Authors:K. Sueki, K. Akiyama, K. Kikuchi, H. Nakahara, and K. Tomura
The effect of β−-decay on the stability of metallofullerenes was investigated for three decay chains of155Sm-155Eu,161Gd-161Tb and177Yb-177Lu. For the former two cases, the metallofullerenes were found stable even after the β−-decay while in the case of177Yb, the metallofullerene became unstable after β−-decay. The present results point to the fact that metallofullerenes are stable against ordinary β−-decay unstable after β−-decay. The present results point to the fact that metallofullerenes are stable against ordinary β−-decay recoil energies, but they become unstable if the oxidation state of the metal atom is changed by nuclear transformation.
Authors:K. Masumoto, T. Ohtsuki, K. Sueki, K. Kikuchi, and T. Mitsugashira
The11C and14C labeled fullerenes were produced by charged-particle and neutron irradiation, of C60, C70 and their mixture. It was found that a carbon atom of fullerence can be easily exchanged with a radioactive carbon atom produced
by a nuclear reaction. The HPLC method was effective for identification and purification of various labeled fullerene families
as chemically stable compounds. The radiochemically interesting aspect of the results is not only the production of11C and14C labeled fullerenes but also the formation of radioactive higher fullerenes which can be simultaneously produced with high
yield and in carrier-free form.
Authors:K. Sueki, K. Kikuchi, K. Tomura, and H. Nakahara
The stability of 16 kinds of metallofullerenes (9 elements) was investigated against the recoil phenomena associated with
the capture of neutrons by the metal atoms inside the carbon cages. The yields of the unaffected species were obtained by
use of the HPLC separation method and radioactivity measurements. Recoil energy distributions of the metal atoms were calculated
theoretically and the effective energy required for destruction of metallofullerenes from inside by recoiling atoms was estimated
to be about 10 to 15 eV for the metallofullerenes containing lanthanide atoms.
Authors:Y. Ishikawa, T. Kikuchi, T. Sekine, and K. Yoshihara
Concentrations of108mAg,137Cs, and210Pb in oysters (Crassostrea gigas) were measured for about 10 years on the northeast coast of Japan. Silver-108m was detected in oyster samples collected from an open bay, and its concentrations decreased from the initial value of about 30 mBq/kg fresh in the early 1980s to the value of about 10 mBq/kg fresh in the early 1990s. This decrease could be mainly explained by effects of the ocean current in the early 1980s, and the coastal sea water thereafter, as well as by the advection and diffusion in the ocean. In the nearly-closed bays, concentrations of108mAg and210Pb in oysters were remarkably lower than in the open bays. It suggests that scavenging of silver and lead from the sea water effectively occurred in the nearly-closed bays. In contrast, concentrations of137Cs in oysters were similar in the open bays and in the nearly-closed bays.
Authors:T. Oi, K. Horio, R. Kikuchi, and H. Takahashi
Gases released during the conversion of NH4Zr2(PO4)3 to HZr2(PO4)3 were identified using an apparatus in which gases released from a sample placed in a thermogravimetric analyzer were directly introduced to a gas cell of an IR spectrometer. Such acidic gases as N2O and NO were detected besides the basic NH3 gas, and their formation mechanism was discussed.
Authors:K. Sueki, K. Akiyama, Y. Zhao, I. Ito, Y. Ohkubo, K. Kikuchi, M. Katada, and H. Nakahara
We made systematic studies of lanthanoid metallofullerenes on the following three properties using the radiochemical method: (1) the relative production yields of metallofullerene species, (2) variation of the HPLC retention time among M(III)@C82 species, and (3) the effects of the reactor irradiation on the survival yields of each metallofullerene species. The production yields of M@C82 relative to La@C82 were found to decrease as the atomic number of M became larger and as the number of atom ratio, M/C, in the carbon rod became larger. On the other hand, the production yields of M1M2@C82, relative to that of LuM@C82 were found to increase for the larger atomic number. The retention time for the M(III)@C82 species in the Buckyprep column was found to become slightly longer for the larger atomic number but it becomes abruptly larger for Gd, and Tb by about 5%. The overall effects of the reactor irradiation on the survival yields (or retention yields) of M@C82 species were found to be (19.7±2.1)%.
Authors:H. Yoshino, K. Murata, Y. Yamamura, T. Tsuji, H. Nishikawa, K. Kikuchi, and I. Ikemoto
The effect of thermal treatment on the electrical conductivity was studied for a quasi-one-dimensional organic conductor,
(DIMET)2I3 (DIMET=dimethyl(ethylenedithio)tetrathiafulvalene). After heating the samples up to a temperature between 340 and 370 K,
the electric resistivity was measured at low temperature down to 2 K and under pressure up to 1.6 Gpa. (DIMET)2I3 shows irreversible decrease in the electric resistivity between 350 and 356 K on heating. It was found that the heating above
350 K suppresses the spin-density-wave transition at 40 K and another metal-insulator transition appears at 18 K.
Authors:W. Sato, K. Sueki, K. Kikuchi, K. Kobayashi, S. Suzuki, Y. Achiba, H. Nakahara, Y. Ohkubo, F. Ambe, and K. Asai
Time-differential perturbed angular correlation method was applied to Ce@C82 in order to investigate the electronic properties of the encaged Ce atom. The nuclear quadrupole frequency of the nuclear
spin of the Ce was successfully determined as ωQ = 6.5(3)·107 rad/s, which is much greater than what has already been estimated for Ce4+ and La3+ in other compounds. By comparing the present value with the values for the Ce4+ and La3+, it was inferred that the valence state of the encaged Ce atom is trivalent.
Authors:K. Akiyama, K. Sueki, H. Haba, K. Tsukada, M. Asai, T. Yaita, Y. Nagame, K. Kikuchi, M. Katada, and H. Nakahara
We have, previously, reported on the HPLC elution behavior of the Th, Pa, U, Np, and Am metallofullerenes and the UV/vis/NIR absorption spectra of the Th@C84 and U@C82 species. In this paper, the followings are reported: (1) Pu metallofullerenes were produced and their HPLC elution behavior was investigated using a radiotracer technique. The HPLC chromatogram of this metallofullerene was found to be almost the same as that of the Np and Am metallofullerenes. (2) The oxidation states of Th@C84 and U@C82 produced in macroscopic quantities were examined by XANES (X-ray absorption near edge structure) measurements. The oxidation state of the U atom in the C82 fullerene cage was estimated to be 3+ with the formal charge of the ionic molecule being U3+@C823-.
Authors:K. Kobayashi, M. Kuwano, K. Sueki, K. Kikuchi, Y. Achiba, H. Nakahara, N. Kananishi, M. Watanabe, and K. Tomura
Advantages and uniqueness of radiochemical techniques in fullerene studies are pointed out. Some experimental data are presented on metallofullerenes production yields, HPLC elution behaviors of Y, La, Gd containing fullerenes, encapsulation of a new metal in the carbon cage, stability of the carbon cage against recoil energy, and the distribution of metallofullerenes among various organs of rats.