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Journal Articles

Effects of the nuclear structure of fission fragments on the high-energy prompt fission $$gamma$$-ray spectrum in $$^{235}$$U($$n_{rm th},f$$)

Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, R.; L$'e$guillon, R.; Ogawa, Tatsuhiko; Soldner, T.*; K$"o$ster, U.*; Pollitt, A.*; Hambsch, F.-J.*; et al.

Physical Review C, 100(4), p.044610_1 - 044610_7, 2019/10

 Times Cited Count:6 Percentile:76.03(Physics, Nuclear)

Journal Articles

A New detector system for the measurement of high-energy prompt $$gamma$$-rays for low-energy neutron induced fission

Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, R.; L$'e$guillon, R.*; Ogawa, Tatsuhiko; Soldner, T.*; Hambsch, F.-J.*; A$"i$che, M.*; Astier, A.*; et al.

Nuclear Instruments and Methods in Physics Research A, 906, p.88 - 96, 2018/10

 Times Cited Count:3 Percentile:45.99(Instruments & Instrumentation)

We have developed a new setup to measure prompt fission $$gamma$$-ray spectra in neutron induced fission up to energies sufficient to reveal the structure associated with giant dipole resonances of fission fragments. The setup consists of multi-wire proportional counters, to detect both fission fragments in coincidence, and two large volume (101.6 mm in diameter and 127.0 mm in length) LaBr$$_{3}$$(Ce) scintillators, to measure the $$gamma$$-rays. The setup was used to obtain the prompt fission $$gamma$$-ray spectrum for thermal neutron induced fission of $$^{235}$$U at the PF1B cold-neutron beam facility of the Institut Laue-Langevin, Grenoble, France. We have successfully measured the $$gamma$$-ray spectrum up to energies of about 20 MeV, what extends the currently known $$gamma$$-ray spectrum limit to higher energies by approximately a factor of two.

Journal Articles

Measurement of high-energy prompt $$gamma$$-rays from neutron induced fission of U-235

Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, R.; L$'e$guillon, R.; Ogawa, Tatsuhiko; Soldner, T.*; Hambsch, F.-J.*; Astier, A.*; Pollitt, A.*; et al.

EPJ Web of Conferences, 146, p.04036_1 - 04036_4, 2017/09

 Times Cited Count:3 Percentile:92.06

The measurement of the prompt fission $$gamma$$-ray spectrum (PFGS) is quite important to study the de-excitation process of neutron-rich fission fragments as well as to generate data required to design a generation-IV reactors. The PFGS measured for spontaneous fission of $$^{252}$$Cf shows a broad hump at energies more than 8 MeV. This is interpreted as a giant dipole resonance (GDR) of the fragments centered around 15 MeV. To understand how the GDR is populated in the fission process, one needs to measure the PFGS for the reactions with the mass yields different from the spontaneous fission of $$^{252}$$Cf, such as (n,f). The measurements of the PFGS for (n,f), however, are limited less than 9 MeV even in the recent experiment. This prompts us to make a new measurement to extend the know PFGS up to 20 MeV. The measurement has been carried out at the PF1B beam line of Institut Laue-Langevin. In this contribution we will present the results obtained the measurement.

Journal Articles

Magnetic excitations in overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$

Wakimoto, Shuichi; Yamada, Kazuyoshi*; Tranquada, J. M.*; Frost, C. D.*; Swainson, I.*; Birgeneau, R. J.*

Physica C, 460-462(1), p.166 - 169, 2007/09

 Times Cited Count:1 Percentile:7.1(Physics, Applied)

Spin excitations of overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ ($$0.25 leq x leq 0.30$$) have been studied by neutron scattering utilizing triple-axis and time-of-flight spectrometers. Low-energy excitation spectra ($$omega leq 10$$ $$sim$$meV) for all of the superconducting samples show a maximum around $$omega = 6$$ meV with a maximum value of dynamic spin susceptibility $$chi''(omega)$$ that decreases linearly with ${it T$_{rm c}$}$ as doping increases. The magnetic scattering cross section finally disappears at $$x=0.30$$, coincident with the disappearance of bulk superconductivity. Time-of-flight measurements for $$x=0.25$$ and $$0.30$$ shows markedly suppressed magnetic scattering intensities at intermediate energies (20$$leq$$$$omega$$$$leq$$80$$sim$$meV) in contrast to those of the stripe-ordered La$$_{1.875}$$Ba$$_{0.125}$$CuO$$_{4}$$. These facts imply a cooperative correlation between the dynamic incommensurate state and the superconductivity.

Journal Articles

Disappearance of antiferromagnetic spin excitations in overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$

Wakimoto, Shuichi; Yamada, Kazuyoshi*; Tranquada, J. M.*; Frost, C. D.*; Birgeneau, R. J.*; Zhang, H.*

Physical Review Letters, 98(24), p.247003_1 - 247003_4, 2007/06

 Times Cited Count:80 Percentile:91.81(Physics, Multidisciplinary)

Magnetic excitations for energies up to $$sim100$$ meV are studied for over-doped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ with $$x=0.25$$ and $$0.30$$, using time-of-flight neutron spectroscopy. Comparison of spectra integrated over the width of an antiferromagnetic Brillouin zone demonstrates that the magnetic scattering at intermediate energies,$$20 leq omega leq 100$$ meV, progressively decreases with over-doping. This strongly suggests that the magnetism is not related to Fermi surface nesting, but rather is associated with a decreasing volume fraction of (probably fluctuating) antiferromagnetic bubbles.

Oral presentation

Spin Excitations of overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$

Wakimoto, Shuichi; Birgeneau, R. J.*; Frost, C. D.*; Kagedan, A.*; Kim, H.*; Swainson, I.*; Tranquada, J. M.*; Yamada, Kazuyoshi*; Zhang, H.*

no journal, , 

Spin excitations of LSCO in the overdoped regime has been studied by neutron scattering. Incommensurate excitations around 6 meV which are clearly observed in the $$x=0.25$$ sample decrease with $$T_c$$ as doping increases, and finally, become unobservable at $$x=0.30$$ coincidentally with the disappearance of bulk superconductivity. High-energy measurements performed at the MAPS spectrometer show remarkably weakened magnetic excitations of the overdoped samples also in the high energy region. These observations are apparently consistent with a microscopic phase separation of the overdoped samples into the superconducting and Fermi liquid phases based on muSR results. In contrast, magnetization measurements of overdoped LSCO with and without Zn impurities have revealed that the superconductivity vanishes in the overdoped regime as a result of a competition between the superconductivity and paramagnetism which is induced even in the Zn-free overdoped LSCO.

Oral presentation

Neutron scattering study of magnetic excitations in overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$

Wakimoto, Shuichi; Yamada, Kazuyoshi*; Tranquada, J. M.*; Frost, C. D.*; Birgeneau, R. J.*; Zhang, H.*

no journal, , 

Neutron scattering experiments have been performed on the overdoped La$$_{2-x}$$Sr$$_{x}$$CuO$$_{4}$$ ($$0.25 leq x leq 0.30$$). Low energy magnetic excitations ($$omega leq 10$$ meV) show incommensurate peaks for the superconducting samples with a maximum at $$sim 6$$ meV in the energy spectrum. As doping increases, the maximum of the dynamic susceptibility decreases linearly with $$T_c$$ and, finally, the low energy excitations become unobservable at $$x=0.30$$ coincidentally with the disappearance of bulk superconductivity. Time-of-flight measurements revealed that magnetic excitations for $$x=0.25$$ are markedly suppressed in the intermediate energy range ($$20 leq omega leq 80$$ meV), which is apparently consistent with a microscopic phase separation into a superconducting region which retains the antiferromagnetic correlations and a Fermi liquid region which has no magnetic correlations.

Oral presentation

Spin fluctuation and its anisotropy in La$$_{2-x}$$(Sr,Ba)$$_{x}$$CuO$$_{4}$$

Wakimoto, Shuichi; Fujita, Masaki*; Gu, G.*; Kakurai, Kazuhisa; Matsuda, Masaaki; Takeda, Masayasu; Tranquada, J. M.*; Yamada, Kazuyoshi*; Birgeneau, R. J.*; Frost, C. D.*

no journal, , 

To study effects of the stripe structure to the magnetic excitations in the high-$$T_c$$ cuprates, we have performed polarized neutron scattering study on La$$_{1.875}$$Ba$$_{0.125}$$CuO$$_{4}$$ and La$$_{1.92}$$Sr$$_{0.08}$$CuO$$_{4}$$. The former shows robust stripe order whereas the latter has only weak order of stripes. The former shows spin fluctuations which are confined in the CuO$$_2$$ plane, correspondingly to the confinement of the ordered spins in the plane. The latter shows nearly isotropic spin fluctuations. These observations imply that the low-energy spin excitations are strongly affected by the stripe order, which is important to understand the origin of the universal magnetic dispersion in the high-$$T_c$$ cuprates.

Oral presentation

Measurement of high energy $$gamma$$-ray spectrum accompanied by neutron induced fission of $$^{235}$$U

Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, R.; Ogawa, Tatsuhiko; Soldner, T.*; Hambsch, F.-J.*; Frost, R.*; Tsekhanovich, I.*; Petrache, C. M.*

no journal, , 

The Japanese government has a plan to remove the melted reactor fuel for the full deconstruction of Fukushima I Nuclear Power Plants. The removal of the fuel must be carried out without reaching the criticality of the fuel. However, it is quite difficult to monitor the increased fission rate due to the background $$gamma$$-rays from the fission products in the fuel. Here we are proposing to develop a system based on the use of the high energy $$gamma$$-rays accompanied by fission. In order to design the system, it is essential to know the spectrum of prompt fission $$gamma$$-rays up to more than 7 MeV for $$^{235}$$U(n,f) reaction. However, no data are available in the $$gamma$$-ray energy range larger than 7 MeV. This prompted us to make a new measurement to extend the known prompt $$gamma$$-ray energy spectrum up to 20 MeV. The measurement has been carried out at the PF1b beam line of the Institut Laue-Langevin. In this contribution, we will present the results obtained the measurement.

Oral presentation

Measurement of high energy $$gamma$$-ray spectrum accompanied by neutron induced fission of $$^{235}$$U, 2

Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, R.; Ogawa, Tatsuhiko; Soldner, T.*; Hambsch, F.-J.*; Frost, R.*; Tsekhanovich, I.*; Petrache, C. M.*

no journal, , 

The Japanese government has a plan to remove the melted reactor fuel for the full deconstruction of Fukushima I Nuclear Power Plants. The removal of the fuel must be carried out without reaching the criticality of the fuel. However, it is quite difficult to monitor the increased fission rate due to the background $$gamma$$-rays from the fission products in the fuel. Here we are proposing to develop a system based on the use of the high energy $$gamma$$-rays accompanied by fission. In order to design the system, it is essential to know the spectrum of prompt fission $$gamma$$-rays up to more than 7 MeV for $$^{235}$$U(n,f) reaction. However, no data are available in the $$gamma$$-ray energy range larger than 7 MeV. This prompted us to make a new measurement to extend the known prompt $$gamma$$-ray energy spectrum up to 20 MeV. The measurement has been carried out at the PF1b beam line of the Institut Laue-Langevin. In this contribution, we will present the results obtained the measurement.

Oral presentation

Measurement of high-energy prompt fission $$gamma$$-rays from neutron induced fission of $$^{235}$$U

Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, R.; L$'e$guillon, R.; Ogawa, Tatsuhiko; Soldner, T.*; Hambsch, F.-J.*; A$"i$che, M.*; Astier, A.*; et al.

no journal, , 

The Japanese government has a plan to remove the fuel debirs for the full deconstruction of Fukushima I Nuclear Power Plants. The fuel debris must be removed without reaching criticality. However, it is difficult to monitor the fission rate due to the background $$gamma$$ rays coming from long-lived fission products. We are proposing to develop a system based on the use of the high-energy prompt fission $$gamma$$ rays, whose energies are high enough to be separated from the background. To design the system, it is essential to know the spectrum of prompt fission $$gamma$$ rays up to more than 7 MeV for $$^{235}$$U($$n, f$$). So far, no data are available in the $$gamma$$-ray energy range larger than 7 MeV. This prompted us to make a new measurement to extend the $$gamma$$-ray spectrum limit to higher energies. The measurement has been carried out at the PF1b cold-neutron beam facility of the Institut Laue-Langevin. In this contribution we will present the results obtained the measurement.

Oral presentation

Measurement of high-energy prompt fission $$gamma$$ rays in $$^{235}$$U(n$$_{th}$$,f)

Ogawa, Tatsuhiko; Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, R.; L$'e$guillon, R.*; Soldner, T.*; Hambsch, F.-J.*; A$"i$che, M.*; Astier, A.*; et al.

no journal, , 

Measurement of $$gamma$$-rays emitted from fission of actinide has been conducted for radiation transport analysis in reactors, safety of spent fuel, and fundamental nuclear physics. In earlier studies, $$gamma$$-rays up to 8 MeV were measured because they are those emitted by fission fragments at excited states. According to some theoretical studies, however, some fission fragments have excitation energy up to 20 MeV and they emit $$gamma$$-rays above 8 MeV. In this study, the $$gamma$$-rays produced by fission of $$^{235}$$U induced by thermal neutrons were measured with LaBr scintillators at the high-flux reactor in the Institut Laue Langevin. The obtained $$gamma$$-ray spectrum agreed with the earlier measurement below 8 MeV, forms a bump above 10 MeV, and smoothly continued up to 20 MeV. The measurement in this study clarified the $$gamma$$-ray energy spectrum attributed to fission reactions up to 20 MeV in case of $$^{235}$$U(n$$_{th}$$,f).

Oral presentation

Measurement of high-energy prompt fission $$gamma$$ rays in $$^{235}$$U(n$$_{th}$$,f)

Ogawa, Tatsuhiko; Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, R.; L$'e$guillon, R.*; Soldner, T.*; Hambsch, F.-J.*; A$"i$che, M.*; Astier, A.*; et al.

no journal, , 

Measurement of $$gamma$$-rays emitted from fission of actinide has been conducted for radiation transport analysis in reactors, safety of spent fuel, and fundamental nuclear physics. In earlier studies, $$gamma$$-rays up to 8 MeV were measured because they are those emitted by fission fragments at excited states. According to some theoretical studies, however, some fission fragments have excitation energy up to 20 MeV and they emit $$gamma$$-rays above 8 MeV. In this study, the $$gamma$$-rays produced by fission of $$^{235}$$U induced by thermal neutrons were measured with LaBr scintillators at the high-flux reactor in the Institut Laue Langevin. The obtained $$gamma$$-ray spectrum agreed with the earlier measurement below 8 MeV, forms a bump above 10 MeV, and smoothly continued up to 20 MeV. The measurement in this study clarified the $$gamma$$-ray energy spectrum attributed to fission reactions up to 20 MeV in case of $$^{235}$$U(n$$_{th}$$,f).

Oral presentation

Measurement of high-energy prompt fission $$gamma$$-ray emission in $$^{235}$$U ($$n_{rm th},f$$)

Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, R.; L$'e$guillon, R.*; Ogawa, Tatsuhiko; Soldner, T.*; K$"o$ster, U.*; Hambsch, F.-J.*; Kawano, Toshihiko*; et al.

no journal, , 

Oral presentation

Measurements of prompt fission $$gamma$$ rays in $$^{235}$$U(n$$_{th}$$,f)

Makii, Hiroyuki; Nishio, Katsuhisa; Hirose, Kentaro; Orlandi, R.; Leguillon, R.*; Ogawa, Tatsuhiko; Soldner, T.*; Hambsch, F.-J.*; Frost, R. J. W.*; Tsekhanovich, I.*; et al.

no journal, , 

We have measured $$gamma$$ rays accompanied by the $$^{235}$$U(n$$_{th}$$,f) reaction in the $$gamma$$-ray energy region up to about 20 MeV at the PF1b cold-neutron beam facility of the Institut Laue-Langevin (ILL), Grenoble, France. The obtained spectra exhibit local bump structures. The origins of these bump structures will be discussed using statistical model calculations.

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