High flux neutron production from C beams on heavy targets

Spallation neutrons produced from ¹²C ions at 18 and 44 GeV on Cu and Pb targets were studied as well as thermalization in appropriate moderators. The irradiation were performed at the Dubna LHE Synchrophasotron. Results are given for thermal and fast neutrons estimated and compared with different experimental methods.     

Fast neutron emission from partial fusion heavy ion reactions

The Boltzmann master equation theory which succesfully reproduces the spectra of fast nucleons emitted in fusion and quasi-fusion heavy ion reactions is used to predict the spectra of fast nucleons in coincidence with a projectile-like fragment in the interaction of 35 MeV/ nucleon¹⁴N with¹⁶⁵Ho. In particular it is shown that the spectra of neutrons in coincidence with a high energy projectile-like fragment emitted at a very forward angle with energy corresponding to the beam velocity may be reproduced satisfactorily assuming an elastic breakup of the projectile followed by fusion of one of the fragments with the target nucleus.     

Search for beta-delayed proton emission from $$^{11}$$Be

The European Physical Journal A - A deterministic treatment of sequential neutron emission, based on recursive equations of the residual temperatures, was applied to numerous fission cases (i.e. 49...     

On-line orientation of bromine isotopes

Assignments for the principal Nilsson configuration in light β⁺-decaying bromine isotopes were proposed in a contribution to the OLNO-1 conference. These assignments were made on the basis of magnetic moments derived from the temperature dependence of anisotropies in daughter Se isotopes observed in the DOLIS-COLD facility at Daresbury. Anisotropy measurements have since been extended to a lower base temperature in^74m Br and^72g Br decay, leading to more stringent limits on the ground state moment of⁷²Br. The proposed π[312]3/2 configuration for⁷⁵Br has also now been confirmed by a measurement of the sign of its magnetic moment. This was done by observing the β-asymmetry in⁷⁵Br decay using high purity Si detectors mounted within the dilution refrigerator.     

Study of short-lived bromine isotopes

First experiments in the systematic study of the structure of ground states and isomeric states of Br isotopes as function of neutron number at ISOLDE, CERN are reported. The isotopes^{74g.74m,77,78,84g,84m}Br have been implanted into iron and studied with the techniques of low temperature nuclear orientation and nuclear magnetic resonance of oriented nuclei (NMR/ON). The experiments were performed with the NICOLE on-line nuclear orientation set-up using the isotope separator ISOLDE-3. NMR/ON experiments were successful for^74mBr with continuous on-line implantation and for⁷⁷Br. Using as value of the hyperfine field B_hf(BrFe)=+81.3S (3) T we obtain |g (^74mBr)|=0.455 (3) and |g (⁷⁷Br)|=0.6492 (3). Static nuclear orientation data have been measured for all above mentioned isotopes. From these data we derive |μ(⁷⁸Br, I=1)|=0.13 (3) and |μ(^84gBr, I=2)|=1.9 (7). The results are discussed within the systematics of the bromine isotopes.     

Investigation of neutron emission from relativistic heavy ion interactions by nuclear tracks

Fast neutrons produced in 44 and 22 GeV ¹²C+Cu interactions have been recorded and analysed with a CR-39 detector stack. The irradiation of the CR-39 stack to fast neutrons was carried out at the accelerator Synchrophasotron, Joint Institute for Nuclear Research, Dubna, Russia. Areal and volume densities of tracks induced by fast neutrons in the CR-39 at different positions and for different etching time have been measured. The neutron production ratio of 44 GeV to 22 GeV ¹²C+Cu interactions has been obtained, which is 2.17 ± 0.30 by areal track density, or 2. 12±0.33 by step etch technique, or 2.03±0.34 by volume track density measurement. These results confirm that the production rate at 44 GeV ¹²C+Cu interactions is more than theoretical estimation.     

Intense Bessel-like beams arising from pyramid-shaped microtips

We show both numerically and experimentally that intense, narrow, and low-divergence beams of light are produced at the apex of dielectric pyramid-shaped microtips. These beams exhibit a Bessel transverse profile but are narrower than the usual Bessel beam, allowing for a significant enhancement of the light intensity inside the beam. They are generated by axicon-like structures with submicrometric height imprinted in glass by combining optical lithography and chemical etching. The resulting beams are experimentally imaged using fluorescence microscopy, in remarkable agreement with numerical computations.     

Intense electron emission from carbon fiber cathodes

We studied the emission properties of carbon fiber cathodes. These cathodes were made either of a single carbon fiber or of carbon fabric, or of an array of carbon fiber bundles. It was found that an intense emission of electrons occurs from a plasma which is formed on the carbon fiber surface as a result of a flashover process. In addition, the time delay in the appearance of the electron emission with respect to the start of the accelerating voltage pulse was found to depend strongly on the voltage growth rate. A simple model of the plasma formation is suggested. Received 12 March 2001     

Intense emission from a grid-stabilized plasma cathode

Intense emission from a grid-stabilized plasma cathode based on a glow discharge with an expanded anode area is studied. In the electrode system of the ion source, the potential difference between a large-mesh grid electrode (a hole diameter of 4–6 mm) and cathode and anode plasma reaches 200 V and the glow discharge current is up to 1 A. The current distribution over the electrodes of the plasma cathode is taken, and the dependences of the electron extraction efficiency and electron-emitting-plasma potential on the gas pressure and discharge parameters are obtained. A relationship between the geometric parameters of the grid, cathode plasma potential, and efficiency of electron extraction from the plasma is derived. It is shown that stable intense emission from the plasma cathode can be provided in wide ranges of gas pressure and discharge current by varying the geometry and mesh size of the plasma cathode grid. Discharge contraction in the grid plane at elevated gas pressures is explained. It is assumed that the emitting plasma becomes inhomogeneous due to variation in the thickness of near-electrode layers in the holes of the grid, which makes the distribution of the emission current from the plasma more nonuniform.     

Intense high-energy proton beams from Petawatt-laser irradiation of solids

An intense collimated beam of high-energy protons is emitted normal to the rear surface of thin solid targets irradiated at 1 PW power and peak intensity 3x10(20) W cm(-2). Up to 48 J ( 12%) of the laser energy is transferred to 2x10(13) protons of energy >10 MeV. The energy spectrum exhibits a sharp high-energy cutoff as high as 58 MeV on the axis of the beam which decreases in energy with increasing off axis angle. Proton induced nuclear processes have been observed and used to characterize the beam.     

Intense laser-driven energetic proton beams from solid density targets

The effects of target density on proton acceleration driven by an intense sub-ps laser pulse are investigated using two-dimensional hybrid particle-in-cell simulations. Results show that at higher density the target-normal-sheath acceleration (TNSA) is more effective than shock acceleration for protons from a plastic target. Furthermore a lower-density target is favorable to higher energy of the TNSA protons. Moreover, the longitudinal electric fields at the target surfaces may reveal typical inhomogeneous structures for a long acceleration time. The conversion efficiency of laser energy into particle (electron, proton, and C(+) ion) energy is found to increase with decreasing target density.     

Systematics of neutron emission probabilities from delayed neutron precursors

A simple correlation based on the gross theory ofβ-decay is derived between the neutron emission probabilitiesP _n of delayed neutron precursors, theirβ-decay energies and the neutron binding energies of the daughter nuclei. The correlation is shown to be valid for delayed neutron precursors among the fission products. TheP _n-values of several expected but still unidentified neutron precursors are estimated together with their contributions to the delayed neutron groups in thermal-neutron induced fission of²³⁵U. Some aspects of theβ-strength function for transitions into highly excited states are discussed.     

Electrical transport characteristic of carbon nanotube after mass-separated ultra-low-energy oxygen ion beams irradiation

Mass-separated ultra-low-energy oxygen ion beams were irradiated to the single-walled carbon nanotubes (SWCNTs) under an ultra-high-vacuum pressure of 10⁻⁷ Pa for the purpose of achieving n-type conduction of nanotubes. The ion beam energy was 25 eV, which was close to the displacement energy of graphite. The incident angle of the ion beam was normal to the target nanotube. The ion dose ranged from 3.3 × 10¹¹ to 3.8 × 10¹² ions/cm². The structure of SWCNTs after the ion irradiation was investigated. The CNTs still have a clear single-walled structure after the ion irradiation. The graphite structure is distorted and some defects are induced in the nanotube by the oxygen irradiation. The oxygen ions with the ion energy of 25 eV are irradiated to the field effect transistor (FET) device with the nanotube channel. The n-type characteristic appears upon the oxygen ion irradiation, and the device exhibits ambipolar behavior. The defects induced by the ion irradiation may act as the n-type dopants.     

Delayed-neutron emission from short-lived Br and I isotopes

Rapid radiochemical separation techniques have been used to investigate the delayed-neutron emission from bromine and iodine isotopes produced by thermal-neutron induced fission of ²³⁵U. The nuclides 0.63 sec ⁹¹Br, 0.26 sec ⁹²Br and 0.41 sec ¹⁴¹I have been identified as delayed-neutron precursors. Relative neutron abundances of these and of the known precursors ^87–90Br and ^137–140I have been measured and absolute neutron abundances and neutron emission probabilities have been deduced. The P_n values are discussed within a simple semiempirical picture.     

High-multiplicity neutron emission from muon capture

The nuclear excitation function resulting from muon captures on pairs of nucleons which is induced by meson-exchange currents, is used to calculate the probabilities of high-multiplicity (X⩾6) neutron emission. For muon capture in ²⁰⁹Bi these are found to be 8 × 10⁻³ for X = 6, 3.5 × 10⁻³ for X = 7 and 0.7 × 10⁻³ for X = 8. Results are presented also for Pb, Ho and Ag. The agreement with existing experiments is very good.     

Nuclear moments of neutron deficient iridium isotopes from laser spectroscopy

Laser spectroscopy measurements have been performed on neutron deficient iridium isotopes. The hyperfine structure and isotope shift of the optical Ir I transition 5d⁷6s^{2 4}F_9/2 → 5d⁷6s6p ⁶F_11/2 at 351.5 nm have been studied for the ^182–189Ir, and ^191,193Ir isotopes. The nuclear magnetic and quadrupole moments were obtained from the HFS measurements and the changes of the mean square charge radii from the IS measurements. A large mean square charge radius change between ¹⁸⁷Ir and ¹⁸⁶Ir and between and has been observed. This revised version was published online in August 2006 with corrections to the Cover Date.     

ISOL beams of hafnium isotopes and isomers

The production of ISOL beams of hafnium is described. Radioactive Hf isotopes were produced at ISOLDE by 1.4 GeV proton-induced spallation in Ta and W foils. Chemical evaporation in form of HfF₄ and mass separation in the molecular sideband HfF₃⁺ after electron impact ionization provided intense and pure beams. Beams of ^158-185Hf and short-lived isomers down to 1.1 s ^177mHf were observed, but the method could be extended to reach even more exotic isotopes: down to about ¹⁵⁴Hf (N=82) on the neutron-deficient side and up to neutron-rich ¹⁸⁸Hf.     

On-line production of neutron rich isotopes from uranium carbide targets

Experiments done using on-line mass separation of neutron-rich nuclei produced by 1 GeV proton beam on natural U by spallation reactions are performed to study the characteristics of different UCx targets. Special attention is devoted to reliably extract isotopic yields in case of complex decay schemes and to the valuation of release efficiency of some isotopic chains. New gamma-branching measuremet for ⁹²Rb are obtained. In addition, a formalism is developed to disantangle the contribution of β-decay in the target from direct production by fission and to provide more consistent data for the interpretation of release curves. Some results are shown for the Cs and Rb isotopic chains.