R. Hayano

Cesium-137 deposition and contamination of Japanese soils due to the Fukushima nuclear accident

The largest concern on the cesium-137 (137Cs) deposition and its soil contamination due to the emission from the Fukushima Daiichi Nuclear Power Plant (NPP) showed up after a massive quake on March 11, 2011. Cesium-137 (137Cs) with a half-life of 30.1 y causes the largest concerns because of its deleterious effect on agriculture and stock farming, and, thus, human life for decades. Removal of 137Cs contaminated soils or land use limitations in areas where removal is not possible is, therefore, an urgent issue. A challenge lies in the fact that estimates of 137Cs emissions from the Fukushima NPP are extremely uncertain, therefore, the distribution of 137Cs in the environment is poorly constrained. Here, we estimate total 137Cs deposition by integrating daily observations of 137Cs deposition in each prefecture in Japan with relative deposition distribution patterns from a Lagrangian particle dispersion model, FLEXPART. We show that 137Cs strongly contaminated the soils in large areas of eastern and northeastern Japan, whereas western Japan was sheltered by mountain ranges. The soils around Fukushima NPP and neighboring prefectures have been extensively contaminated with depositions of more than 100,000 and 10,000 MBq km-2, respectively. Total 137Cs depositions over two domains: (i) the Japan Islands and the surrounding ocean (130–150 °E and 30–46 °N) and, (ii) the Japan Islands, were estimated to be more than 5.6 and 1.0 PBq, respectively. We hope our 137Cs deposition maps will help to coordinate decontamination efforts and plan regulatory measures in Japan.

Production and detection of cold antihydrogen atoms.

A theoretical underpinning of the standard model of fundamental particles and interactions is CPT invariance, which requires that the laws of physics be invariant under the combined discrete operations of charge conjugation, parity and time reversal. Antimatter, the existence of which was predicted by Dirac, can be used to test the CPT theorem—experimental investigations involving comparisons of particles with antiparticles are numerous. Cold atoms and anti-atoms, such as hydrogen and antihydrogen, could form the basis of a new precise test, as CPT invariance implies that they must have the same spectrum. Observations of antihydrogen in small quantities and at high energies have been reported at the European Organization for Nuclear Research (CERN) and at Fermilab, but these experiments were not suited to precision comparison measurements. Here we demonstrate the production of antihydrogen atoms at very low energy by mixing trapped antiprotons and positrons in a cryogenic environment. The neutral anti-atoms have been detected directly when they escape the trap and annihilate, producing a characteristic signature in an imaging particle detector.

A New Measurement of Kaonic Hydrogen X-rays

The KN system at threshold is a sensitive testing ground for low energy QCD, especially for the explicit chiral symmetry breaking. Therefore, we have measured the K-series x rays of kaonic hydrogen atoms at the DANE electron-positron collider of Laboratori Nazionali di Frascati, and have de- termined the most precise values of the strong-interaction energy-level shift and width of the 1s atomic state. As x-ray detectors, we used large-area silicon drift detectors having excellent energy and timing resolution, which were developed especially for the SIDDHARTA experiment. The shift and width were determined to be ǫ1s = 283 ± 36(stat) ± 6(syst) eV and 1s = 541± 89(stat) ± 22(syst) eV, respectively. The new values will provide vital constraints on the theoretical description of the low-energy KN interaction.

Observation of Kaonic Hydrogen K α X Rays

We have measured the shift and width of the kaonic hydrogen 1s state due to the {ovr K}N strong interaction. We have observed, for the first time, distinct K-series kaonic hydrogen x rays with good signal-to-noise ratio in the energy spectrum. The measured energy shift and width were determined to be {Delta}E(1s)=-323{plus_minus}63(stat){plus_minus}11(syst)eV (repulsive) and {Gamma}(1s)=407{plus_minus}208(stat){plus_minus}100(syst)eV,respectively. {copyright} {ital 1997} {ital The American Physical Society}

Confinement of antihydrogen for 1,000 seconds

Antihydrogen has been created, trapped and stored for 1,000 s. The improved holding time means that we now have access to the ground state of antimatter—long enough to test whether matter and antimatter obey the same physical laws.

Precision spectroscopy of pionic 1s states of Sn nuclei and evidence for partial restoration of chiral symmetry in the nuclear medium

Deeply bound 1s states of pi(-) in (115,119,123)Sn were preferentially observed using the Sn(d,3He) pion-transfer reaction under the recoil-free condition. The 1s binding energies and widths were precisely determined and were used to deduce the isovector parameter of the s-wave pion-nucleus potential to be b1=-(0.115+/-0.007)m(-1)(pi). The observed enhancement of |b(1)| over the free piN value (b(free)1/b1=0.78+/-0.05) indicates a reduction of the chiral order parameter, f*pi(rho)2/f2pi approximately 0.64, at the normal nuclear density, rho=rho(0).

Two-photon laser spectroscopy of antiprotonic helium and the antiproton-to-electron mass ratio

Physical laws are believed to be invariant under the combined transformations of charge, parity and time reversal (CPT symmetry). This implies that an antimatter particle has exactly the same mass and absolute value of charge as its particle counterpart. Metastable antiprotonic helium (He+) is a three-body atom consisting of a normal helium nucleus, an electron in its ground state and an antiproton () occupying a Rydberg state with high principal and angular momentum quantum numbers, respectively n and l, such that n ≈ l + 1 ≈ 38. These atoms are amenable to precision laser spectroscopy, the results of which can in principle be used to determine the antiproton-to-electron mass ratio and to constrain the equality between the antiproton and proton charges and masses. Here we report two-photon spectroscopy of antiprotonic helium, in which 3He+ and 4He+ isotopes are irradiated by two counter-propagating laser beams. This excites nonlinear, two-photon transitions of the antiproton of the type (n, l) → (n − 2, l − 2) at deep-ultraviolet wavelengths (λ = 139.8, 193.0 and 197.0 nm), which partly cancel the Doppler broadening of the laser resonance caused by the thermal motion of the atoms. The resulting narrow spectral lines allowed us to measure three transition frequencies with fractional precisions of 2.3–5 parts in 109. By comparing the results with three-body quantum electrodynamics calculations, we derived an antiproton-to-electron mass ratio of 1,836.1526736(23), where the parenthetical error represents one standard deviation. This agrees with the proton-to-electron value known to a similar precision.

Internal radiocesium contamination of adults and children in Fukushima 7 to 20 months after the Fukushima NPP accident as measured by extensive whole-body-counter surveys

The Fukushima Dai-ichi NPP accident contaminated the soil of densely-populated regions in Fukushima Prefecture with radioactive cesium, which poses significant risks of internal and external exposure to the residents. If we apply the knowledge of post-Chernobyl accident studies, internal exposures in excess of a few mSv/y would be expected to be frequent in Fukushima. Extensive whole-body-counter surveys (n = 32,811) carried out at the Hirata Central Hospital between October, 2011 and November, 2012, however show that the internal exposure levels of residents are much lower than estimated. In particular, the first sampling-bias-free assessment of the internal exposure of children in the town of Miharu, Fukushima, shows that the 137Cs body burdens of all children (n = 1,383, ages 6–15, covering 95% of children enrolled in town-operated schools) were below the detection limit of 300 Bq/body in the fall of 2012. These results are not conclusive for the prefecture as a whole, but are consistent with results obtained from other municipalities in the prefecture, and with prefectural data.

Evidence for a bound state of the Σ4 He hypernucleus

Abstract We report data which imply the existence of a Σ-nucleus bound state, formed in a (K−, π−) reaction at rest on a 4He target. A peak was found, which we attribute to the formation of the Σ 4 He ground state, corresponding to ΔM≡M( 4 Σ He)−M( 4 He)=267.7±0.3 (statistical) −0.1+1.1 (systematic) MeV (B Σ + =3.2 MeV . The width of the peak was deduced to be 4.6±0.5 (statiscal) +1.6−1.3 (systematic) MeV. No clear peak was found in the corresponding region of the (K−, π+) spectrum. We assign I= 1 2 and S=0 to this state.

Antiprotonic helium and CPT invariance

We review recent progress in the laser and microwave spectroscopy of antiprotonic helium atoms carried out at CERNs Antiproton Decelerator facility (AD). Laser transitions were here induced between Rydberg states (n, l) and (n ± 1, l − 1) of (n ~ 40 and l n − 1 being the principal and orbital angular momentum quantum numbers of the antiproton orbit). Successive refinements in the experimental techniques improved the fractional precision on the frequencies from 3 parts in 106 to ~1 part in 108. These included a radiofrequency quadrupole decelerator, which reduced the energy of the antiprotons from 5.3 MeV (the energy of the beam emerging from AD) to ~100 keV. This enabled the production of in ultra-low density targets, where collisional effects with other helium atoms are negligible. A continuous wave pulse-amplified dye laser, stabilized against a femtosecond optical frequency comb, was then used to measure the frequencies with ppb-scale precision. This progress in the experimental field was matched by similar advances in computing methods for evaluating the expected transition frequencies in three-body QED calculations. The comparison of experimental (νexp) and theoretical (νth) frequencies for seven transitions in and five in yielded an antiproton-to-electron mass ratio of . This agrees with the known proton-to-electron mass ratio at the level of ~2 × 10−9. The experiment also set a limit on any CPT-violating difference between the antiproton and proton charges and masses, to a 90% confidence level. If on the other hand we assume the validity of the CPT invariance, the result can be taken to be equal to mp/me. This can be used as an input to future adjustments of fundamental constants. The hyperfine structure of a state in has also been measured by microwave spectroscopy to a precision of 3 × 10−5. This corresponds to the accuracy of the most precise three-body QED calculations. Further increases in the experimental precision may soon yield an improvement in the value of the antiproton magnetic moment.