Heavy lithium isotope <Superscript>11,12</Superscript>Li production in pion absorption reactions on a <Superscript>14</Superscript>C radioactive target

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: E _R = 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.     

Spectroscopy of the <Superscript>9</Superscript>Li isotope in stopped-pion absorption reactions

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 E _x = 9.1 ± 0.1 MeV, lying above the threshold of ⁹Li decay into ⁶He + t, is observed for the first time.     

Spectroscopy of 7Li in stopped pion absorption reactions

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.     

Searching for rare cluster configurations of <Superscript>14</Superscript>C nuclei in the pion absorption reaction

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.     

Search for superheavy hydrogen isotopes <Superscript>4,5</Superscript>H in reactions of pion absorption by <Superscript>10,11</Superscript>B nuclei

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 E _R = 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.     

One-neutron stripping reactions of <Superscript>11</Superscript>Be and <Superscript>19</Superscript>C on light target

We have calculated the one-neutron absorption cross-section and the longitudinal momentum distribution of the core fragment coming out from the breakup of ¹¹Be and ¹⁹C on ⁹Be target at 63 MeV/A and 88 MeV/A beam energies respectively. The reaction mechanism is treated within the framework of the eikonal approximation. The effective range of the nuclear interaction between the core and the valence neutron within the projectile has been determined by comparing the predicted stripping cross-section with the recently measured one. The effective range for ¹⁹C has been found to be smaller than that for ¹¹Be. It qualitatively indicates that ¹⁹C is slightly more halo than ¹¹Be. The smaller width, predicted as well as measured, of the LMD of ¹⁸C than ¹⁰Be also strengthens this fact. The experimental data concerning the LMD of core fragments have been well represented.      

Spectroscopy of the <Superscript>5</Superscript>H superheavy hydrogen isotope

The formation of the ⁵H superheavy hydrogen isotope was experimentally sought in the reactions induced by stopped π^? mesons absorbed by ⁹Be nuclei. Peaks in missing-mass spectra were observed in two reaction channels, ⁹Be(π^?, pt)X and ⁹Be(π^?, dd)X, and were attributed to the ⁵H resonance states. The lowest state has parameters Er=5.5±0.2 MeV and Г=5.4±0.5 MeV [E_r is the resonance energy measured from the (triton + two neutrons) threshold]. Therefore, ⁵H is bound more weakly than ⁴H. Excited states of ⁵H were also observed. All three resonance levels (E_1r=10.6±0.3 MeV, Г_1r=6.8±0.5 MeV; E_2r=18.5±0.4 MeV, Г_2r=4.8±1.3 MeV; E_3r=26.7±0.4 MeV, Г_3r=3.6±1.3 MeV) can decay into five free nucleons.     

Multineutron photonuclear reactions on the <Superscript>197</Superscript>Au isotope

An experiment on irradiation of the ¹⁹⁷Au isotope by a beam of bremsstrahlung γ-rays of maximum energy E _γ ^m = 70 MeV has been carried out at the RTM-70 race-track microtron of the INP MSU. Residual activity spectra of the irradiated sample were measured. Multiparticle photonuclear reactions on the ¹⁹⁷Au nucleus are observed. Photonuclear reactions with emission of as many as six neutrons are observed for the first time.     

Level structure of lithium isotope <Superscript>6</Superscript>Li

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.     

Cosmogenic radionuclides <Superscript>14</Superscript>C and <Superscript>10</Superscript>Be: Solar activity and climate

The problem of the use of such cosmogenic nuclides as ¹⁴C and ¹⁰Be in natural archives for reconstruction of both the solar activity and the cosmic-ray intensity is discussed. The climate-dependent processes of the formation, transport, and deposition of these nuclides to Earth’s archives must be taken into account for adequate processing of information derived from such archives.     

Yields of multiparticle photoneutron reactions on the <Superscript>209</Superscript>Bi isotope

The relative yields of multiparticle photoneutron reactions on the ²⁰⁹Be isotope with emission of two to seven neutrons from the nucleus are measured. The experiment was carried out with the bremsstrahlung beam from the RTM-70 pulsed race-track microtron (INP, MSU) with a maximum photon energy E _γ ^m = 67.7 MeV.     

Search for superheavy hydrogen isotopes <Superscript>6</Superscript>H and <Superscript>7</Superscript>H in stopped π-absorption reactions

Experimental search for superheavy hydrogen isotopes ⁶H and ⁷H was performed in the stopped pion absorption on ⁹Be and ¹¹B nuclei. The structures in the missing-mass spectra were observed in the reaction channels ⁹Be(π^-, pd )X and ¹¹B(π^-, p⁴He)X . Four states of ⁶H were proposed. Evidences for ⁷H formation were obtained in the reaction channels ⁹Be(π^-, pp)X and ¹¹B(π^-, p³He)X .     

Formation of primary particles in stopped pion absorption reactions

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.     

Study of the Involvement of <Superscript>8</Superscript>Be and <Superscript>9</Superscript>B Nuclei in the Dissociation of Relativistic <Superscript>10</Superscript>C, <Superscript>10</Superscript>B,and <Superscript>12</Superscript>C Nuclei

The results obtained by estimating the contribution of 8Be and 9B nuclei to the coherent dissociation of ¹⁰C, ¹⁰B, and ¹²C relativistic nuclei in nuclear track emulsions (“white” stars) are presented. The selection of white stars accompanied by 9B leads to a distinct peak appearing in the distribution of the excitation energy of 2α2p ensembles and having a maximum at 4.1 ± 0.3 MeV. A 8Be nucleus manifests itself in the coherent-dissociation reaction ¹⁰B → ²He + H with a probability of (25 ± 5)%, (14 ± 3)% of it being due to 9B decays. The ratio of the branching fractions of the ⁹B + n and ⁹Be + p mirror channels is estimated at 6 ± 1. An analysis of the relativistic dissociation of ¹²C nuclei in a nuclear track emulsion revealed nine 3α events corresponding to the Hoyle state.     

The origin of the background radioactive isotope <Superscript>127</Superscript>Xe in the sample of Xe enriched in <Superscript>124</Superscript>Xe

The results of investigation of ¹²⁷Xe radioactive isotope production in the xenon sample enriched in ¹²⁴Xe, ¹²⁶Xe, ¹²⁸Xe are presented. The isotope is supposed to be the source of the background events in the low-background experiment on search for 2K-capture of ¹²⁴Xe. In this work we consider two channels of ¹²⁷Xe production: the neutron knock-out from ¹²⁸Xe nucleus by cosmogenic muons and the neutron capture by ¹²⁶Xe nucleus. For the first channel the upper limit of the cross section of ¹²⁷Xe production was found to be σ ≤ 0.007 × 10^?24 cm² at 95% C.L. For the second channel the value obtained for the cross section was found to be equal to σ = (2.74 ± 0.4) × 10^?24 cm², which coincides well, within the statistical error, with reference value.     

Evolution of Airy structure in <Superscript>12</Superscript>C(<Superscript>12</Superscript>C, <Superscript>12</Superscript>C)<Superscript>12</Superscript>C between 5 and 10 MeV/A

We investigate the properties of a global optical potential, which describes the ¹²C + ¹²C elastic-scattering data between 70 and 130 MeV, within the nearside/farside and barrier-wave/internal-wave decomposition techniques. Particular emphasis is laid on the discussion of the incomplete absorption features of this system, and especially on the properties of the Airy minima which are observed in the experimental excitation function. The complicated angular and energy evolution of the data is explained in terms of the interference of a small set of scattering subamplitudes with a much simpler behavior.Received: 2 September 2003, Revised: 25 September 2003, Published online: 5 February 2004PACS: 24.10.-i Nuclear reaction models and methods - 24.10.Ht Optical and diffraction models - 25.70.Bc Elastic and quasielastic scattering     

Solar activity over last ten thousand years based on the data of <Superscript>10</Superscript>Be and <Superscript>14</Superscript>C cosmogeneous isotopes

The data on the ¹⁰Be accumulation rate in Greenland glacier (GRIP project) are discussed. Spectral analysis of the data over the last 9000 years is carried out. The spectral line intensity in the low-frequency range (periods from 100 to 1000 years) is much higher (approximately by a factor of 20), than in the frequency range of the 11-year solar activity cycle. This fact suggests that the processes responsible for the variations in the ¹⁰Be production rate with a time scale of 100–1000 years significantly differ from those determining the 11-year cyclicity of solar activity.     

The knockout reaction of <Superscript>15</Superscript>C on a <Superscript>9</Superscript>Be target at intermediate energies

In this work, neutron knockout reactions of ¹⁵C on a ⁹Be target at energy 103 and 250 MeV/nucleon are studied. Using the Eikonal approximation of the Glauber model, total neutron removal cross sections, the stripping and diffractive cross sections as well as ¹⁴C longitudinal momentum distributions are determined in both ¹⁵C ground state and exited states of the wave function. We compared the results of our calculations with the available experimental data obtained recently. The calculated cross sections of ¹⁵C and ¹⁴C reactions, as well as the momentum distribution are in relatively good agreement with available data.     

Dynamical decay process of <Superscript>219, 220</Superscript>Ra<Superscript>*</Superscript> formed in <Superscript>10, 11</Superscript>B + <Superscript>209</Superscript>Bi reactions

The excitation functions for both the evaporation residue and fission have been calculated for ¹⁰B + ²⁰⁹Bi and ¹¹B + ²⁰⁹Bi reactions forming compound systems ^{219, 220}Ra^* , using the dynamical cluster-decay model (DCM) with effects of deformations and orientations of the nuclei included in it. In addition to this, the excitation functions for complete fusion (CF) are obtained by summing the fission cross-sections, neutron evaporation and charged particle evaporation residue cross-sections produced through the axn\ensuremath \alpha xn and pxn\ensuremath pxn (x = 2, 3, 4) emission channels for the ²¹⁹Ra system at various incident centre-of-mass energies. Experimentally the CF cross-sections are suppressed and the observed suppression is attributed to the low binding energy of ^{10, 11}B which breaks up into charged fragments. The reported complete fusion (CF) and incomplete fusion (ICF) excitation functions for the ²¹⁹Ra system are found to be nicely fitted by the calculations performed in the framework of DCM, without invoking a significant contribution from quasi-fission. Although DCM has been applied for a number of compound nucleus decay studies in the recent past, the same is being used here in reference to ICF and subsequent decay processes along with the CF process. Interestingly the main contribution to complete fusion cross-section comes from the fission cross-section at higher incident energies, which in DCM is found to consist of an asymmetric fission window, shown to arise due to the deformation and orientation effects of formation and decay fragments.