Norio Nogawa

Deposition of fission and activation products after the Fukushima Dai-ichi nuclear power plant accident

The Great Eastern Japan Earthquake on March 11, 2011, damaged reactor cooling systems at Fukushima Dai-ichi nuclear power plant. The subsequent venting operation and hydrogen explosion resulted in a large radioactive nuclide emission from reactor containers into the environment. Here, we collected environmental samples such as soil, plant species, and water on April 10, 2011, in front of the power plant main gate as well as 35xa0km away in Iitate village, and observed gamma-rays with a Ge(Li) semiconductor detector. We observed activation products ((239)Np and (59)Fe) and fission products ((131)I, (134)Cs ((133)Cs), (137)Cs, (110m)Ag ((109)Ag), (132)Te, (132)I, (140)Ba, (140)La, (91)Sr, (91)Y, (95)Zr, and (95)Nb). (239)Np is the parent nuclide of (239)Pu; (59)Fe are presumably activation products of (58)Fe obtained by corrosion of cooling pipes. The results show that these activation and fission products, diffused within a month of the accident.

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

A Method to Estimate the Fast-Neutron Fluence for the Hiroshima Atomic Bomb

A new method to estimate the fast-neutron fluence of the Hiroshima atomic bomb is proposed. 63 Ni produced by the 63 Cu(n, p) 63 Ni reaction provides a unique measure by which to estimate the fast-neutron fluence of the Hiroshima/Nagasaki atomic bombs, because the half-life of 63 Ni is 100 years and 70% of the 63 Ni produced in a copper piece presently exists after 50 years. Using the neutron spectrum given in DS86 and the estimated cross section, we found that a piece of copper of about 10 g which was exposed at a point around 100 m from the hypocenter gives a measurable amount of 63 Ni using a low-background liquid scintillation counter. For the measurement of 63 Ni, accelerator mass spectrometry also seems to be applicable.

An Upper Limit for the Mass of the Electron Anti-neutrino From the Ins Experiment

Abstract The β-spectrum in 3 H decay has measured at INS with an energy resolution of 10–16 eV. The overall response function of the spectrometer system was reliably obtained with a reference 109 Cd source having the same chemical structure as the 3 H source. An upper limit of 32 eV has been obtained for the mass of the electron anti-neutrino with statistical and systematic errors.

Precise measurement of Ag KLL Auger-spectrum

Abstract The Ag KLL Auger spectrum has been measured with an energy resolution of 8 eV. The energies and the intensities of all nine lines are precisely determined with 1–2 orders of magnitude better accuracies than those in the previous experiment. The data obtained are found to be in good agreement with the theoretical calculations.

A method to detect low-level 63Ni activity for estimating fast neutron fluence from the Hiroshima atomic bomb

The Hiroshima and Nagasaki atomic bombs resulted in the worst reported exposure of radiation to the human body. The data of survivors have provided the basis for the risk estimation for ionizing radiation, and thus are widely used as the basis of radiation safety. In this report we have studied a new method to detect the low-level 63Ni activity in copper samples in order to estimate the fast neutron fluence from the Hiroshima atomic bomb. Only 0.8 x 10(-3) Bq g(-1) of 63Ni is expected to be produced by the atomic bomb in a copper sample with the 63Cu(n, p)63Ni reaction at a distance of 500 m from the hypocenter. Our method has the required level of sensitivity for determination of the fast neutron fluence out to distances of at least 500 m, and perhaps as far as 1,000 m. We have already investigated and collected some bomb-irradiated copper samples for further study.

Measurements of the Production Cross Sections of Tritium from Oxygen Using p-Be and p-Li Neutrons up to En = 38 MeV

The production cross sections of tritium from oxygen have been measured in p-Be and p-Li neutron fields installed at the sectorfocusing (SF) cyclotron of the Institute for Nuclear Study (INS), University of Tokyo. Irradiations were performed with the semi-monoenergetic neutrons produced from the Be(p,n)B reaction at proton energies from 20 up to 40 MeV in 2.5-MeV steps, and those from Li(p,n)Be in 5-MeV steps with proton intensities of 2—5 μΑ, which yields neutron flux densities from 10 to 10 n/cm/sec at the position of sample irradiation. The neutron energy spectra were determined by an NE-213 scintillation counter. The tritium produced in the water used as the oxygen target was extracted by a distillation method, and measured by a liquid scintillation counter. The excitation functions for the 0(n,t)N reaction, measured by the p-Be and p-Li neutrons, agreed well with each other within the experimental uncertainties. The obtained results have been compared with the general trend in the (n,t) cross sections as a function of the atomic number of the target appearing in the literature.

Study of energy loss of 18 keV β-rays in a Langmuir-Blodgett thin film

Abstract The energy loss of 18 keV β-rays in a very thin Langmuir-Blodgett film of a chemical compound, arachidic acid, has been studied.

Neutrino Mass and End-Point Energy of ^3H β-Decay

The end-point energy of 3 H β-decay is re-examined and found as E 0 =18582.5±4.1 eV by a new measurement of the electron energy spectrum at INS. Also, an upper limit of the electron anti-neutrino mass is obtained as m ν <29 eV by combining with the result of a previous experiment.

Excitation function for 63Cu(n,p)63Ni reaction in neutron energy range up to 15 MeV

The excitation function for the (63)Cu(n,p)(63)Ni reaction has been measured by activation method using the 4.5 MV Dynamitron accelerator of the Fast Neutron Laboratory of Tohoku University. Copper plates and hollow spherical copper shells were irradiated by neutrons of various energy up to 14.9 MeV produced by the T(p,n), D(d,n), and T(d,n) reactions. The (63)Ni produced in the irradiated copper target was chemically separated. The beta-rays emitted from the extracted (63)Ni were measured by a liquid scintillation method. The cross sections obtained were compared with the evaluated data files of JENDL-3.3, ENDF/B-VI and FENDL/A-2.0. Consequently, it is found that FENDL/A-2.0 is consistent with our experimental data in the energy range studied in this work. The effect of proton shell appeared in the excitation function obtained is also discussed.