Search

A few years ago we observed anomalous electron-positron angular correlations for the 18.15 MeV M1 transition of8Be. This was interpreted as the creation and decay of an intermediate bosonic particle with a mass ofm0c2=16.70±0.35(stat )±0.5(sys) MeV, which is now called X17. The possible relation of the X17 boson to the dark matter problem triggered an enormous interest in the wider physics community. We also observed a similar anomaly in4He, which could be described also by the creation and subsequent decay of the same X17 particle. Very recently, the11B proton capture reaction was used for exciting the 17.2 MeV broad (Γ=1.15 MeV) resonance in12C and studying their internal pair creation decay. Anomalies were observed in the angular correlation of the electron-positron pairs, which together with the8Be and4He data provides kinematic evidence for the X17 particle and supports their vector boson and fifth force explanation.

Angular correlation spectra of ${e}^{+}{e}^{\ensuremath{-}}$ pairs produced in the $^{3}\mathrm{H}(p,{e}^{+}{e}^{\ensuremath{-}})^{4}\mathrm{He}$ nuclear reaction have been studied at ${E}_{p}=510$, 610, and 900 keV proton energies. The main features of the spectra can be understood by taking into account the internal and external pair creations following the proton capture by $^{3}\mathrm{H}$. However, these processes cannot account for an observed peak around ${115}^{\ensuremath{\circ}}$ in the angular correlation spectra. This anomalous excess of ${e}^{+}{e}^{\ensuremath{-}}$ pairs can be described by the creation and subsequent decay of a light particle during the direct capture process. The derived mass of the particle is ${m}_{\mathrm{X}}{c}^{2}=16.94\ifmmode\pm\else\textpm\fi{}0.12(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.21(\mathrm{syst})$ MeV. According to the mass this is likely the same X17 particle, which we recently suggested [Phys. Rev. Lett. 116, 042501 (2016)] for describing the anomaly observed in the decay of $^{8}\mathrm{Be}$.

In a 2016 paper, an anomaly in the internal pair creation on the M1 transition depopulating the 18.15 MeV isoscalar 1+ state on 8Be was observed. This could be explained by the creation and subsequent decay of a new boson, with mass mXc2 = 16.70 MeV. Further experiments of the same transition with an improved and independent setup were performed, which constrained the mass of the X17 boson (mXc2) and its branching ratio relative to the γ-decay of the 8Be excited state (BX), to mXc2 = 17.01(16) MeV and BX = 6(1) 10−6, respectively. Using the latter setup, the e+e− pairs depopulating the 21 MeV Jπ = 0− 0+ transition in 4He were investigated and a resonance in the angular correlation of the pairs was observed, which could be explained by the same X17 particle, with mass mXc2 = 16.98 ± 0.16(stat) ± 0.20(syst) MeV.

A new method, based on the excitation of the anti-analog giant dipole resonance (AGDR) in (p, n) reaction, for measuring the neutron-skin thickness has been tested. The gamma-decay of the AGDR to the isobaric analog state (IAS) has been measured. The difference in excitation energy of the AGDR and IAS was calculated. By comparing the theoretical results with the measured one, the Delta R-pn value for Sn-124 was deduced to be 0.209 +/- 0.066 fm. The present method provides a new possibility for measuring neutron-skin thickness of very exotic nuclei. DOI:10.5506/APhysPolB.44.559

Electron-positron angular correlations were remeasured for the 17.6 MeV ( J π = 1 + → 0 + ) ground state transition in 8 Be using an improved setup compared to the one we used previously. Significant deviations from the internal pair creation was observed at large angles in the angular correlations, which supports that, in an intermediate step, a neutral isoscalar particle with a mass of 17.0 ±0.2(stat) ±0.5(sys) MeV/ c 2 and J π = 1 + was created.

The emerging experimental program for photofission research at ELI-NP is briefly summarized. GEANT4 Monte Carlo simulations, providing estimates of the collimated beam profile of the ELI-NP gamma beam: beam energy bandwidth and beam spot dimensions, the required target dimensions, and fission fragment emission rates, their mass and energy distributions, have been reported, which ensure the feasibility of high-resolution studies of the multiple-humped fission barrier. A spectrometer consisting of four ionization chambers coupled to Si strip detectors, called ELI-BIC, is being developed for these measurements, and is briefly discussed.

Electron-positron angular correlations were remeasured for the 17.6 MeV $(J^π = 1^+ \to 0^+)$ ground state transition in $^8Be$ using an improved setup compared to one we used previously. Significant deviations from the internal pair creation was observed at large angles in the angular correlations, which supports that, in an intermediate step, a neutral isoscalar particle with a mass of 17.0±0.5 (stat)±0.5 (sys) $MeV/c^2$ and $J^π = 1^+$ was created.

Prototypes of the Low Energy Neutron detector Array (LENA) have been tested and compared with detailed GEANT simulations. LENA will consist of plastic scintillation bars with the dimensions 1000×45×10 mm3. The tests have been performed with γ - ray sources and neutrons originating from the neutron-induced fission of 235U. The simulations agreed very well with the measured response and were therefore used to simulate the response to mono-energetic neutrons with different detection thresholds. LENA will be used to detect low-energy neutrons from (p,n)-type reactions with low momentum transfer foreseen at the R3B and EXL setups at FAIR, Darmstadt.

Recently, we observed anomalous internal pair creation for the M1 transition depopulating the 18.15 MeV isoscalar 1$^+$ state in $^8$Be. We observed a significant (σ = 7.37) peak-like deviation from the predicted angular correlation of the e+ e pairs at θ = 140°. To the best of our knowledge no nuclear physics related description of such deviation can be made. However, the deviation can be described by assuming the creation and subsequent decay of a boson with mass of ≈17 MeV. In order to clarify the interpretation, we re-investigated the $^8$Be anomaly with an improved, and independent setup. We have confirmed the signal of the assumed X(17) particle and constrained its mass (m$_0$c $^2$ = 17.01(16) MeV) and branching ratio compared to the γ-decay (B$_x$ = 6(1) × 10$^{−6}$).

Results of the first direct observation of the true ternary fission of 234Pa* nucleus are presented. The yield of the effect depending on the experimental geometry is about 10−5/binary fission. Mass of the lightest fragment in the triplet lies mainly in the range of 20–40 a.m.u. An intimate connection between the effect and known cluster decay as well as conventional binary fission is briefly discussed.

The full-energy peak efficiency calibration and the energy resolution measurements of the 2 in . × 2 in . LaBr 3 γ -ray detector are presented for γ -ray energies in the 700 keV–17.6 MeV range. Measurements were done using a combination of proton-capture nuclear reactions on Al 27 , Na 23 , K 39 , Li 7 and B 11 for high-energy γ -rays, and radioactive sources such as Co 60 and Eu 152 for the lowest energies. At high energies, two γ -rays in a cascade from proton resonance capture were employed using Al, Na 2 WO 4 , K 2 SO 4 and LiBO 2 targets. The obtained results were compared to the simulations performed using a GEANT4 code.

Electron-positron angular correlations were measured for the isovector magnetic dipole 17.6 MeV (J^{π}=1^{+}, T=1) state→ground state (J^{π}=0^{+}, T=0) and the isoscalar magnetic dipole 18.15 MeV (J^{π}=1^{+}, T=0) state→ground state transitions in ^{8}Be. Significant enhancement relative to the internal pair creation was observed at large angles in the angular correlation for the isoscalar transition with a confidence level of >5σ. This observation could possibly be due to nuclear reaction interference effects or might indicate that, in an intermediate step, a neutral isoscalar particle with a mass of 16.70±0.35(stat)±0.5(syst) MeV/c^{2} and J^{π}=1^{+} was created.

Y. Fujita1,2 H. Fujita1 T. Adachi1 C.L. Bai3 A. Algora4,5 G.P.A. Berg6 P. von Brentano7 G. Colo8 M. Csatlos5 J.M. Deaven9 E. Estevez-Aguado4 C. Fransen7 D. De Frenne10 K. Fujita1 E. Ganioglu11 C.J. Guess9 J. Gulyas5 K. Hatanaka1 K. Hirota1 M. Honma12 D. Ishikawa1 E. Jacobs10 A. Krasznahorkay5 H. Matsubara1 K. Matsuyanagi13 R. Meharchand9 F. Molina4 K. Muto14 K. Nakanishi1 A. Negret15 H. Okamura1 H.J. Ong1 T. Otsuka16 N. Pietralla7 G. Perdikakis9 L. Popescu17 B. Rubio4 H. Sagawa13 P. Sarriguren18 C. Scholl7 Y. Shimbara19 Y. Shimizu1 G. Susoy11 T. Suzuki1 Y. Tameshige1 A. Tamii1 J.H. Thies20 M. Uchida1 T. Wakasa1 M. Yosoi1 R.G.T. Zegers1 K.O. Zell7 J. Zenihiro1

Y. Fujita et al.; 15 pags.; 6 figs.; 7 tabs.; PACS number(s): 21.10.Hw, 25.55.Kr, 27.40.+z, 25.40.Ep

Electron-positron angular correlations were measured for the isovector magnetic dipole 17.6 MeV (J^{π}=1^{+}, T=1) state→ground state (J^{π}=0^{+}, T=0) and the isoscalar magnetic dipole 18.15 MeV (J^{π}=1^{+}, T=0) state→ground state transitions in ^{8}Be. Significant enhancement relative to the internal pair creation was observed at large angles in the angular correlation for the isoscalar transition with a confidence level of5σ. This observation could possibly be due to nuclear reaction interference effects or might indicate that, in an intermediate step, a neutral isoscalar particle with a mass of 16.70±0.35(stat)±0.5(syst) MeV/c^{2} and J^{π}=1^{+} was created.

The fission probability of U-236 as a function of the excitation energy has been measured with high energy resolution using the U-235(d, pf) reaction in order to study hyperdeformed (HD) rotational bands. Rotational band structures with a moment of inertia of theta = 217 +/- 38 h(2)/MeV have been observed, corresponding to hyperdeformed configurations. From the level density of the rotational bands the excitation energy of the ground state in the third minimum was determined to be 2.7 +/- 0.4 MeV.The excitation energy of the lowest hyperdeformed transmission resonance and the energy dependence of the fission isomer population probability enabled the determination of the height of the inner fission barrier E-A = 5.05 +/- 0.20 MeV and its curvature parameter h omega(A) = 1.2 MeV. Using this new method the long-standing uncertainties in determining the height of the inner potential barrier in uranium isotopes could be resolved. (c) 2005 Elsevier B.V. All rights reserved.

After a short overview of the methods applied for measuring the neutron-skin thickness, we present the recent experimental results for the neutron-skin thicknesses of the 112–124 Sn even-even isotopes and of 208 Pb. We have used inelastic alpha scattering to excite the giant dipole resonance (GDR). The cross section of this process depends strongly on ΔR np /R, the relative neutron-skin thickness. We have also measured the excitation of the spin-dipole resonance (SDR) to deduce the neutron-skin thickness since the summed L=1 strength of the SDR is sensitive to it. The results obtained are in good agreement with the previous experimental and theoretical ones.

Progress in the experimental techniques used to investigate superdeformed fission isomers in the actinides allowed for detailed spectroscopic results of collective properties as well as for the identification of the rotational structure of multiphonon vibrational excitations. A novel approach could be established to determine the depth of the second potential well.

The excitation energy spectrum of fission resonances has been measured with high energy resolution using the 235U(d,pf) reaction in order to study hyperdeformed (HD) rotational bands and HD nuclear shapes. The moments of inertia of the rotational bands and the energy of the ground state in the third minimum were determined. Another signature of these highly deformed states, their enhanced α decay, was also observed. By studying cold or compact fission in the 232Th(n,f) reaction around HD resonances, we obtained data for heavy clustering.

An absolute full-energy peak efficiency calibration of a Clover-type composite germanium gamma-ray detector system is presented. The efficiency curve was measured in the energy range of 120 keV–12.2 MeV for the first time, using the combination of proton-capture nuclear reactions and radioactive sources, such as 56Co, 60Co, 66Ga and 152Eu. At high energies gamma-ray pairs from proton resonance capture on 27Al, 23Na, 39K and 11B were employed using evaporated Al, Na2WO4, K2SO4 and LiBO2 targets, respectively. The experimental data were fitted with a single polynomial function on log–log scale using a recently developed method. The add-back factor is found to increase quadratically with the energy, in contrast to the previously suggested linear relationship. The efficiency gain with respect to a single detector is about one order of magnitude at 10 MeV energy.

At the Extreme Light Infrastructure - Nuclear Physics facility (ELI-NP), high-power laser systems together with high-brilliance gamma beams are the main research tools. The status of the construction of the facility is reported. The emerging photofission experimental program with brilliant gamma beams at ELI-NP is presented with emphasis on the prepared day-one experiments. The physics cases of the flagship experiments at ELI-NP are discussed, as well as the related instruments which are under construction for their realization.

The leading theory for dark matter used to be WIMPs (weakly interacting massive particles) that only interacted via gravity and the weak force, making them very hard to detect. Following recent research results, though, a new theory of dark matter actually postulates bosons in the 10 MeV to 10 GeV range [1]. A number of attempts were made to find such particles by using data from running facilities or reanalysing data of preceding experiments, but no evidence has been found yet [1, 2]. In the near future, many ongoing experiments are expected to extend those regions in mass and coupling strength which are so far unexplored [3–5].

Background: The Gamow-Teller response of $^{40}\mathrm{Ar}$ is important for the use of liquid argon as a medium for neutrino detection. An ambiguity about the Gamow-Teller strength for the excitation of ${1}^{+}$ states at 2290 and 2730 keV in $^{40}\mathrm{K}$ results in a significant uncertainty for neutrino capture rates. This ambiguity is caused by the large discrepancy observed between strengths extracted from $^{40}\mathrm{Ar}$($p$, $n$) charge-exchange data and the transition strengths for the analog transitions studied in the $\ensuremath{\beta}$ decay of $^{40}\mathrm{Ti}$.Purpose: This study was aimed at resolving the ambiguity between the results from the $^{40}\mathrm{Ar}$($p$, $n$) charge-exchange and $^{40}\mathrm{Ti}$ $\ensuremath{\beta}$-decay data.Method: Shell-model calculations in the $sd\text{\ensuremath{-}}pf$ shell with a new interaction (WBMB-C) were used to study differences between the structure of the transitions from $^{40}\mathrm{Ar}$ and $^{40}\mathrm{Ti}$. Distorted-wave Born approximation reaction calculations were used to investigate uncertainties in the extraction of Gamow-Teller strength from the $^{40}\mathrm{Ar}$($p$, $n$) data. New high-resolution data for the $^{40}\mathrm{Ar}$($^{3}\mathrm{He}$,$t$) reaction were used to gain further insight into the charge-exchange reaction mechanism and to provide more information to test the validity of the shell-model calculations.Results: The shell-model calculations showed that interference between amplitudes associated with $pf$ and $sd$ components to the low-lying Gamow-Teller transitions, in combination with a difference in Coulomb energy shifts for $^{40}\mathrm{Ar}$ and $^{40}\mathrm{Ti}$, can produce the differences on the scale of those observed between the $^{40}\mathrm{Ar}$ charge-exchange and $^{40}\mathrm{Ti}$ $\ensuremath{\beta}$-decay data. In combination with the difference in nuclear penetrability of the ($p$, $n$) and ($^{3}\mathrm{He}$,$t$) probes, the different contributions from amplitudes associated with transitions in the $pf$ and $sd$ shells are likely also responsible for the observed discrepancy between the ratio of the cross sections for the low-lying ${1}^{+}$ states in the $^{40}\mathrm{Ar}$($p$, $n$) and $^{40}\mathrm{Ar}$($^{3}\mathrm{He}$,$t$) data.Conclusions: On the basis of this study, it is recommended to use Gamow-Teller strengths extracted from the $^{40}\mathrm{Ar}$($p$, $n$) data, not the $^{40}\mathrm{Ti}$ $\ensuremath{\beta}$-decay data, for the calculation of neutrino capture rates. Further theoretical studies are required to achieve a consistent quantitative description for the energy differences between low-lying ${1}^{+}$ states in $^{40}\mathrm{K}$ and $^{40}\mathrm{Sc}$ and the experimentally observed Gamow-Teller strengths.

Y. Fujita et al. ; 5 pags. ; 3 figs. PACS numbers: 24.30.Cz, 25.55.Kr, 27.40.+z, Gamow-Teller (GT) transitions in atomic nuclei are sensitive to both nuclear shell structure and effective residual interactions. The nuclear GT excitations were studied for the mass number A=42, 46, 50, and 54 >f-shell> nuclei in (He3, t) charge-exchange reactions. In the Ca42→Sc42 reaction, most of the GT strength is concentrated in the lowest excited state at 0.6 MeV, suggesting the existence of a low-energy GT phonon excitation. As A increases, a high-energy GT phonon excitation develops in the 6-11 MeV region. In the Fe54→Co54 reaction, the high-energy GT phonon excitation mainly carries the GT strength. The existence of these two GT phonon excitations are attributed to the 2 fermionic degrees of freedom in nuclei. © 2014 American Physical Society., This work was in part supported by MEXT, Japan (Grants No. 13002001, No. 15540274, and No. 18540270); MICINN, Spain (Grant No. FPA200806419-C02-01). Y. F. and B. R. acknowledge the support of the Japan-Spain collaboration program by JSPS and CSIC.

The intermediate structure of fission resonances of 240Pu was observed with an experimental energy resolution of 7 keV in the excitation energy region of E ∗ =3.8 –5.6 MeV using the 239Pu(d, pf)240Pu reaction. Two-vibrational resonance groups centered at E ∗ =4.6 MeV and 5.1 MeV, and attributed to the excitation of three and four β-phonons, were resolved into individual substates, which could be assigned to the low-spin members of Kπ=0+ superdeformed (SD) rotational bands. In the region of the lower E ∗ =4.6 MeV resonance individual moments of inertia of six well separated bands could be extracted for the first time with values of Θ/ℏ2 around 157 MeV−1, close to that of the ground state band in the second well. From the level density of these Kπ=0+ band heads the excitation energy of the SD ground state was determined to (2.25±0.20) MeV, in agreement with earlier estimates from excitation functions.

Spectroscopic studies in the superdeformed shape isomer of 240Pu using γ-spectroscopy, conversion electron spectroscopy and transmission resonance spectroscopy have been performed. In a high-resolution and high-efficiency γ-spectroscopy experiment the out-of-band decays of several excited superdeformed rotational sequences with K=2− and 1− could be identified together with evidence for a weakly populated 0− octupole band. Surprisingly, no low-lying collective quadrupole excitations could be observed. Complementary information could be obtained in conversion electron measurements in coincidence with isomeric fission, resulting in the first identification of the lowest s-vibrational K=0+ band. For all rotational bands the variation of the moment of inertia with spin could be studied. A predominant population of negative parity states in the second well could be observed, which can be explained by the selective population and depopulation of the second minimum. Complementary transmission resonance measurements have been performed, yielding new information on the fine structure of high-lying (s-)vibrational multi-phonon states. A new method could be established to determine the excitation energy of the fission isomer ground state from measured level densities.

The 233 U(d,pf) 234 U reaction has been studied with high energy resolution. The observed fission resonances in the excitation energy range of 4.75 ≤E ∗ ≤ 5.40 MeV were described as members of rotational bands with rotational parameters characteristic to the hyperdeformed nuclear shape (ℏ 2 /2 θ =2.1±0.2 keV). Information on the K values of the bands has been obtained from fission fragment angular distribution measurements. The level density of the most strongly excited J =3 states has been compared to the prediction of the back-shifted Fermi-gas formula and the energy of the ground state in the third minimum has been estimated to be E III = 3.1 ± 0.4 MeV.

Measurements of γ-ray, γγ-coincidence and internal conversion electron spectra from the 106 Cd( α , nγ ) 109 Sn reaction were carried out at 15–20 MeV α-particle bombarding energies with Ge(HP) γ-ray and superconducting magnetic lens plus Si(Li) electron spectrometers. The energies, relative intensities, internal conversion coefficients and coincidence relations of the 109 Sn transitions were determined, and a more complete, consistent level scheme has been deduced. Spin and parity values have been determined from the internal conversion coefficients, the bombarding-energy dependence of the side-feeding intensities of the states and the available γ-ray angular distribution data. The level scheme was interpreted in the framework of the quasi-particle shell model.

A selection of the properties of large volume, cylindrical 3.5” x 8” LaBr 3 :Ce scintillation detectors coupled to a 3.5” PMT (model R10233-1000SEL from HAMAMATSU) and a special designed Voltage Divider (LABRVD) will be discussed. A number of 10 of such detectors constitute the HECTOR + array which, in fall 2012, measured at GSI coupled to the AGATA DEMOSTRATOR at the PRESPEC experimental setup. These crystals are among the largest ever produced and needed to be characterized. We have performed several tests and here we discuss, in particular, the energy resolution measured using monochromatic γ −ray sources and in-beam reactions producing γ −rays up to 22.6 MeV. As already measured in two previous works a saturation in the energy resolution was observed in case of high energy gamma rays. Crystal non-homogeneities and PMT gain drifts can affect the resolution of measurements especially in case of high energy γ −rays.

Positive parity intruder bands were searched for in the experimental data obtained from 113,115 In( α , nγ ) 116,118 Sb reactions. Two bands were found both in 116 Sb and 118 Sb, which are based on the 7 + isomeric states of 116,118 Sb, having the πg 9 2 −1 νd 5 2 intruder configuration. The bands were interpreted on the basis of interacting boson-fermion-fermion model calculation, resulting in a reasonable description of the energies and electromagnetic properties of the states observed.

Excited states of {sup 112}Sb were investigated through the {sup 112}Sn(p,n{gamma}){sup 112}Sb reaction. {gamma}-ray, {gamma}{gamma}-coincidence, and internal conversion electron spectra were measured with Ge(HP) {gamma} and superconducting magnetic lens plus Si(Li) electron spectrometers at 8.5, 8.9, 9.1, and 9.3 MeV bombarding proton energies. A significantly extended level scheme was constructed. Spins and parities have been assigned to the levels from Hauser-Feshbach analysis of reaction cross sections, internal conversion coefficients, angular distribution of the {gamma} rays, and decay properties of the states. The low lying states were assigned to proton-neutron multiplets on the basis of their decay properties. The energy splitting of these multiplets have been calculated using the parabolic rule. {copyright} {ital 1997} {ital The American Physical Society}

The $\ensuremath{\beta}$-feeding probabilities for three important contributors to the decay heat in nuclear reactors, namely ${}^{102,104,105}$Tc, have been measured using the total absorption spectroscopy technique. For the measurements, sources of very high isobaric purity have been obtained using a Penning trap (JYFLTRAP). A detailed description of the data analysis is given and the results are compared with high-resolution measurements and theoretical calculations.

The photofission cross-section of 238U was measured at sub-barrier energies as a function of the gamma-ray energy using, for the first time, a monochromatic, high-brilliance, Compton-backscattered gamma-ray beam. The experiment was performed at the High Intensity gamma-ray Source (HIgS) facility at beam energies between E=4.7 MeV and 6.0 MeV and with ~3% energy resolution. Indications of transmission resonances have been observed at gamma-ray beam energies of E=5.1 MeV and 5.6 MeV with moderate amplitudes. The triple-humped fission barrier parameters of 238U have been determined by fitting EMPIRE-3.1 nuclear reaction code calculations to the experimental photofission cross section., 5 pages, 3 figures

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.

A neutron spectrometer, the European Low-Energy Neutron Spectrometer (ELENS), has been constructed to study exotic nuclei in inverse-kinematics experiments. The spectrometer, which consists of plastic scintillator bars, can be operated in the neutron energy range of 100 keV to 10 MeV. The neutron energy is determined using the time-of-flight technique, while the position of the neutron detection is deduced from the time-difference information from photomultipliers attached to both ends of each bar. A novel wrapping method has been developed for the plastic scintillators. The array has a larger than 25% detection efficiency for neutrons of approximately 500 keV in kinetic energy and an angular resolution of less than 1 degree. Details of the design, construction and experimental tests of the spectrometer will be presented., Comment: 10 pages, 13 figures

The gamma-decay of the anti-analog of the giant dipole resonance (AGDR) has been measured to the isobaric analog state excited in the p(124Sn,n) reaction at a beam energy of 600 MeV/nucleon. The energy of the transition was also calculated with state-of-the-art self-consistent random-phase approximation (RPA) and turned out to be very sensitive to the neutron-skin thickness (\DeltaR_(pn)). By comparing the theoretical results with the measured one, the \DeltaR_(pn) value for 124Sn was deduced to be 0.175 \pm 0.048 fm, which agrees well with the previous results. The energy of the AGDR measured previously for ^(208)Pb was also used to determine the \DeltaR_(pn) for ^(208)Pb. In this way a very precise \DeltaR_(pn) = 0.181 \pm 0.031 neutron-skin thickness has been obtained for 208Pb. The present method offers new possibilities for measuring the neutron-skin thicknesses of very exotic isotopes., 5 pages, 3 figures

The fission probability of 232Pa was measured as a function of the excitation energy in order to search for hyperdeformed (HD) transmission resonances using the (d,pf) transfer reaction on a radioactive 231Pa target. The experiment was performed at the Tandem accelerator of the Maier-Leibnitz Laboratory (MLL) at Garching using the 231Pa(d,pf) reaction at a bombarding energy of E=12 MeV and with an energy resolution of dE=5.5 keV. Two groups of transmission resonances have been observed at excitation energies of E=5.7 and 5.9 MeV. The fine structure of the resonance group at E=5.7 MeV could be interpreted as overlapping rotational bands with a rotational parameter characteristic to a HD nuclear shape. The fission barrier parameters of 232Pa have been determined by fitting TALYS 1.2 nuclear reaction code calculations to the overall structure of the fission probability. From the average level spacing of the J=4 states, the excitation energy of the ground state of the 3rd minimum has been deduced to be E(III)=5.05 MeV., Comment: 6 pages, 8 figures

Two new research facilities will be ready for operation very soon (MEGa-Ray at Liver-more National Laboratory) or start construction (ELI-Nuclear Physics in Bucharest), both providing highly brilliant γ beams with so far unprecedented properties via Compton backscattering of laser photons from a high-quality, relativistic electron beam. With these intense, monochromatic γ beams, a new era of photonuclear physics will be enabled. A new research campaign is proposed to exploit the unprecedented properties of these highly-brilliant, novel γ beams on highly-selective studies of extremely deformed nuclei in the multiple-humped potential energy landscape of the actinides via photofission. With the unique γ beam bandwidth of ΔE/E = 10−3, we can aim at resolving individual resonances which could never be achieved so far due to the limited γ bandwidth of bremsstrahlung beams. Exploratory, non-bremsstrahlung photofission experiments are going to be performed very soon at the HIγS facility (Duke University, USA) to ...

Gamow‐Teller (GT) transitions are mediated by the στ operator. Owing to its simplicity and also its spin‐isospin nature, GT transitions play key roles in the studies of nuclear structure as well as astro‐nuclear processes. In violent neutrino‐induced reactions at the core‐collapse stage of type II supernovae, Gamow‐Teller (GT) transitions starting from stable as well as unstable pf‐shell nuclei play important roles. We study GT transitions starting from 47Ti in a high‐resolution (3He,t) charge‐exchange reactions at 0° and at an intermediate incident energy of 140 MeV/nucleon at Research Center for Nuclear Physics (RCNP), Osaka. Individual GT transitions up to high excitations were observed. Assuming the isospin symmetry for the strengths of Tz = ±3/2→±1/2 analogous GT transitions, we can deduce the detailed strength distribution starting from mirror unstable nucleus 47Mn.