Stability of <Superscript>244–260</Superscript>Fm isotopes against alpha and cluster radioactivity

Taking Coulomb and proximity potentials as the interacting barrier we have studied the cold valley in the radioactive decay of ^244–260Fm isotopes. It is found that in addition to alpha particle minima, other minima occur at S, Ar and Ca clusters. We have computed the half-lives and other characteristics of different clusters emitted from these parents treating parent, daughter and emitted cluster as spheres. Our study reveals that most of these parents are unstable against alpha and heavy cluster (⁴⁶Ar, ^48,50Ca) emissions and stable against light cluster emission, except ⁸Be from ^244–248Fm isotopes. The most probable clusters from these parents are predicted to be ⁴⁶Ar, ^48,50Ca which indicate the role of doubly or near doubly magic clusters (Z = 20, N = 28) and also stress the role of doubly magic ²⁰⁸Pb daughter. The computed half-lives for alpha decay are in good agreement with the experimental data. It is found that the presence of neutron excess in the parent nuclei slows down the cluster decay process. The effect of quadrupole (β ₂) and hexadecapole (β ₄) deformations of parent and fragments on half-lives are also studied. It is found that inclusion of β ₂ and β ₄ reduces the height and shape of the barrier (increases barrier penetrability) and hence the half-life decreases.     

Gamow-Teller 1<Superscript>+</Superscript> states in <Superscript>112–124</Superscript>Sb isotopes

The violated supersymmetry property of the pairing interaction between nucleons were restored using the Pyatov method [Pyatov and Salamov, Nucleonica 22, 127 (1977)]. The eigenvalues and eigenfunctions of the restored Hamiltonian with the separable residual Gamow-Teller effective interactions in the particle-hole and particle-particle channels were solved within the framework of proton-neutron quasirandom phase approximation (pnQRPA). The Gamow-Teller resonance energies for ^112–124Sb isotopes and the differential cross-sections for Sn(³He, t)Sb reactions at E(³He) = 200 MeV occurring by the excitation of the Gamow-Teller resonance state were calculated. The calculated values were compared with other calculations and the corresponding experimental data.     

<Emphasis Type="Italic">J</Emphasis><Superscript>π</Superscript>0<Superscript>−</Superscript> levels in <Superscript>156</Superscript>Gd and <Superscript>158</Superscript>Gd

The 0^? states in the ¹⁵⁶Gd nucleus at E = 1952.38 keV and in the ¹⁵⁸Gd nucleus at E = 2269.16 keV are established on the basis of an analysis of available data on even-even deformed nuclei. From data on the deexcitation of the levels and on the probability of their population by beta transitions, it is found that these states have a two-particle proton structure. A comparison of our data with information about the 0^? levels in the ¹⁷⁰Yb and ¹⁷⁶Hf nuclei makes it possible to conclude that J^π0^? two-particle states exist at an excitation energy of about 2 MeV and higher.     

Cold valleys in the radioactive decay of <Superscript>248–254</Superscript>Cf isotopes

Based on the concept of cold valley in cold fission and fusion, we have investigated the cluster decay process in ^248–254Cf isotopes. In addition to alpha particle minima, other deep minima occur for S, Ar and Ca clusters. It is found that inclusion of proximity potential does not change the position of minima but minima become deeper. Taking Coulomb and proximity potential as interacting barrier for post-scission region, we computed half-lives and other characteristics for various clusters from these parents. Our study reveals that these parents are stable against light clusters and unstable against heavy clusters. Computed half-lives for alpha decay agree with experimental values within two orders of magnitude. The most probable clusters from these parents are predicted to be ⁴⁶Ar, ^48,50Ca which indicate the role of doubly or near doubly magic clusters in cluster radioactivity. Odd A clusters are found to be favorable for emission from odd A parents. Cluster decay model is extended to symmetric region and it is found that symmetric fission is also probable which stresses the role of doubly or near doubly magic ¹³²Sn nuclei. Geiger-Nuttal plots were studied for various clusters and are found to be linear with varying slopes and intercepts.      

Neutron and proton shell closure in the superheavy region via cluster radioactivity in <Superscript>280–314</Superscript>116 isotopes

Based on the concept of cold valley in fission and fusion, the radioactive decay of superheavy^280–314116 nuclei was studied taking Coulomb and proximity potentials as the interacting barrier. It is found that the inclusion of proximity potential does not change the position of minima but minima become deeper which agrees with the earlier findings of Gupta and co-workers. In addition to alpha particle minima, the other deepest minima occur for ⁸Be, ^12,14C clusters. In the fission region two deep regions are found each consisting of several comparable minima, the first region centred on ²⁰⁸Pb and the second is around ¹³²Sn. The cluster decay half-lives and other characteristics are computed for various clusters ranging from alpha particle to ⁷⁰Ni. The computed half-lives for alpha decay match with the experimental values and with the values calculated using Viola-Seaborg-Sobiczewski (VSS) systematic. The plots connecting computed Q values and half-lives against neutron number of daughter nuclei were studied for different clusters and it is found that the next neutron shell closures occur at N = 162, 172 and 184. Isotopic and isobaric mass parabolas are studied for various cluster emissions and minima of parabola indicate neutron shell closure at N = 162, 184 and proton shell closure at Z = 114. Our study shows that ₁₆₂²⁷⁶114 is the deformed doubly magic and ₁₈₄²⁹⁸114 is the spherical doubly magic nuclei.      

Experimental Determination of the Effective Resonance Absorption Integrals of <Superscript>238</Superscript>U and <Superscript>158</Superscript>Gd in Urania–Gadolinia Rods

The experimental procedure and the results of determination of the effective resonance neutron absorption integrals of ²³⁸U and ¹⁵⁸Gd for isolated UO₂–Gd₂O₃ rods are presented. Measurements were performed using the activation method. UO₂–Gd₂O₃ rods were irradiated in the neutron field with the Fermi spectrum formed at the center of the core of the F-1 research reactor at the National Research Centre Kurchatov Institute.     

Inversion of the <Emphasis Type="Italic">K</Emphasis><Superscript>π</Superscript>=1<Superscript>−</Superscript> states in <Superscript>156</Superscript>Gd and <Superscript>170</Superscript>Yb

For the ¹⁵⁶Gd and ¹⁷⁰Yb nuclei, where the inversion of levels in the K^π=1^? bands is observed, the energies of rotational levels are calculated on the basis of the Coriolis interaction model for the states of two bands whose quantum numbers are K^π=1^?. New 0^? levels are introduced in ¹⁷⁰Yb, and the structure of ¹⁷⁰Er is refined. The interaction parameters calculated for six nuclei are considered within the structure predicted by the quasiparticle-phonon model.     

Cross sections for the photofission of <Superscript>243</Superscript>Cm, <Superscript>245</Superscript>Cm, <Superscript>249</Superscript>Bk,and <Superscript>249</Superscript>Cf isotopes in the energy range from the threshold to 10–12 MeV

The relative method was used to measure the photofission cross sections for ²⁴³Cm and ²⁴⁹Cf isotopes in the energy range from 6 to 12 MeV, for ²⁴⁵Cm in the energy range from 5 to 10 MeV, and for ²⁴⁹Bk in the energy range from 5.5 to 10 MeV. The measurements were performed with an energy step of 50 to 200 keV by using the microtron installed at the Institute of Physics and Power Engineering (Obninsk). The cross section for ²³⁸U photofission was used as a reference in these measurements. Data on the cross sections for ²⁴³Cm, ²⁴⁵Cm, and ²⁴⁹Bk photofission were obtained for the first time, while data on the cross section for ²⁴⁹Cf photofission were obtained for the first time only in the energyregion E<10 MeV. The data on the ²⁴⁵Cm nucleus suggest that, in the energy region around 6 MeV, the cross section for its photofission has a maximum, which is likely to be due to the low-energy resonance structure of the dipole-photoabsorption cross section. For ²⁴⁹Cf, an anomalously large value of the photo fission cross section is observed in the region of the first maximum of the giant dipole resonance (E≈11 MeV). By comparing the energy dependences obtained for the fissilities of the ²⁴³Cm and ²⁴⁹Bk isotopes from photofission data with the fissilities from direct-reaction data, it is found that the observed fission thresholds agree and that there is a plateau-like dependence at energies above 7.5 MeV. For the ²⁴⁵Cm and ²⁴⁹Cf nuclei, there are no similar data for performing such a comparison. Data on the fissilities as obtained from the present series of relative measurements that employ the microtron bremsstrahlung spectrum are analyzed.     

Cluster decay of <Superscript>112−122</Superscript>Ba isotopes from ground state and as an excited compound system

The decay properties of various even–even isotopes of barium in the range 112 ≤A ≤ 122 is studied by modifying the Coulomb and proximity potential model for both the ground and excited state decays, using recent mass tables. Most of the values predicted for ground state decays are within the experimental limit for measurements (T_1/2 < 10³⁰ s). The minimum T_1/2 value refers to doubly magic or nearly doubly magic Sn (Z= 50) as the daughter nuclei. A comparison of log ₁₀(T_1/2) value reveals that the exotic cluster decay process slows down due to the presence of excess neutrons in the parent nuclei. The half-lives are also computed using the Universal formula for cluster decay (UNIV) of Poenaru et al and the Universal decay law (UDL) of Qi et al, and are compared with CPPM values and found to be in good agreement. A comparison of half-life for ground and excited systems reveals that probability of decay increases with a rise in temperature or otherwise, inclusion of excitation energy decreases the T_1/2 values.     

Laser excited fluorescence of molecular iodine <Superscript>127</Superscript>I and <Superscript>129</Superscript>I isotopes in the 632–637 nm spectral region

Experimental and theoretical studies of fluorescence of long-lived molecular iodine ¹²⁷I and ¹²⁹I isotopes excited by radiation emitted by frequency-tunable semiconductor laser were conducted for the first time. The results obtained demonstrate the potential of development of real-time laser detector of the isotopes in question.     

Detailed Investigations of Neutron–Neutron Angular Correlations in Slow-Neutron-Induced Fission of <Superscript>233</Superscript>U, <Superscript>235</Superscript>U,and <Superscript>239</Superscript>Pu

An experiment devoted to studying neutron–neutron angular correlations in the slow-neutroninduced fission of ²³³U, ²³⁵U and ²³⁹Pu nuclei was performed. The experimentally determined angular dependence of the number of neutron–neutron coincidences was compared with the results of a Monte Carlo simulation for various values of the neutron-detection threshold in the range between 490 and 2080 keV. It was found that the experimental angular distributions in question can be described well under the assumption that 2% to 5% of all prompt fission neutrons are emitted isotropically in the laboratory frame. Probably, such neutrons can be interpreted as so-called scission neutrons directly associated with the nuclear-rupture instant. Energy distributions of this component were also obtained from the present analysis.     

The evaluation of the branching ratios of the decays φ(1020)→2π<Superscript>+</Superscript>2π<Superscript>−</Superscript>π<Superscript>0</Superscript>, π<Superscript>+</Superscript>π<Superscript>−</Superscript>3π<Superscript>0</Superscript>

Combining the Okubo-Zweig-Iizuka rule in the decay φ→ρπ→π⁺π^?π⁰ with the ρ→4π decay amplitudes, we calculate the φ→2π⁺2π^?π⁰ and φ→π⁺π^?3π⁰ ones. The partial widths of the above φ decays are evaluated, and the excitation curves in e⁺e^? annihilation are obtained, assuming reasonable particular relations among the parameters characterizing the anomalous terms of the HLS Lagrangian. The evaluated branching ratios B_φ→π⁺_π^?_3π⁰ ≈ 2 × 10^?7 and B_φ→2π⁺_2π^?_π⁰ ≈ 7 × 10^?7 are such that, with the luminosity L=500 pb^?1 attained at DAΦNE φ factory, one may already possess about 1685 events of the decays φ→5π.     

Potential energy of <Superscript>∞</Superscript>H<Stack><Subscript>2</Subscript><Superscript>-</Superscript></Stack>(<Superscript>2</Superscript>∑<Stack><Subscript>u</Subscript><Superscript>+</Superscript></Stack> in the bound-state region

An accurate calculation of the lowest negative electronic state of H ₂ ^- (fixed nuclei) is reported using the CCSD(T) method and doubly augmented cc-pv5z basis set. Comparison has been made with the reference data by Senekowitsch et al. [Chem. Phys. Lett. 111 (1984) 211]. Owing to larger size of the basisset and inclusion of triple excitations, no vertical shift in this work is necessary to reproduce the asymptotics of H + H ^-. In addition, the effect of basis-set truncation is estimated, based on the complete-basis-set extrapolation method. The contribution of correlated electron-proton motion to the electron-energy curve for H₂ ^– dynamics is pointed out.Dedicated to Prof. Jií Horáek on the occasion of his 60th birthday.     

Emission spectroscopy of the A<Superscript>1</Superscript>Π–X<Superscript>1</Superscript>Σ<Superscript>+</Superscript> system of AlH

The high-resolution emission spectrum of the A¹ Π–X¹Σ⁺ transition of AlH was observed in the 18 000–25 000 cm^-1 spectral region using a conventional spectroscopic technique. The AlH molecules were excited in an Al hollow-cathode lamp filled with a mixture of Ne carried gas and a trace amount of NH₃. The emission from the discharge was observed with a plane grating spectrograph and recorded by a photomultiplier tube. In total 163 transition wave numbers belonging to six bands (0-0,1 and 1-0,1,2,3) were precisely measured and rotationally analysed. In the final fit the present data have been combined with available high-resolution measurements of the vibration-rotation bands by White et al. [J. Chem. Phys. 99, 8371 (1993)]. This procedure enabled extracting molecular constants for the A¹ Π and X¹ Σ⁺ states of AlH. A very slight local perturbation has been discovered in the v=1 vibration level of the A¹ Π state at J=5. This was probably caused by the interaction with the a³Π state.     

Gain characteristics of 980 nm-pumped Er<Superscript>3+</Superscript>–Tm<Superscript>3+</Superscript>–Pr<Superscript>3+</Superscript>-co-doped fiber

We present a numerical model of Er³⁺–Tm³⁺–Pr³⁺-co-doped fiber amplifier pumped with 980 nm laser for the first time, to the best of our knowledge. The rate and power propagation equations are solved numerically to analyze the effects of the pump power and active ion concentrations on the gains at 1310, 1470, 1530, 1600, 1650 nm windows. The results show that with pump power of 200 mW and when Pr³⁺, Tm³⁺, Er³⁺ concentrations are around 2.0×10²⁴, 3.0×10²⁴, 1.5×10²⁴ (ions/m³), respectively, the signals at 1470, 1530, 1600 nm may be nearly equally amplified with gain of 11–12.0 dB in the active fiber with length of 11.0 m, and the signals at 1310, 1470 and 1600 nm windows may be nearly equally amplified with gain of 12.0 dB in the active gain medium with length of 15.0 m. With pump power of 300 mW, the signals at 1470, 1530, 1600 nm may be nearly equally amplified with a gain of 16.0 dB in the active medium with a length of 15.0 m.     

Decays of baryon resonances into ΛK<Superscript>+</Superscript>, ΣK<Superscript>+</Superscript> and Σ<Superscript>+</Superscript>K<Superscript>0</Superscript>

Cross-sections, beam asymmetries, and recoil polarisations for the reactions γp → K ⁺Λ;γp → K ⁺Σ⁰, and γp → K ⁰Σ⁺ have been measured by the SAPHIR, CLAS, and LEPS Collaborations with high statistics and good angular coverage for centre-of-mass energies between 1.6 and 2.3 GeV. The combined analysis of these data with data from π and η photoproduction reveals evidence for new baryon resonances in this energy region. A new P₁₁ state with mass 1840 MeV and width 140 MeV was observed contributing to most of the fitted reactions. The data demand the presence of two D₁₃ states at 1875 and, optimistically, at 2170 MeV.     

Production of residual radioactive nuclei in thin <Superscript>209</Superscript>Bi, <Superscript>nat</Superscript>Pb, <Superscript>206</Superscript>Pb, <Superscript>207</Superscript>Pb,and <Superscript>208</Superscript>Pb targets bombarded with 0.04–2.6 GeV protons

The results of the experimental measurement and numerical simulation of the cross sections for residual radioactive nuclei production in thin ²⁰⁹Bi, ^natPb, ²⁰⁶Pb, ²⁰⁷Pb, and ²⁰⁸Pb targets bombarded with protons in the energy range from 0.04 to 2.6 GeV are reported. The nuclide production cross sections were measured using γ spectrometry with a high-resolution Ge detector. The experimental data include a total of 5972 reaction cross sections at 11 proton energy values. The results are compared to the data from other laboratories reported in 80 papers. The model calculations were carried out using eight simulation code packages: LAHET, INCL4 + ABLA, CEM03, LAQGSM + GEM2, CASCADE, CASCADE-2004, CASCADO, and LAHETO. A detailed analysis of discrepancies between the measured and calculated data is presented.     

Charge transfer in energetic Li<Superscript>2+</Superscript>–H and He<Superscript>+</Superscript>–He<Superscript>+</Superscript> collisions

The total cross sections for charge transfer in Li²⁺-H and He⁺-He⁺ collisions have been calculated, using the four body first Born approximation with correct boundary conditions (CB1-4B) and four body continuum distorted wave method (CDW-4B) in the energy range 10–5000 keV/amu. The role of dynamic electron correlations is examined as a function of the impact energy. The present results call for additional experimental data at higher impact energies than presently available.