Research Center For Nuclear Physics Research Articles

Effects of repulsive three-body force in 12C + 12C scattering at 100A MeV

The angular distribution of 12C + 12C scattering at an incident energy of 100A MeV has been measured. The elastic and inelastic scatterings in 12C to the excitation energies of up to ∼45 MeV were measured simultaneously for the first time with the high-resolution Grand Raiden spectrometer at the Research Center for Nuclear Physics (RCNP). The angular distributions of the elastic scattering to the ground state (01+) and inelastic scattering to the 4.44 MeV (21+) excited state were precisely obtained in the angular range of 1.0°–7.5° with a step of 0.1°. Additionally, the angular distribution was obtained for the sum of the cross sections for excitation energies above the 4.44 MeV state up to 11 MeV, which includes the 7.65 MeV (02+), 9.64 MeV (31−), and 10.30 MeV (22+) states, in addition to probably the simultaneous excitation of the 4.44 MeV state in the projectile and the target nuclei. Those combined data provide a means to study the effects of channel coupling on the elastic cross section. The observed angular distributions are compared with theoretical calculations based on three double-folding models with complex G-matrix interactions, the CEG07b, MPa, and ESC models. The importance of three-body repulsive forces included in the CEG07b and MPa models will be discussed.

Real Time Conference 2014 Overview

This article presents an overview of the 19th Real Time Conference held last May 26-30, 2014, at the Nara Prefectural New Public Hall, Nara, Japan, organized by the Research Center for Nuclear Physics of the Osaka University. The program included many invited talks and oral sessions offering an extensive overview on the following topics: real-time system architectures, intelligent signal processing, fast data transfer links and networks, trigger systems, data acquisition, processing-farms, control, monitoring and test systems, emerging real-time technologies, new standards, real-time safety and security, and some feedback on experiences. In parallel to the oral and poster presentations, industrial exhibits by companies, workshops and short courses also ran through the week.

Performance of a new Electron-Tracking Compton Camera under intense radiations from a water target irradiated with a proton beam

We have developed an electron-tracking Compton camera (ETCC) for use in next-generation MeV gamma ray telescopes. An ETCC consists of a gaseous time projection chamber (TPC) and pixel scintillator arrays (PSAs). Since the TPC measures the three dimensional tracks of Compton-recoil electrons, the ETCC can completely reconstruct the incident gamma rays. Moreover, the ETCC demonstrates efficient background rejection power in Compton-kinematics tests, identifies particle from the energy deposit rate (dE/dX) registered in the TPC, and provides high quality imaging by completely reconstructing the Compton scattering process. We are planning the ``Sub-MeV gamma ray Imaging Loaded-on-balloon Experiment'' (SMILE) for our proposed all-sky survey satellite. Performance tests of a mid-sized (30 cm)3 ETCC, constructed for observing the Crab nebula, are ongoing. However, observations at balloon altitudes or satellite orbits are obstructed by radiation background from the atmosphere and the detector itself [1]. The background rejection power was checked using proton accelerator experiments conducted at the Research Center for Nuclear Physics, Osaka University. To create the intense radiation fields encountered in space, which comprise gamma rays, neutrons, protons, and other energetic entities, we irradiated a water target with a 140 MeV proton beam and placed a SMILE-II ETCC near the target. In this situation, the counting rate was five times than that expected at the balloon altitude. Nonetheless, the ETCC stably operated and identified particles sufficiently to obtain a clear gamma ray image of the checking source. Here, we report the performance of our detector and demonstrate its effective background rejection based in electron tracking experiments.

Effect of tensor interactions in 16O studied via (p,d) reaction

The differential cross sections of the 16O(p,d) reaction populating the ground state and several low-lying excited states in 15O were measured using 198-, 295- and 392-MeV proton beams at the Research Center for Nuclear Physics (RCNP), Osaka University, to study the effect of the tensor interactions in 16O. Dividing the cross sections for each excited state by the one for the ground state and comparing the ratios over a wide range of momentum transfer, we found a marked enhancement of the ratio for the positive-parity state(s). The observation is consistent with large components of high-momentum neutrons in the ground-state configurations of 16O due possibly to the tensor interactions.

Spin-Ml and El responses of nuclei probed by proton inelastic scattering

We pick up two studies on the nuclear responses from the recent experiments of high-resolution proton inelastic scattering at the Research Center for Nuclear Physics, Osaka University; 1) study of the nuclear symmetry and the neutron skin thickness by the measurement of energy electric dipole (El) response of 208Pb, and 2) study of the tensor correlation in the ground state by the measurement of the spin-Ml responses of even-even self-conjugate nuclei in the sd-shell nuclei.

大阪大学核物理研究センター・AVF サイクロトロン棟の耐震改修工事に伴う放射線管理区域境界の変更とサイクロトロン用放射線管理インターロックシステムの更新

大阪大学核物理研究センター・AVF サイクロトロン棟の耐震改修工事に伴う放射線管理区域境界の変更とサイクロトロン用放射線管理インターロックシステムの更新

Measurements of Cross Sections for Neutron-induced Reactions on Chromium and Yttrium Targets at 197 MeV

Reaction cross sections for Cr and Y induced by neutrons at 197 MeV were measured by using 7Li(p,n) reaction at N0 beam line in the Research Center for Nuclear Physics (RCNP), Osaka University. To estimate quasi-monoenergetic neutron cross sections, Cr and Y samples were irradiated on the two angles of 0∘ and 25∘ relative to the axis of the primary proton beam. The measured cross section data in the natCr(n,x) and 89Y(n,x) reactions are compared to the JENDL high-energy file and the literature proton values, respectively. The results obtained are also compared to the cross section data for the same target materials with 287 and 386 MeV neutrons in our previous work.

Studies of extraction and transport system for highly charged ion beam of 18 GHz superconducting electron cyclotron resonance ion source at Research Center for Nuclear Physics

An 18 GHz superconducting electron cyclotron resonance ion source is installed to increase beam currents and to extend the variety of ions especially for highly charged heavy ions which can be accelerated by cyclotrons of Research Center for Nuclear Physics (RCNP), Osaka University. The beam production developments of several ions from B to Xe have been already done [T. Yorita, K. Hatanaka, M. Fukuda, M. Kibayashi, S. Morinobu, H.Okamura, and A. Tamii, Rev. Sci. Instrum. 79, 02A311 (2008) and T. Yorita, K. Hatanaka, M. Fukuda, M. Kibayashi, S. Morinobu, H.Okamura, and A. Tamii, Rev. Sci. Instrum. 81, 02A332 (2010)] and the further studies for those beam extraction and its transport have been done in order to increase the beam current more. The plasma electrode, extraction electrode, and einzel lens are modified. Especially extraction electrode can be applied minus voltage for the beam extraction and it works well to improve the extracted beam current. The extraction voltage dependences of transmission and emittance also have been studied for beam current improvement which is injected into azimuthally varying field cyclotron at RCNP.

Evidence of tensor interactions in16O observed via (p,d) reaction

We measured the differential cross sections of the 16 O(p,d) reaction populating the ground state and several low-lying excited states in 15 O using 198-, 295- and 392-MeV proton beams at the Research Center for Nuclear Physics (RCNP), Osaka University, to study the effect of the tensor interactions in 16 O. Dividing the cross sections for each excited state by the one for the ground state and comparing the ratios over a wide range of momentum transfer, we found a marked enhancement of the ratio for the positive-parity state(s). The observation is consistent with large components of high-momentum neutrons in the ground-state configurations of 16 O due possibly to the tensor interactions.

Neutron Dosimetry in Quasi-Monoenergetic Fields of 244 and 387 MeV

This paper describes the results of neutron spectrometry and dose measurements using a Bonner Sphere Spectrometer (BSS) at the ring cyclotron facility of the Research Center for Nuclear Physics (RCNP), Osaka University, Japan. Quasi-monoenergetic neutron fields were generated using the 7Li (p,n)7Be reaction and 246 and 389 MeV protons. Neutrons produced at 0° and 30° emission angles were extracted into a time-of-flight (TOF) tunnel, and the energy spectra were measured at a distance of 35 m from the target. To deduce the corresponding neutron spectra from thermal to the nominal maximum energy, the BSS data were unfolded using the MSANDB code and response functions were calculated by Monte Carlo (MC) methods. These spectra are compared to spectral measurements using NE213 organic liquid scintillators applying the TOF method. The results are discussed in terms of ambient dose equivalent H* (10) and compared with the readings of other instruments operated during the experiment.

High-resolution study of Gamow-Teller transitions in the47Ti(3He,t)47V reaction

In this work we have studied ${T}_{z}=+2\ensuremath{\rightarrow}+1$, Gamow-Teller (GT) transitions in the $^{48}\mathrm{Ti}(^{3}\mathrm{He},t)^{48}\mathrm{V}$ charge-exchange reaction at 140 MeV/nucleon and ${0}^{\ensuremath{\circ}}$ at the Research Center for Nuclear Physics, Osaka. From the high-resolution facility, consisting of a high-dispersion beamline and the Grand Raiden spectrometer, the spectrum had an energy resolution of 21 keV, among the best achieved. Individual GT transitions were observed and GT strength was derived for each state populated up to an excitation energy of 12 MeV. The total sum of the $B$(GT) strength observed in discrete states was 4.0, which is 33% of the sum-rule-limit value of 12. The results were compared with the results of shell-model calculations carried out with the GXPF1J interaction. The measured $B$(GT) distribution was also compared with that obtained in the $(^{3}\mathrm{He},t)$ charge-exchange reaction on $^{47}\mathrm{Ti}$. On the assumption of isospin symmetry the $\ensuremath{\beta}$ spectrum of the ${T}_{z}=\ensuremath{-}2$ nucleus $^{48}\mathrm{Fe}$ was deduced from the observed spectrum in the $^{48}\mathrm{Ti}(^{3}\mathrm{He},t)^{48}\mathrm{V}$ reaction and this predicted spectrum was compared with the measured one.

Level structure of30S and its importance in the26Si(α,p)29P and29P(p,γ)30S reaction rates

The level structure of ${}^{30}$S was studied via the ${}^{28}$Si(${}^{3}$He,n) and ${}^{32}$S(p,t) reactions at the Nuclear Science Laboratory of the University of Notre Dame and the Research Center for Nuclear Physics of the University of Osaka, Japan. Important experimental information on the energy levels, decay branching ratios, and tentative spin assignments is extracted to calculate the reaction rates for ${}^{29}$P(p,$\ensuremath{\gamma}$)${}^{30}$S and ${}^{26}$Si($\ensuremath{\alpha}$,p)${}^{29}$P, which play a critical role in the reaction flow in explosive hydrogen burning.

High-resolution96Zr(3He,t) experiment and the matrix element for double-βdecay

The Gamow-Teller (GT) strength distribution has been investigated in a high-resolution (${}^{3}$He,$t$) charge-exchange experiment on the double-beta ($\ensuremath{\beta}\ensuremath{\beta}$) decaying nucleus ${}^{96}$Zr. The experiment was carried out at the Osaka University Research Center for Nuclear Physics (RCNP) with a 420 MeV incident ${}^{3}$He beam and the Grand Raiden magnetic spectrometer. A final-state energy resolution of 32 keV was achieved. A large fraction of the low-energy GT${}^{\ensuremath{-}}$ strength is identified in a single state at 694 keV. A similar observation has been made in a ${}^{96}$Mo($d$,${}^{2}$He)${}^{96}$Nb experiment at 120 keV resolution for the GT${}^{+}$ strength. It is found that this single state makes up nearly 100$%$ of the nuclear matrix element for the ${}^{96}$Zr two-neutrino double-beta ($2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) decay.

High-resolution100Mo(3He,t)100Tc charge-exchange experiment and the impact on double-βdecays and neutrino charged-current reactions

The Gamow-Teller (GT) strength distribution has been investigated in a high-resolution (${}^{3}$He,$t$) charge-exchange experiment on the double-beta ($\ensuremath{\beta}\ensuremath{\beta}$) decaying nucleus ${}^{100}$Mo. The experiment was carried out at the Osaka University Research Center for Nuclear Physics (RCNP) with a 420 MeV incident ${}^{3}$He beam and the Grand Raiden magnetic spectrometer. A final-state energy resolution of 33 keV was achieved. It was found that nearly the entire low-energy (up to $\ensuremath{\approx}4$ MeV) ${\mathrm{GT}}^{\ensuremath{-}}$ strength is concentrated in the ground-state transition to ${}^{100}$Tc, which is interpreted as a result of the particular neutron and proton sub-shell occupancies. The impact on the matrix elements for the two-neutrino double-beta ($2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) decay and the use of ${}^{100}$Mo as a neutrino detection material is discussed.

High resolution (3He,t) experiment on the double-βdecaying nuclei128Te and130Te

Gamow-Teller (GT) strength distributions have been investigated in a high-resolution (${}^{3}$He,$t$) charge-exchange experiment on the double-$\ensuremath{\beta}$ ($\ensuremath{\beta}\ensuremath{\beta}$ ) decaying nuclei ${}^{128}$Te and ${}^{130}$Te. The experiment was carried out at the Research Center for Nuclear Physics, Osaka, with a 420-MeV incident ${}^{3}$He beam and the Grand Raiden magnetic spectrometer. A final-state energy resolution of 35 keV was achieved. The extracted GT strength distributions at low excitation energies in the final nuclei ${}^{128}$I and ${}^{130}$I are presented and discussed in the context of the $\ensuremath{\beta}\ensuremath{\beta}$ decay matrix elements for the two tellurium nuclei. The additional neutron pair in ${}^{130}$Te seems to produce a moderate increase in the fragmentation of the low-energy GT distribution.

Wide-window gas target system for high resolution experiment with magnetic spectrometer

A gas target system has been developed for nuclear scattering experiments with a highly dispersive spectrometer at small scattering angles including 0°. The system is equipped with a gas cell that has a wide beam window of 44mm in width and 14mm in height. The size is sufficient to pass a dispersed beam, which is essential for high energy-resolution measurement. A gas handling system allows target gas that is often limited in quantity, to be collected for reuse. Typical areal density is 1mg/cm2 for 20Ne or 36Ar gas. The target can be operated either at room temperature or at the liquid nitrogen temperature. The gas target has been employed in a proton inelastic-scattering experiment at 295MeV with the Grand Raiden spectrometer at the Research Center for Nuclear Physics. A good energy resolution of 20keV (FWHM) has been achieved at scattering angles of 0–4.5°.

Response Measurement of a Bonner Sphere Spectrometer for High-Energy Neutrons

Response measurements of a Bonner sphere spectrometer (BSS) were performed for high-energy neutrons up to 400 MeV in quasi-monoenergetic neutron fields at the Research Center for Nuclear Physics (RCNP), Osaka University. The quasi-monoenergetic neutron field was generated by a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> Li(p,n) reaction with the resulting spectra consisting of a monoenergetic high-energy peak followed by an unwanted continuum tail down to the low-energy region. Two-angle differential measurements for a variety of Bonner spheres were performed to obtain monoenergetic responses by subtracting the tail contributions. Discussions were made on data analysis for tail subtraction. While each Bonner sphere had a different energy response, good agreements were seen in the responses between the MCNPX calculations and the measurements with a suitable subtraction. Response calculations were also made for the whole spectra obtained by unfolding the measured BSS data, with results that reproduce well the measured responses.

Investigation of the Giant Monopole Resonance in the Cd and Pb Isotopes: The Asymmetry Term in Nuclear Incompressibility and the MEM Effect

The giant monopole resonance (GMR) has been investigated in the even-A Cd and Pb isotopes 112−124 Cd, and 204−208 Pb, with the aim of obtaining a confirmatory value for the asymmetry term in nuclear incompressibility, Kτ , and to test the Mutual Enhancement Magicity (MEM) effect in nuclear incompressibilities. The latter was advanced as a possible explanation of the puzzling softness of the Sn and Cd nuclei, as evidenced by their low GMR energies as compared to theoretical predictions. The GMR results in the Cd isotopes give a value Kτ = �490± 100 MeV, in close agreement with the value obtained previously from the Sn isotopes. Our results rule out the MEM effect as an explanation of the aforementioned softness observed for the Sn and Cd nuclei. The asymmetry term of nuclear incompressibility, Kτ , associated with the neutron-excess (NZ), is crucial in obtaining the radii of neutron stars in the equation of state (EOS) calculations. 1)-4) It has been suggested that the radius of a neutron star whose mass is between about 1.0 and 1.5 solar masses (M� )i s mostly determined by the density dependence of the symmetry-energy term. 5),6) In recent measurements on the giant monopole resonance (GMR) in the even- A Sn isotopes (A = 112 � 124), we had obtained an value for this term, Kτ = �550 ± 100 MeV. 7),8) This number is in agreement with the value Kτ = �500 +125100 MeV, obtained by Centelles et al. 9) from constraints put by neutron- skin data from anti-protonic atoms across the mass table; Kτ = �500 ± 50 MeV obtained by Sagawa et al. 10) by comparing our Sn GMR data with calculations using different Skyrme Hamiltonians and RMF Lagrangians; and, Kτ = �370 ± 120 MeV obtained from an analysis of the isotopic transport ratios in medium- energy heavy-ion reactions. 11) Combined with the value of K∞ = 240 ± 10 MeV extracted from data on GMR and the other compression-mode, the isoscalar giant dipole resonance (ISGDR), 12),13) this value for Kτ may provide a means of selecting the most appropriate of the interactions commonly used in nuclear structure and EOS calculations. To confirm the value of Kτ obtained from the GMR in the Sn isotopes, we have investigated the GMR in the another series of isotopes, viz. 106,110,112,114,116 Cd using inelastic scattering of 400-MeV α particles at extremely forward angles, including 0 ◦ . The measurements were performed at the Research Center for Nuclear Physics (RCNP) at Osaka University, Japan, using the Grand Raiden spectrometer. The experimental techniques and data analysis procedures were identical to those in the measurements described previously for the Sn isotopes. 7),8)

High-resolution (3He,t) reaction on the double-βdecaying nucleus136Xe

A (${}^{3}\text{He},t$) charge-exchange reaction experiment on the double-beta decaying nucleus ${}^{136}$Xe has been performed at an incident energy of 420 MeV with the objective to measure the Gamow-Teller (GT) strength distribution in ${}^{136}$Cs. The measurements have been carried out at the dispersion-matched WS beam line and the Grand Raiden spectrometer of the Research Center for Nuclear Physics in Osaka, where an energy resolution of 42 keV was achieved. A new gas cell with thin windows made of polyethylene naphthalate has been employed as a target. The extracted GT strength distribution is confronted with the rather long $2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay half-life of ${}^{136}$Xe.

Calibration of a Bonner sphere spectrometer in quasi-monoenergetic neutron fields of 244 and 387 MeV

This paper describes the results of calibration measurements for a Bonner sphere spectrometer (BSS) with 3He proportional counter performed in quasi-monoenergetic neutron fields at the Research Center for Nuclear Physics (RCNP) at the University of Osaka, Japan. Using 246 MeV and 389 MeV proton beams, neutron fields with nominal peak energies of 244 MeV and 387 MeV were generated via 7Li(p,n)7Be reactions. At high energies, the neutron spectra were measured by means of the time-of-flight (TOF) method. The low-energy part of the neutron spectra were determined by BSS measurements down to thermal energies using the MSANDB unfolding code and three different sets of response functions. These were obtained by means of Monte Carlo (MC) calculations including various codes and intra-nuclear cascade (INC) models. Unfolded BSS fluence rates were additionally confirmed by GEANT4 calculations. For calibration of the BSS, measured count rates were corrected for low-energy contributions and compared with count rates calculated using TOF data and various response functions. In addition, measured response values were compared with mono-energetic response calculations, and best agreement was found with GEANT4 results using the Bertini INC model.