[Show abstract][Hide abstract] ABSTRACT: Production of Hf and Lu high-spin isomers has been experimentally studied in spallation reactions induced by intermediate energy protons. Targets of enriched 179Hf (91%) and natHf were bombarded with protons of energy in the range from 90 to 650 MeV provided by the internal beam of the Dubna Phasotron synchrocyclotron. The activation yields of the reaction products were measured by using the γ-ray spectroscopy and radiochemistry methods. The production cross-sections obtained for the 179m2Hf, 178m2Hf and 177mLu isomers are similar to the previously measured values from the spallation of Ta, Re and W targets. Therefore, the reactions involving emission of only a few nucleons, like (p,p′), (p,p′n) and (p,2pn), can transfer high enough angular momentum to the final residual nuclei with reasonable large cross-sections. A significant gain in the isomeric yields was obtained when enriched 179Hf targets were used. The mass distribution of the residual nuclei was measured over a wide range of masses and the fission-to-spallation ratio could be deduced as a function of the projectile energy. Features of the reaction mechanism are briefly discussed.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 03/2009; · 1.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We consider the possibility that multiphoton sidebands to Mössbauer transitions should be produced for nuclei embedded in displacive-type ferroelectric crystals in the paraelectric phase, by modulating the hyperfine electric-field gradient acting at the nuclear sites with the aid of an electric radiofrequency field. It is calculated that the intensity of the first-order sideband to the 14.4 keV transition of 57Fe, incorporated in a BaTiO3 crystal having a dielectric constant of 3 103, becomes 9% of the intensity of the parent line when the crystal is polarized by a static electric field of 107 V/m and a parallel radiofrequency electric field of 3 106 V/m, oscillating at 2.9 MHz.
[Show abstract][Hide abstract] ABSTRACT: A process for transferring energy from electron shells into nuclear excitation, NEET, has offered the promise for modulating nuclear properties at accessible levels of power. It had been proven recently by exciting a nuclear level of 197Au with synchrotron radiation, but measured couplings were far below theoretical objectives. Reported here is an extension of that approach for excitation to 178Hf m2 isomeric nuclei. Isomeric targets were irradiated with X-rays in the beamline BL01B1 at the synchrotron radiation source SPring-8. Energies were tuned from 9 to 13 keV. In this range an excitation branch attributed to NEET was found to have a probability of 2 × 10−3 relative to L-shell photoionization. The resulting emission of exoergic γ-photons was observed from the target at a rate approaching the theoretical maximum.
[Show abstract][Hide abstract] ABSTRACT: In this paper we have demonstrated that the negative and positive corona discharge in air at atmospheric pressure is a convenient physical method for the initiation of the high-reaction-rate polymerization process of the linseed oil. The different stages of the polymerization process were investigated by infrared (IR) spectroscopy and the formation of the linseed oil polymer was evaluated by the presence of the C-O-C bands.
[Show abstract][Hide abstract] ABSTRACT: The Hf-178m2 nuclear spin isomer stores 2.45 MeV of energy for a half life of 31 years. Unperturbed, such nuclei radiate away the stored energy through the emission of gamma photons from electromagnetic (EM) transitions occurring within the nuclei. It has been shown that the irradiation of samples containing such nuclei with pulsed X-rays can accelerate the rate of the EM transitions by relaxing the selection rules upon changes of angular momenta. To date, most work has been done with incident X-ray energies between 9 and 10 keV, and in such cases the acceleration of the rate of gamma emission is immediate. Reported here is a channel for deexcitation excited by more energetic X-rays that results in a cascade of gamma transitions that includes a 4 second statistical time lag. This more protracted release of the energy stored in samples of the Hf-178m2 nuclear isomers encourages consideration of potential mechanical and thermal applications.
Journal de Physique IV (Proceedings) 06/2005; · 0.29 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A nuclear-XAFS effect occurs during the scattering of electrons or X-ray photons when the excitation of inner shell electrons couples both energy and angular momentum into nuclear channels of excitation. Nuclear transitions can be induced if the density of excited states of the nucleus enclosed by the electrons is high enough. The 31-yr isomeric state, 178m2Hf satisfies the condition for excitation by monochromatic X-rays from synchrotron sources. Strong effects upon such nuclei are studied.
Radiation Physics and Chemistry 10/2004; · 1.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Yields and cross-sections of the radioactive nuclides produced after the irradiation of natural composition W and enriched 186W targets at the Dubna synchrocyclotron were measured using the γ-ray spectroscopy methods with high-resolution Ge detectors. Among the detected nuclides we identified the spallation and fission products. High-spin isomeric states in the Hf and Lu nuclides were populated and the isomer-to-ground state ratios could be estimated. The nuclide yields were calculated using the LAHET code at six different values of the proton energy in the range from 100 to 800 MeV both for the natW and enriched 186W targets. The measured isotope yields are in general good agreement with the calculations. A shortcoming of the code is the inability to predict isomer-to-ground state ratios. The experimental data show that the 177mLu, 178m2Hf and 179m2Hf high-spin isomers are produced with a 2.5 times higher yield in the 97% enriched 186W target as compared to the natW target under identical irradiation conditions. This makes significance for the creation of high-activity isomeric sources. The mass-distribution of the products and the fission-to-spallation ratio were also deduced and compared with theory prediction.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 07/2004; 527(3):609–623. · 1.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: High reaction rate mechanisms of oils polymerization are reported in a wire-to-plane corona discharge electrode configuration at atmospheric pressure. Spectral measurements are performed at different stages of the polymerization process, as well as optical investigation of the oil polymer layers.
[Show abstract][Hide abstract] ABSTRACT: The productivity of the spallation reactions at proton energies of 100–660 MeV for accumulation of the radioactive isotopes and isomers has been studied experimentally. Spectra of Ta and Re targets activated at Dubna synchrocyclotron were measured using the methods of radiochemistry and gamma spectroscopy. Many radioactive products of the spallation and fission reactions are identified, and their yields are compared with the LAHET code simulations. Cross-sections σm and isomer-to-ground state ratios σm/σg are deduced for nuclear isomers, in particular, for high-spin isomers, as 178m2Hf, 179m2Hf and 177mLu. Spin distributions for the spallation-residue nuclei are estimated to understand the σm/σg ratios. Possibilities to optimize the methods for the long-lived isomers production are discussed, and it would be a necessary step on the way to accumulate such exotic radionuclides in milligram amount under reasonable cost and radiation safety conditions.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 08/2002; · 1.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this work a compact electron beam source, a preionized controlled open-ended hollow cathode discharge, is used for the ablation of an anodic target. Time-resolved spectroscopic measurements of the optical emission of the filamentary and plume plasmas, both created by the electron beam, are presented and electron beam parameters are given. These latter are compared to preliminary measurements in a channel-spark.
ALT'01 INTERNATIONAL CONFERENCE ON ADVANCED LASER TECHNOLOGIES; 01/2002
[Show abstract][Hide abstract] ABSTRACT: Because of the high density of energy storage and the large cross section for its release, nuclear spin isomers have attracted
considerable recent interest. The triggering of induced gamma emission from them has encouraged efforts to develop intense
sources of short-wavelength radiation. One of the more interesting examples is the 16+ 4-qp isomer of 178Hf which stores 2.445 MeV for a half-life of 31 years meaning that as a material, such isomeric 178Hf would store 1.3 GJ/g. Recently, a sample containing 6.3×1014 nuclei of the isomer of 178Hf was irradiated with X-ray pulses derived from a device operated at 15 mA to produce bremsstrahlung radiation with end point
energies set to values between 60 and 90 keV. Emission of gamma radiation from the sample was increased by 1–2% above the
quiescent value of spontaneous emission. Such an accelerated decay of the 178Hf isomer is consistent with an integrated cross section of 2.2×10−22 cm2 keV if the resonant absorption of the X-rays takes place below 20 keV as indicated by the use of selective absorbing filters
in the irradiating beam. The work reported here describes the current experimental focus and results recently obtained with
the use of coincident detection of emitted gamma photons by several detectors.
[Show abstract][Hide abstract] ABSTRACT: A Reply to the Comment by Silviu Olariu and Agata Olariu. Also D. P. McNabb, et al. also P. von Neumann-Cosel and A. Richter. (c) 2000 The American Physical Society.
[Show abstract][Hide abstract] ABSTRACT: The energy distribution function of the electron beam produced in a transient hollow cathode discharge is measured using a method which is based on the collector self-biasing, allowing an access very close to the extraction hole. The distribution obtained is a mainly polyenergetic one extending over a range of up to some tenths of kiloelectronvolts. It is composed both of runaway electrons, whose energies we assume are equal to the instant discharge voltage, and a main part composed of a monotonically decreasing energy distribution. The ratio between these two populations is around 10% and strongly increases with distance from the extraction hole.
Journal of Physics D Applied Physics 03/2000; 33(7):819. · 2.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A sample containing 6.3×1014 nuclei of the 16+ isomer of 178Hf having a half-life of 31 yr and an excitation energy of 2.446 MeV was irradiated with x-ray pulses from a device operated
at 15 mA to produce bremsstrahlung with an endpoint energy of 90 keV. The gamma spectra of the isomeric target were taken
with a Ge detector. The intensity of the 325.5-keV (6+ → 4+) transition in the ground-state band of 178Hf was found to increase by about 2%. Such an enhanced decay of the 178Hf isomer is consistent with an integrated cross section value of 3×10−23 cm2 keV if resonance absorption occurs within energy ranges corresponding to the maxima of the x-ray flux, either near 20 keV
or at the energies of the characteristic emission lines of W.
Physics of Atomic Nuclei 01/2000; 63(12):2067-2072. · 0.60 Impact Factor