A new dual-type DMA for measuring nanoparticles emitted from combustion engines

A new dual-type differential mobility analyzer (dual-type DMA) was developed in order to detect transient number concentrations of airborne nanoparticles with diameters centralized at around 10 nm (for nuclei mode particles) and 100 nm (for accumulation mode particles) in automobile exhaust gas. The apparatus divides the gas sample into two parts, and each part is sent through one of two coaxially nested sections for analysis. For the scanning mode measurement, the nanoparticles are charged by ²⁴¹Am and their size distributions are determined by varying the applied voltage over 2 min. The transient mode measurement, on the other hand, fixes the voltages for the two sections at peaks near 10 and 100 nm in order to monitor the transient behavior of the exhaust nanoparticles. The measurement principles and design of the dual-type DMA are detailed and the results for time response experiments are presented using model nanoparticles charged by a corona charger. The transient concentrations of the nuclei mode and the accumulation mode particles from a diesel engine were shown to be detected by this method, when ²⁴¹Am was used for charging the particles.This revised version was published online in August 2005 with a corrected issue number.     

Multimode approach to 241Am and 237Np fission induced by 660-MeV protons

The results obtained by measuring cross sections for the formation of fragments originating from ²⁴¹Am and ²³⁷Np fission induced by 660-MeV protons are presented. The charge and mass distributions of fragments are analyzed within the multimode-fission model, symmetric and asymmetric fission channels being separated. The contributions of various fission components are estimated, and the fission cross sections for the ²⁴¹Am and ²³⁷Np nuclei are calculated along with the fissilities of these nuclei.     

Investigation of the formation of residual nuclei from radioactive 237Np and 241Am targets in reactions with 660-MeV protons

The burning of radioactive waste is investigated. Targets from ²⁴¹Am and ²³⁷Np were irradiated with 0.66-GeV proton beams. The cross sections for the formation of 60 and 80 residual nuclei from ²³⁷Np and ²⁴¹Am are determined. The experimental results are compared with the theoretical cross sections calculated by the cascade-evaporation model.     

Angular anisotropy of the alpha emission from241Am nuclei oriented by magnetic hyperfine interaction

Angular anisotropy of the alpha emission from²⁴¹Am nuclei oriented by magnetic hyperfine interaction at low temperatures in ZrFe₂-host have been observed. The sign of the anisotropy indicates unambiguously the enhanced alpha emission from the poles of²⁴¹Am nucleus. The value of magnetic hyperfine field on²⁴¹Am nuclei have been estimated from the temperature dependence of the anisotropy.     

Particularization of alpha contamination using CR-39 track detectors

Solid-state nuclear track detectors have found wide use in various domains of science and technology, e.g. in environmental experiments. The measurement of alpha activity on sources in an environment, such as air is not easy because of short penetration range of alpha particles. Furthermore, measurement of alpha activity by most gas ionization detectors suffers from high background induced by the accompanying gamma radiation. Solid state nuclear track detectors (SSNTDs) have been used successfully as detecting devices and as a passive system to detect alpha contamination on different surfaces. This work presents the response of CR-39 (for two types) to alpha particles from two sources, ²³⁸Pu with energy 5 MeV and ²⁴¹Am with energy 5.4 MeV. The methods of etching and counting are investigated, along with the achievable linearity, efficiency and reproducibility. The sensitivity to low activity and energy resolution are studied.      

Alpha particle bias ionization in a pulsed nitrogen laser

This work reports the role of alpha particles generated by Americium (²⁴¹Am) stripes placed inside the discharge channel in providing a bias ionized background plasma before, during, and after the discharge of the N₂ TE UV laser (337.1 nm) circuit. The enhancement in stimulated radiation output characteristics in terms of gas pressure, charging voltage, and pulse width, with and without alpha particles, are shown. The increased laser yield is interpreted qualitatively through plasma impedance in the discharge circuit. PACS 42.60.By; 42.60.Lh     

Measurement of cross sections for the reactions 241Am(n, 2n) and 241Am(n, 3n)

The cross sections for the reactions ²⁴¹Am(n, 2n)²⁴⁰Am and ²⁴¹Am(n, 3n)²³⁹Am are measured for several neutron-energy values in the range 13.42–14.86 MeV. An upper limit on the cross section for the reaction ²⁴¹Am(n, α)²³⁸Np is also obtained.     

Investigation of the n+-p-π-p+ structure of silicon avalanche diodes by charged particles

+ -p-π-p⁺ silicon avalanche diodes for the detection of heavy charged particles. Two sets of measurements of the alpha spectrum of ²⁴¹Am were carried out, one without a collimator and one with a collimator. The obtained alpha spectra for all bias voltages differ substantially from the spectrum obtained with a conventional semiconductor detector. The experiments clarified the amplification mechanism of the type n⁺-p-π-p⁺ silicon avalanche detector for charged particles. We demonstrated that the reasons for the unconventional alpha spectra are the mechanisms of internal amplification and also the specific detector design. Received: 14 July 1997/Accepted: 12 January 1998     

Photofission of americium isotopes in the energy range 6–12 MeV

By means of the reference method, the cross sections for the fission of the ²⁴¹Am, ^242m Am, and ²⁴³Am isotopes were measured at the microtron of the Institute of Physics and Power Engineering (Obninsk). These measurements, which employed the cross section for ²³⁸U photofission as a reference, covered the energy range 6–12 MeV scanned with a variable step of 50 to 200 keV. Data on ^242m Am photofission in the energy range 6–12 MeV and ²⁴³Am photofission in the region between 6 and 7 MeV were obtained for the first time. New results for ²⁴¹Am reveal that the cross sections for ²⁴¹Am photofission from previous studies of the present author were exaggerated. The new results for this isotope comply well with data of other authors. It is not confirmed that the fissility of ²⁴¹Am is less than the fissility of ²⁴³Am. The energy dependences of the fissilities of the americium isotopes from photofission data are compared with those that were obtained for these fissilities from data on direct reactions like ²⁴⁰Pu(³He, df)²⁴¹Am. The results of this comparison show that the observed fission thresholds and the plateaulike dependences at energies above 7.5 MeV from the two types of studies comply well. The present data show evidence that, in the energy region around 6 MeV, the photofission cross section has a maximum, which is associated, in all probability, with the low-energy resonance structure in the cross section for dipole photoabsorption.     

New experimental data on the 10B(n, αt)4He reaction

A new technique is described that makes it possible to detect reaction products with the escape of charged particles occurring on components of working gas under the action of fast neutrons. This technique is unique since it offers the possibility of studying reactions for which more than two charged particles are generated in an output channel. This work studies interactions between neutrons and ¹⁰B nuclei, where two α-particles and tritium nucleus are produced as reaction products.     

Particularization of α contamination using CR-39 track detectors

Solid-state nuclear track detectors (SSNTDs) have found wide use in various domains of science and technology, e.g. in environmental experiments. Measurement of α activity on sources in an environment, such as air, is not easy because of the short penetration range of the α particles. Furthermore, the measurement of α activity by most gas ionization detectors suffers from the high background induced by the accompanying gamma radiation. SSNTDs have been used successfully as detecting devices as passive system to detect the α contamination of different surfaces. This work presents the response of CR-39 (for two types) to α particles from two sources, ²³⁸Pu with energy 5 MeV and ²⁴¹Am with energy 5.4 MeV. The methods of etching and counting are investigated, along with the achievable linearity, efficiency and reproducibility. The sensitivity to low activity and energy resolution are studied.     

Yields and cross sections of the 241Am(γ, n)240mfAm and 243Am(γ, n)242mf-Am reactions in the E1 giant resonance region

The ratio of delayed to prompt fission yields has been measured for ²⁴¹Am and ²⁴³Am samples irradiated by a bremsstrahlung photon pulsed beam over the energy range E_γmax = 10–80 MeV. The relative probabilities of ^240mfAm and ^242mfAm isomer production and the cross sections of the ²⁴¹Am(γ, n)^240mfAm and ^243Am(γ, n)^242mfAm reactions were deduced from the yields measured in the E1 giant resonance region.     

Fission isomers in Cm and Bk isotopes

A new extremely shortlived fission isomer presumably in²⁴⁵Bk has been detected following the bombardment of²⁴³Am with⁴He particles of 26 MeV. Proton bombardment of²⁴³Am gives some evidence for the excitation of two shortlived fission activities which are tentatively assigned to isomers in^241,242Cm. When irradiating targets of²³⁷Np,²⁴¹Am, and²⁴³Am with deuterons in the energy range from 12 to 20 MeV previously known isomers are observed. Excitation functions are given for the production of these fission isomers.     

Diffractive scattering of loosely bound nuclei involving two charged clusters on nuclei

The theory of diffractive interaction between loosely bound nuclei featuring two charged clusters and nuclei is developed with allowance for Coulomb interaction. The differential cross sections for the scattering of ⁶Li, ⁷Be, and ⁸B nuclei on ¹²C nuclei are calculated, and the results of these calculations are compared with data from recent experiments.     

Fission fragment energy correlation measurements for the sub-barrier (nth, f) of 241Am and 243Am

Fission-fragment mass and kinetic-energy distributions and their correlations have been studied for the sub-barrier fission of the odd-odd ²⁴²Am and ²⁴⁴Am nuclei resulting from thermal neutron capture in ²⁴¹Am and ²⁴³Am. Unwanted events were eliminated by a coherence test based on the time of flight. The ²⁴³Am mass distribution is more asymmetric and shows structures at μ_H ≈ 139 and 144, compared with that for ²⁴¹Am which is smooth and structureless. The structure at μ_H ≈ 144 is caused by deformed neutron shells at N ≈ 88 in the heavy fragment and $\text{N ≧ 60}$ in the light fragment. While the 〈E_K〉 at symmetry for ²⁴¹Am is ≈ 19 MeV higher than that for ²³⁵U, it is shifted upwards only ≈ 6.5–10 MeV in the other mass regions. However, 〈E_K〉 at symmetry for ²⁴³Am is ≈ 6 MeV lower than for ²⁴¹Am and this decrease tapers down to ≈ 1 MeV for μ_H > 135. These data show a decrease in the total fragment deformation for ²⁴¹Am at symmetry as predicted by calculations. However, the ²⁴³Am data show a sudden change back to higher deformation.     

Central collisions of24Mg nuclei with heavy emulsion group of nuclei (Br,Ag) at 4.5 AGeV/c momentum

Central collisions of²⁴Mg nuclei with the heavy (AgBr) group of emulsion nuclei are selected and analysed according to several selecting criteria. Theoretical calculations concerning cross sections for central events, average number of interacting protons from both projectile and target nuclei, multiplicity distributions of shower particles and dispersions, all based on the Glauber model, are performed to evaluate various criteria to select central events. The selection criterion based on the high multiplicity of total charged particles provides satisfactory agreement with the theoretical calculations.     

Elastic hadron scattering on Li isotopes at intermediate energies

The elastic scattering of hadrons (protons, charged pions, and positively charged kaons) on ^6,7,8Li nuclei is analyzed on the basis of Glauber-Sitenko diffraction theory. A few nuclear-wave-function versions found within two-and three-particle potential cluster models are used in the calculations. It is shown that the application of these wave functions in diffraction theory makes it possible to describe adequately the experimental differential cross sections and analyzing powers in hadron scattering at intermediate energies. In this study, particular attention is given to a comparison of the scattering of different particles on the same target nucleus, as well as to a comparison of scattering of particles of the same sort on different target nuclei.     

The investigation of oxidized silver nanoparticles prepared by thermal evaporation and radio-frequency sputtering of metallic silver under oxygen

The investigation of oxidized silver nanoparticles by the photoemission (XPS, UPS) and HRTEM methods was performed. The nanoparticles of oxidized silver were obtained in the vacuum chamber by two methods of synthesis: thermal evaporation of silver nanoparticles followed by transferring in convective gas flow and sputtering of oxidized clusters under the action of plasma. Both methods indicated that oxygen interaction with silver nanoparticles depends strongly on its size. It was shown that the chemical bonding of oxygen species stabilized on small particles differs from the oxygen species adsorbed on bulk silver surfaces (monocrystals, foils and large particles). The low charged oxygen with molecular type of bonding stabilizes on particles of size approximately 5 nm and smaller. Increasing particle size leads to the dissociation of molecular oxygen species and the formation of strongly charged oxygen composed of oxide nanoparticles like Ag₂O or AgO type. The presence of extended defects in the microdomain large nanoparticles facilitates the formation of Ag₂O or AgO layers covering metallic nanosilver.     

Nanoparticle Charging in a Twin Hewitt Charger

A new unipolar charger for aerosol nanoparticles has been developed. In this twin Hewitt charger two corona discharge zones are connected by a charging zone where the nanoparticle aerosol flows. Ions move into the charging zone alternating from each corona discharging zone by means of a square-wave voltage. The operation parameters of the device have been experimentally investigated at standard conditions with the goal to optimize the extrinsic charging efficiency in N₂ carrier gas. It has been found that there exists an optimal length of the charging channel for each gas flow rate through the charger which minimizes losses of charged particles and at the same time having a sufficient large n _iont-product. Extrinsic charging efficiencies of some 30% for particles with a diameter of 10 nm are obtained.     

Superparamagnetic silica nanoparticles with immobilized metal affinity ligands for protein adsorption

Superparamagnetic silica-coated magnetite (Fe₃O₄) nanoparticles with immobilized metal affinity ligands were prepared for protein adsorption. First, magnetite nanoparticles were synthesized by co-precipitating Fe²⁺ and Fe³⁺ in an ammonia solution. Then silica was coated on the Fe₃O₄ nanoparticles using a sol–gel method to obtain magnetic silica nanoparticles. The condensation product of 3-Glycidoxypropyltrimethoxysilane (GLYMO) and iminodiacetic acid (IDA) was immobilized on them and after charged with Cu²⁺, the magnetic silica nanoparticles with immobilized Cu²⁺ were applied for the adsorption of bovine serum albumin (BSA). Scanning electron micrograph showed that the magnetic silica nanoparticles with an average size of 190 nm were well dispersed without aggregation. X-ray diffraction showed the spinel structure for the magnetite particles coated with silica. Magnetic measurement revealed the magnetic silica nanoparticles were superparamagnetic and the saturation magnetization was about 15.0 emu/g. Protein adsorption results showed that the nanoparticles had high adsorption capacity for BSA (73 mg/g) and low nonspecific adsorption. The regeneration of these nanoparticles was also studied.