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論文

Detailed $$alpha$$-decay study of $$^{180}$$Tl

Andel, B.*; Andreyev, A.; Antalic, S.*; Barzakh, A.*; Bree, N.*; Cocolios, T. E.*; Comas, V. F.*; Diriken, J.*; Elseviers, J.*; Fedorov, D. V.*; et al.

Physical Review C, 96(5), p.054327_1 - 054327_11, 2017/12

 パーセンタイル:100(Physics, Nuclear)

A detailed $$alpha$$-decay spectroscopy study of $$^{180}$$Tl has been performed at ISOLDE (CERN). Z-selective ionization by the Resonance Ionization Laser Ion Source (RILIS) coupled to mass separation provided a high-purity beam of $$^{180}$$Tl. Fine-structure $$alpha$$ decays to excited levels in the daughter $$^{176}$$Au were identified and an $$alpha$$-decay scheme of $$^{180}$$Tl was constructed based on an analysis of $$alpha$$-$$gamma$$ and $$alpha$$-$$gamma$$ -$$gamma$$ coincidences. Multipolarities of several $$gamma$$-ray transitions deexciting levels in $$^{176}$$Au were determined. Based on the analysis of reduced $$alpha$$-decay widths, it was found that all $$alpha$$ decays are hindered, which signifies a change of configuration between the parent and all daughter states.

論文

Changes in mean-squared charge radii and magnetic moments of $$^{179-184}$$Tl measured by in-source laser spectroscopy

Barzakh, A.*; Andreyev, A.; Cocolios, T. E.*; de Groote, R. P.*; Fedorov, D. V.*; Fedosseev, V. N.*; Ferrer, R.*; Fink, D. A.*; Ghys, L.*; Huyse, M.*; et al.

Physical Review C, 95(1), p.014324_1 - 014324_12, 2017/01

 被引用回数:10 パーセンタイル:8.11(Physics, Nuclear)

Hyperfine structure and isotope shifts have been measured for the ground and isomeric states in the neutron deficient isotopes $$^{179-184}$$Tl using the 276.9 nm transition. The experiment has been performed at the CERN Isotope Separator On-Line facility using the in-source resonance-ionization laser spectroscopy technique. Spins for the ground states in $$^{179,181,183}$$Tl have been determined as $$I$$ = 1/2. Magnetic moments and changes in the nuclear mean-square charge radii have been deduced. By applying the additivity relation for magnetic moments of the odd-odd Tl nuclei the leading configuration assignments were confirmed. A deviation of magnetic moments for isomeric states in $$^{182,184}$$Tl from the trend of the heavier Tl nuclei is observed. The charge radii of the ground states of the isotopes $$^{179-184}$$Tl follow the trend for isotonic (spherical) lead nuclei. The noticeable difference in charge radii for ground and isomeric states of $$^{183,184}$$Tl has been observed, suggesting a larger deformation for the intruder-based 9/2$$^{-}$$ and 10$$^{-}$$ states compared to the ground states. An unexpected growth of the isomer shift for $$^{183}$$Tl has been found.

論文

$$alpha$$-decay study of $$^{182,184}$$Tl

Van Beveren, C.*; Andreyev, A.; Barzakh, A. E.*; Cocolios, T. E.*; de Groote, R. P.*; Fedorov, D.*; Fedosseev, V. N.*; Ferrer, R.*; Ghys, L.*; Huyse, M.*; et al.

Journal of Physics G; Nuclear and Particle Physics, 43(2), p.025102_1 - 025102_22, 2016/02

 被引用回数:5 パーセンタイル:36.63(Physics, Nuclear)

$$alpha$$-decay spectroscopy of $$^{182,184}$$Tl has been performed at the CERN isotope separator on-line (ISOLDE) facility. New fine-structure $$alpha$$ decays have been observed for both isotopes. $$alpha$$-decay branching ratios of 0.089(19)$$%$$, 0.047(6)$$%$$ and 1.22(30)$$%$$ have been deduced for the (10$$^{-}$$), (7$$^{+}$$) and (2$$^{-}$$) states respectively in $$^{184}$$Tl and a lower limit of 0.49$$%$$ for the $$alpha$$-decay branching ratio of $$^{182}$$Tl. A new half-life of 9.5(2) s for the (2$$^{-}$$) state in $$^{184}$$Tl and 1.9(1) s for the low-spin state in $$^{182}$$Tl has been deduced. Using $$alpha$$-$$gamma$$ coincidence analysis, multiple $$gamma$$ rays were observed de-exciting levels in $$^{178,180}$$Au fed by $$^{182,184}$$Tl $$alpha$$ decays. The $$gamma$$ transitions connecting these low-lying states in $$^{178,180}$$Au are essential to sort the data and possibly identify bands from inbeam studies in these isotopes. Owing to the complex fine-structure $$alpha$$ decays and limited knowledge about the structure of the daughter nuclei, only partial level schemes could be constructed for both gold isotopes in the present work. Reduced $$alpha$$-decay widths have been calculated and are compared with values obtained in neighboring odd-A and even-A thallium isotopes. Except for the allowed $$alpha$$ decay of the $$^{184}$$Tl (10$$^{-}$$) state, the other fine-structure $$alpha$$ decays observed in this study are hindered. This points to strong structural changes between parent thallium and daughter gold isotopes.

論文

Excitation energy dependence of fragment-mass distributions from fission of $$^{180,190}$$Hg formed in fusion reactions of $$^{36}$$Ar + $$^{144,154}$$Sm

西尾 勝久; Andreyev, A. N.*; Chapman, R.*; Derkx, X.*; D$"u$llmann, C. E.*; Ghys, L.*; He${ss}$berger, F. P.*; 廣瀬 健太郎; 池添 博*; Khuyagbaatar, J.*; et al.

Physics Letters B, 748, p.89 - 94, 2015/09

 被引用回数:9 パーセンタイル:26.51(Astronomy & Astrophysics)

Mass distributions of fission fragments from the compound nuclei $$^{180}$$Hg and $$^{190}$$Hg formed in fusion reactions $$^{36}$$Ar+$$^{144}$$Sm and $$^{36}$$Ar+$$^{154}$$Sm, respectively, were measured at initial excitation energies of $$E^*$$($$^{180}$$Hg)=,33$$-$$66 MeV and $$E^*$$($$^{190}$$Hg)=,48$$-$$71 MeV. In the fission of $$^{180}$$Hg, the mass spectra were well reproduced by assuming only an asymmetric-mass division, with most probable light and heavy fragment masses $$bar{A}_{rm L}$$/$$bar{A}_{rm H}=$$79$$/$$101. The mass asymmetry for $$^{180}$$Hg agrees well with that obtained in the low-energy $$beta^textrm{+}$$/EC-delayed fission of $$^{180}$$Tl, from our earlier ISOLDE(CERN) experiment. Fission of $$^{190}$$Hg is found to proceed in a similar way, delivering the mass asymmetry of $$bar{A}_{rm L}$$/$$bar{A}_{rm H}=$$83$$/$$107, throughout the measured excitation energy range. The persistence as a function of excitation energy of the mass-asymmetric fission for both proton-rich Hg isotopes gives strong evidence for the survival of microscopic effects up to effective excitation energies of compound nuclei as high as 40,MeV. This behavior is different from fission of actinide nuclei and heavier mercury isotope $$^{198}$$Hg.

論文

Internal decay of the (10$$^{-}$$) intruder state in $$^{184}$$Tl

Van Beveren, C.*; Andreyev, A.; Barzakh, A.*; Cocolios, T. E.*; Fedorov, D.*; Fedosseev, V. N.*; Ferrer, R.*; Huyse, M.*; K$"o$ster, U.*; Lane, J. F. W.*; et al.

Physical Review C, 92(1), p.014325_1 - 014325_8, 2015/07

 被引用回数:6 パーセンタイル:39.07(Physics, Nuclear)

Decay spectroscopy of $$^{184}$$Tl has been performed at the CERN Isotope Separator On-Line (ISOLDE) facility. An excitation energy of 506.1(1) keV and a half-life of 47.1(7) ms of the intruder based (10$$^{-}$$) state have been extracted. The internal decay characteristics of this state are determined and discussed, extending the systematics of such states in the even-mass thallium nuclei below neutron midshell at N = 104. The retardation factors of the isomeric M2 and E3 transitions are deduced and compared with retardation factors in neighboring odd-mass and even-mass thallium isotopes. The new information is combined with a review of hindered and unhindered $$alpha$$-decay data of $$^{187-192}$$Bi populating levels in daughter nuclei $$^{183-188}$$Tl and supports the interpretation of the intruder character of the (10$$^{-}$$) state in $$^{184}$$Tl.

論文

$$beta$$-delayed fission of $$^{180}$$Tl

Elseviers, J.*; Andreyev, A. N.*; Huyse, M.*; Van Duppen, P.*; Antalic, S.*; Barzakh, A.*; Bree, N.*; Cocolios, T. E.*; Comas, V. F.*; Diriken, J.*; et al.

Physical Review C, 88(4), p.044321_1 - 044321_13, 2013/10

 被引用回数:26 パーセンタイル:9.87(Physics, Nuclear)

The detailed analysis of the $$beta$$-delayed fission data of $$^{180}$$Tl is presented. The experiment was performed by producing a pure beam of $$^{180}$$Tl by means of highly selective resonance laser ionization followed by mass separation with the ISOLDE isotope separator. A surprising asymmetric mass distribution of fission fragments from $$^{180}$$Hg, the daughter of $$^{180}$$Tl $$beta$$ decays, was obtained. Here, the energy calibration of the silicon detectors, which is crucial for a proper determination of the fission fragments' energy and mass split, is presented and the total kinetic energy and its dependence on the mass split ratio is discussed. A more precise $$beta$$-delayed fission probability of 3.2(2)$$times$$10$$^{-3}$$$$%$$ was deduced.

論文

Measurement of the first ionization potential of astatine by laser ionization spectroscopy

Rothe, S.*; Andreyev, A. N.*; Antalic, S.*; Borschevsky, A.*; Capponi, L.*; Cocolios, T. E.*; De Witte, H.*; Eliav, E.*; Fedorov, D. V.*; Fedosseev, V. N.*; et al.

Nature Communications (Internet), 4, p.1835_1 - 1835_6, 2013/05

 被引用回数:50 パーセンタイル:5.27(Multidisciplinary Sciences)

The radioactive element astatine exists only in trace amounts in nature. Its properties can therefore only be explored by study of smallest quantities of artificially produced isotopes or by performing theoretical calculations. One of the most important properties influencing the chemical behaviour is the energy required to remove one electron from the valence shell, referred to as the ionization potential (IP). Here we use laser spectroscopy to probe the optical spectrum of astatine near the ionization threshold. The observed series of Rydberg states allowed the deduction of the IP of the astatine atom for the first time. New ab initio calculations were performed to support the experimental result. The measured value of IP(At) serves as a benchmark for quantum chemistry calculations of the properties of astatine as well as for the theoretical prediction of the ionization potential of super-heavy element 117, the heaviest homologue of astatine.

論文

$$alpha$$-decay spectroscopy of the chain $$^{179}$$Tl$$^{g}$$ $$rightarrow$$ $$^{175}$$Au$$^{g}$$ $$rightarrow$$ $$^{171}$$Ir$$^{g}$$ $$rightarrow$$ $$^{167}$$Re$$^{m}$$

Andreyev, A. N.*; Liberati, V.*; Antalic, S.*; Ackermann, D.*; Barzakh, A.*; Bree, N.*; Cocolios, T. E.*; Diriken, J.*; Elseviers, J.*; Fedorov, D.*; et al.

Physical Review C, 87(5), p.054311_1 - 054311_8, 2013/05

 被引用回数:13 パーセンタイル:27.16(Physics, Nuclear)

$$alpha$$-decay studies of $$^{179}$$Tl$$^{g}$$ and its dahghter products $$^{175}$$Au$$^{g}$$ and $$^{171}$$Ir$$^{g}$$ were carried out in two complementary experiments at the mass separator ISOLDE (CERN) and velocity filter SHIP (GSI). The nucluesu $$^{175}$$Au$$^{g}$$ has $$alpha$$ decay properties of half-life 207 ms and $$alpha$$-decay energy 6433 keV. The ground state spins and parities for $$^{175}$$Au and $$^{171}$$Ir were determined to be 1/2$$^{+}$$.

論文

First prompt in-beam $$gamma$$-ray spectroscopy of a superheavy element; The $$^{256}$$Rf

Rubert, J.*; Dorvaux, O.*; Gall, B. J. P.*; Greenlees, P. T.*; Asfari, Z.*; Piot, J.*; Andersson, L. L.*; 浅井 雅人; Cox, D. M.*; Dechery, F.*; et al.

Journal of Physics; Conference Series, 420, p.012010_1 - 012010_10, 2013/03

 パーセンタイル:100

初めての超重元素即発インビーム$$gamma$$線分光実験を$$^{256}$$Rfを対象に行った。MIVOC法を用いた大強度$$^{50}$$Tiビームの開発を行い、実験を成功させた。$$^{256}$$Rfの回転励起状態をスピン20 $$hbar$$まで観測し、その慣性能率を導出した。これらのデータから、陽子数104には大きな変形閉殻が存在しないことが明らかとなった。

論文

Fission-barrier heights of neutron-deficient mercury nuclei

Veselsk$'y$, M.*; Andreyev, A. N.*; Antalic, S.*; Huyse, M.*; M$"o$ller, P.*; 西尾 勝久; Sierk, A. J.*; Van Duppen, P.*; Venhart, M.*

Physical Review C, 86(2), p.024308_1 - 024308_8, 2012/08

 被引用回数:11 パーセンタイル:35.22(Physics, Nuclear)

The recently measured probabilities of the beta-delayed fission for $$^{178,180}$$Tl are used to deduce the fission-barrier heights of the daughter isotopes $$^{178,180}$$Hg, undergoing low-energy fission. Four alternative $$beta$$-decay strength functions and four variants of the statistical model of de-excitation of the daughter nucleus are used to determine the fission-barrier height for $$^{180}$$Hg. Depending on the choice of the model, the deduced fission-barrier heights appear to be between 10 and 40% smaller than theoretical estimates. This observation is verified also for fission-barrier heights extracted using the probability of $$beta$$-delayed fission of $$^{178}$$Tl. The spread in extracted fission barrier heights results mainly from uncertainties in the magnitude of the pairing gap at the saddle configuration.

論文

Shell-structure and pairing interaction in superheavy nuclei; Rotational properties of the $$Z$$=104 nucleus $$^{256}$$Rf

Greenlees, P. T.*; Rubert, J.*; Piot, J.*; Gall, B. J. P.*; Andersson, L. L.*; 浅井 雅人; Asfari, Z.*; Cox, D. M.*; Dechery, F.*; Dorvaux, O.*; et al.

Physical Review Letters, 109(1), p.012501_1 - 012501_5, 2012/07

 被引用回数:37 パーセンタイル:11.7(Physics, Multidisciplinary)

104番元素$$^{256}$$Rfの回転励起構造をインビーム$$gamma$$線核分光の手法により初めて観測することに成功した。$$^{256}$$Rfは回転励起構造が観測された最も重い原子核であり、今回の結果は重い極限に位置する原子核の一粒子軌道殻構造と対相関に関する貴重な情報を与える。今回の実験で得られた$$^{256}$$Rfの回転状態の慣性能率の値は、陽子数104における変形閉殻の存在を明確に否定し、近年の数多くの自己無撞着平均場モデルの予測と異なる結果を示した。

論文

Alpha-$$gamma$$ decay studies of $$^{253}$$No and its daughter products $$^{253}$$Md, $$^{249}$$Fm

He${ss}$berger, F. P.*; Antalic, S.*; Ackermann, D.*; Kalaninov$'a$, Z.*; Heinz, S.*; Hofmann, S.*; Streicher, B.*; Kindler, B.*; Kojouharov, I.*; Kuusiniemi, P.*; et al.

European Physical Journal A, 48(5), p.75_1 - 75_9, 2012/05

 被引用回数:17 パーセンタイル:23.24(Physics, Nuclear)

Nuclear structure and decay of the isotope $$^{253}$$No and its decay products $$^{249}$$Fm and $$^{253}$$Md were investigated by means of $$alpha$$-$$gamma$$ spectroscopy. Besides the established strong $$alpha$$ transitions from the 9/2$$^{-}$$[734] Nilsson level in $$^{249}$$Fm, populated predominantly by the $$alpha$$ decay of $$^{253}$$No, into the ground-state(gs) rotational band, a couple of weaker $$alpha$$ lines were observed and placed into the $$^{249}$$Fm level scheme. The transition from the 7/2$$^{-}$$ level in $$^{249}$$Es, populated by the $$alpha$$ decay of $$^{253}$$Md, into the 9/2$$^{+}$$ member of the gs rotational band, so far established for other odd-mass Es isotopes, was observed clearly. The GEANT4 simulations were performed to investigate the influence of energy summing between $$alpha$$ particles and conversion electrons (CE) on the shape of the $$alpha$$ spectra at different implantation energies, leading to evidence for a weak $$alpha$$ decay branch of $$^{253}$$No into the gs of $$^{249}$$Fm or the ground-state rotational band, respectively.

論文

Isomeric states in $$^{253}$$No and $$^{253}$$Fm

Antalic, S.*; He${ss}$berger, F. P.*; Ackermann, D.*; Heinz, S.*; Hofmann, S.*; Kalaninov$'a$, Z.*; Kindler, B.*; Khuyagbaatar, J.*; Kojouharov, I.*; Kuusiniemi, P.*; et al.

European Physical Journal A, 47(5), p.62_1 - 62_12, 2011/05

 被引用回数:18 パーセンタイル:20.4(Physics, Nuclear)

Nuclear structure and decay of isomer in $$^{253}$$No were investigated. The isotope was produced by the reaction $$^{48}$$Ca+$$^{207}$$Pb. The excitation energy of the known single-particle isomeric state (5/2$$^{+}$$[622]) was measured by delayed coincidence between $$gamma$$-rays and implanted evaporation residues and was placed into the level scheme. In addition, decay of a high-lying multi-quasiparticle isomer in $$^{253}$$No was studied using e$$^{-}$$-$$gamma$$ coincidence measurements. A rotational band populated by its de-excitation was identified in $$^{253}$$No. A new isomeric state in $$^{253}$$Fm was observed and a partial-level scheme for this isotope is suggested. In addition $$gamma$$ transitions from excited levels are reproduced for $$^{253}$$Md.

論文

New type of asymmetric fission in proton-rich nuclei

Andreyev, A. N.*; Elseviers, J.*; Huyse, M.*; Van Duppen, P.*; Antalic, S.*; Barzakh, A.*; Bree, N.*; Cocolios, T. E.*; Comas, V. F.*; Diriken, J.*; et al.

Physical Review Letters, 105(25), p.252502_1 - 252502_5, 2010/12

 被引用回数:120 パーセンタイル:3.19(Physics, Multidisciplinary)

A very exotic process of $$beta$$-delayed fission of $$^{180}$$Tl is studied in detail by using resonant laser ionization with subsequent mass separation at ISOLDE (CERN). In contrast to common expectations, the fission-fragment mass distribution of the post-$$beta$$-decay daughter nucleus $$^{180}$$Hg ($$N$$/$$Z$$ = 1.25) is asymmetric. This asymmetry is more surprising since a mass-symmetric split of this extremely neutron-deficient nucleus would lead to two $$^{90}$$Zr fragments, with magic $$N$$ = 50 and semi-magic $$Z$$ = 40. This is a new type of asymmetric fission, not caused by large shell effects related to fragment magic proton and neutron numbers, as observed in the actinide region. The newly-measured branching ratio for $$beta$$-delayed fission of $$^{180}$$Tl is 3.6(7)$$times$$10$$^{-3}$$ %.

論文

Decay studies of K isomer in $$^{254}$$No

He${ss}$berger, F. P.*; Antalic, S.*; Sulignano, B.*; Ackermann, D.*; Heinz, S.*; Hofmann, S.*; Kindler, B.*; Khuyagbaatar, J.*; Kojouharov, I.*; Kuusiniemi, P.*; et al.

European Physical Journal A, 43(1), p.55 - 66, 2010/01

 被引用回数:53 パーセンタイル:4.71(Physics, Nuclear)

$$gamma$$-rays decay study of two K isomers in $$^{254}$$No was performed. Two new transitions of 778 and 856 keV could be attributed to the decay pattern of $$^{254m1}$$No (T$$_{1/2}$$=275 ms). The population of an excited band built up on this isomer ($$K$$$$^{pi}$$=8$$^{-}$$) by the decay of $$^{252m2}$$No (198 $$mu$$s) could be proven. A spontaneous fission branch of 2.0$$times$$10$$^{-4}$$ was measured for $$^{252m1}$$No, and upper limit of 1.2$$times$$10$$^{-4}$$ was estimated for $$^{252m2}$$No. These values demonstrate the high stability of multi-quasiparticle configuration against spontaneous fission.

論文

Decay studies of neutron-deficient lawrencium isotopes

Antalic, S.*; He${ss}$berger, F. P.*; Hofmann, S.*; Ackermann, D.*; Heinz, S.*; Kindler, B.*; Kojouharov, I.*; Kuusiniemi, P.*; Leino, M.*; Lommel, B.*; et al.

European Physical Journal A, 38(2), p.219 - 226, 2008/11

 被引用回数:25 パーセンタイル:16.66(Physics, Nuclear)

The radioactive decay of the isotopes $$^{254-256}$$Lr and their daughter products was investigated by means of $$alpha$$, prompt $$alpha-gamma$$ and delayed conversion electron$$-gamma$$ coincidence spectroscopy. The experiment was carried out at GSI by using the velocity filter SHIP to separate evaporation residues, produced in the reaction $$^{48}$$Ca+$$^{209}$$Bi, from the primary beams. In $$^{255}$$Lr, a second short-lived isomer with a half-life of 1.91 ms was found. For $$^{254,256}$$Lr, new data for $$gamma$$ transitions of levels in $$^{250,252}$$Md populated by $$alpha$$ decay were observed. The constructed level schemes are useful for the nuclear structure theory.

論文

Identification of a K isomer in $$^{252}$$No

Sulignano, B.*; Heinz, S.*; He${ss}$berger, F. P.*; Hofmann, S.*; Ackermann, D.*; Antalic, S.*; Kindler, B.*; Kojouharov, I.*; Kuusiniemi, P.*; Lommel, B.*; et al.

European Physical Journal A, 33(4), p.327 - 331, 2007/09

 被引用回数:56 パーセンタイル:4.37(Physics, Nuclear)

The $$K$$-isomer with a half-life of 100 ms has been discovered in the nucleus $$^{252}$$No. The nucleus was produced in the fusion-evaporation reacion $$^{206}$$Pb($$^{48}$$Ca,2n)$$^{252}$$No. The experiment was carried out at the velocity filter SHIP of GSI. The isomeric state is located at an excitation energy of 1254 keV and is interpreted as a two quasi-neutron state with $$K$$=8$$^{-}$$. The isomeric state has direct connection to the rotational states of 8$$^{+}$$ in $$^{252}$$No. Also the rotational states of 6$$^{+}$$ and 4$$^{+}$$ was feeded via the octupole band with $$K$$=2$$^{-}$$. The isomeric state and the ground state was populated with the equal intensity in the fusion-evaporation reaction.

論文

The Reaction $$^{48}$$Ca+$$^{238}$$U $$rightarrow$$ $$^{286}$$112$$^{*}$$ studied at the GSI-SHIP

Hofmann, S.*; Ackermann, D.*; Antalic, S.*; Burkhard, H. G.*; Comas, V. F.*; Dressler, R.*; Gan, Z.*; Heinz, S.*; Heredia, J. A.*; He${ss}$berger, F. P.*; et al.

European Physical Journal A, 32(3), p.251 - 260, 2007/06

 被引用回数:202 パーセンタイル:0.36(Physics, Nuclear)

The fusion reaction of $$^{48}$$Ca projectiles with$$^{238}$$U target nuclei was studied at the velocity filter SHIP of GSI. Two decay chains were measured, which fully confirm data that were previously assigned to the isotope $$^{283}$$112 in experiments at the Flerov Laboratory in Dubna. Two other events are consistent with a 50 % spontaneous fission (SF) branch of this isotope. The mean value obtained for the half-life of $$^{283}$$112 is (6.9$$^{+6.9}_{-2.3}$$) s, the $$alpha$$ energy is (9.520$$pm$$0.015) MeV, and the total kinetic energy (TKE) of SF is (238$$pm$$14) MeV. The half-life of the $$alpha$$ decay daughter nucleus $$^{279}$$Ds is (0.18$$^{+0.32}_{-0.07}$$) s, and the TKE of SF is (210$$^{+32}_{-11}$$) MeV. The cross-section deduced from all four events is (0.72$$^{+0.58}_{-0.35}$$) pb, measured at an excitation energy of 34.6 MeV of the compound nucleus $$^{286}$$112.

論文

Alpha-$$gamma$$ decay studies of $$^{255}$$Rf, $$^{251}$$No and $$^{247}$$Fm

He${ss}$berger, F. P.*; Hofmann, S.*; Ackermann, D.*; Antalic, S.*; Kindler, B.*; Kojouharov, I.*; Kuusiniemi, P.*; Leino, M.*; Lommel, B.*; Mann, R.*; et al.

European Physical Journal A, 30(3), p.561 - 569, 2006/12

 被引用回数:39 パーセンタイル:9.44(Physics, Nuclear)

$$^{255}$$Rf, $$^{251}$$No及び$$^{247}$$Fmについて、$$alpha$$線と$$gamma$$線の検出による崩壊核分光実験を行った。実験は、ドイツ重イオン研究所の線形加速器施設UNILACにおける反跳生成核分離装置SHIPを用いて行った。SHIPで分離された蒸発残留核を焦点に設置したシリコン検出器に打ち込んだ。この検出器で$$alpha$$崩壊を検出し、また近くに設けたGe検出器で$$gamma$$線を検出した。これら同位体は、$$^{207}$$Pb($$^{50}$$Ti,2n)$$^{255}$$Rf及びこの$$^{255}$$Rfの$$alpha$$崩壊核種として生成し、さらに$$^{206}$$Pb($$^{48}$$Ca,3n)$$^{251}$$No反応及びこの$$^{251}$$Noの$$alpha$$崩壊核種として生成した。解析から次のことがわかった。(1)$$^{251}$$Noには半減期1.0秒のアイソマがあることがわかっていたが、このエネルギー準位が106keVであることがわかった。(2)また、$$^{251}$$Noには2$$mu$$sの半減期を持つ第2のアイソマがあり、$$^{206}$$Pb($$^{48}$$Ca,3n)$$^{251}$$No反応で直接生成されることがわかった。このアイソマは、2本の$$gamma$$線とコインシデンスし、解析から励起エネルギーが1700keV以上の準位にあることが示唆された。この2本の$$gamma$$線は、$$^{255}$$Rfの$$alpha$$崩壊につづく$$gamma$$遷移と一致した。

論文

Alpha-$$gamma$$ decay studies of $$^{255}$$No

He${ss}$berger, F. P.*; Hofmann, S.*; Ackermann, D.*; Antalic, S.*; Kindler, B.*; Kojouharov, I.*; Kuusiniemi, P.*; Leino, M.*; Lommel, B.*; Mann, R.*; et al.

European Physical Journal A, 29(2), p.165 - 173, 2006/08

 被引用回数:33 パーセンタイル:11.58(Physics, Nuclear)

The decay of $$^{255}$$No was investigated by means of $$alpha$$-$$gamma$$ spectroscopy. The experiment was carried out by using the velocity filter SHIP at GSI. The isotope was produced in the reactions $$^{208}$$Pb($$^{48}$$Ca,n)$$^{255}$$No, $$^{209}$$Bi($$^{48}$$Ca,2n)$$^{255}$$Lr (EC)-$$>$$ $$^{255}$$No, and $$^{238}$$U($$^{22}$$Ne,5n)$$^{255}$$No. Decay data for $$alpha$$-$$gamma$$ coincidence measurements were obtained, and the level structures of the daughter nucleus $$^{251}$$Fm were obtained, including the tentative assignment of (1) 9/2$$^{-}$$ for ground state and (2) 5/2$$^{+}$$ for the 200 keV isomeric state with $$T_{1/2}$$=21 $$mu$$s.

口頭

陽子過剰原子核の核分裂

西尾 勝久; Andreyev, A. N.*; Elseviers, J.*; Huyse, M.*; Van Duppen, P.*; Antalic, S.*; Barzakh, A.*; Bree, N.*; Cocolios, T. E.*; Comas, V. F.*; et al.

no journal, , 

陽子過剰な原子核$$^{180}$$Hgの低励起エネルギー核分裂を測定した。CERN-ISOLDEにおいて$$^{180}$$Tlをアイソトープ分離し、このベータ崩壊によって娘核$$^{180}$$Hgを励起さることで、この核分裂を観測した(ベータ崩壊遅延核分裂)。核分裂特性を調べたところ、中性子数50の閉殻を有する$$^{90}$$Zr原子核は生成されず、質量数80と100に収率の最大を有する非対称な核分裂を示した。また、原子力機構タンデム加速器において、陽子過剰原子核のインビーム核分裂実験を行った。この結果、ウランなど従来の核分裂と異なり、励起エネルギーが増加しても質量非対称度が変化しないことがわかった。

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