzed fusion process. We calculate a production cross section of 6 Li from the catalyzed fusion ( He 4 X − ) + d → Li 6 + X − by solving the Schrodinger equation exactly for three-body system of 4 He, d and X . We utilize the state-of-the-art coupled-channel method, which is known to be very accurate to describe other three-body systems in nuclear and atomic reactions. The importance of the use of appropriate nuclear potential and the exact treatment of the quantum tunneling in the fusion process are emphasized. We find that the astrophysical S -factor at the Gamow peak corresponding to T = 10 keV is 0.038 MeV barn. This leads to the 6 Li abundance from the catalyzed process as Li 6 | CBBN ≃ 4.3 × 10 −11 ( D / 2.8 × 10 −5 ) ( [ n X − / s ] / 10 −16 ) in the limit of long lifetime of X . Particle physics implication of this result is also discussed.

Distribution of Artificial Radionuclides in Abandoned Cattle in the Evacuation Zone of the Fukushima Daiichi Nuclear Power Plant

The Fukushima Daiichi Nuclear Power Plant (FNPP) accident released large amounts of radioactive substances into the environment. In order to provide basic information for biokinetics of radionuclides and for dose assessment of internal exposure brought by the FNPP accident, we determined the activity concentration of radionuclides in the organs of 79 cattle within a 20-km radius around the FNPP. In all the specimens examined, deposition of Cesium-134 (134Cs, half-life: 2.065 y) and 137Cs (30.07 y) was observed. Furthermore, organ-specific deposition of radionuclides with relatively short half-lives was detected, such as silver-110m (110mAg, 249.8 d) in the liver and tellurium-129m (129mTe, 33.6 d) in the kidney. Regression analysis showed a linear correlation between the radiocesium activity concentration in whole peripheral blood (PB) and that in each organ. The resulting slopes were organ dependent with the maximum value of 21.3 being obtained for skeletal muscles (R2 = 0.83, standard error (SE) = 0.76). Thus, the activity concentration of 134 Cs and 137Cs in an organ can be estimated from that in PB. The level of radioactive cesium in the organs of fetus and infants were 1.19-fold (R2 = 0.62, SE = 0.12), and 1.51-fold (R2 = 0.70, SE = 0.09) higher than that of the corresponding maternal organ, respectively. Furthermore, radiocesium activity concentration in organs was found to be dependent on the feeding conditions and the geographic location of the cattle. This study is the first to reveal the detailed systemic distribution of radionuclides in cattle attributed to the FNPP accident.

Effects of radioactive caesium on bull testes after the Fukushima nuclear plant accident

We aimed to investigate the effect of chronic radiation exposure associated with the Fukushima Daiichi Nuclear Plant accident on the testis from 2 bulls. Estimated dose of internal exposure in one bull was 0.7–1.2 mGy (134Cs) and 0.4–0.6 mGy (137Cs) and external exposure was 2.0 mGy (134Cs) and 0.8 mGy (137Cs) (196 days). Internal dose in the other was 3.2–6.1 mGy (134Cs) and 1.8–3.4 mGy (137Cs) and external dose was 1.3 mGy (134Cs) and 0.6 mGy (137Cs) (315 days). Sperm morphology and spermatogenesis were within normal ranges. 134, 137Cs radioactivity was detected but Cs was not detectable in the testis by electron probe microanalysis. Thus, adverse radiation-induced effects were not observed in bull testes following chronic exposure to the above levels of radiation for up to 10 months. Since we could analyse a limited number of testes, further investigation on the effects of ionizing radiation on spermatogenesis should be extended to more animals.

Big Bang Nucleosynthesis Reactions Catalyzed by a Long Lived Negatively Charged Leptonic Particle

An accurate quantum three-body calculation is performed for the new type of big-bang nucleosynthesis (BBN) reactions that are catalyzed by a long-lived negatively-charged, massive leptonic particle (called X^-) such as the supersymmetric (SUSY) particle stau. The reactions studied here includes, i) 4He-transfer reactions such as (4He X)+d --> 6Li+X, ii) radiative capture reactions such as (7Be X)+ p --> (8B X) + gamma, iii) three-body breakup reactions such as (7Li X)+ p --> 4He+4He+X, iv) charge-exchange reactions such as (p X)+4He -->(4He X) +p, and v) neutron induced reactions such as (8Be X)+ n -->9Be+X, where (A X) denotes a Coulombic bound state of a nucleus A and X^-. In recent papers it has been claimed that some of the catalyzed BBN reactions have significantly large cross sections so as to markedly change the abundances of some elements, not only giving a solution to the 6Li-7Li problem (calculated underproduction of 6Li by a factor of 1000 and overproduction of 7Li+7Be by a factor of nearly 3) but also imposing strong restrictions on the lifetime and the primordial abundance of X^-. However, most of the calculations of these reaction cross sections in the literature were performed assuming too naive models or approximations that are unsuitable for the complicated low-energy nuclear reactions. We use a high-accuracy few-body calculational method developed by the authors, and provide precise cross sections and rates of these catalyzed BBN reactions for use in the BBN network calculation.

Radiolytic formation of Tc(IV) oxide colloids

Summary Technetium(IV) oxide colloids were radiolytically formed by γ irradiation of aqueous solutions of pertechnetate (TcO4−). Pertechnetate solutions (5.5×10−5-2.9×10−4 M) were irradiated with bremsstrahlung from an electron linear accelerator at 40 and 17 °C. The color of irradiated solutions gradually changed to brownish black, suggesting the formation of Tc(IV) oxide colloids (TcO2·nH2O). A transmission electron microscopy (TEM) analysis showed that the size of colloids distributed around 30 to 130 nm in diameter. The characteristic X-rays from technetium and oxygen were simultaneously detected from colloid particles at the TEM measurements. Round-shaped colloids were produced by irradiation at 40 °C, whereas irregular-shaped colloid particles composed of tiny particles (2 nm in diameter) were produced at 17 °C. The concentration of TcO4− in the target solution gradually decreased with an increase of the absorbed dose, corresponding to an increase of the colloid yield. The yield of colloids sharply increased in the solution deaerated by Ar bubbling before irradiation, but strongly suppressed in the solution saturated with oxygen (O2) or nitrous oxide (N2O) gas. The fact suggests that hydrated electrons play an important role in the course of the reduction of TcO4− and that Tc(IV) oxide colloids were formed via successive disproportionation reactions of Tc(VI) and Tc(V). The formation mechanisms of Tc(IV) oxide colloids are discussed.

NON-ADIABATIC HIGH-PRECISION CALCULATION OF ANTIPROTONIC HELIUM ATOMCULES

The energy levels of the metastable states of Coulombic exotic three-body systems were calculated with the non-adiabatic coupled rearrangement channel method. The resonant boundary condition of the metastable levels is taken into account. Relativistic and QED corrections on the energies were made. Excellent agreement between corrected wavelengths and experimental data was achieved. This agreement gave the best limit of the antiproton mass with 10-7 uncertainty.

HIGH-ACCURACY 3-BODY COUPLED-CHANNEL CALCULATION OF METASTABLE STATES OF ANTIPROTONIC HELIUM ATOMS

Abstract High-precision Coulomb three-body calculation is performed for energies of metastable states of the antiprotonic helium atom having large interacting angular momenta of 30–40. Use is made of coupled-rearrangement-channel variational method with Jacobian-coordinate Gaussian basis functions which has successfully been employed in the study of various few-body systems. The resonant boundary condition of the metastable levels is explicitly taken into consideration within the complex-coordinate-rotation method. Observed transition wavelength are precisely reproduced by the calculation.

Numerical accuracy of the energy levels of antiprotonic helium atoms

We evaluate the numerical accuracy of our Coulomb three-body calculation by the complex coordinate rotation method. We examine convergence of eigenenergies of antiprotonic helium atoms. The exotic atom having both atomic and molecular characters is effectively described with the coupled rearrangement channel method. The relative numerical accuracy for the transition frequencies which are to be compared with the observed values by ASACUSA collaboration is estimated to be 9 ppb on average.

High-Precision Calculation of the Energy Levels and Auger Decay Rates of the Metastable States of the Antiprotonic Helium Atoms

We precisely calculated the energy levels and the Auger decay rates of the antiprotonic helium atoms with the coupled rearrangement channel method and the complex-coordinate-rotation method. Calculated transition frequencies were in excellent agreement with observed values. This agreement gives best limit of the antiproton mass with 5×10−8 uncertainty.