T. Kawabata, H. Akimune, H. Fujita, Y. Fujita, M. Fujiwara, K. Hara, K. Hatanaka, M. Itoh, Y. Kanada-En'yo, S. Kishi, K. Nakanishi, H. Sakaguchi, Y. Shimbara, A. Tamii, S. Terashima, M. Uchida, T. Wakasa, Y. Yasuda, H. P. Yoshida, M. Yosoi
The cluster structures of the excited states in $^{11}$B are studied by analyzing the isoscalar monopole and quadrupole strengths in the $^{11}$B($d$,$d'$) reaction at $E_d=200$ MeV. The excitation strengths are compared with the predictions by the shell-model and antisymmetrized molecular-dynamics (AMD) calculations. It is found that the large monopole strength for the $3/2^-_3$ state at $E_x=8.56$ MeV is well described by the AMD calculation and is an evidence for a developed $2α+t$ cluster structure.
A. Yoshimi, H. Hara, T. Hiraki, Y. Kasamatsu, S. Kitao, Y. Kobayashi, K. Konashi, R. Masuda, T. Masuda, Y. Miyamoto, K. Okai, S. Okubo, R. Ozaki, N. Sasao, O. Sato, M. Seto, T. Schumm, Y. Shigekawa, S. Stellmer, K. Suzuki, S. Uetake, M. Watanabe, A. Yamaguchi, Y. Yasuda, Y. Yoda, K. Yoshimura, M. Yoshimura
Nuclear resonant excitation of the 29.19-keV level in $^{229}$Th with high-brilliance synchrotron- radiation and detection of its decay signal, are proposed with the aim of populating the extremely low-energy isomeric state of $^{229}$Th.The proposed experiment, known as nuclear resonant scattering (NRS), has the merit of being free from uncertainties about the isomer level energy. However, it requires higher time resolution and shorter tail in the response function of the detector than that of conventional NRS experiments because of the short lifetime of the 29.19-keV state. We have fabricated an X-ray detector system which has a time resolution of 56 ps and a shorter tail function than the previously reported one. We have demonstrated an NRS experiment with the 26.27-keV nuclear level of $^{201}$Hg for feasibility assessment of the $^{229}$Th experiment. The NRS signal is clearly distinct from the prompt electronic scattering signal by the implemented detector system. The half-life of the 26.27-keV state of $^{201}$Hg is determined as 629 $\pm$ 18 ps which is better precision by a factor three than that reported to date.
T. Wakasa, G. P. A. Berg, H. Fujimura, K. Fujita, K. Hatanaka, M. Ichimura, M. Itoh, J. Kamiya, T. Kawabata, Y. Kitamura, E. Obayashi, H. Sakaguchi, N. Sakamoto, Y. Sakemi, Y. Shimizu, H. Takeda, M. Uchida, Y. Yasuda, H. P. Yoshida, M. Yosoi
The cross section of the ${}^{16}{\rm O}(p,p'){}^{16}{\rm O}(0^-,T=1)$ scattering was measured at a bombarding energy of 295 MeV in the momentum transfer range of $1.0 \mathrm{fm^{-1}}$ $\le$ $q_{\rm c.m.}$ $\le$ $2.1 \mathrm{fm^{-1}}$. The isovector $0^-$ state at $E_x$ = 12.8 MeV is clearly separated from its neighboring states owing to the high energy resolution of about 30 keV. The cross section data were compared with distorted wave impulse approximation (DWIA) calculations employing shell-model wave functions. The observed cross sections around $q_{\rm c.m.}$ $\simeq$ $1.7 {\rm fm^{-1}}$ are significantly larger than predicted by these calculations, suggesting pionic enhancement as a precursor of pion condensation in nuclei. The data are successfully reproduced by DWIA calculations using random phase approximation response functions including the $Δ$ isobar that predict pionic enhancement.
S. Terashima, H. Sakaguchi, H. Takeda, T. Ishikawa, M. Itoh, T. Kawabata, T. Murakami, M. Uchida, Y. Yasuda, M. Yosoi, J. Zenihiro, H. P. Yoshida, T. Noro, T. Ishida, S. Asaji, T. Yonemura
Cross sections and analyzing powers for proton elastic scattering from $^{116,118,120,122,124}$Sn at 295 MeV have been measured for a momentum transfer of up to about 3.5 fm$^{-1}$ to deduce systematic changes of the neutron density distribution. We tuned the relativistic Love-Franey interaction to explain the proton elastic scattering of a nucleus whose density distribution is well known. Then, we applied this interaction to deduce the neutron density distributions of tin isotopes. The result of our analysis shows the clear systematic behavior of a gradual increase in the neutron skin thickness of tin isotopes with mass number.
Y. K. Gupta, U. Garg, J. T. Matta, D. Patel, T. Peach, J. Hoffman, K. Yoshida, M. Itoh, M. Fujiwara, K. Hara, H. Hashimoto, K. Nakanishi, M. Yosoi, H. Sakaguchi, S. Terashima, S. Kishi, T. Murakami, M. Uchida, Y. Yasuda, H. Akimune, T. Kawabata, M. N. Harakeh
The isoscalar giant monopole resonance (ISGMR) strength distribution in $^{24}$Mg has been determined from background-free inelastic scattering of 386-MeV $α$ particles at extreme forward angles, including 0$^{\circ}$. The ISGMR strength distribution has been observed for the first time to have a two-peak structure in a light-mass nucleus. This splitting of ISGMR strength is explained well by microscopic theory in terms of the prolate deformation of the ground state of $^{24}$Mg.
T. Li, U. Garg, Y. Liu, R. Marks, B. K. Nayak, P. V. Madhusudhana Rao, M. Fujiwara, H. Hashimoto, K. Kawase, K. Nakanishi, S. Okumura, M. Yosoi, M. Itoh, M. Ichikawa, R. Matsuo, T. Terazano, M. Uchida, T. Kawabata, H. Akimune, Y. Iwao, T. Murakami, H. Sakaguchi, S. Terashima, Y. Yasuda, J. Zenihiro, M. N. Harakeh
The strength distributions of the giant monopole resonance (GMR) have been measured in the even-A Sn isotopes (A=112--124) with inelastic scattering of 400-MeV $α$ particles in the angular range $0^\circ$--$8.5^\circ$. We find that the experimentally-observed GMR energies of the Sn isotopes are lower than the values predicted by theoretical calculations that reproduce the GMR energies in $^{208}$Pb and $^{90}$Zr very well. From the GMR data, a value of $K_τ = -550 \pm 100$ MeV is obtained for the asymmetry-term in the nuclear incompressibility.
M. Itoh, S. Kishi, H. Sakaguchi, H. Akimune, M. Fujiwara, U. Garg, K. Hara, H. Hashimoto, J. Hoffman, T. Kawabata, K. Kawase, T. Murakami, K. Nakanishi, B. K. Nayak, S. Terashima, M. Uchida, Y. Yasuda, M. Yosoi
Isoscalar giant resonances and low spin states in $^{32}$S have been measured with inelastic $α$ scattering at extremely forward angles including zero degrees at E$_α$ = 386 MeV. By applying the multipole decomposition analysis, various excited states are classified according to their spin and parities (J$^π$), and are discussed in relation to the super deformed and $^{28}$Si + $α$ cluster bands.
M. Hunyadi, H. Hashimoto, T. Li, H. Akimune, H. Fujimura, M. Fujiwara, Z. Gacsi, U. Garg, K. Hara, M. N. Harakeh, J. Hoffman, M. Itoh, T. Murakami, K. Nakanishi, B. K. Nayak, S. Okumura, H. Sakaguchi, S. Terashima, M. Uchida, Y. Yasuda, M. Yosoi
Proton decay from the 3$\hbarω$ isoscalar giant dipole resonance (ISGDR) in $^{58}$Ni has been measured using the ($α,α'p$) reaction at a bombarding energy of 386 MeV to investigate its decay properties. We have extracted the ISGDR strength under the coincidence condition between inelastically scattered $α$ particles at forward angles and decay protons emitted at backward angles. Branching ratios for proton decay to low-lying states of $^{57}$Co have been determined, and the results compared to predictions of recent continuum-RPA calculations. The final-state spectra of protons decaying to the low-lying states in $^{57}$Co were analyzed for a more detailed understanding of the structure of the ISGDR. It is found that there are differences in the structure of the ISGDR as a function of excitation energy.
D. Q. Fang, Y. G. Ma, X. Y. Sun, P. Zhou, Y. Togano, N. Aoi, H. Baba, X. Z. Cai, X. G. Cao, J. G. Chen, Y. Fu, W. Guo, Y. Hara, T. Honda, Z. G. Hu, K. Ieki, Y. Ishibashi, Y. Ito, N. Iwasa, S. Kanno, T. Kawabata, H. Kimura, Y. Kondo, K. Kurita, M. Kurokawa, T. Moriguchi, H. Murakami, H. Ooishi, K. Okada, S. Ota, A. Ozawa, H. Sakurai, S. Shimoura, R. Shioda, E. Takeshita, S. Takeuchi, W. D. Tian, H. W. Wang, J. S. Wang, M. Wang, K. Yamada, Y. Yamada, Y. Yasuda, K. Yoneda, G. Q. Zhang, T. Motobayashi
The proton-proton momentum correlation functions ($C_{pp}(q)$) for kinematically complete decay channels of $^{23}$Al $\rightarrow$ p + p + $^{21}$Na and $^{22}$Mg $\rightarrow$ p + p + $^{20}$Ne have been measured at the RIKEN RI Beam Factory. From the very different correlation strength of $C_{pp}(q)$ for $^{23}$Al and $^{22}$Mg, the source size and emission time information were extracted from the $C_{pp}(q)$ data by assuming a Gaussian source profile in the correlation function calculation code (CRAB). The results indicated that the mechanism of two-proton emission from $^{23}$Al was mainly sequential emission, while that of $^{22}$Mg was mainly three-body simultaneous emission. By combining our earlier results of the two-proton relative momentum and the opening angle, it is pointed out that the mechanism of two-proton emission could be distinguished clearly.
Y. G. Ma, D. Q. Fang, X. Y. Sun, P. Zhou, Y. Togano, N. Aoi, H. Baba, X. Z. Cai, X. G. Cao, J. G. Chen, Y. Fu, W. Guo, Y. Hara, T. Honda, Z. G. Hu, K. Ieki, Y. Ishibashi, Y. Ito, N. Iwasa, S. Kanno, T. Kawabata, H. Kimura, Y. Kondo, K. Kurita, M. Kurokawa, T. Moriguchi, H. Murakami, H. Ooishi, K. Okada, S. Ota, A. Ozawa, H. Sakurai, S. Shimoura, R. Shioda, E. Takeshita, S. Takeuchi, W. D. Tian, H. W. Wang, J. S. Wang, M. Wang, K. Yamada, Y. Yamada, Y. Yasuda, K. Yoneda, G. Q. Zhang, T. Motobayashi
Two-proton relative momentum ($q_{pp}$) and opening angle ($θ_{pp}$) distributions from the three-body decay of two excited proton-rich nuclei, namely $^{23}$Al $\rightarrow$ p + p + $^{21}$Na and $^{22}$Mg $\rightarrow$ p + p + $^{20}$Ne, have been measured with the projectile fragment separator (RIPS) at the RIKEN RI Beam Factory. An evident peak at $q_{pp}\sim20$ MeV/c as well as a peak in $θ_{pp}$ around 30$^\circ$ are seen in the two-proton break-up channel from a highly-excited $^{22}$Mg. In contrast, such peaks are absent for the $^{23}$Al case. It is concluded that the two-proton emission mechanism of excited $^{22}$Mg is quite different from the $^{23}$Al case, with the former having a favorable diproton emission component at a highly excited state and the latter dominated by the sequential decay process.
Y. Yasuda, T. K. Suzuki, T. Kozasa
May 22, 2019·astro-ph.SR·PDF We develop a magnetohydrodynamical model of Alfvén wave-driven wind in open magnetic flux tubes piercing the stellar surface of Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) stars, and investigate the physical properties of the winds. The model simulations are carried out along the evolutionary tracks of stars with initial mass in the range of 1.5 to 3.0 $M_{\odot}$ and initial metallicity $Z_{\rm ini}$=0.02. The surface magnetic field strength being set to be 1G, we find that the wind during the evolution of star can be classified into the following four types; the first is the wind with the velocity higher than 80 km s$^{-1}$ in the RGB and early AGB (E-AGB) phases; the second is the wind with outflow velocity less than 10 km s$^{-1}$ seen around the tip of RGB or in the E-AGB phase; the third is the unstable wind in the E-AGB and thermally pulsing AGB (TP-AGB) phases; the fourth is the stable massive and slow wind with the mass-loss rate higher than 10$^{-7} M_{\odot}$ yr$^{-1}$ and the outflow velocity lower than 20 km s$^{-1}$ in the TP-AGB phase. The mass-loss rates in the first and second types of wind are two or three orders of magnitude lower than the values evaluated by an empirical formula. The presence of massive and slow wind of the fourth type suggests the possibility that the massive outflow observed in TP-AGB stars could be attributed to the Alfvén wave-driven wind.
T. Kawabata, H. Akimune, H. Fujimura, H. Fujita, Y. Fujita, M. Fujiwara, K. Hara, K. Y. Hara, K. Hatanaka, T. Ishikawa, M. Itoh, J. Kamiya, S. Kishi, M. Nakamura, K. Nakanishi, T. Noro, H. Sakaguchi, Y. Shimbara, H. Takeda, A. Tamii, S. Terashima, H. Toyokawa, M. Uchida, H. Ueno, T. Wakasa, Y. Yasuda, H. P. Yoshida, M. Yosoi
The $^{11}$B($^3$He$, t$), $^{11}$B($d, d'$), and $^{11}$B($p, p'$) reactions were measured at forward scattering angles including $0^\circ$ to study the isovector and isoscalar spin-flip M1 strengths in $^{11}$B. The measured $^{11}$B($^3$He$, t$) cross sections were compared with the results of the distorted-wave impulse-approximation (DWIA) calculation, and the Gamow-Teller (GT) strengths for low-lying states in $^{11}$C were determined. The GT strengths were converted to the isovector spin-flip M1 strengths using the isobaric analog relations under the assumption of the isospin symmetry. The isoscalar spin-flip M1 strengths were obtained from the ($d, d'$) analysis by assuming that the shape of the collective transition form factor with the same $ΔJ^π$ is similar in the $^{11}$B($d, d'$) and $^{12}$C($d, d'$) reactions. The obtained isovector and isoscalar strengths were used in the DWIA calculations for the $^{11}$B($p, p'$) reaction. The DWIA calculation reasonably well explains the present $^{11}$B($p, p'$) result. However, the calculated cross section for the 8.92-MeV 3/2$^-_2$ state was significantly smaller than the experimental values. The transition strengths obtained in the shell-model calculations were found to be 20-50% larger than the experimental strengths. The transition strengths for the neutrino induced reactions were estimated by using the isovector and isoscalar spin-flip M1 strengths. The present results are quantitatively in agreement with the theoretical estimation discussing the axial isoscalar coupling in the neutrino scattering process, and are useful in the measurement of the stellar neutrinos using the neutral- and charged-current reactions on $^{11}$B.
H. J. Ong, I. Tanihata, A. Tamii, T. Myo, K. Ogata, M. Fukuda, K. Hirota, K. Ikeda, D. Ishikawa, T. Kawabata, H. Matsubara, K. Matsuta, M. Mihara, T. Naito, D. Nishimura, Y. Ogawa, H. Okamura, A. Ozawa, D. Y. Pang, H. Sakaguchi, K. Sekiguchi, T. Suzuki, M. Taniguchi, M. Takashina, H. Toki, Y. Yasuda, M. Yosoi, J. Zenihiro
We have measured 16O(p,d) reaction using 198-, 295- and 392-MeV proton beams to search for a direct evidence on the effect of the tensor interactions in light nucleus. Differential cross sections of the one-neutron transfer reactions populating the ground states and several low-lying excited states in 15O were measured. Comparing the ratios of the cross sections for each excited state to the one for the ground state over a wide range of momentum transfer, we found a marked enhancement for the positive-parity state(s). The observation indicates large components of high-momentum neutrons in the initial ground-state configurations, due possibly to the tensor interactions.
T. Kawabata, H. Akimune, H. Fujimura, H. Fujita, Y. Fujita, M. Fujiwara, K. Hara, K. Hatanaka, K. Hosono, T. Ishikawa, M. Itoh, J. Kamiya, M. Nakamura, T. Noro, E. Obayashi, H. Sakaguchi, Y. Shimbara, H. Takeda, T. Taki, A. Tamii, H. Toyokawa, N. Tsukahara, M. Uchida, H. Ueno, T. Wakasa, K. Yamasaki, Y. Yasuda, H. P. Yoshida, M. Yosoi
A windowless and self-supporting ice target is described. An ice sheet with a thickness of 29.7 mg/cm$^2$ cooled by liquid nitrogen was placed at the target position of a magnetic spectrometer and worked stably in the $^{16}$O$(p,p')$ experiment at $E_{p}=392$ MeV. Background-free spectra were obtained.
Y. Shigekawa, K. Sawamura, S. Hashiba, M. Kaneko, Y. Yamakita, R. Masuda, H. Kazama, Y. Yasuda, H. Haba, A. Shinohara, Y. Kasamatsu
The nucleus of uranium-235 ($^{235}$U) possesses an exceptionally low-energy isomeric state, $^{235m}$U. Unlike most radioactive nuclides, whose nuclear-decay half-lives are constant, the half-life of $^{235m}$U varies with its chemical environment$^{1,2}$ owing to interactions with outer-shell electrons in the internal-conversion (IC) process. However, the mechanism underlying this half-life variation, particularly the role of molecular bonding beyond simple electron-density effects$^{1,2}$, remains unresolved. Here, we investigate variations in the half-lives of $^{235m}$U and the corresponding IC-electron energy spectra for uranyl (UO2$^{2+}$) compounds with different halide ligands. The half-lives of $^{235m}$U are measured to be 25.32(4), 26.05(8), 25.84(3), and 25.44(3) min for uranyl fluoride, chloride, bromide, and iodide, respectively, indicating that the half-life increases with increasing ligand electronegativity, with the exception of uranyl fluoride. The shortest half-life observed for uranyl fluoride is attributed to the smallest number of 6p electrons occupying bonding orbitals, as indicated by the IC-electron energy spectra and quantum chemical calculations. This work provides the first observation of a significant variation in a nuclear decay process driven by changes in molecular orbital formation, paving the way toward a deeper understanding of interactions between a nucleus and electrons involved in chemical bonding.
B. K. Nayak, U. Garg, M. Koss, T. Li, E. Martis, H. Fujimura, M. Fujiwara, K. Hara, K. Kawase, K. Nakanishi, E. Obayashi, H. P. Yoshida, M. Itoh, S. Kishi, H. Sakaguchi, M. Uchida, Y. Yasuda, M. Yosoi, R. G. T. Zegers, H. Akimune, M. N. Harakeh, M. Hunyadi
The excitation and subsequent proton decay of the isoscalar giant dipole resonance (ISGDR) in $^{208}$Pb have been investigated via the $^{208}$Pb($α, α^{\prime}p)^{207}$Tl reaction at 400 MeV. Excitation of the ISGDR has been identified by the difference-of-spectra method. The enhancement of the ISGDR strength at high excitation energies observed in the multipole-decomposition-analysis of the singles $^{208}$Pb($α,α^{\prime}$) spectra is not present in the excitation energy spectrum obtained in coincidence measurement. The partial branching ratios for direct proton decay of ISGDR to low-lying states of $^{207}$Tl have been determined and the results are compared with predictions of continuum random-phase-approximation (CRPA) calculations.
Z. H. Yang, F. M. Marqués, N. L. Achouri, D. S. Ahn, T. Aumann, H. Baba, D. Beaumel, M. Böhmer, K. Boretzky, M. Caamaño, S. Chen, N. Chiga, M. L. Cortés, D. Cortina, P. Doornenbal, C. A. Douma, F. Dufter, J. Feng, B. Fernández-Domínguez, Z. Elekes, U. Forsberg, T. Fujino, N. Fukuda, I. Gašparić, Z. Ge, R. Gernhäuser, J. M. Gheller, J. Gibelin, A. Gillibert, B. M. Godoy, Z. Halász, T. Harada, M. N. Harakeh, A. Hirayama, S. W. Huang, N. Inabe, T. Isobe, J. Kahlbow, N. Kalantar-Nayestanaki, D. Kim, S. Kim, M. A. Knösel, T. Kobayashi, Y. Kondo, P. Koseoglou, Y. Kubota, I. Kuti, C. Lehr, P. J. Li, Y. Liu, Y. Maeda, S. Masuoka, M. Matsumoto, J. Mayer, H. Miki, M. Miwa, I. Murray, T. Nakamura, A. Obertelli, N. Orr, H. Otsu, V. Panin, S. Park, M. Parlog, S. Paschalis, M. Potlog, S. Reichert, A. Revel, D. Rossi, A. Saito, M. Sasano, H. Sato, H. Scheit, F. Schindler, T. Shimada, Y. Shimizu, S. Shimoura, I. Stefan, S. Storck, L. Stuhl, H. Suzuki, D. Symochko, H. Takeda, S. Takeuchi, J. Tanaka, Y. Togano, T. Tomai, H. T. Törnqvsit. J. Tscheuschner, T. Uesaka, V. Wagner, K. Wimmer, H. Yamada, B. Yang, L. Yang, Y. Yasuda, K. Yoneda, L. Zanetti, J. Zenihiro
The tetraneutron has been drawing the attention of the nuclear physics community for decades, but a firm conclusion on its existence and properties is still far from being reached despite many experimental and theoretical efforts. New measurements have recently been performed at RIBF with the SAMURAI spectrometer by applying complementary reaction probes, which will help to pin down the properties of this four-neutron system.
M. Hedden, U. Garg, B. Kharraja, S. Zhu, M. Uchida, H. Sakaguchi, T. Murakami, M. Yosoi, H. Takeda, M. Itoh, T. Kawabata, T. Taki, T. Ishikawa, N. Tsukuhara, Y. Yasuda, M. Fujiwara, H. Fujimura, H. P. Yoshida, E. Obayashi, K. Hara, H. Akimune, M. N. Harakeh, M. Volkerts
The isoscalar giant dipole resonance (ISGDR) has been investigated in 208Pb using inelastic scattering of 400 MeV alpha particles at forward angles, including 0deg. Using the superior capabilities of the Grand Raiden spectrometer, it has been possible to obtain spectra devoid of any "instrumental" background. The ISGDR strength distribution has been extracted from a multipole-composition of the observed spectra. The implication of these results on the experimental value of nuclear incompressibility are discussed.
T. Kawabata, H. Akimune, G. P. A. Berg, H. Fujimura, H. Fujita, Y. Fujita, M. Fujiwara, K. Hara, K. Hatanaka, K. Hosono, T. Ishikawa, M. Itoh, J. Kamiya, M. Nakamura, T. Noro, E. Obayashi, H. Sakaguchi, Y. Shimbara, H. Takeda, T. Taki, A. Tamii, H. Toyokawa, M. Uchida, H. Ueno, T. Wakasa, K. Yamasaki, Y. Yasuda, H. P. Yoshida, M. Yosoi
Cross sections and polarization transfer observables in the $^{16}$O$(p,p')$ reactions at 392 MeV were measured at several angles between $θ_{lab}=$ 0$^\circ$ and 14$^\circ$. The non-spin-flip ($ΔS=0$) and spin-flip ($ΔS=1$) strengths in transitions to several discrete states and broad resonances in $^{16}$O were extracted using a model-independent method. The giant resonances in the energy region of $E_x=19-$27 MeV were found to be predominantly excited by $ΔL=1$ transitions. The strength distribution of spin-dipole transitions with $ΔS=1$ and $ΔL=1$ were deduced. The obtained distribution was compared with a recent shell model calculation. Experimental results are reasonably explained by distorted-wave impulse approximation calculations with the shell model wave functions.
B. K. Nayak, U. Garg, M. Hedden, M. Koss, T. Li, Y. Liu, P. V. Madhusudhana Rao, S. Zhu, M. Itoh, H. Sakaguchi, H. Takeda, M. Uchida, Y. Yasuda, M. Yosoi, H. Fujimura, M. Fujiwara, K. Hara, T. Kawabata, H. Akimune, M. N. Harakeh
The strength distribution of the isoscalar giant dipole resonance (ISGDR) in $^{58}$Ni has been obtained over the energy range 10.5--49.5 MeV via extreme forward angle scattering (including 0$^{\circ}$) of 386 MeV $α$ particles. We observe a ``bi-modal'' ${E1}$ strength distribution for the first time in an A $<$ 90 nucleus. The observed ISGDR strength distribution is in good agreement with the predictions of a recent QRPA calculation.