Search

The Superconducting Analyzer for Multi-particles from Radioisotope beams, SAMURAI, with a large angular and momentum acceptance has entered into the phase of physics experiments. Several experiments have been already run with invariant mass spectroscopy using heavy ions and neutrons, as well as missing mass spectroscopy, by introducing detector arrays around the reaction target upstream of the dipole magnet. Many user devices will be introduced to be coupled with SAMURAI. In the Day-Two phase, an experimental program, SAMURAI08, was performed which took advantage of the large momentum acceptance property of SAMURAI. In this experiment, two or more particles with different Z and A / Z were detected at the focal plane in coincidence. Analysis details are reported as an example for similar experiment in future. A variety of experiments are waiting to be performed, which means that SAMURAI is now open for use by RIBF users.

International audience; A search for new isotopes in the neutron-rich rare-earth region has been carried out using a 345 MeV=nucleon 238U beam at the RIKEN Nishina Center RI Beam Factory. Fragments produced were analyzed and identified using the BigRIPS in-flight separator. We observed a total of 29 new neutron-rich isotopes: 153Ba, 154,155,156La, 156,157,158Ce, 156,157,158,159,160,161Pr, 162,163Nd, 164,165Pm, 166,167Sm, 169Eu, 171Gd, 173,174Tb, 175,176Dy, 177,178Ho, and 179,180Er.

Two-proton relative momentum ($q_{pp}$) and opening angle ($\theta_{pp}$) 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 $\theta_{pp}$ 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.

A search for new proton-rich isotopes using projectile fragmentation of a 345-MeV/nucleon 124Xe beam has been performed with the BigRIPS in-flight separator at the RIKEN Nishina Center RI Beam Factory. Projectile fragments were identified by measuring the time of flight, magnetic rigidity, and energy loss in the BigRIPS separator. Projectile fragments then were transported downstream of the BigRIPS separator and re-identified by measuring the time of flight and total kinetic energy. Through such particle re-identification, we have discovered four new isotopes 81,82Mo and 85,86Ru located near the proton drip line. The 76Y and 78Zr isotopes near the proton drip line also were identified, supporting the previous report on their discovery. Furthermore, we have obtained the first clear evidence for the particle instability of 103Sb. Based on the systematics of measured production yields, the upper limit values were evaluated for the half-lives of the particle-unbound isotopes 81Nb,85Tc, and 103Sb.

Very neutron-rich $Z\ensuremath{\sim}60$ isotopes produced by in-flight fission of a 345 MeV/nucleon $^{238}\mathrm{U}$ beam at the RI Beam Factory, RIKEN Nishina Center, have been studied by delayed $\ensuremath{\gamma}$-ray spectroscopy. New isomers were discovered in the neutron-rich $N=100$ isotones $^{162}\mathrm{Sm}, ^{163}\mathrm{Eu}$, and $^{164}\mathrm{Gd}$. Half-lives, $\ensuremath{\gamma}$-ray energies, and relative intensities of these isomers were obtained. Level schemes were proposed for these nuclei and the first ${2}^{+}$ and ${4}^{+}$ states were assigned for the even-even nuclei. The first ${2}^{+}$ and ${4}^{+}$ state energies decrease as the proton numbers get smaller. The energies and the half-lives of the new isomers are very similar to those of ${4}^{\ensuremath{-}}$ isomers known in less neutron-rich $N=100$ isotones $^{168}\mathrm{Er}$ and $^{170}\mathrm{Yb}$. A deformed Hartree-Fock with angular momentum projection model suggests ${K}^{\ensuremath{\pi}}={4}^{\ensuremath{-}}$ two-quasiparticle states with $\ensuremath{\nu}7/2[633]\ensuremath{\bigotimes}\ensuremath{\nu}1/2[521]$ configurations with similar excitation energy. The results suggest that neutron-rich $N=100$ nuclei are well deformed and the deformation gets larger as $Z$ decreases to 62. The onset of $K$ isomers with the same configuration at almost the same energy in $N=100$ isotones indicates that the neutron single-particle structures of neutron-rich isotones down to $Z=62$ do not change significantly from those of the $Z=70$ stable nuclei. Systematics of the excitation energies of new isomers can be explained without the predicted $N=100$ shell gap.

Isotopic production cross sections were measured for proton- and deuteron-induced reactions on 93 Nb by means of the inverse kinematics method at RIKEN Radioactive Isotope Beam Factory. The measured production cross sections of residual nuclei in the reaction 93 Nb + p at 113 MeV/u were compared with previous data measured by the conventional activation method in the proton energy range between 46 and 249 MeV. The present inverse kinematics data of four reaction products (90 Mo, 90 Nb, 88 Y, and 86 Y) were in good agreement with the data of activation measurement. Also, the model calculations with PHITS describing the intra-nuclear cascade and evaporation processes generally well reproduced the measured isotopic production cross sections.

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.

The reduced transition probability B(E2;0gs+→21+) for the proton-rich nucleus 28S was determined experimentally using intermediate-energy Coulomb excitation. The resultant B(E2) value 181(31) e2fm4 is smaller than those of neighboring N = 12 isotones and Z = 16 isotopes. The double ratio |Mn/Mp|/(N/Z) of the 0gs+→21+ transition in 28S was obtained to be 1.9(2) by evaluating the Mn value from the known B(E2) value of the mirror nucleus 28Mg, showing the hindrance of proton collectivity relative to that of neutrons. These results indicate the emergence of the magic number Z = 16 in 28S.

Reaction cross sections with various kinds of breakup channels for neutron-rich carbon isotopes 18–20C and for 9Be impinging on a liquid hydrogen target were investigated at 40 MeV/nucleon. The nuclides of interest were produced via projectile fragmentation from a 63 MeV/nucleon 40Ar beam and were separated in flight at the RIKEN projectile fragment separator (RIPS). The combination of the large-acceptance superconducting TOF spectrometer, TOMBEE (TOF Mass analyzer for exotic BEam Experiment), with a liquid hydrogen target, CRYPTA (CRYogenic ProTon and Alpha target system), enables simultaneous measurements of several reaction channels: the reaction cross sections ( σ R ), individual elemental fragmentation cross sections ( σ Δ Z ), charge-changing cross sections ( σ cc ), neutron-removal cross sections ( σ − x n ), and charge-pickup cross sections ( σ Δ Z + 1 ) for 19,20C; σ Δ Z , σ − x n , and σ Δ Z + 1 for 18C; and σ R for 9Be. The present σ R of 9Be on proton, σ R = 397 ± 23 mb , measured in the inverse kinematics, was consistent with the previous measurements using proton beams at different laboratories. The σ R of 19C and 20C on proton were determined to be σ R = 754 ± 22 mb and σ R = 791 ± 34 mb , respectively. Taking into account the beam energy and target dependence of σ R , the present σ R are found to be considerably enhanced compared with those measured at around 1 GeV/nucleon. The σ Δ Z + 1 appears to increase with the mass number of the projectiles, and it significantly contributes to σ R in the present energy range. The finite-range optical-limit and few-body Glauber model analyses were performed for σ R to study the nuclear matter density distributions and to derive the relative strength of the s-wave components of the valence neutrons in 19C and 20C. A neutron halo structure of 19C is confirmed with an s-wave dominance of the valence neutron when the effect of the charge-pickup reaction is taken into account. The large σ − n of 19C and σ − 2 n of 20C also support the decoupled structures of 18C +n and 18C + 2 n , respectively. The σ cc of 19C and 20C agree with each other within their experimental uncertainties, which might indicate a similar proton density distribution in 19C and 20C. The σ Δ Z decreases monotonically without the even–odd effect as the number of removed protons increases.

Two-proton relative momentum distributions from the break-up channels 23Al→p+p+21Na and 22Mg→p+p+20Ne at an energy of 60–70 A MeV have been measured together with two-proton opening angles at the projectile fragment separator beamline (RIPS) in the RIKEN Ring Cyclotron Facility. The results demonstrate the existence of diproton emission component from single-step 2He for highly excited 23Al and 22Mg.

An experiment of 22 Mg and 20 Ne beams bombarding on a 12 C target at an energy of 60~70 A MeV has been performed at the RIKEN projectile fragment separator (RIPS) in the RIKEN Ring Cyclotron Facility to study the two-proton correlated emission from 22 Mg and 20 Ne excited states. The two-protons momentum correlation functions have been obtained for 22 Mg and 20 Ne , respectively. The trajectories of the 22 Mg decayed products (20 Ne + p + p ) were also measured to get the angular correlations between the two protons in Center of Mass of decaying system by relativistic-kinematics reconstruction. The results exhibit that 22 Mg has the features of 2 He cluster decay mechanism.

The Coulomb dissociation of the proton-rich nuclei 31 Cl was studied experimentally using 31 Cl beams at 58 MeV/nucleon with a lead target. The relative energy between the reaction products, 30 S and proton, was obtained. The first excited state in 31 Cl was observed which is relevant to the resonant capture of stellar 30 S (p,γ)31 Cl reaction.

Experiments of 23 Al and 22 Mg radioactive beams bombarding a 12 C target at an energy of 60 ~70 A MeV have been performed at the projectile fragment separator beamline (RIPS) in the RIKEN Ring Cyclotron Facility to study the two-proton emission from 23 Al and 22 Mg excited states, respectively. The trajectorie of the decay products, namely 21 Na + p + p from 23 Al and 20 Ne + p + p from 22 Mg , are clean identified. The relative momentum and opening angle between two protons in the rest frame of three body decay channels are obtained by relativistic-kinematics reconstruction. The results demonstrate that there are some di-proton emission components from 2 He cluster for the excited 23 Al and 22 Mg .

The neturon rich nucleus 13B was studied via the proton transfer reaction 4He(12Be,13B \gamma) at 50AMeV. The known 4.83-MeV excited state was strongly populated and its spin and parity were assigned to 1/2+ by comparing the angular differential cross section data with DWBA calculations. This low-lying 1/2+ state is interpreted as a proton intruder state and indicates a deformation of the nucleus., Comment: 16 pages, 3 figures

Mean lifetime tau of the isomeric O-2(+) state in Be-12 has been determined by measuring decay spectra of delayed y-rays from stopped Be-12 2 nuclei produced by the projectile fragmentation of O-18 at 100 A MeV. A consistent value of tau = 331 +/- 12 ns was obtained from the time spectra of the E2 gamma decay to the 2(1)(+) state and the positron annihilation following the E0 decay to the ground state. Based on the observed branching ratio between the E2 and E0 decays, transition strengths of the two decay modes were deduced to be B(E2; O-2(+) -> 2(1)(+)) = 7.0 +/- 0.6 e(2) fm(4) and 2 1 1 (O-2(+) Sigma(i) e(i) r(i)(2) O-1(+)), = 0.87 +/- 0.03 e fM(2), respectively. (C) 2007 Elsevier B.V. All rights reserved.

The proton shell structure in neutron-rich fluorine 23 F was investigated using the in-beam γ -ray spectroscopy technique via the proton transfer reaction onto the 22 O nucleus. We also measured the α inelastic scattering on 23 F, the neutron knockout from 24 F, and the two-nucleon knockout from 25 Ne using a cocktail secondary beam. The excited states were identified by de-excitation γ -rays coincident with outgoing 23 F, and we found the proton single-particle states at 2268 and 4059 keV by comparison of the population strengths among these reactions. These states were respectively assigned to have l = 0 and l = 2 by the angular distributions obtained in the transfer reaction, and therefore they were considered to have the configurations of π s 1 / 2 and π d 3 / 2 . The excitation energies of these states are located at higher excitation energies than the shell model predictions for the USD and SDPF-M interactions, which may indicate that the centroid energy gaps between π d 5 / 2 and π s 1 / 2 are wider than predictions.

The proton shell structure in neutron-rich fluorine 23F was investigated using the in-beam γ-ray spectroscopy technique via the proton transfer reaction onto the 22O nucleus. We also measured the α inelastic scattering on 23F, the neutron knockout from 24F, and the two-nucleon knockout from 25Ne using a cocktail secondary beam. By comparison of the population strengths for excited states in these reactions, we deduced the character of the excited states. The levels and γ-decay scheme in 23F were proposed based on de-excitation γ-rays and the products of these reactions. We found that the 2268- and 4059-keV levels have strong proton single-particle nature of the s 1 / 2 and d 3 / 2 orbitals, respectively, by analysis of the population strengths and the angular distributions of the states. These single-particle states are located at higher excitation energies than the shell model predictions for the USD and SDPF-M interactions, which indicates that the centroid energy gaps for π d 5 / 2 – π s 1 / 2 and π d 5 / 2 – π d 3 / 2 are wider than predicted.

The paper reports on the test of the newly developed RIKEN-ATOMKI CsI(Tl) array. It is demonstrated that high-quality detectors with excellent light collection efficiency and narrow resolution distribution could be produced. The setup has been commissioned in the study of the reaction of 22O + CD2. In the present paper, we summarize the results mainly on the (d, d′) channel. From the cross section for the transition between the ground state and the first 2+ state, we could deduce the “matter” deformation parameter to be β M=0.23±0.02 by distorted wave analysis. Comparing this data with previous measurements it can be concluded that 22O isotope has moderate and similar neutron and proton deformations.

The 0 g . s . + → 2 1 + excitation of the neutron-rich nucleus 28Ne has been investigated via heavy-ion inelastic scattering in reversed kinematics. The B ( E 2 ; 0 g . s . + → 2 1 + ) value was determined to be 132 ( 23 ) e 2 fm 4 , which is smaller than expected from the low excitation energy of the first 2 1 + state. A comparison with theoretical predictions suggests that the suppressed collectivity in 28Ne is characteristic of nuclei lying on the boundary of the ‘island of inversion’.

The proton shell structure in neutron-rich fluorine 23F was investigated using the in-beam γ-ray spectroscopy technique via the proton transfer reaction onto the unstable nucleus 22O, in addition to α inelastic scattering on 23F, and the neutron-knockout reaction from 24F. The level and γ-decay scheme in 23F was deduced from de-excitation γ-ray-particle coincidence events. We found that a single-particle state at 4.061 MeV has a large contribution from the d shell by the analysis of population strengths and the angular distribution for the state. We reported here the present experiment and the preliminary results.

The radiative width of the 3/2+ state at 6.793 MeV in 15O has been experimentally determined to be Γγ=0.95+0.60−0.95 eV by intermediate-energy Coulomb excitation. Our result independently supports the recent studies which point to a minor contribution of this state to the astrophysical rate of the 14N(p,γ)15O reaction in the CNO-cycle hydrogen burning in massive stars.

The energy of the first excited state of the very neutron-rich nucleus 30 Ne was determined by proton inelastic scattering. A liquid hydrogen target was bombarded by a beam of radioactive 30 Ne at 48 MeV/nucleon, and energies of the de-excitation γ rays emitted from the excited 30 Ne were measured. The observed transition is likely to be the one from the first 2 + state to the ground state of 30 Ne. The excitation energy, 791(26) keV, is lower than that of 32 Mg, indicating enhancement of deformation as the neutron excess increases in the N =20 isotones. The results indicate that 30 Ne belongs to the ‘island of inversion’.

The effect of passive iron converters was investigated at energies of 20–140 MeV: An enhanced detection efficiency for neutron energies above 70 MeV was found using iron converters of 2–3 cm thickness. The experimental findings will be implemented in a high-efficiency large-area detector for neutrons in the energy range 100–200 MeV at the National Superconducting Cyclotron Laboratory. r 2003 Elsevier Science B.V. All rights reserved. PACS: 29.40.Mc

A large enhancement of the 13 C(α,n) 16 O reaction cross section at low energy limit due to the sub-threshold state in 17 O has been predicted, explaining the neutron source of s-process nucleosynthesis. By the 13 C( 6 Li,d) 17 O transfer reaction, we had deduced the resonance strength of the state. Contrary to the predictions, the sub-threshold state was found to have very small contribution to the astrophysical S factor.

Radioactive-ion (RI) beams of 10 C, 14 O, 12N and 11 C with energies low 10 A MeV were produced by using a low-energy in-flight RI beam separator newly constructed by CNS, University of Tokyo. Using the 12 N and 11 C beams, some resonance states were identified in the proton elastic scattering 12 N+p and 11 C+p, respectively.

Resonance states in 12N were studied by using the resonance elastic scattering of 11 C + p with a low-energy radioactive ion beam of 11C at 3.5 MeV/nucleon and a thick (CH2)n target. The 11C beam was separated by a newly installed CNS radioactive ion beam separator (CRIB). The energy spectrum of recoil protons was measured at laboratory scattering angles around θLAB=0° to identify resonance states in 12N. The spin-parity values of Jπ=3− and (2)+ have been determined for the levels at the excitation energies of Ex=3.1 and 3.6 MeV in 12N, respectively, suggesting a small contribution of the 3.1-MeV level to the 11C(p, γ )12N stellar reaction.

The effect of passive iron converters on the detection efficiency of neutrons in a plastic scintillator was investigated at energies of 20–140 MeV. An enhanced detection efficiency for neutron energies above 70 MeV was found using iron converters of 2–3 cm thickness. The experimental results are compared to a simulation. 2002 Elsevier Science B.V. All rights reserved.

A novel technique with a radioactive isotope beam has been employed for in-beam γ -ray spectroscopy of a very neutron-rich isotope 34 Mg. The excited 34 Mg were produced by the projectile fragmentation reaction induced by a radioactive 36 Si beam at 50 MeV/nucleon on a 385 mg/cm 2 9 Be target. Deexcitation γ rays were detected in coincidence with the 34 Mg fragments. The measured excitation energy, 660±10 keV, implies a large deformation of 34 Mg.

A new inorganic polymer coagulant of polysilicato-iron (PSI) was evaluated as an alternative to aluminium coagulant. In this study, long-term performance of PSI on coagulation, sedimentation and filtration for phytoplankton, turbidity and DOC in raw water from a eutrophic reservoir were evaluated by a pilot plant in comparison with PAC. PSI was found to be more effective in the coagulation and removal in comparison with PAC. The flocs formed by PSI could be settled more quickly than those by PAC and, therefore, the size of sedimentation facilities can be reduced by the introduction of PSI. PSI was able to produce filtered water with low turbidity and colour. The number of phytoplankton cells in the filtered water of PSI was smaller than that of PAC. Most of the residual flocs in the settled water were trapped in the coarse layer of anthracite, and this result suggested that a higher rate of filtration can be achieved with PSI by increasing particle size of the filter media.

Isotopic production cross sections in the proton- and deuteron-induced spallation reactions on 93 Zr at an energy of 105 MeV/u were measured in inverse kinematics conditions for the development of realistic nuclear transmutation processes for long-lived fission products (LLFPs) with neutron and light-ion beams. The experimental results were compared to the PHITS calculations describing the intra-nuclear cascade and evaporation processes. Although an overall agreement was obtained, a large overestimation of the production cross sections for the removal of a few nucleons was seen. A clear shell effect associated with the neutron magic number N = 50 was observed in the measured isotopic production yields of Zr and Y isotopes, which can be reproduced reasonably by the PHITS calculation.

The $^{240}\mathrm{Am}(n,f$) cross section has been measured for the first time above 4 MeV, using the surrogate-ratio method over the neutron energy range of 200 keV to 14 MeV. The reactions $^{243}\mathrm{Am}(p,tf$) and $^{238}\mathrm{U}(p,tf$), which proceed through the fissioning excited nuclei $^{241}\mathrm{Am}$* and $^{236}\mathrm{U}$*, were used as surrogates for the desired $^{240}\mathrm{Am}(n,f$) and $^{235}\mathrm{U}(n,f$) reactions. The experiment was fielded using the STARLiTeR detector system with a recently commissioned VME-based data acquisition system. The 38.4-MeV proton beam used in these measurements was provided by the K150 cyclotron at the Texas A Cyclotron Institute. The measured $^{240}\mathrm{Am}(n,f$) cross section disagrees with many of the most recent evaluations, and a reevaluation is recommended.

The quadrupole collectivity of neutron-rich even-even neon and magnesium nuclei around $N=20$, ${}^{28,30}\mathrm{Ne}$, and ${}^{32,34,36}$Mg, was studied via proton inelastic scattering on a liquid hydrogen target by in-beam $\ensuremath{\gamma}$-ray spectroscopy in inverse kinematics. The angle-integrated cross sections for the first ${2}^{+}$ states of these nuclei were determined by measuring de-excitation $\ensuremath{\gamma}$ rays. The deformation lengths were extracted from the angle-integrated cross sections using distorted-wave calculations. The deformation length of ${}^{30}$Ne (${\ensuremath{\delta}}_{(p,{p}^{\ensuremath{'}})}=1.{59}_{\ensuremath{-}0.09}^{+0.08}$ fm) is smaller than that of ${}^{32}$Mg ($1.{83}_{\ensuremath{-}0.11}^{+0.10}$ fm), which exhibits the largest quadrupole collectivity among the neutron-rich $N=20$ isotones. Along the magnesium isotopic chain, the deformation lengths of ${}^{34}$Mg and ${}^{36}$Mg were deduced to be $2.{30}_{\ensuremath{-}0.10}^{+0.09}$ fm and $1.{90}_{\ensuremath{-}0.17}^{+0.16}$ fm, respectively. The evolution of quadrupole deformation in the vicinity of ${}^{32}$Mg is discussed by comparing the present results with the theoretical calculations.

The location of low-lying states in the very neutron-rich isotope 34 Mg has been determined for the first time. In-beam γ -ray spectroscopy was performed using a two-step fragmentation reaction. Two strong γ -lines were observed at 660(10) keV and 1460(20) keV, which are tentatively attributed to the 2 + 1 →0 + g.s. and 4 + 1 →2 + 1 transitions in 34 Mg, respectively. These tentative assignments lead to a very low energy for the 2 + 1 state and a large E (4 + 1 )/ E (2 + 1 ) ratio of about 3.2, in agreement with the expectations for a well deformed isotope.

Angular distributions of the Coulomb dissociation of B-8 in the field of Pb-208 at E(in) = 51.9 MeV/u were measured at 0 degrees less than or equal to theta(8) less than or equal to 10 degrees and 0.5 less than or equal to E(rel) less than or equal to 2.25 MeV. The data were analyzed using a quantum mechanical method where E1, E2 and l = 2 nuclear amplitudes are included. Although systematic effects could be large, the extracted E2 components appear to be considerably smaller than any theoretical predictions reported so far.

Using a ${}^{13}$O beam, we have observed proton decays of ${}^{12}$N and ${}^{13}$O excited states following proton-knockout and inelastic interactions on a ${}^{9}$Be target. The excited states were determined from detected two- and three-body exit channels using the invariant mass method. The width of the second excited state of ${}^{12}$N was determined to be 55(20) keV, considerably smaller than the value listed in the ENSDF data base. Three new excited states of narrow width ($\ensuremath{\Gamma}l50$ keV) were observed in ${}^{13}$O from the $p$+${}^{12}$N and 2$p$+${}^{11}$C exit channels. One of these states (${E}^{*}$ = 3.67 MeV) was found to sequentially decay to the second excited of ${}^{12}$N. We again found these data to be inconsistent with the listed decay width. The ramifications for the astrophysically interesting ${}^{11}$C($p$,$\ensuremath{\gamma}$)${}^{12}$N reaction are given.

Elastic N-13 + C-13 cross sections are measured at center-of-mass energies of 8.15, 10.0, and 14.75 MeV, using a radioactive N-13 beam and position-sensitive solid-state detectors. The N-13 + C-13 angular distributions display oscillations beyond 80 degrees and even a significant rise at large angles for the two higher energies. These data are analyzed in the framework of the optical model including a parity-dependent term necessary to explain the backward behavior. This parity term is among the strongest encountered in heavy-ion collisions. Its properties are close to those of the parity term reproducing the N-13 + C-12 elastic scattering in the same energy range. Its long-range nature indicates that the parity dependence arises from a single rather than from a double exchange. One-pion charge exchange between the valence nucleons seems to possess the necessary properties as qualitatively shown by a simple molecular model.

The Coulomb-dissociation cross section for the process B-8 --> Be-7 + p in the field of Pb-208 was measured at E(B-8) = 46.5 A MeV. The Be-7(p,gamma)B-8 cross section relevant to the high-energy B-8 solar-neutrino production was extracted at E(C.M.) = 0.6 - 1.7 MeV. Two theoretical models on the structure of 8B were used to evaluate possible corrections due to M1 and E2 admixtures to the dominant E1 cross sections. Their overall effect is shown to be small regardless of the choice of the models. The present result is consistent with the results of the direct measurements of Filippone et al. and Vaughn et al. within errors. This result suggests further studies with the Coulomb-dissociation method to extract astrophysical S-17 factor at similar to 20 keV relevant to the high-energy solar-neutrino flux.

The N-13+C-12 and C-13+C-12 elastic cross sections are measured at the center-of-mass energies of 7.8, 9.6, and 14.2 MeV, using radioactive N-13 and stable C-13 beams and position-sensitive solid-state detectors. These data are analyzed with the optical model assuming the same real central part of the nuclear potential for both systems as suggested by charge symmetry. The N-13+C-12 angular distributions display a significant backward rise which arises from a parity dependence of the nucleus-nucleus interaction, as for the mirror C-13+C-12 system. The corresponding parity terms in both potentials are similar when the different charges of the exchanged nucleons and their different binding energies are properly taken into account. A smaller imaginary part is obtained for N-13+C-12 than for C-13+C-12, which might be due to a smaller number of open-two-body inelastic and direct reaction channels.

Ion-implanted silicon detectors were irradiated with 18-150 MeV /sup 16/O, 20 MeV /sup 40/Ar, and 53 MeV /sup 110/Xe. A linear increase of the leakage current was observed as a function of the particle fluence up to 2.2/spl times/10/sup 8/ cm/sup -2/. Extracted damage factors are proportional to the averaged nuclear stopping power over five orders of magnitude covering heavy ions studied in the present work and also protons of 25-800 MeV energies. >

The Coulomb excitation of a very neutron-rich nucleus 32Mg to its 2+ state was studied using an unstable nuclear beam of 32Mg at 49.2 MeV/u with a 208Pb target. The B(E2) value of 454±78 e2fm4 was extracted by a coupled channel analysis. The value is in good agreement with recent predictions. It confirms a large deformation for 32Mg suggested by the low excitation energy of the 2+ state, and points to the vanishing of the N = 20 shell gap.

International audience; We have measured the production rates and production cross sections for a variety of radioactive isotopes which were produced from 124Xe, 48Ca, and 238U beams at an energy of 345 MeV/nucleon using the BigRIPS separator at the RIKEN Nishina Center RI Beam Factory (RIBF). Proton-rich isotopes with atomic numbers Z = 40 to 52 and neutron-rich isotopes with Z = 5 to 16 were produced by projectile fragmentation of the 124Xe and 48Ca beam on Be targets, respectively. Neutron-rich isotopes with Z = 20 to 59 were produced by in-flight fission of the 238U beam, in which both Be and Pb were used as production targets. The measured production rates and production cross sections were compared with those of the LISE++ calculations, and overall fairly good agreement has been obtained. Furthermore, in the measurements with the 124Xe beam, we have discovered four new isotopes on the proton-drip line, 85,86Ru and 81,82Mo, and obtained the clear evidence that 103Sb is particle unbound with an upper limit of 49 ns for the half-life. The measurements of projectile-fragment momentum distributions have been also performed with the 124Xe beam, in which the low-momentum tails of the distributions have been measured for the first time at the energy of 345 MeV/nucleon.

A large acceptance and high magnetic rigidity spectrometer facility, SAMURAI is under construction at RlKEN. We plan to perform breakup reaction experiments that focus on the proton rich nuclei structure. The Si tracker needs to detect multiple nuclear fragments from the breakup reaction simultaneously. Atomic numbers of those fragments lie between 1 and 50. In the case of Sn breakup reaction, the energy deposition of fully stripped Z=50 fragment is 2500 times as large as that of Z=1 fragment. In order to realize such measurements, an amplifier with wide dynamic range of more than 2500 is required. Because it must operate under vacuum, it is necessary to minimize the amount of material. Therefore, we developed an amplifier IC which satisfies the requirements by implementing a square root gain response circuit.

Following neutron knockout from an ${}^{13}$O beam, ${}^{12}$O fragments were created and the three decay products following two-proton decay were detected. A new ground-state mass was determined by the invariant mass method implying a decay kinetic energy of 1.638(24) MeV, and the width was found to be less than 72 keV. The latter is inconsistent with previous measurements with lower experimental resolutions but consistent with theoretical estimates. The isobaric analog of ${}^{12}$O in ${}^{12}$N was produced from proton knockout reactions with the same beam and decayed by two-proton emission to the isobaric analog state in ${}^{10}$B with a decay kinetic energy of 1.165(29) MeV. It represents only the second case of an analog state where two-proton decay is the only isospin- and energy-conserving particle decay mode. With our measurements of the mass excesses of ${}^{12}$O and its analog, the quadratic form of the isobaric multiplet mass equation was found to fit the $A=12$ quintet and any deviations are less than the magnitude found for the $A=8$ quintet and $A=7$ and 9 quartets.

The reduced transition probability B(E2; 0(gs)(+) -> 2(1)(+)) for S-28 was obtained experimentally using Coulomb excitation at 53 MeV/nucleon. The resultant B(E2) value 181(31) e(2)fm(4) is smaller than the expectation based on empirical B(E2) systematics. The double ratio vertical bar M-n/M-p vertical bar/(N/Z) of the 0(gs)(+) -> 2(1)(+) transition in S-28 was determined to be 1.9(2) by evaluating the M-n value from the known B(E2) value of the mirror nucleus Mg-28, showing the hindrance of proton collectivity relative to that of neutrons. These results indicate the emergence of the magic number Z = 16 in the vertical bar T-z vertical bar = 2 nucleus S-28.

The cross section for Coulomb dissociation of $^{8}\mathrm{B}$---the $^{208}\mathrm{Pb}(^{8}\mathrm{B}^{7}\mathrm{Be}p)^{208}\mathrm{Pb}$ reaction---was measured using a $^{8}\mathrm{B}$ radioactive beam of 46.5 MeV/nucleon energy, and the cross section for the $^{7}\mathrm{Be}(p,\ensuremath{\gamma})^{8}\mathrm{B}$ capture reaction was deduced at low energies; ${E}_{\mathrm{c}.\mathrm{m}.}=0.6\ensuremath{-}1.7$ MeV. The extracted astrophysical ${S}_{17}$ factors were found to be consistent with the values measured by Vaughn et al. and Filippone et al. This result encourages further experimental studies extended to lower relative energies for a new determination of the ${S}_{17}$ value relevant to the $^{8}\mathrm{B}$ solar neutrino flux.