Evidence of new isotopes:169, 170Ir,166, 167, 168Re

At the Darmstadt UNILAC newα-emitting nuclei were produced in the bombardment of⁸⁹Y and⁹³Nb targets using⁸⁴Kr ions with energies in the range of 5.1 to 5.5 MeV/u, and 5.8 to 6.4 MeV/u, and using⁸⁶Kr ions with energies in the range of 5.6 to 6.0 MeV/u. Reaction recoils emitted from the targets were stopped and transported with argon to a collection site. Using three alpha detectors and spectrum multiscaling, energies and half-lives were measured. Ir and Re isotopes were identified by cross bombardments, excitation function data andα-systematics. The decay characteristics of the new species are as follows: Estimates onα-branching ratios have been obtained for^{169, 170}Os and^{166, 167, 168}Re.     

Molecular dynamics study of structural damage in amorphous silica induced by swift heavy-ion radiation

In this paper, the radiation defects induced by the swift heavy ions and the recoil atoms in amorphous SiO₂ were studied. The energy of recoil atoms induced by the incident Au ions in SiO₂ was calculated by using Monte Carlo method. Results show that the average energies of recoils reach the maximum (200?eV for Si and 130?eV for O, respectively) when the incident energy of Au ion is 100?MeV. Using Tersoff/zbl potential with the newly built parameters, the defects formation processes in SiO₂ induced by the recoils were studied by using molecular dynamics method. The displacement threshold energies (E_d) for Si and O atoms are found to be 33.5 and 16.3?eV, respectively. Several types of under- and over-coordinated Si and O defects were analyzed. The results demonstrate that Si₃, Si₅, and O₁ are the mainly defects in SiO₂ after radiation. Besides, the size of cylindrical damage region produced by a single recoil atom was calculated. The calculation shows that the depth and the radius are up to 2.0 and 1.4?nm when the energy of recoils is 200?eV. Finally, it is estimated that the Au ion would induce a defected track with a diameter of 4?nm in SiO₂.     

Reactions on 209Bi induced by intermediate energy protons and the effect of direct reactions

Excitation functions and ranges of recoil nuclei in the ²⁰⁹Bi(p, 3n)²⁰⁷Po, ²⁰⁹Bi(p, 4n) ²⁰⁶Po and ²⁰⁹Bi(p, p3n)²⁰⁶Bi reactions have been measured for incident energies from 18 MeV up to 52 MeV. It has been found that the recoil ranges in (p, p3n) reactions are rather shorter than those in (p, 4n), and that beyond E_p = 40 MeV the high energy tail of the excitation function for (p, p3n) is roughly flat, in contrast to the decreasing tail for (p, 4n). A theoretical analysis of the excitation functions and of the nuclear recoil ranges has been made. It has been found that in (p, p3n) reactions the direct process plays a very important part in the reaction mechanism. It is also found that the reaction mechanisms of (p, 3n) and (p, 4n) reactions should be interpreted by means of an admixture of the equilibrium compound process and the pre-equilibrium decay process at bombarding energies up to 40 MeV and 50 MeV, respectively, and that the direct process seems to appear at bombarding energies higher than these respective energies.     

An imaging spectrometer based on high resolution microscopy of fluorescent aluminum oxide crystal detectors

Fluorescent Nuclear Track Detector (FNTD) technology was tested as an imaging, spectroscopic tool for radionuclide analysis. This investigation intended to distinguish between characteristic α-particles of ²³⁹Pu (5.2 MeV), ²³⁴U (4.8 MeV) and ²³⁸U (4.2 MeV). FNTDs are Al₂O₃:C,Mg single crystals with color centers that undergo radiochromic transformation. FNTD readout is non-destructive and is performed with fluorescence laser scanning confocal microscopy. Ionization events register in the detector as bright fluorescent features on a weak fluorescent background. Images were acquired at several incrementing depths in the detector to produce 3D datasets. Spectroscopic information was obtained by measuring α-particle range in the detector after 3D image reconstruction. The resolution of this technique is fundamentally limited by particle range straggling (about 3.8% (k = 1) at these α-particle energies). The spectroscopic line-width as full width at half maximum (FWHM) was determined to be 0.4 MeV enabling discrimination between the isotopes of interest.     

Nuclear interaction dynamics in the 56Fe (α, xn) reaction

Neutron spectra and angular distributions in the ⁵⁶Fe (α, xn) reaction are measured at α-particle energies of 12.5, 16.3, 18.3, 26.8, and 45.2 MeV. The measurements are performed using time-of-flight fast neutron spectrometers on pulsed accelerators. The measured data are analyzed in the context of equilibrium, preequilibrium, and direct nuclear reaction mechanisms. The contributions from equilibrium, preequilibrium, and direct mechanisms of neutron emission are studied over a wide range of α-particle energies.     

The 15N(p, α)12C reaction with polarized protons from 0.34 to 1.21 MeV

A polarized beam was used to measure angular distributions of the analyzing power of the ¹⁵N(p, α)C reaction at 0.34 MeV and at five energies from 0.92 to 1.21 MeV. The analyzing power can be fitted with associated Legendre polynomials, P₁¹ and P¹₂ sufficing to describe the results except near 1.2 MeV where P₃¹ is also required. Polarization excitation functions were measured throughout the entire energy range at angles where the polynomials P¹₂ and P¹₃ are zero. A polarization contour map is given.     

Level density parameters of47Ti and50V

The energy distribution of the protons andα-particles from the reactions⁴⁷Ti(α, α′),⁴⁷Ti(α, p) and⁵⁰V(p, α) was measured in the angular range from 60° to 150°. The energies of the incoming particles were 15.35 MeV forα-particles and 13.85 MeV for protons. The results can be described in the frame of the statistical model of the nuclear reactions. The level density parameters could be determined by comparing the experimental data with the theoretical results. The values for the backshifted Fermi gas model are⁴⁷Ti:a=6.6±0.6MeV^?1,Δ=?0.5±0.3 MeV⁵⁰V:a=6.3±0.6 MeV^?1,Δ=?1.0±0.3 MeV.     

The reactions48Ca(d,t)47Ca and48Ca(3He, α)47Ca

The reactions⁴⁸Ca(d, t)⁴⁷Ca and⁴⁸Ca(³He, α)⁴⁷Ca have been measured at incident energies of 17 and 18 MeV, respectively and analysed by DWBA. Besides strong transitions to the groundstate and two unresolved states at aboutE _x =2.60 MeV relatively strong transitions withl=2 are observed at higher excitation energies in the (³He, α) reaction. The observedl=1 and higherl=3 transitions are rather weak indicating that particle-hole components in the⁴⁸Ca groundstate are relatively small.     

Search for intermediate structure in 36Ar via the 24Mg(12C, α)32S reaction

The ²⁴Mg(¹²C,α)³²S reaction was investigated in the energy range E_c.m. = 11.9–19.4 MeV by measuring excitation functions of the α₀ and α₁ groups. Angular distributions (θ_c.m. = 12–97°) were also measured at a number of energies. The excitation functions were subjected to a statistical analysis by means of evaluating correlation and deviation functions; no statistically significant anomalies were found. The α₀ angular distributions display fairly high angular-momentum selectivity as pairs of Legendre polynomials provide acceptable fits to most of them: however, only one, at E_c.m. = 18.1 MeV, is strongly dominated by a single partial wave, l = 11. Excitation functions as well as angular distributions of both α₀ and α₁ cross sections were found to be in good qualitative agreement with Hauser-Feshbach calculations throughout the energy range studied. Thus, the analysis of the data shows that intermediate resonant structures, if present, are weak and interfere strongly with the statistical compound-nucleus background, which effectively prevents their clear observation and identification in the present study.     

Properties of unbound high-spin states in27Al

Selectively excited high-spin states in²⁷Al have been located by the reaction¹²C(¹⁶O,p)²⁷Al. The excitation functions of these states have been measured at incident energiesE _cm=18.7 to 30.1 MeV at intervals of 150 keV. They exhibit maxima of presumably non-statistical origin. At four different energies the subsequent decay of the²⁷Al states has been studied by detecting the final heavy recoils with the Munich recoil spectrometer in coincidence with the proton emitted in the first stage of the reaction. Using this new method branching ratios of theγ-, α-, andn-decay have been measured. Based on angular correlation arguments spins up to 27/2? have been determined within the experimental accuracy of 1–2?. The observations suggest a superdeformed shape of²⁷Al at least in some of the states.     

The 18O(p, α)15N cross section at low energies

The ¹⁸O(p, α)¹⁵N reaction cross section has been measured over the energy range 661 keV > E_c.m > 223 keV. The S-function was extrapolated to energies of astrophysical interest using the R-matrix theory. The S-factor, S₀, is estimated to be 46 MeV · b which is a factor of 3 larger than the value used in a recent tabulation of nuclear reaction rates. The effects of broad levels near the proton threshold are discussed.     

Relativistic core binding energies of selected atoms: Comparison with experiment and other calculations

Single-configuration Dirac—Fock binding energies are reported for K 2p, Rb 3p, Cs 3d, Mg 1s, Zn 2p, and Cd 3d as well as for the corresponding levels in the cations of these elements and the neighboring rare gases. The results are compared with similar Dirac—Slater and Hartree—Fock calculations, and with experiment. It is found that the calculated binding energies are generally in very good agreement with experiment and are superior to the Dirac—Slater and Hartree—Fock results. The relativistic contribution is shown to be significant even for lighter atoms.     

Physical properties of hot,dense matter: The general case

The thermodynamic properties of hot, dense matter are examined in the density range 10^?5 fm^?3 ? n ? 0.35 fm^?3 and the temperature range 0 ? T ? 21 MeV, for fixed lepton fractions Y_? = 0.4, 0.3 and 0.2 and for matter in β-equilibrium with no neutrinos. Three phases of the matter are considered: the nuclei phase is assumed to consist of Wigner-Seitz cells with central nuclei surrounded by a nucleon vapor containing also α-particles; in the bubbles phase the cell contains a central spherical bubble of nucleon vapor surrounded by dense nuclear matter; the third phase is that of uniform nuclear matter. All are immersed in a sea of leptons (electrons and neutrinos) and photons. The nuclei and bubbles are described by a compressible liquid drop model which is self-consistent in the sense that all of the constituent properties — bulk, surface, Coulomb energies and other minor contributions — are calculated from the same nuclear effective hamiltonian, in this case the Skyrme 1' interaction. The temperature dependence of all of these energies is included, for bulk and surface energies by direct calculation, for the Coulomb energy by combining in a plausible way the usual electrostatic energy and the numerical results pertaining to a hot Coulomb plasma. Lattice contributions to the Coulomb energy are an essential ingredient, and lattice modifications to the nuclear translational energy are included. A term is constructed to allow also for the reduced density of excited states of light nuclei. All of these modifications incorporate necessary physical effects which modify significantly the matter properties in some regions.     

Cluster states in the neutron excess nucleus 22Ne

High-spin states of the ²²Ne nucleus in the excitation energy range of 15–30 MeV have been studied. The angular correlation method has been used to determine the spins of excited states. A number of new states with high angular momenta—20.0 MeV (9^?), 20.7 MeV (11^?), 21.6 MeV (9^?), 22.2 MeV (12⁺), and 25.0 MeV (9^?)—have been revealed. They are intensely populated in the reaction ¹⁴C(¹²C, α₁)²²Ne* → α₂ + ¹⁸O and correspond to the rotational bands of various structures.     

Range and range straggling of oxygen implanted into silicon at energies between 2 and 20 MeV

Oxygen profiles in silicon implanted with energies between 2 and 20 MeV by means of a Tandem accelerator have been investigated with a microprobe after bevelling the sample surface. It is shown that the measured profiles correspond to the implantation profiles when the microprobe is operated with a well focussed 2 keV electron beam. The projected ion ranges and the profiles thus obtained are compared with theoretical profiles which have been calculated by a Monte Carlo simulation of the stopping procedure. Takingk=1.30k _LSS for the electronic stopping coefficient in the LSS region up to 2.55 MeV and a constant value of 162 eV/Å for the electronic stopping at higher energies the calculation yields satisfactory range estimates, whereas the range straggling is systematically too small up to 13% in comparison with the experimental results.     

Light-particle emission in the reactions of 16O with Ti

Inclusive energy spectra and angular distributions for heavy ions $\text{(Z ≧ 3)}$ produced in the reactions of 227 MeV and 310 MeV ¹⁶O with Ti were measured. Also measured at the projectile energy of 310 MeV were energy and angular correlations between light charged particles (Z ≦ 2) and heavy ions. From comparisons with statistical model calculations upper limits to the complete fusion cross sections of 647 mb and 265 mb were derived for projectile energies of 227 MeV and 310 MeV, respectively. At 310 MeV the cross section of incomplete fusion processes was estimated to be over 505 mb. Emission of fast, high-energy α-particles and protons was observed to be a characteristic feature of quasi-elastic, deep-inelastic and fusion-like reactions. Average multiplicities of fast light particles in coincidence with heavy ions at +20° and +40° were estimated to be of the order of 1. The prompt emission of light appears to be the principal mechanism which limits complete fusion. A second component of α-particles observed in coincidence with deep-inelastic projectile-like fragments and having an energy comparable to Coulomb energies of particles emitted from target-like and projectile-like fragments appears as an excess yield in the direction of the recoiling target-like fragments. This component cannot be accounted for in terms of sequential emission processes and may result from a mechanism other than the one which leads to fast particle emission.     

Identification of the nuclide 226U

Identification of the uranium isotope ²²⁶U is reported. This nuclide was produced in bombardments of ²³²Th with 140 MeV ⁴He ions. It is observed to decay by α-particle emission with a half-life of 0.5±0.2 sec and has an α-particle energy of E_α = 7.43±0.03 MeV, giving a Q-value of Q_α = 7.56±0.03 MeV. Detection was achieved by on-line counting and pulsed-cyclotron beam techniques. It is also observed that the maximum yields for (α, p(x ? 1 )n) reactions are about ten times greater than those for (α, xn) reactions at these energies.     

Giant resonance decays in 20Ne, 22Ne and interference effects with quasifree scattering processes

The charged particle (c) decay from excited states up to the giant quadrupole resonance (GQR) in ²⁰Ne has been studied in a kinematically complete ²⁰Ne(α, α′ c) coincident experiment at E_α = 155 MeV. Angular correlation functions and branching ratios are extracted for the α₀, α₁ and p₀ decay channels. The (α, α′ α₀) angular correlation functions are analysed in PWBA in terms of coherent interference with the quasifree scattering process leading to the same final states. Good fits to the data are achieved over a large range of excitation energies. Branching ratios have been extracted and compared to results of Hauser-Feshbach calculations. Above E_x = 12.5 MeV excitation energy a discrepancy was found between the experimentally observed α₀ branching ratios and the HF predictions. These results yield evidence for a direct α₀ decay mechanism of the split isoscalar giant quadrupole resonance in ²⁰Ne. Some results are presented also for a ²²Ne(α, α′ c) coincidence experiment. Qualitative comparison has been made between the general decay behaviour of the two Ne isotopes.     

Isospin mixing observed in the reaction 12C(6Li, α)14N

The reaction ¹²C(¹²Li, α)¹⁴N was studied to investigate the isospin mixing of high-lying levels in ¹⁸F. Excitation functions and angular distributions of the α-transitions to the ground, first and second excited states in ¹⁴N were measured for bombarding energies from 3.2 to 8.0 MeV. The isospin-forbidden cross section for the excitation of the lowest T = 1 state in ¹⁴N at 2.31 MeV was found to lie between 1–2 % of that of the allowed transitions. A partial wave analysis of the α₁ angular distribution data revealed a strong resonance with J^π = 2⁺ at E_x = 15.99 MeV. Arguments are presented which tentatively identify this resonance as being due to two close-lying 2⁺ levels with different isospin.