Search

A description of a procedure for selecting events during the absorption of stopped pions in thin targets is presented. This approach is based on the use of two monitor Si-detectors and a “live” target, which is also an Si-detector, as the last layers of the moderator. Setting the thresholds on monitor detectors and analyzing signals from a “live” target allow one to select pions with a residual range corresponding to the target thickness and reliably exclude the background from stops in the monitor system. It is shown that this method provides an efficiency of identifying stopped π–-mesons of 90%.

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.

The possibility of fabrication of powders from alloy 25Kh15KA for synthesizing permanent magnets by the method of selective laser melting is considered. The method is used to make specimens of permanent magnets 10 × 10 × 9 mm size with a density meeting the State Standard for 25Kh15KA magnets produced by the standard metallurgical process to obtain a coercivity of 45.4 kAm, a residual induction of 1.02 T and a maximum magnetic energy 24 kJm3 . It is shown that the morphology of the particles and the granulometric composition of the powders fabricated by gas atomizing are better than those of the mixtures of elementary Fe, Cr and Co powders and of the powders produced by centrifugal sputtering of molten alloy 25Kh15KA from a scull-melting crucible rotated at controlled speed.

The possibility of fabrication of granulate based on an alloy of the Fe – Cr – Co system with reduced (7 – 10%) cobalt content for synthesizing permanent magnets by the MIM process is considered. A multicomponent granulate composition (polyformaldehyde, high-pressure polyethylene, stearic acid, beeswax) of spherical powders of the Fe – Cr – Co alloy with reduced cobalt content is produced by gas sputtering (average particle diameter 4.2 μm, degree of polydispersity 0.75). The microstructure of the granulate and its granulometric composition are studied. The characteristics of the granulate (the mean diameter of the particles, their morphology and degree of polydispersity) exceed qualitatively the characteristics of the Catamold 42CrMo4 high-quality granulate produced by the BAFS Company.

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.

A survey of experimental results on the level structure in the heavy helium isotope $${}^{6}$$ He that were obtained in reactions induced by stopped pion absorption in $${}^{9}$$ Be, $${}^{10,11}$$ B, and $${}^{12}$$ C 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.

A study of the $$^{11}$$ B( $$^{3}$$ He,d) $$^{12}$$ C reaction at incident $$^{3}$$ He energy $$\hbox {E}_{{lab}}$$ = 25 MeV has been performed at the K-130 cyclotron at the University of Jyvaskyla, Finland. Differential cross sections have been measured for the 13.35 MeV state and for the states with excitation energy around 20 MeV in $$^{12}$$ C. The data were analyzed with the DWBA method. A tentative assignment, 4 $$^{-}$$ , is given for the state at 13.35 MeV in a joint study of the reaction and inelastic scattering of $$\alpha $$ -particles with the energy of 110 MeV. For the state at 20.98 MeV, the possible spin-parity 3 $$^{-}$$ and the isospin T = 0 are assigned for the first time. Our model description of the broad state at 21.6 MeV is consistent with the previous assignments of isospin T = 0 and spin-parity of 2 $$^{+}$$ or 3 $$^{-}$$ . The excited state at 22.4 MeV may have possible spin-parities of either 6 $$^{+}$$ or 5 $$^{-}$$ . The collected statistics was insufficient to solve this question. Rotational bands which can exist in $$^{12}$$ C were presented.

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.

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.

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.

An overview of radiophysical investigations of the lunar soil and plasma shell by active radar detection with the use of spacecraft is presented. The possibility is analyzed of conducting bistatic measurements using the Irkutsk Incoherent Scattering Radar and the onboard radar system RLK-L which is being developed for the orbital station of the Luna-Resurs mission.

Helium 5Hе states are sought in missing-mass (MM) spectra from reactions of the absorption of stopped pions: 10В(π−, dt)Х and 11В(π−, tt)Х. The experiment is conducted using the LANL accelerator equipped with a two-arm semiconductor charged-particle spectrometer. The parameters of the ground state agree with the literature data. The best fit for the first excited level is obtained at Er = 1.8(5) MeV and Γ = 4.7(7) MeV. Neither of the two reactions produce statistically significant evidence for the presence of highly excited (Ex ≥ 20 MeV) states of 5Hе.

The current state of studies in the field of development of multilayer semiconductor systems (semiconductor detector (SCD) telescopes), which allow the energy to be precisely measured within a large dynamic range (from a few to a few hundred MeV) and the particles to be identified in a wide mass range (from pions to multiply charged nuclear fragments), is presented. The techniques for manufacturing the SCD telescopes from silicon and high-purity germanium are described. The issues of measuring characteristics of the constructed detectors and their impact on the energy resolution of the SCD telescopes and on the quality of the experimental data are considered. Much attention is given to the use of the constructed semiconductor devices in experimental studies at accelerators of PNPI (Gatchina), LANL (Los Alamos) and CELSIUS (Uppsala).

An experimental scientific equipment for implementing temperature-controlled protein crystallization in capillaries under microgravity has been developed, fabricated, and tested. This crystallization method, providing on-line separate control of crystal growth both in the stage of nucleation of crystals and during their further growth, requires small amounts of protein solution. The equipment has been tested on board of Foton-M4 spacecraft (growth of lysozyme protein crystals of high structural quality in microgravity) using a cyclogram developed in ground-based experiments. The results obtained have demonstrated efficiency and importance of the developed equipment and method for growing biomacromolecular crystals of high-structural quality.

The characteristics of two modifications of the semiconductor (s.c.d.) setup consisting of telescopes on the basis of silicon detectors are presented. These settings allow performing a precision measurement of energy in a large dynamic range (from a few to hundreds of MeV) and particle identification in a wide range of masses. The issues of measurement of the characteristics of s.c.d. telescopes and their impact on the quality of the obtained experimental data are considered. Considerable attention is paid to the use of created semiconductor devices for the search for and spectroscopy of light exotic nuclei on the accelerators of PNPI (Gatchina) and LANL (Los Alamos).

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.

The results based on the spectroscopy of superheavy hydrogen isotopes (4−7H), heavy helium isotopes (6,7He), and heavy lithium isotopes (7−12Li) produced in stopped pion absorption by light nuclei were analyzed. Search for nuclear states was performed in inclusive and correlation measurements of missing mass spectra. A broad range of excitation energies studied in correlation measurements provided the possibility of search for isobaric analog states and cluster resonances. A comparison with experimental and theoretical results of other authors was conducted.

Analysis of the two-dimensional Dalitz plot measured in the reaction 14C(π–, pd)X allows us to follow the absorption of pions by cluster 3p and identify signs of the configuration 3p + 11Li in the 14C nucleus. The highly excited state of 12,13Be beryllium isotopes with excitation energies E* ≈ 30 MeV and which decay with the emission of hydrogen isotopes is observed for the first time: 12Be* → p + 11Li and 13Be* → d + 11Li.

The results from analyzing the yields of protons (p), deuterons (d), and tritons (t) formed in the absorption of stopped π– mesons by intranuclear clusters are presented. The contributions from cluster absorption to the production of hydrogen isotopes in stopped pion absorption reactions are determined. Phenomenological formulas are proposed for describing the mass number (A) dependences of the yields of the primary protons with ∼15% precision in the mass number range of 6 < A < 209 (and of the primary deuterons and tritons in the mass number range of 59 < A < 209). Evidence is observed of the constancy of the ratio between the elemental absorption widths for the absorption of pions by pp and pn pairs over the investigated range of mass numbers.

The level structure of lithium isotope 6Li is studied in the reaction of the absorption of stopped pions 12С(π−, tt)X. States are sought up to excitation energies of ~40 MeV in the missing mass spectrum. Data on highly excited states are analyzed to determine their origins. The final results are compared to those from searches for the highly excited states of heavier lithium isotopes produced in the reaction of the absorption of stopped pions.

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.

Highly excited states of 6He are sought in the reactions involved in the absorption of stopped pions by 10,11B nuclei. Several levels in 6He are observed for the first time. A state with Ex ≈ 9.3(2) MeV and Γ ≈ 1.0(4) MeV is seen to form in two reactions: 10B(π−, pt)X and 11B(π−, dt)X. Two states are seen to form in the 10B(π−, pt)X reaction channel at energies above the threshold of 6He decay into two tritons (Ex ≥ 12.3 MeV): one state with Ex = 22(1) MeV, Γ = 2.7(1.4) MeV and the other with Ex = 27.0(8) MeV, Γ = 2.5(1.1) MeV.

Results are presented from analyzing the yields of protons (p), deuterons (d), and tritons (t) in pre-equilibrium stopped pion absorption reactions. Phenomenological formulas are proposed for describing the mass-number (A) dependences of these yields accurate to within 10–20% in the mass-number range of 6 < A < 209 (59 < A < 209 for t). The final results do not contradict the hypothesis that the predominant role in the formation of deuterons and tritons is played by pick-up on the surface of nuclei.

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 formation of the 7He heavy isotope has been studied in the 11B(π−, pt)7He, 11B(π−, dd)7He, and 10B(π−, pd)7He reactions of absorption of stopped π− mesons. No indications of the existence of a low-lying level with E x ∼ 1 MeV have been obtained in any of the three reactions. The existence of three narrow states with excitation energies E x = 3.1(1), 4.90(15), and 6.65(15) MeV has been proven. Highly excited states with E x = 16.9(5) MeV, Γ = 1.0(3) MeV, E x = 19.8(3) MeV, Γ = 1.5(3) MeV, and E x = 24.8(4) MeV, Γ = 4.6(7) MeV have been identified.

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 excited states of light neutron-rich isotopes were studied in the reactions of stopped pion absorption. The level structure of the superheavy hydrogen isotopes 4–7H, heavy helium isotopes 6,7He and lithium isotopes 6-12Li were determined up to the excitation energy ∼ 30 MeV. For most nuclei results were obtained in several reaction channels. The wide range of excitation energies provided the possibilities to study isobar-analog states and cluster resonances. Our data are compared with theoretical and experimental results obtained up to now.

Experimental results are presented for the spectra and yields of t and 3He produced by nuclei in the reaction of stopped pion absorption. Contributions from different processes in the formation of particles are determined using a phenomenological model. The ratio of t and 3He yields agrees with the hypothesis of particle formation during the pre-equilibrium stage in the process of deuteron pick-up by primary nucleons on the surface of a nucleus.

Three narrow (Γ ≤ 0.5 MeV) low-lying states of 7He with excitation energies of 3.2(1) MeV, 4.9(2) MeV and 6.65(15) MeV are observed simultaneously for the first time in reactions of the absorption of stopped π−-mesons 11B(π−,pt)7He and 11B(π−,dd)7He. No indications of the existence of a level in the area of Ex ∼ 1 MeV are found. Highly excited 7He states with parameters Ex = 19.6(3) MeV, Γ = 1.7(4) MeV and Ex = 25.2(6) MeV, Γ= 4.8(9) MeV are observed.

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.

Highly excited states of the 8Li isotope are sought in absorption reactions of π− mesons stopped by 10,11B isotopes. The ground and three excited states of the 8Li isotope are observed in inclusive measurements of reactions 10B(π−, d)X and 11B(π−, t)X. The states with excitation energies Ex ≈ 8.7 and 10.1 MeV are observed for the first time in correlation measurements of reactions 10B(π−, dt)X and 11B(π−, tt)X.

The origin of the 9Li isotope is sought in missing-mass spectra measured in 11B(π−, d)X, 12C(π−, pd)X, and 14C(π−, dt)X stopped-pion absorption reactions. The parameters of the three observed low-lying excited states coincide with the literature data. A state with excitation energy Ex = 9.1 ± 0.1 MeV, lying above the threshold of 9Li decay into 6He + t, is observed for the first time.

Experimental results on the yields and spectra of protons produced during the absorption of stopped pions by nuclei are presented. The measurements were performed on the accelerator at the St. Petersburg Nuclear Physics Institute, Russian Academy of Sciences, using a two-arm semiconductor spectrometer of charged particles on a set of nuclei that includes light nuclei 6,7Li, 9Be, 10,11B, and 12C; medium nuclei 28Si, 40Ca, 59Co, and 93Nb; tin isotopes 114,117,120,124Sn; and heavy nuclei 169Tm, 181Ta, and 209Bi. The A dependences of the proton yields and their components are obtained. Some indications of the dominant role of pion absorption on intranuclear pp pairs in the formation of fast protons are presented.

A search for the 10Li formation was performed in missing mass spectra measured in stopped pion absorption reactions 14C(π−, pt)X and 14C(π−, dd)X. Three excited states of 10Li were found. The broad state with a resonance energy of ER = 6.13 ± 0.11 MeV has the highest excitation energy in comparison with levels observed earlier.

The structure of excited levels in the 7Li isotope is studied via inclusive and correlation measurements in the stopped π− meson absorption reactions 10B(π−, t)X and 12C(π−, dt)X, respectively. The experiment is conducted using a low-energy pion beam at the LAMPF meson factory. Analysis of the missing mass spectra reveals 7Li states with the resonance parameters (E x , Γ) (4.7, 0.1), (6.6, 0.9), (7.3, 0.1), (9.1, 2.8), and (9.6, 0.4) MeV. A highly excited state with E x ≈ 11.2 MeV (i.e., an isobar analog of 7He) is observed in the 10B(π−,t)X reaction. An excited state with E x = 10.3 ± 0.1 MeV and γ = 1.8 ± 0.4 Mev is observed for the first time in the 12C(π−,dt)X reaction.

Correlation measurements of the reaction of stopped pion absorption 11B(π−, tt)X are made with a semiconductor double-arm charged particle spectrometer on a low-energy pion beam at the LAMPF meson factory. Analysis of a two-dimensional Dalitz plot and the momentum distribution of the residual nucleus allows us to identify the absorption of pions in a 6Li intranuclear cluster and demonstrate the configuration 6Li + 5Heg.s is present in the 11B nucleus.

A method for producing 10Be isotope from spent rods of the emergency protection and compensation systems of a fast neutron reactor is described. This isotope has found application in targets and radioactive beams for experiments at modern heavy-ion accelerators. The mass of 10Be obtained using this technique is 2.7 mg, which is five times the mass of this isotope produced throughout the world to date. A method for determining the 10Be concentration in the source material and intermediate fractions of its processing has been developed. This method is based on analysis of γ and β spectra of samples, measured by HPGe and Si(Li) detectors. A prototype of the 10Be oxide target has been manufactured. The parameters of the target prototype have been determined, and its vacuum testing has been performed.

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 results from an experimental search for the production of heavy lithium isotopes 11,12Li in stopped π−-meson absorption reactions on a 14C radioactive target are presented. A pronounced peak is observed in the missing mass spectrum of the 14C(π−, pp)X reaction, which is associated with the formation of a nucleon-unstable 12Li state with the following resonance parameters: ER = 4.0 ± 0.2 MeV and Γ = 1.1 ± 0.2 MeV. Resonance parameters of three low-lying 11Li excited states were determined in the 14C(π−, pd)X, reaction.

Review of the experimental results on the search for and the spectroscopy of the superheavy hydrogen isotopes 4–7H obtained in stopped π−-meson absorption by 9Be and 11Be nuclei is presented. Study of light neutron-rich nuclei is a principal line in developing modern views on the properties of nuclear forces and determination of nuclear properties near the drip line. The present method of investigation relies on precision measurements of energy of charged particles emitted after pion absorption by nuclei. Important advantages of this method are the practically accurate initial state energy and momentum, as well as the possibility to study a wide range of excitation energy. In the frames of this method new results were obtained on level structures of the isotopes 4–6H and indications on 7H production. Comparison with other experimental and theoretical results is performed.

The results of searching for production of superheavy hydrogen isotopes 4,5H in reactions of absorption of stopped π− mesons by 10,11B nuclei are reported. A peak near 3 MeV was observed in the missing mass spectra measured in the reactions 10,11B(π−, t4He)X, 10B(π−, d4He)X, and 10B(π−, t3He)X. A structure caused by two 5H states with the resonance energies ER = 5.2 and 10.4 MeV was observed in the missing mass spectra measured in the reactions 11B(π−, d4He)X, 11B(π−, t3He)X, and 10B(π−, d3He)X.

The methods for measuring the thickness of dead layers in Si(Li) and HPGe detectors using radioactive sources of electrons, γ rays, and α particles are proposed. Following the developed procedure, it is possible to determine the thickness of these layers with an error of ∼1%.

Experimental search for superheavy hydrogen isotopes 6 H and 7 H was performed in the stopped pion absorption on 9 Be and 11 B nuclei. The structures in the missing-mass spectra were observed in the reaction channels 9 Be(� ,pd)X and 11 B(� ,p 4 He)X. Four states of 6 H were proposed. Evidences for 7 H formation were obtained in the reaction channels 9 Be(� ,pp)X and 11 B(� ,p 3 He)X.