Bulletin of the American Physical Society
4th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 59, Number 10
Tuesday–Saturday, October 7–11, 2014; Waikoloa, Hawaii
Session 1WH: Applications of Nuclear Reactions with Gamma-rays and Surrogates for Neutrons |
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Chair: Calvin Howell, Duke University Room: Kona 2 |
Tuesday, October 7, 2014 9:00AM - 9:30AM |
1WH.00001: The Science of Nuclear Materials Detection using gamma-ray beams: Nuclear Resonance Fluorescence Invited Speaker: Hideaki Ohgaki An atomic nucleus is excited by absorption of incident photons with an energy the same as the excitation energy of the level, and subsequently a gamma-ray is emitted as it de-excites. This phenomenon is called Nuclear Resonance Fluorescence and mostly used for studies on Nuclear Physics field. By measuring the NRF gamma-rays, we can identify nuclear species in any materials because the energies of the NRF gamma-rays uniquely depend on the nuclear species. For example, $^{\mathrm{235}}$U has an excitation level at 1733~keV. If we irradiate a material including $^{235}$U with a gamma-ray tuned at this excitation level, the material absorbs the gamma-ray and re-emits another gamma-ray immediately to move back towards the ground state. Therefore we can detect the $^{\mathrm{235}}$U by measuring the re-emitted (NRF) gamma-rays. Several inspection methods using gamma-rays, which can penetrate a thick shielding have been proposed and examined. Bertozzi and Ledoux have proposed an application of nuclear resonance fluorescence (NRF) by using bremsstrahlung radiations. However the signal-to-noise (SN) ratio of the NRF measurement with the bremsstrahlung radiation is, in general, low. Only a part of the incident photons makes NRF with a narrow resonant band (meV-eV) whereas most of incident radiation is scattered by atomic processes in which the reaction rate is higher than that of NRF by several orders of magnitudes and causes a background. Thus, the NRF with a gamma-ray quasi-monochromatic radiation beam is proposed. The monochromatic gamma-rays are generated by using laser Compton scattering (LCS) of electrons and intense laser photons by putting a collimator to restrict the gamma-ray divergence downstream. The LCS gamma-ray, which is energy-tunable and monochromatic, is an optimum apparatus for NRF measurements We have been conducted NRF experiment for nuclear research, especially with high linear polarized gamma-ray generated by LCS, to survey the distribution of M1 strength in MeV region in LCS facility in AIST, Japan. As well, 1-D, 2-D isotope imaging by using LCS gamma-ray and NRF has been conducted. Since 2009 we have started a development of a non-destructive inspection system under the MEXT program in Japan. Series of experiments of the developing system have been conducted in HIGS facility in Duke University and JAEA Kansai Photon Science Institute. We will report on the recent result of these experiments in the workshop. [Preview Abstract] |
Tuesday, October 7, 2014 9:30AM - 10:00AM |
1WH.00002: Next Generation Laser-Compton Gamma-ray Beam Facilities Invited Speaker: Ying Wu Since late 1970s, laser driven Compton gamma-ray beam facilities have been developed, contradicted and operated around the world for basic science research in nuclear physics and astrophysics, and for applied research in the areas of national security and industrial applications. Currently, TUNL's High Intensity Gamma-ray Source (HIGS) located at Duke University campus is the most intense Compton gamma-ray beam facility dedicated for scientific research. Driven by a high power storage ring Free-Electron Laser (FEL), HIGS produces nearly monochromatic, highly polarized gamma-ray beams from 1 to 100 MeV, with its peak performance of total flux up to few 1E10 g/s and a spectral flux of more than 1E3 g/s/eV in the few MeV to 10 MeV region. The next generation Compton gamma-ray sources will be developed using advanced laser technologies. This talk will provide an overview of new Compton gamma-beam projects, including the ELI-NP (Extreme Light Infrastructure - Nuclear Physics) project in Romania and the HIGS upgrade project - HIGS2. [Preview Abstract] |
Tuesday, October 7, 2014 10:00AM - 10:30AM |
1WH.00003: Applications Using High Flux LCS gamma-ray Beams: Nuclear Security and Contributions to Fukushima Invited Speaker: Mamoru Fujiwara Nuclear nonproliferation and security are an important issue for the peaceful use of nuclear energy. Many countries now collaborate together for preventing serious accidents from nuclear terrorism. Detection of hidden long-lived radioisotopes and fissionable nuclides in a non-destructive manner is useful for nuclear safeguards and management of nuclear wastes as well as nuclear security. After introducing the present situation concerning the nuclear nonproliferation and security in Japan, we plan to show the present activities of JAEA to detect the hidden nuclear materials by means of the nuclear resonance fluorescence with energy-tunable, monochromatic gamma-rays generated by Laser Compton Scattering (LCS) with an electron beam. The energy recovery linac (ERL) machine is now under development with the KEK-JAEA collaboration for realizing the new generation of gamma-ray sources. The detection technologies of nuclear materials are currently developed using the existing electron beam facilities at Duke University and at NewSubaru. These developments in Japan will contribute to the nuclear security program in Japan and to the assay of melted nuclear fuels in the Fukushima Daiichi nuclear power plants. [Preview Abstract] |
Tuesday, October 7, 2014 10:30AM - 11:00AM |
1WH.00004: COFFEE BREAK |
Tuesday, October 7, 2014 11:00AM - 11:30AM |
1WH.00005: Theory \& Modeling for Surrogate Reactions Invited Speaker: Jutta Escher Obtaining reliable cross sections for reactions involving unstable nuclei remains a formidable task, and direct measurements have to be complemented by theoretical predictions and indirect methods. Indirect approaches come with their own challenges, as experimental observables have to be related to the quantity of interest. The surrogate method, for instance, aims at determining cross sections for compound-nuclear reactions on unstable targets by producing the compound nucleus via an alternative (transfer or inelastic scattering) reaction and observing the subsequent decay via $\gamma$ emission, particle evaporation, or fission. A complete theoretical treatment involves integrating descriptions of direct and compound-nucleus reactions, including modeling of compound-nuclear decays. This presentation will give an outline of the surrogate approach and the challenges involved in extracting cross sections from the measurements. Progress made in understanding and describing the nuclear processes involved in a surrogate reaction will be discussed, and applications to neutron-induced fission, neutron capture, and (n,2n) reaction will be presented. Open questions and prospects will be considered. [Preview Abstract] |
Tuesday, October 7, 2014 11:30AM - 12:00PM |
1WH.00006: Recent Experimental Progress on Surrogate Reactions Invited Speaker: Cornelius Beausang Reactions on unstable nuclei are important in a wide variety of nuclear physics scenarios. Cross sections for neutron (or light charged particle) induced reactions on target nuclei spanning the chart of the nuclei are important for nuclear astrophysics (r-process, s-process rp- and p-processes etc.), for nuclear energy generation and for national security applications. Many such reactions occur on short-lived unstable nuclei. Even with the present generation of radioactive beam facilities, many such reactions are difficult, if not impossible, to measure directly. For these reactions, often the surrogate reaction technique provides the only option to provide some experimental guidance for the calculations. The experimental and theoretical techniques required are described in some detail in the recent review article by Escher et al. [1]. Originally introduced in the 1970's [2,3] the last decade has seen a resurgence of interest in the surrogate technique [1]. Various ratio techniques, external, internal and hybrid, have been developed to minimize the effect of target contamination. In the actinide region, a large number of surrogate (n,f) cross sections have been measured. In general, these show agreement to within 5-10{\%}, with directly measured (n,f) data where these data exist (benchmarking), for equivalent neutron energies ranging from $\sim$ 100 keV up to tens of MeV. For (n,$\gamma )$ reactions, measurements have been attempted for select nuclei in various mass regions (A $\sim$ 90, 150 and 235) and for these the agreement with directly measured data is less good. The various experimental techniques employed will be described as well as the current state of the experimental data. Some future directions will be described. \\[4pt] [1] J.E. Escher et al., Reviews of Modern Physics 84, 353, (2012) and references therein. \\[0pt] [2] J.D. Cramer and H.C. Britt, Nucl. Sci. Eng. 41, 177 (1970) and Phys. Rev. C 2, 2350 (1970). \\[0pt] [3] H.C. Britt and J.B. Wilhelmy Nucl. Sci. Eng. 72, 222, (1979). [Preview Abstract] |
Tuesday, October 7, 2014 12:00PM - 12:30PM |
1WH.00007: Fission data by surrogate reactions Invited Speaker: Kentaro Hirose A project of the fission data measurement for actinides (fragment mass distribution, cross sections and neutron multiplicities) using multi-nucleon transfer reactions is running at Japan Atomic Energy Agency (JAEA). Actinide targets such as $^{238}$U and $^{232}$Th were irradiated with $^{18}$O beam and fission induced by a nucleon transfer was observed. The experiment was performed at the tandem accelerator facility of Japan Atomic Energy Agency. A target of $^{232}$Th ($\sim150~\mu$g/cm$^2$) and $^{238}$U ($\sim80 \mu$g/cm$^2$) deposited on a 100-$\mu$g/cm$^2$ thick nickel foil was bombarded with 157.7 MeV $^{18}$O beam. The scattered projectile-like nuclei were detected by a segmented $\Delta$E-E silicon telescope located at the forward angle with respect to the beam. The thicknesses of $\Delta$E and E detector are 75 $\mu$m and 300 $\mu$m, respectively. From the scattered particle, the compound nucleus was identified. Fission fragments by multi-nucleon transfer fission were detected in coincidence using four multi-wire proportional counters (MWPCs) located at 45 and 135 degree with a distance of 224 mm from the target. Around the reaction chamber, 12 liquid scintillators were placed to detect the fission neutrons. Mass split of each fission event was determined using the mass and momentum conservation. We obtained the mass distributions for $^{239, 240}$U, $^{239-242}$Np and $^{241-243}$Pu using the $^{238}$U target and for $^{232-234}$Th, $^{233-236}$Pa and $^{237}$U using the $^{232}$Th target. As well as the fission fragment mass distribution, fission cross sections by the surrogate ratio method and the fission neutron multiplicities will also be shown in the conference. [Preview Abstract] |
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