Search

The structure of levels of the 8He heavy helium isotope has been studied in the 9Be $$({{\pi }^{ - }},p)X$$ and 10B $$({{\pi }^{ - }},pp)X$$ stopped pion absorption reactions. Measurements have been performed with a two-arm multilayer semiconductor spectrometer at the LANL. Indications to the existence of a soft dipole mode at the excitation energy $${{E}_{x}} \approx 3$$ MeV have been obtained. A state with a high excitation energy of 12.2(5) MeV has been observed for the first time.

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.

A determination of the coordinates of charged particle stops is one of the tasks that have to be solved in a wide class of experiments. A method based on the use of semiconductor detectors (SCD) to determine the stops of particles (muons and pions) was proposed and experimentally tested. The dependence that allows calculating the stopping point of the pions in the tagging system was obtained experimentally. This dependence can be used to optimize the thickness values of monitor detectors.

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.

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.

Results on the research of spectra and yields of p, d, t formed in the reaction of stopped pion absorption by atomic nuclei are presented. Unique data on charged particle formation on 17 isotopes have been obtained in wide mass range (6 < A < 209). Empirical model is proposed that allows to describe A-dependence of primary proton yields (with 10-15% precision) and to estimate the ratio of the elementary widths of pion absorption on pn and pp pairs R’ = 3.3±0.5.

The experimental search for the production of heavy lithium isotopes 10-12 Li was carried out in the stopped π - -mesons absorption reactions on the radioactive target 14 C. Study of 10 Li has been performed in the missing mass spectra in 14 С(π - , pt)X and 14 С(π - , dd)X reactions. Three excited states of 10 Li were identified, thus, the broad state with a resonance energy E r = 6.1 ± 0.1 MeV has the highest excitation energy, compared with the previously observed levels. The resonance parameters of three low-lying excited states of 11 Li were determined in the 14 С(π - , pd)X reaction. In the 14 С(π - , pp)X reaction evidence for a 12 Li excited state E r = 4.0 ± 0.2 MeV and Γ = 1.1 ± 0.2 MeV has been found.

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 M∍B) state with the high excitation energy ≈ 16 MeV was observed in the 14C(π−, t4He)7He reaction.

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.

In the present work we have analyzed evaporation spectra and yields of p,d,t formed in the reaction of stopped pion absorption. It is shown that the values of equilibrium temperature obtained through the usage of proposed model are in agreement with the values obtained in various other experiments. We also discuss the A-dependences of the evaporation yields and consider possible contributions of the “indirect” evaporation processes.

The excited states of heavy helium isotope 6He were studied in stopped pion absorption in the reactions 9Be(

Level structure of 8He has been studied in the reaction of stopped pion absorption by 9Be nuclei. The missing mass spectrum in the range 0 MeV ≤ MM ≤ 10 MeV has been described by the superposition of phase-space distributions and the three states of 8He. Parameters of these states have been compared with data of other experimental and theoretical works.

The experimental search for the production of heavy lithium isotopes 10-12Li was carried out in the stopped π−-mesons absorption reactions on the targets 11B, 12,14C. Study of 10Li was performed in the correlation and inclusive measurements of reactions 12C(π−,pp)X, 14C(π−,pt)X, 14C(π−,dd)X and 11B(π−,p)X. Three highly excited states of 10Li with the resonance energies Er = 6.1 ± 0.1 MeV, 7.8 ± 0.1 MeV and 10.1 ± 0.1 MeV were identified together with the well-known levels. The resonance parameters of three low-lying excited states of 11Li were determined in the 14C(π−,pd)X reaction. In the 14C(π−,pp)X reaction 12Li excited state with Er = 4.0 ± 0.2 MeV and an indication on a level with Er ≈ 7 MeV were found.

The level structure of superheavy hydrogen and heavy helium isotopes with A = 5, 6, 7 was studied in stopped pion absorption by light nuclei. The measurements were performed at low energy pion channel of LANL with two-arm multilayer semiconductor spectrometer. Excited states of the 5-7H and 5-7He were observed in several reaction channels on the 9Be and 10,11B nuclei. Several excited levels were found only in our measurements. Candidate on isobar-analog state of the 6H ground states with Er ~ 5.5 MeV was observed in the reaction 10B(π−,pt)X.

The analysis of 2-dimentional Dalitz' diagram, measured in 14C(π-, pd)X reaction, allowed to distinguish the pion absorption by p intranuclear cluster and to obtain an indication on the existence of 3p + 11Li configuration in 14C nucleus. Highly excited states of 12,13Be isotopes were found with the energy of Ex ≈ 30 MeV for the first time. It was shown that these states decay as follows 12Be*→p + 11Li and 13Be*→d + 11Li.

Results of the study of spectra and yields of p, d, t formed in stopped pion absorption by nuclei are presented. Data on charged particle formation have been obtained for 17 isotopes in wide atomic mass range (6 < A < 209). Empirical model was proposed to describe A- dependences of primary p, d, t yields.

Search for isobar-analog states (IAS) of superheavy hydrogen isotopes 5-7H was performed among the high-excited states of helium isotopes 5-7He. The excited spectra were measured in stopped pion absorption by light nuclei. The experiment was performed at low energy pion channel of LANL with two-arm multilayer semiconductor spectrometer. Excited states of 5-7He were observed in three-body reaction channels on 10,11B nuclei. Several excited levels were observed for the first time. 6He excited state with Ex = 27.0(8) MeV observed in 10B(π-,pt)X channel is an IAS candidate for 6H with Er ~ 5.5 MeV. 7He excited state with Ex = 24.8(4) MeV observed in 10B(π-,pd)X, nB(π-,pt)X and nB(π-,dd)X channels is an IAS candidate for 7H with Er ~ 3 MeV.

Inclusive differential cross sections of 4,6,8 He, 6,7,8 Li formation in p 9 Be interactions at T p = 1 GeV have been measured. Enhancement of the 8 He yield is observed in the spectator momentum range ( P c ), which is evidence for the process of virtual Δ ++ -isobar knock-out from 9 Be. The ratio of the spectroscopic factors of (Δ ++ 8 He) and (p 8 Li) configurations in 9 Be is estimated to be (6±3) × 10 −4 .