2019, Chernyshev, B. A., Gurov, Y. B., Lapushkin, S. V., Leonova, T. I., Sandukovsky, V. G., Чернышев, Борис Андреевич, Гуров, Юрий Борисович, Леонова, Татьяна Игоревна

© Published under licence by IOP Publishing Ltd.Level structure of 8He has been studied in the reaction of stopped pion absorption by 11B nuclei 11B(π-,pd)X. The experiment was carried out at the LANL with a two-arm semiconductor spectrometer. The missing mass spectrum in the range 0 MeV < MM < 50 MeV has been described by the superposition of phase-space distributions and the six states of 8He. Parameters of these states have been compared with data of other experimental and theoretical works.

2019, Gurov, Y. B., Karpukhin, V. S., Lapushkin, S. V., Leonova, T. I., Pritula, R. V., Chernyshev, B. A., Sandukovsky, V. G., Гуров, Юрий Борисович, Леонова, Татьяна Игоревна, Чернышев, Борис Андреевич

© 2019, Pleiades Publishing, Ltd.The spectra of 3,4He charged particles produced in stopped pion absorption by nuclei were measured for 17 nuclei in the mass-number range of 6 ≤ A ≤ 209 by means of a semiconductor spectrometer. These data were analyzed on the basis of a phenomenological model where the absorption reaction in question is treated as a three-stage process: primary absorption by intranuclear clusters, preequilibrium stage, and evaporation stage. It is shown that a dominant contribution to the production of helium isotopes with energies not less than 20 MeV comes from the preequilibrium stage. The contribution of the knockout and pickup mechanisms to 3,4He production is estimated.

2020, Demyanova, A. S., Ogloblin, A. A., Chernishev, B. A., Goncharov, S. A., Gurov, Y. B., Lapushkin, S. V., Чернышев, Борис Андреевич, Гуров, Юрий Борисович

A study of the neutron structure of the ground state of He-7 has been performed by means of registration and analysis of the decay channels of the residual nuclei following absorption of stopped pions. In particular, the reaction Be-9 (pi(-),d)X have been investigated where X denotes any system with five neutrons and two protons - the constituencies of a H-7 nucleus. It was shown that the structure of H-7 is determined by correlations of two neutrons in the states He-6 (0(+)), He-6 (2(+)) and one neutron in the shell p(3/2). The He-4+3n structure is not manifested in the ground state of H-7. The obtained results are consistent with the known data on considerable mixture of configurations "He-6 in its ground and first excited states plus a neutron" in the ground state of H-7. Comparison of the diffraction components of the differential cross-sections of the charge-exchange reactions (t, He-3) measured on Li-6 and Li-7 allowed extracting the radius of particle-unstable nucleus H-7. The latter occurred to be approximately equal to those of He-6 and H-7. The obtained result indicates to existence of the halo-like structure in H-7.

2020, Gurov, Y. B., Lapushkin, S. V., Leonova, T. I., Tel'kushev, M. V., Chernyshev, B. A., Sandukovsky, V. G., Гуров, Юрий Борисович, Леонова, Татьяна Игоревна, Чернышев, Борис Андреевич

© 2020, Pleiades Publishing, Ltd.A survey of experimental results on the level structure in the heavy heliumisotope 6He that were obtained in reactions induced by stopped pion absorption in 9Be, 10,11B, and 12C light nuclei is presented. The respective measurements were performed on the low-energy pion channel of the accelerator at the Los Alamos National Laboratory (LANL) by means of a two-arm semiconductor spectrometer. A high statistical significance of the results was attained over a broad excitation-energy range extending up to 40 MeV. Several highly excited states, including t + t cluster resonances, were revealed for the first time.

2019, Demyanova, A. S., Goncharov, S. A., Ogloblin, A. A., Sandukovsky, V. G., Chernyshev, B. A., Gurov, Y. B., Lapushkin, S. V., Чернышев, Борис Андреевич, Гуров, Юрий Борисович

© 2019, Pleiades Publishing, Inc.A study of the neutron structure of the ground state of 7He has been performed by means of registration and analysis of the decay channels of the residual nuclei following absorption of stopped pions. In particular, the reactions 9Be(π−, d)X and 11B(π−, dd)X have been investigated where X denotes any system with five neutrons and two protons — the constituencies of a 7He nucleus. The results point out to the existence of a halo-like configuration of the ground state of 7He with all three neutrons outside of the alpha particle core. The structure of this complicated halo-like state is determined by the correlations of neutrons in the p3/2 and p1/2 shells. The result would be in agreement with the previous works pointing out to a considerable mixing of configurations containing neutrons in the p3/2 and p1/2 states.

2019, Chernyshev, B., Gurov, Y., Lapushkin, S., Karpukhin, V., Sandukovsky, V., Schurenkova, T., Чернышев, Борис Андреевич, Гуров, Юрий Борисович, Щуренкова, Татьяна Дмитриевна

© Published under licence by IOP Publishing Ltd.The production of the 7He states was studied in the reactions of stopped pion absorption by carbon isotopes: 12C(π-, p4He)7He, 12C(π-, d3He)7He and 14C(π-, t4He)7He. Measurements were performed using two-arm multilayer semiconductor spectrometer. The ground and excited states were observed in all three reactions. Narrow (Γ < 2 MB) state with the high excitation energy ≈ 16 MeV was observed in the 14C(π-, t4He)7He reaction.

2020, Demyanova, A. S., Ogloblin, A. A., Sandukovsky, V. G., Chernyshev, B. A., Gurov, Y. B., Lapushkin, S. V., Leonova, T. I., Чернышев, Борис Андреевич, Гуров, Юрий Борисович, Леонова, Татьяна Игоревна

© 2020 Published under licence by IOP Publishing Ltd.Formation of the 7He heavy isotope was studied in the reactions of stopped pion absorption by light nuclei 9Be, 10,11B and 12,14C. Measurements were performed using the two-arm multilayer semiconductor spectrometer. Contrary to the results of other studies, we observed several narrow highly excited states (Ex > 16 MeV) of 7He. From the analysis of the continuous excitation spectrum in reactions 9Be(π-, d)X and 11B(π-, dd)X it was obtained first indication that the 4He+3n structure is not present in the ground state of 7He.

2019, Gurov, Y. B., Lapushkin, S. V., Leonova, T. I., Sandukovsky, V. G., Chernyshev, B. A., Гуров, Юрий Борисович, Леонова, Татьяна Игоревна, Чернышев, Борис Андреевич

© 2019, Allerton Press, Inc.Abstract: The structure of the levels of heavy helium isotope 8He is investigated using the reactions of stopped-pion absorption by carbon isotopes 12С(π−, p3He)X, 14С(π−, d4He)X, and 14С(π−, t3He)X. Measurements are made with the two-arm multilayer semiconductor spectrometer at the LANL accelerator. Excited states of the 8He nucleus with energies of excitation of up to ~ 20 MeV are sought using the measured missing-mass spectra for these reactions. An excited state with Ex ≈ 6.4 MeV and Г ≤ 1 MeV is observed for the first time. Its structure is probably due to two valence nucleons on the (1p1/2)2 shell.

2020, Sandukovsky, V. G., Chernyshev, B., Gurov, Y. B., Lapushkin, S. V., Leonova, T. I., Schurenkova, T., Telkushev, M. V., Чернышев, Борис Андреевич, Гуров, Юрий Борисович, Леонова, Татьяна Игоревна, Щуренкова, Татьяна Дмитриевна

© Published under licence by IOP Publishing Ltd.The formation of the 10He states was studied in the reaction of stopped pion absorption 14C(π-, p 3He)X. Measurements were carried out using two-Arm multilayer semiconductor spectrometer and "radioactive"target consisting of 76% 14C and 23% 12C. The contribution of uncontrolled impurities in the target was ≤ 1%. In order to determine the contribution of the 12C impurity measurements were performed on an isotope pure carbon 12C target. An indication on the excitation state with Ex ∼ 6 MeV (Er ∼ 7 MeV) was observed in missing mass spectrum of 14C(π-, p 3He)X reaction. Comparison with theoretical and experimental results obtained by other authors was performed.

2020, Gurov, Y. B., Lapushkin, S. V., Leonova, T. I., Sandukovsky, V. G., Chernyshev, B. A., Гуров, Юрий Борисович, Леонова, Татьяна Игоревна, Чернышев, Борис Андреевич

© 2020, Allerton Press, Inc.Abstract: An experimental search is conducted for the formation of the heavy 9He isotope of helium upon the absorption of stopped pions by 14C nuclei. The structure of 9He levels in the missing mass spectra in reactions 14C(π–, p4He)Х and 14C(π–, d3He)Х is studied. A state with a high energy of excitation of 12.5 MeV and a state width of 1.5 MeV is detected for the first time. Suppression of the formation of ground state 9He in the considered reactions is established.