Discovery of

The new isotope ^{39}Na, the most neutron-rich sodium nucleus observed so far, was discovered at the RIKEN Nishina Center Radioactive Isotope Beam Factory using the projectile fragmentation of an intense ^{48}Ca beam at 345 MeV/nucleon on a beryllium target. Projectile fragments were separated and identified in flight with the large-acceptance two-stage separator BigRIPS. Nine ^{39}Na events have been unambiguously observed in this work and clearly establish the particle stability of ^{39}Na. Furthermore, the lack of observation of ^{35,36}Ne isotopes in this experiment significantly improves the overall confidence that ^{34}Ne is the neutron dripline nucleus of neon. These results provide new key information to understand nuclear binding and nuclear structure under extremely neutron-rich conditions. The newly established stability of ^{39}Na has a significant impact on nuclear models and theories predicting the neutron dripline and also provides a key to understanding the nuclear shell property of ^{39}Na at the neutron number N=28, which is normally a magic number.

Two-Neutron Halo is Unveiled in

We report the measurement of reaction cross sections (σ_{R}^{ex}) of ^{27,29}F with a carbon target at RIKEN. The unexpectedly large σ_{R}^{ex} and derived matter radius identify ^{29}F as the heaviest two-neutron Borromean halo to date. The halo is attributed to neutrons occupying the 2p_{3/2} orbital, thereby vanishing the shell closure associated with the neutron number N=20. The results are explained by state-of-the-art shell model calculations. Coupled-cluster computations based on effective field theories of the strong nuclear force describe the matter radius of ^{27}F but are challenged for ^{29}F.

Location of the Neutron Dripline at Fluorine and Neon.

A search for the heaviest isotopes of fluorine, neon, and sodium was conducted by fragmentation of an intense ^{48}Ca beam at 345 MeV/nucleon with a 20-mm-thick beryllium target and identification of isotopes in the large-acceptance separator BigRIPS at the RIKEN Radioactive Isotope Beam Factory. No events were observed for ^{32,33}F, ^{35,36}Ne, and ^{38}Na and only one event for ^{39}Na after extensive running. Comparison with predicted yields excludes the existence of bound states of these unobserved isotopes with high confidence levels. The present work indicates that ^{31}F and ^{34}Ne are the heaviest bound isotopes of fluorine and neon, respectively. The neutron dripline has thus been experimentally confirmed up to neon for the first time since ^{24}O was confirmed to be the dripline nucleus nearly 20 years ago. These data provide new keys to understanding the nuclear stability at extremely neutron-rich conditions.

Discovery of

The discovery of the important neutron-rich nucleus _{20}^{60}Ca_{40} and seven others near the limits of nuclear stability is reported from the fragmentation of a 345 MeV/u ^{70}Zn projectile beam on ^{9}Be targets at the radioactive ion-beam factory of the RIKEN Nishina Center. The produced fragments were analyzed and unambiguously identified using the BigRIPS two-stage in-flight separator. The eight new neutron-rich nuclei discovered, ^{47}P, ^{49}S, ^{52}Cl, ^{54}Ar, ^{57}K, ^{59,60}Ca, and ^{62}Sc, are the most neutron-rich isotopes of the respective elements. In addition, one event consistent with ^{59}K was registered. The results are compared with the drip lines predicted by a variety of mass models and it is found that the models in best agreement with the observed limits of existence in the explored region tend to predict the even-mass Ca isotopes to be bound out to at least ^{70}Ca.

Guillain-Barré syndrome in a local area in Japan, 2006-2015: an epidemiological and clinical study of 108 patients.

BACKGROUND AND PURPOSE: Many epidemiological studies of Guillain-Barré syndrome (GBS) and Fisher syndrome (FS) have been conducted in Europe and America. In contrast, epidemiological studies are rare in Asia where the GBS subtypes differ from those in Western countries. This study was undertaken to clarify the incidence of GBS and FS in a local area in Japan as well as their seasonal trends. METHOD: Seventy-one GBS and 37 FS patients were recorded from 2006 to 2015 in an area of approximately 1.5 million inhabitants in Japan. The incidence, seasonal trends and clinical features of GBS and FS were examined. RESULTS: The incidence rate of GBS was 0.42 cases per 100 000 person-years and that of FS was 0.22 cases per 100 000 person-years. The incidence of GBS increased with age and FS affected predominantly patients aged from 45 to 64 years old. There was some seasonal clustering of acute motor axonal neuropathy (AMAN) and FS in spring and summer, but it was not significant. AMAN and FS patients had a high frequency of preceding infection (AMAN, 68% gastrointestinal infection; FS, 65% upper respiratory infection). Antecedent respiratory infection was significantly associated with FS as an outcome. Serum antibodies to ganglioside GM1 were detected in 71% of AMAN patients and antibodies to GQ1b were detected in 81% of FS patients. CONCLUSIONS: Our study offers evidence of a lower incidence of GBS and a higher incidence of FS in a local area in Japan than in Western countries.

Time-Reversal Measurement of the p-Wave Cross Sections of the

The cross sections of the ^{7}Be(n,α)^{4}He reaction for p-wave neutrons were experimentally determined at E_{c.m.}=0.20-0.81 MeV slightly above the big bang nucleosynthesis (BBN) energy window for the first time on the basis of the detailed balance principle by measuring the time-reverse reaction. The obtained cross sections are much larger than the cross sections for s-wave neutrons inferred from the recent measurement at the n_TOF facility in CERN, but significantly smaller than the theoretical estimation widely used in the BBN calculations. The present results suggest the ^{7}Be(n,α)^{4}He reaction rate is not large enough to solve the cosmological lithium problem, and this conclusion agrees with the recent result from the direct measurement of the s-wave cross sections using a low-energy neutron beam and the evaluated nuclear data library ENDF/B-VII.1.

Hindered proton collectivity in 16(28)S12: possible magic number at Z=16.

The reduced transition probability B(E2;0(gs)(+)→2(1)(+)) for (28)S 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 |M(n)/M(p)|/(N/Z) of the 0(gs)(+)→2(1)(+) transition in (28)S was determined to be 1.9(2) by evaluating the M(n) value from the known B(E2) value of the mirror nucleus (28)Mg, showing the hindrance of proton collectivity relative to that of neutrons. These results indicate the emergence of the magic number Z=16 in the |T(z)|=2 nucleus (28)S.

Observation of a large reaction cross section in the drip-line nucleus 22C.

Reaction cross sections (sigma(R)) for 19C, 20C and the drip-line nucleus 22C on a liquid hydrogen target have been measured at around 40A MeV by a transmission method. A large enhancement of sigma(R) for 22C compared to those for neighboring C isotopes was observed. Using a finite-range Glauber calculation under an optical-limit approximation the rms matter radius of 22C was deduced to be 5.4+/-0.9 fm. It does not follow the systematic behavior of radii in carbon isotopes with N < or = 14, suggesting a neutron halo. It was found by an analysis based on a few-body Glauber calculation that the two-valence neutrons in 22C preferentially occupy the 1s(1/2) orbital.

Combination chemotherapy of intraperitoneal carboplatin and intravenous paclitaxel in suboptimally debulked epithelial ovarian cancer.

The objective of this study was to retrospectively assess the efficacy and safety of combination chemotherapy of intraperitoneal (IP) carboplatin and intravenous (IV) paclitaxel in suboptimally debulked ovarian cancer. Between March 1998 and March 2006, 44 patients with histologically confirmed epithelial ovarian carcinoma or peritoneal carcinoma with a residual mass greater than 1 cm received combination chemotherapy of IV paclitaxel and IP carboplatin. Administration of IV paclitaxel at 175 mg/m(2) immediately followed by IP carboplatin at an area under the curve of 6 was scheduled every 3 weeks for at least six cycles. The diagnosis and stage were ovarian carcinoma stage II in 8, III in 25, and IV in 6 cases, and peritoneal carcinoma stage III in 5 cases. Eighty-three percent of patients completed more than six cycles of chemotherapy. The incidences of grade 3/4 hematologic toxicities were 41 (93%) for neutrocytopenia, 10 (41%) for thrombocytopenia, and 18 (23%) for anemia. Observed grade 3/4 nonhematologic toxicities were 1 (2%) for allergy, 1 (2%) for fatigue, 1 (2%) for vomiting, 1 (2%) for liver dysfunction, and 4 (9%) for peripheral neuropathy. Two patients (5%) encountered catheter problems (one obstruction and one infection). Overall response rate was 80% (16 complete response, 19 partial response, 3 stable disease, and 6 progressive disease). Median progression-free survival and overall survival were 24 and 31 months, respectively. Combination chemotherapy of IP carboplatin and IV paclitaxel is effective and safe in suboptimally debulked ovarian cancer, and further evaluation is warranted.

Spectroscopic study of neutron shell closures via nucleon transfer in the near-dripline nucleus 23O.

Neutron single particle energies have been measured in 23O using the 22O(d,p)23O*-->22O+n process. The energies of the resonant states have been deduced to be 4.00(2) MeV and 5.30(4) MeV. The first excited state can be assigned to the nu d3/2 single particle state from a comparison with shell model calculations. The measured 4.0 MeV energy difference between the nu s1/2 and nu d3/2 states gives the size of the N=16 shell gap which is in agreement with the recent USD05 ("universal" sd from 2005) shell model calculation, and is large enough to explain the unbound nature of the oxygen isotopes heavier than A=24. The resonance detected at 5.3 MeV can be assigned to a state out of the sd shell model space. Its energy corresponds to a approximately 1.3 MeV sized N=20 shell gap, therefore, the N=20 shell closure disappears at Z=8 in agreement with Monte Carlo shell model calculations using SDPF-M interaction.