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論文

Construction of a new multi-reflection time-of-flight mass spectrograph at RAON

Moon, J. Y.*; 伊藤 由太; 他13名*

Journal of the Korean Physical Society, 9 Pages, 2024/12

https://doi.org/10.1007/s40042-024-01237-x
 被引用回数：0 パーセンタイル：0.00(Physics, Multidisciplinary)

A new large-scale heavy-ion accelerator complex, RAON (Rare isotope Accelerator complex for ON-line experiments), in Korea has implemented the state-of-art device, multi-reflection time-of-flight mass spectrometer (MRTOF-MS) for the mass spectrometry of the exotic nuclei. Using the multi-reflections of ions between a pair of grid-free mirror electrodes and therefore extending the fly length, it can achieve the incredibly high mass resolving power of within a short measurement time of $$<$$ 10 ms, providing the nuclear mass of the exotic nuclei with a high-precision level of sub-ppm. The device is coupled to one of the beamlines in the ISOL experimental hall, ready for participating in the longstanding topics of nuclear structure in the outskirts of the nuclear chart and nucleosynthesis of heavy elements in explosive astrophysical environments. The exclusively high mass resolving power is also advantageous for reducing the isobaric contaminants that rare isotope ion beam facilities suffer from. In this paper, we present a summary of the construction and current performance of the RAON MRTOF-MS.

論文

Comprehensive mass measurement study of $$^{252}$$Cf fission fragments with MRTOF-MS and detailed study of masses of neutron-rich Ce isotopes

木村 創大*; 伊藤 由太; 他8名*

Physical Review C, 110(4), p.045810_1 - 045810_9, 2024/10

https://doi.org/10.1103/PhysRevC.110.045810
 被引用回数：2 パーセンタイル：74.11(Physics, Nuclear)

We report the mass measurements of neutron-rich isotopes produced via spontaneous fission of $$^{252}$$Cf using a multireflection time-of-flight mass spectrograph. The mass of $$^{155}$$Ce is determined experimentally for the first time. A discrepancy between the experimental and literature values was found for the mass of $$^{127}$$Sb, which was previously deduced through indirect measurements. In comparison with several theoretical predictions, both the values and the trend of the mass excesses of $$^{152sim155}$$Ce cannot be consistently explained. The wide-range and simultaneous mass measurements of the multireflection time-of-flight mass spectrograph enable us to crosscheck the existing mass data, and the conflict between the measured time-of-flight ratio and the extracted mass would imply the necessity of re-examining them.

論文

Mass measurements of neutron-rich $$A approx 90$$ nuclei constrain element abundances

Xian, W.*; 伊藤 由太; 他30名*

Physical Review C, 109(3), p.035804_1 - 035804_10, 2024/03

https://doi.org/10.1103/PhysRevC.109.035804
 被引用回数：1 パーセンタイル：0.00(Physics, Nuclear)

Atomic masses of the neutron-rich isotopes $$^{83,84}$$Ga, $$^{82sim86}$$Ge, $$^{82sim89}$$As, $$^{82,84sim91}$$Se, $$^{85,86,89sim92}$$Br, $$^{89,91,92}$$Kr, and $$^{91}$$Rb have been measured with high precision and accuracy using the multi-reflection time-of-flight mass spectrograph at the RIBF facility. The masses of $$^{88,89}$$As were measured for the first time and the mass uncertainties of $$^{86}$$Ge and $$^{90,91}$$Se were significantly reduced from several hundred keV to below the 10 keV scale. Investigation of shell evolution and potential subshell closures are proceeded by analysis of two-neutron separation energy systematics. As a result of the precise mass measurements, no prominent change on the slope of the two-neutron separation energy beyond $$N=56$$ is observed in Se isotopes, indicating the subshell closure effect at $$N=56$$ of Se does not exist. Also, various leading mass models are compared with the measurements. The impact of the more precisely known data on r-process nucleosynthesis calculations is investigated in light of these new mass measurements, showing a remarkable reduction of reaction-rate uncertainties.

論文

Multi-reflection time-of-flight mass spectroscopy for superheavy nuclides

Schury, P.*; 伊藤 由太; 庭瀬 暁隆*; 和田 道治*

Atoms (Internet), 11(10), p.11100134_1 - 11100134_13, 2023/10

https://doi.org/10.3390/atoms11100134

The atomic masses of isotopes of elements beyond fermium, which can presently only be produced online via fusion-evaporation reactions, have until recently been determined only from $$alpha$$ decay chains reaching nuclides with known atomic masses. Especially in the case of lower-yield nuclides, for which the sufficiently detailed nuclear spectroscopy required to fully determine the nuclear structure is not possible, such indirect mass determinations may suffer systematic errors. For many superheavy nuclides, their decay chains end in spontaneous fission or in $$beta$$-decay prior to reaching nuclides of known mass. To address this dearth of accurate atomic masses, we have developed a multi-reflection time-of-flight mass spectrograph that can make use of decay-correlations to accurately and precisely determine atomic masses for the very low-yield superheavy nuclides.

論文

Discovery of new isotope $$^{241}$$U and systematic high-precision atomic mass measurements of neutron-rich Pa-Pu nuclei produced via multinucleon transfer reactions

庭瀬 暁隆*; 伊藤 由太; 他18名*

Physical Review Letters, 130(13), p.132502_1 - 132502_6, 2023/03

https://doi.org/10.1103/PhysRevLett.130.132502
 被引用回数：39 パーセンタイル：98.35(Physics, Multidisciplinary)

新同位体$$^{241}$$Uを合成し、KISS施設の$$^{238}$$U+$$^{198}$$Pt系の多核子移行反応において、19種類の中性子過剰Pa-Pu同位体の系統的原子量測定が行われた。本実験結果は、この領域の核種において、$$N=152$$シェルギャップに向かう未踏の中性子過剰アクチニド同位体へのアクセスに多核子移行反応が重要な役割を果たすことを実証した。

論文

Study of the $$N=32$$ and $$N=34$$ shell gap for Ti and V by the first high-precision multireflection time-of-flight mass measurements at BigRIPS-SLOWRI

飯村 俊*; Rosenbusch, M.*; 高峰 愛子*; 角田 佑介*; 和田 道治*; Chen, S.*; Hou, D. S.*; Xian, W.*; 石山 博恒*; Yan, S.*; et al.

Physical Review Letters, 130(1), p.012501_1 - 012501_6, 2023/01

https://doi.org/10.1103/PhysRevLett.130.012501
 被引用回数：13 パーセンタイル：88.67(Physics, Multidisciplinary)

The atomic masses of $$^{55}$$Sc, $$^{56,58}$$Ti, and $$^{56-59}$$V have been determined using the high-precision multireflection time-of-flight technique. The radioisotopes have been produced at RIKEN's Radioactive Isotope Beam Factory (RIBF) and delivered to the novel designed gas cell and multireflection system, which has been recently commissioned downstream of the ZeroDegree spectrometer following the BigRIPS separator. For $$^{56,58}$$Ti and $$^{56-59}$$V, the mass uncertainties have been reduced down to the order of 10 keV, shedding new light on the $$N=34$$ shell effect in Ti and V isotopes by the first high-precision mass measurements of the critical species $$^{58}$$Ti and $$^{59}$$V. With the new precision achieved, we reveal the nonexistence of the $$N=34$$ empirical two-neutron shell gaps for Ti and V, and the enhanced energy gap above the occupied $$nu$$p$$_{3/2}$$ orbit is identified as a feature unique to Ca. We perform new Monte Carlo shell model calculations including the $$nu$$d$$_{5/2}$$ and $$nu$$g$$_{9/2}$$ orbits and compare the results with conventional shell model calculations, which exclude the $$nu$$g$$_{9/2}$$ and the $$nu$$d$$_{5/2}$$ orbits. The comparison indicates that the shell gap reduction in Ti is related to a partial occupation of the higher orbitals for the outer two valence neutrons at $$N = 34$$.

論文

Prediction of charge-changing cross sections of low-charged $$^{88}$$Sr, $$^{138}$$Ba and $$^{142}$$Nd ions in a He-gas target at collision energies 50 eV/u - 10 GeV/u

Tolstikhina, I. Yu.*; 伊藤 由太; Shevelko, V. P.*

Nuclear Instruments and Methods in Physics Research B, 532, p.27 - 37, 2022/12

https://doi.org/10.1016/j.nimb.2022.10.002
 被引用回数：4 パーセンタイル：52.14(Instruments & Instrumentation)

電荷$$q=0$$, 1, 2の中性及び低電荷重Sr$$^{q+}$$, Ba$$^{q+}$$及びNd$$^{q+}$$イオンとHe原子の衝突による電子損失断面積及び電子捕獲断面積をエネルギー範囲$$E=50$$eV/u-10GeV/uにおいて予測した。これらの粒子とHe原子の衝突によるEL断面積とEC断面積に関する実験データはほとんどない。比較的低いエネルギー$$E=8$$-30keVにおいて、Sr$$^{1+}$$, Ba$$^{1+}$$及びNd$$^{1+}$$イオンのEL断面積$$sigma_{12}$$を新しい実験平衡電荷状態フラクション$$F_1$$及び$$F_2$$とEC断面積計算から予測した。Ba$$^{1+}$$イオンの予測値$$sigma_{12}=6.8cdot10^{-18}$$cm$$^2$$は、$$E=20$$keV(Fedorenko, 1954)における一つの実験点$$sigma_{12}^{rm exp}=5.7cdot10^{-18}$$cm$$^2$$とよく一致することが示された。EL断面積とEC断面積の計算は、論文で簡単に説明されている利用可能なコンピュータコードによって行われる。理論的に推定された中性原子割合$$F_0$$は、測定された$$F_1$$, $$F_2$$, $$F_3$$電荷状態割合よりもはるかに小さいことがわかった。

論文

New $$K$$ isomers in $$^{248}$$Cf

Orlandi, R.; 牧井 宏之; 西尾 勝久; 廣瀬 健太郎; 浅井 雅人; 塚田 和明; 佐藤 哲也; 伊藤 由太; 洲嵜 ふみ; 永目 諭一郎*; et al.

Physical Review C, 106(6), p.064301_1 - 064301_11, 2022/12

https://doi.org/10.1103/PhysRevC.106.064301
 被引用回数：4 パーセンタイル：52.14(Physics, Nuclear)

The nuclear structure of $$^{248}$$Cf produced by the $$^{18}$$O+$$^{249}$$Cf multinucleon transfer reaction was investigated using $$gamma$$-ray spectroscopy. Analysis of the $$gamma$$-ray spectrum of $$^{248}$$Cf revealed the presence of multiple long-lived (isomeric) excited states at low excitation energies. The energies and half-lives of the isomers contain information on the proton and neutron orbits in the heavy-element region and the deformation of atomic nuclei, and are important data to predict the properties of nuclei in the "island of stability".

論文

The $$^{59}$$Fe(n,$$gamma$$)$$^{60}$$Fe cross section from the surrogate ratio method and its effect on the $$^{60}$$Fe nucleosynthesis

Yan, S. Q.*; Li, X. Y.*; 西尾 勝久; Lugaro, M.*; Li, Z. H.*; 牧井 宏之; Pignatari, M.*; Wang, Y. B.*; Orlandi, R.; 廣瀬 健太郎; et al.

Astrophysical Journal, 919(2), p.84_1 - 84_7, 2021/10

https://doi.org/10.3847/1538-4357/ac12ce
 被引用回数：5 パーセンタイル：33.27(Astronomy & Astrophysics)

The long-lived $$^{60}$$Fe (with a half-life of 2.62 Myr) is a crucial diagnostic of active nucleosynthesis in the Milky Way galaxy and in supernovae near the solar system. The neutron-capture reaction $$^{59}$$Fe(n,$$gamma$$)$$^{60}$$Fe on $$^{59}$$Fe (half-life=44.5 days) is the key reaction for the production of $$^{60}$$Fe in massive stars. This reaction cross section has been previously constrained by the Coulomb dissociation experiment, which offered partial constraint on the E1 $$gamma$$-ray strength function but a negligible constraint on the M1 and E2 components. In this work, for the first time, we use the surrogate ratio method to experimentally determine the $$^{59}$$Fe(n,$$gamma$$)$$^{60}$$Fe cross sections in which all the components are included. We derived a Maxwellian-averaged cross section of 27.5$$pm$$3.5 mb at $$kT$$ = 30 keV and 13.4$$pm$$1.7 mb at $$kT$$ = 90 keV, roughly 10%-20% higher than previous estimates. We analyzed the impact of our new reaction rates in nucleosynthesis models of massive stars and found that uncertainties in the production of $$^{60}$$Fe from the $$^{59}$$Fe(n,$$gamma$$)$$^{60}$$Fe rate are at most 25$$%$$. We conclude that stellar physics uncertainties now play a major role in the accurate evaluation of the stellar production of $$^{60}$$Fe.

論文

$$alpha$$-decay-correlated mass measurement of $$^{206,207g,m}$$Ra using an $$alpha$$-TOF detector equipped multireflection time-of-flight mass spectrograph system

庭瀬 暁隆*; 伊藤 由太; 他26名*

Physical Review C, 104(4), p.044617_1 - 044617_8, 2021/10

https://doi.org/10.1103/PhysRevC.104.044617
 被引用回数：6 パーセンタイル：57.44(Physics, Nuclear)

The atomic masses of the isotopes 206,207Ra have been measured via decay-correlated mass spectroscopy using a multireflection time-of-flight mass spectrograph equipped with an $$alpha$$-TOF detector. The Ra isotopes were produced as fusion-evaporation products in the 51V+159Tb reaction system and delivered by the gas-filled recoil ion separator GARIS-II at RIKEN. The $$alpha$$-TOF detector provides for high-accuracy mass measurements by correlating time-of-flight signals with subsequent $$alpha$$-decay events. The masses of 206Ra and 207g,mRa were directly measured using a multireflection time-of-flight mass spectrograph equipped with an $$alpha$$-TOF detector. The mass excesses of 206,207gRa and the excitation energy of 207mRa were determined to be ME=3540(50)keV/c$$^{2}$$, 3538(15)keV/c$$^{2}$$, and Eex=552(42) keV, respectively. The $$alpha$$-decay branching ratio of 207mRa $$b_alpha$$=0.26(20), was directly determined from decay-correlated time-of-flight signals, and the reduced $$alpha$$ width of 207mRa was calculated to be $$delta^2$$=43 keV from the branching ratio. The spin-parity of 207mRa was confirmed to be J$$^pi$$=13/2$$^+$$ from decay correlated mass measurement results.

論文

Chemical characterization of a volatile dubnium compound, DbOCl$$_3$$

Chiera, N. M.*; 佐藤 哲也; Eichler, R.*; 富塚 知博; 浅井 雅人; 安達 サディア*; Dressler, R.*; 廣瀬 健太郎; 井上 浩樹*; 伊藤 由太; et al.

Angewandte Chemie; International Edition, 60(33), p.17871 - 17874, 2021/08

https://doi.org/10.1002/anie.202102808
 被引用回数：5 パーセンタイル：24.90(Chemistry, Multidisciplinary)

等温ガスクロマトグラフ法を用いて、105番元素ドブニウム(Db)の単一原子を対象として、揮発性オキシ塩化物を合成し、化学的性質を調べた。同一条件下で同族元素ニオブおよびタンタルの揮発性と比較したところ、NbOCl$$_3 > $$ TaOCl$$_3 geq$$ DbOCl$$_3$$の関係が得られた。これはDb分子中の共有結合性が周期表からの予想よりも強くなっているためと考えられる。本成果により、超アクチノイド元素の化学的性質に関する理論計算に対する信頼できる実験データを与えることができた。

論文

First high-precision direct determination of the atomic mass of a superheavy nuclide

Schury, P.*; 伊藤 由太; 小浦 寛之; 他25名*

Physical Review C, 104(2), p.L021304_1 - L021304_7, 2021/08

https://doi.org/10.1103/PhysRevC.104.L021304
 被引用回数：18 パーセンタイル：88.41(Physics, Nuclear)

We present the first direct measurement of the atomic mass of a superheavy nuclide. Atoms of $$^{257}$$Db (Z=105) were produced online at the RIKEN Nishina Center for Accelerator-Based Science using the fusion-evaporation reaction $$^{208}$$Pb($$^{51}$$V, 2n)$$^{257}$$Db. The gas-filled recoil ion separator GARIS-II was used to suppress both the unreacted primary beam and some transfer products, prior to delivering the energetic beam of $$^{257}$$Db ions to a helium gas-filled ion stopping cell wherein they were thermalized. Thermalized $$^{257}$$Db$$^{3+}$$ ions were then transferred to a multireflection time-of-flight mass spectrograph for mass analysis. An alpha particle detector embedded in the ion time-of-flight detector allowed disambiguation of the rare $$^{257}$$Db$$^{3+}$$ time-of-flight detection events from background by means of correlation with characteristic $$alpha$$ decays. The extreme sensitivity of this technique allowed a precision atomic mass determination from 11 events. The mass excess was determined to be 100063(231)$$_{rm stat}$$(132)$$_{rm sys}$$ keV/c$$^{2}$$. Comparing to several mass models, we show the technique can be used to unambiguously determine the atomic number as Z=105 and should allow similar evaluations for heavier species in future work.

論文

Reduction of contaminants originating from primary beam by improving the beam stoppers in GARIS-II

木村 創大*; 伊藤 由太; 他5名*

Nuclear Instruments and Methods in Physics Research A, 992, p.164996_1 - 164996_4, 2021/03

https://doi.org/10.1016/j.nima.2020.164996
 被引用回数：2 パーセンタイル：24.88(Instruments & Instrumentation)

Two independent beam stoppers have been developed for improving the beam separation of the gas-filled recoil ion separator GARIS-II. Performance of these supplemental beam stoppers was investigated by using the $$^{208}$$Pb($$^{18}$$O,3n)$$^{223}$$Th reaction. A160-fold enhancement of the signal-to-noise ratio at the GARIS-II focal plane was observed.

論文

Development of an "$$alpha$$-TOF" detector for correlated measurement of atomic masses and decay properties

庭瀬 暁隆*; 伊藤 由太; 他13名*

Nuclear Instruments and Methods in Physics Research A, 953, p.163198_1 - 169198_8, 2020/02

https://doi.org/10.1016/j.nima.2019.163198
 被引用回数：12 パーセンタイル：71.69(Instruments & Instrumentation)

We have developed a novel detector, referred to as an "$$alpha$$-TOF detector", for correlated measurements of atomic masses and decay properties of low-yield, short-lived radioactive isotopes using a multi-reflection time-of-flight mass spectrograph. By correlating measured time-of-flight signals with decay events, it will be possible to suppress background events and obtain accurate, high-precision mass and half-life values even in cases of very low event rates. An offline test of the -TOF detector has shown that the time-of-flight detection efficiency for 5.48 MeV -rays is more than 90% and yields a time resolution of 250.6(68) ps and an alpha-energy resolution of 141.1(9) keV. Using a two-dimensional spectrum of the correlated -ray energy and time-of-flight, the -rays from mixed sources could be resolved. Subsequent testing using -emitting nuclei extracted offline from a gas cell provide verification of the -ray based characterization.

論文

Study of quasielastic barrier distributions as a step towards the synthesis of superheavy elements with hot fusion reactions

田中 泰貴*; 森田 浩介*; 森本 幸司*; 加治 大哉*; 羽場 宏光*; Boll, R. A.*; Brewer, N. T.*; Van Cleve, S.*; Dean, D. J.*; 石澤 倫*; et al.

Physical Review Letters, 124(5), p.052502_1 - 052502_6, 2020/02

https://doi.org/10.1103/PhysRevLett.124.052502
 被引用回数：33 パーセンタイル：85.88(Physics, Multidisciplinary)

The excitation functions for quasielastic scattering of $$^{22}$$Ne+$$^{248}$$Cm, $$^{26}$$Mg+$$^{248}$$Cm, $$^{48}$$Ca+$$^{238}$$U are measured using a gas-filled recoil ion separator The quasielastic barrier distributions are extracted for these systems and are compared with coupled-channel calculations. The results indicate that the barrier distribution is affected dominantly by deformation of the actinide target nuclei, but also by vibrational or rotational excitations of the projectile nuclei, as well as neutron transfer processes before capture. From a comparison between the experimental barrier distributions and the evaporation residue cross sections for Sg (Z=106), Hs (108), Cn (112), and Lv (116), it is suggested that the hot fusion reactions take advantage of a compact collision, where the projectile approaches along the short axis of a prolately deformed nucleus. A new method is proposed to estimate the optimum incident energy to synthesize unknown superheavy nuclei using the barrier distribution.

論文

A New multi-reflection time-of-flight mass spectrograph for the SLOWRI facility

Rosenbusch, M.*; 伊藤 由太; 他14名*

Nuclear Instruments and Methods in Physics Research B, 463, p.184 - 188, 2020/01

https://doi.org/10.1016/j.nimb.2019.05.058
 被引用回数：12 パーセンタイル：74.60(Instruments & Instrumentation)

A new multi-reflection time-of-flight mass spectrograph for nuclear mass measurements with high precision has been constructed at the SLOWRI facility at RIKEN-RIBF. We aim to couple this new device to a cryogenic gas cell operated at the BigRIPS facility of RIBF. It is part of the SLOWRI project for slowing down and stopping intense radioactive ion beams provided downstream of RIKEN's superconducting ring cyclotron accelerator. In particular, this device is dedicated to be located at the end of the BigRIPS beam line to access ions that are presently guided to beam dumps during in-beam experiments. In this article the apparatus is described in detail.

論文

New excited 2$$^+$$ and 3$$^-$$ two-proton states in $$_{84}^{210}$$Po$$_{126}$$ populated by two-proton transfer

Dupont, E.*; Astier, A.*; Petrache, C. M.*; Lv, B. F.*; Deloncle, I.*; Kiener, J.*; Orlandi, R.; 牧井 宏之; 西尾 勝久; 廣瀬 健太郎; et al.

Physical Review C, 101(1), p.014309_1 - 014309_6, 2020/01

https://doi.org/10.1103/PhysRevC.101.014309
 被引用回数：2 パーセンタイル：20.23(Physics, Nuclear)

Five new 2$$^+$$ levels and one new 3$$^-$$ level were established in $$^{210}$$Po. The states were populated via the $$^{208}$$Pb($$^{12}$$C, $$^{10}$$Be) two-proton reaction experiment, performed at the JAEA Tandem in Tokai. A setup combining Ge, LaBr$$_3$$, and Si telescopes was used to detect in-beam $$gamma$$-rays and ejectile residues. Two-proton configurations were assigned to all new states. All assignments are strongly supported by shell-model calculations.

論文

Optimization of an isothermal gas-chromatographic setup for the chemical exploration of dubnium (Db, Z = 105) oxychlorides

Chiera, N. M.; 佐藤 哲也; 富塚 知博; 浅井 雅人; 伊藤 由太; 白井 香里*; 鈴木 颯人; 床井 健運; 豊嶋 厚史; 塚田 和明; et al.

Journal of Radioanalytical and Nuclear Chemistry, 320(3), p.633 - 642, 2019/06

https://doi.org/10.1007/s10967-019-06505-w
 被引用回数：2 パーセンタイル：17.25(Chemistry, Analytical)

等温ガスクロマトグラフ(IGC)装置を開発し、オンライン気相研究に向けた動作試験をおこなった。核反応によって合成した5族遷移金属ニオブおよびタンタルの短寿命同位体をガスジェット気流によってIGC装置へ直接搬送し、反応ガスとしてSOCl$$_2$$を用いてオキシ塩化物を生成する。このときのNbOCl$$_3$$およびTaOCl$$_3$$の生成条件並びに搬送条件を調べたところ、半減期($$t_{1/2}$$)が約30秒の核種について全体の効率が7%であると見込むことができた。したがって、本IGC装置は$$^{262}$$Db($$t_{1/2}$$=34秒)適用可能であることがわかった。

論文

First direct mass measurements of nuclides around $$Z$$ = 100 with a multireflection time-of-flight mass spectrograph

伊藤 由太*; Schury, P.*; 和田 道治*; 新井 郁也*; 羽場 宏光*; 平山 賀一*; 石澤 倫*; 加治 大哉*; 木村 創大*; 小浦 寛之; et al.

Physical Review Letters, 120(15), p.152501_1 - 152501_6, 2018/04

https://doi.org/10.1103/PhysRevLett.120.152501
 被引用回数：66 パーセンタイル：92.72(Physics, Multidisciplinary)

冷たい核融合反応および熱い融合反応によって生成した変形閉殻中性子数152の近傍に位置する原子核$$^{246}$$Es, $$^{251}$$Fm、および超フェルミウム原子核$$^{249-252}$$Md, $$^{254}$$Noの質量の直接測定を、多反射時間飛行質量分析装置(MR-TOF)を用いて実施した。$$^{246}$$Esおよび$$^{249,250,252}$$Mdの質量測定は世界で初めての成果である。さらに$$^{249,250}$$Mdの質量を$$alpha$$崩壊連鎖のアンカーポイントとして用いて$$^{261}$$Bhおよび$$^{266}$$Mtまでの重い原子核の質量を決定した。これらの新測定された質量を理論質量計算と比較し、巨視的・微視的模型の予測値と良い一致が見られることを示した。近接する3つの質量値から求められる経験的殻ギャップエネルギー$$delta_{2n}$$を今回の質量値から求め、MdおよびLrに対する変形閉殻中性子数$$N=152$$の存在を裏付ける結果を得た。

論文

Observation of doubly-charged ions of francium isotopes extracted from a gas cell

Schury, P.*; 和田 道治*; 伊藤 由太*; 加治 大哉*; 羽場 宏光*; 平山 賀一*; 木村 創大*; 小浦 寛之; MacCormick, M.*; 宮武 宇也*; et al.

Nuclear Instruments and Methods in Physics Research B, 407, p.160 - 165, 2017/06

https://doi.org/10.1016/j.nimb.2017.06.014
 被引用回数：16 パーセンタイル：79.30(Instruments & Instrumentation)

Ac, Ra, FrやRnといった様々な同位体を$$^{48}$$Caビームを用いた原子核融合-蒸発反応にて生成した。エネルギーを持ったイオンはヘリウムガスセル内で止まり、そして引き出される。引き出された個々のイオンは多反射時間飛行質量分光器を用いて同定されるが、アルカリ金属であるFrを含むイオンの荷電状態の主要な価数が(+1価でなく)+2価となるという結果を観測した。

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