Search

This work is devoted to calculating the rate of radiation damage production in a uranium target irradiated with high-energy electrons with an energy of 100 MeV. The Monte Carlo program MCNPX was used to perform a complete mathematical modeling of a complex of processes occurring in a uranium target when irradiated with high-energy electrons: the development of an electromagnetic shower, the production of photoneutrons, the transport of particles in the target and the creation of radiation damage in it. The analysis showed that fragments of U-238 photo-fission give the main input into the rate of damage production in a uranium target which reaches the value of 100 dpa/year. The expected service life of a uranium target under irradiation is 3 years of operation at full accelerator power. [ABSTRACT FROM AUTHOR]

In inverse kinematics, we explored Coulomb fission cross-sections and time scales. Heavier projectiles such as 238U, 132Xe, and 208Pb on lighter targets such as 16O 26Mg, 27Al, 32S, 35Cl, 40,48Ca, 45Sc, 48,50Ti, 56,58Fe, 64Ni, 89Y, 30Si and 65Zn were looked into. The photofission cross-sections and the number of equivalent photons impinge on the target nuclei are important parameters in cross-section assessment. The anticipated cross-sections increases with increase in atomic number of target nuclei. We also explored the time scale of projectile nuclei at various transition levels. The estimated time scales accord well with the available experimental value, which is in the order of picoseconds. In addition, we predicted time scales of 165Ho nuclei in the transition state from 19/2+→15/2+ to 29/2+→25/2+ for which experimental time scales are not available in literature. As a result, Coulomb fission is one of the causes that has severely hampered in the formation of compound nuclei. Prediction of time scales, in particular, would aid in understanding the structure of various energy levels.

The emerging experimental program with brilliant gamma beams at the Extreme Light Infrastructure - Nuclear Physics facility (ELI-NP) is presented with emphasis on the prepared day-one experiments. Ex- periments at ELI-NP will cover nuclear resonance fluorescence measurements, studies of large-amplitude motions in nuclei, photo-fission and photonuclear reactions of astrophysics interest, and measurements of photonuclear reaction cross sections. The physics cases of the flagship experiments at ELI-NP and the performance of the related instruments, which are under construction for their realization, are discussed.

An overview of the main directions of present-day studies with quasimonochromatic γ beams are discussed with an emphasis on the research opportunities which will be offered at the Extreme Light Infrastructure Nuclear Physics (ELI-NP) facility at Magurele near Bucharest in Romania. Experiments with γ beams at the extremes of high temperature and high neutron-to-proton ratios are outlined. Some of the experimental setups for nuclear structure, reaction and astrophysics studies, which are available at ELI-NP, are described. Perspectives for studies of exotic nuclei within the Gamma Factory experiment at CERN are discussed. The expected fission-fragment yields at the Gamma Factory are presented. The perspectives for nuclear structure studies with γ rays with orbital angular momentum are outlined. [ABSTRACT FROM AUTHOR]

In experiments for photofission of 238U with bremsstrahlung, the isomeric yield ratios for 133Xe at the end-point energies Ee = 6.25, 14.5 and 18 MeV and for 135Xe at Ee = 6.25, 12.5 and 14.5 MeV were measured. Isomeric yield ratios were obtained taking into account the contribution from beta-decay of isobaric nuclei to the yields of investigated isotopes. Average angular moments of investigated fission fragments were determined using the statistical model of decay.

The photofission fragment mass yields of actinides are evaluated using a systematic statistical scission point model. In this model, all energies at the scission point are presented as a linear function of the mass numbers of fission fragments. The mass yields are calculated with a new approximated relative probability for each complementary fragment. The agreement with the experimental data is quite good, especially with a collective temperature Tcol of 2 MeV at intermediate excitation energy and Tcol = 1 MeV for spontaneous fission. This indicates that the collective temperature is greater than the value obtained by the initial excitation energy. The generalized superfluid model is applied for calculating the fragment temperature. The deformation parameters of fission fragments have been obtained by fitting the calculated results with the experimental values. This indicates that the deformation parameters decrease with increasing excitation energy. Also, these parameters decrease for fissioning systems with odd mass numbers.

Based on 238U photofission experiments with the bremsstrahlung photons, the isomeric yield ratios were measured for 95Nb and 133Xe nuclei at the end-point energy Ee = 12.5 MeV, and 135Xe nuclei at Ee = 12.0 MeV. Experimental values of isomeric yield ratios were obtained taking into account the contribution from beta-decay of isobaric nuclei in yields of investigated isotopes. Average angular momenta of investigated fission fragments were determined using the statistical model of decay.

• Photofission is a promising technique for nuclear waste package characterization. • 9 MeV linear accelerator parameters and target materials impact the assay performance. • Monte Carlo simulations are conducted in PHITS and MCNP6 codes and compared. • Optimization of the photon flux and reduction of neutron background are conducted. Photofission-based active non-destructive assay is a promising technique for nuclear waste characterization. The latter is challenging due to the presence of actinides, fission products and non-homogeneous matrix. This paper presents an optimization study of a 9 MeV linear electron accelerator used as a source of Bremsstrahlung photons for such photofission applications. The primary focus is made on qualitative and quantitative assessment of the Bremsstrahlung flux, timing characteristics and reduction of background neutrons. Assessment is conducted using Monte Carlo simulations in particle transport codes PHITS and MCNP6 with an objective to compare the simulation results. Our results demonstrate a good agreement between the simulation results of both codes. However, for an effective application of the photofission technique for nuclear waste assay, a careful selection of the target material and introduction of parasitic neutron suppression techniques are necessary. Analysis routines and simulation procedures are described in detail and results are presented. [ABSTRACT FROM AUTHOR]

The total excitation energy as a function of fragment mass (TXE/A) are calculated for neutron induced fission of 235 U and photofission of 238 U by using the statistical model. With comparing the calculated results and the experimental data, the statistical model is modified. In new modified model, TXE are calculated by adding the neutron binding energy to the deformation energy. The calculated results using modified statistical model are in good agreement with the experimental data. Then, the total excitation energy as a function of fragment mass (TXE/A) are evaluated for photofission of Uranium isotopes. [ABSTRACT FROM AUTHOR]

To study the influence of the structural properties of UC x targets on their release properties, several types of targets using different precursors (carbon and uranium) were synthesized, characterized, irradiated and heated leading to the determination of the released fractions of eight elements. In this article, the production rates of these targets are estimated under the use conditions at ALTO, i.e. with targets bombarded by an electron beam (10 μA, 50 MeV). We have simulated the fission number produced using the FLUKA code. Then, we have determined the release efficiency as a function of the half-life of the isotopes using average diffusion coefficients deduced for the elements studied previously. Finally, we compare the production rates obtained from the various targets and conclude that the target must be adapted to the element studied. It is crucial to find in each case the best compromise between the target density and the release efficiency. [ABSTRACT FROM AUTHOR]

Compact mono-energetic photon sources are sought for active interrogation systems to detect shielded special nuclear materials in, for example, cargo containers, trucks and other vehicles. A prototype gamma interrogation source has been designed and built that utilizes the 11B(p,gamma)12C reaction to produce 12 MeV gamma-rays which are near the peak of the photofission cross section. In particular, the 11B(p,gamma)12C resonance at 163 kV allows the production of gammas at low proton acceleration voltages, thus keeping the design of a gamma generator comparatively small and simple. A coaxial design has been adopted with a toroidal-shaped plasma chamber surrounding a cylindrical gamma production target. The plasma discharge is driven by a 2 MHz rf-power supply (capable up to 50 kW) using a circular rf-antenna. Permanent magnets embedded in the walls of the plasma chamber generate a multi-cusp field that confines the plasma and allows higher plasma densities and lower gas pressures. About 100 proton beamlets are extracted through a slotted plasma electrode towards the target at the center of the device that is at a negative 180 kV. The target consists of LaB6 tiles that are brazed to a water-cooled cylindrical structure. The generator is designed to operate at 500 Hz with 20 mu s long pulses, and a 1percent duty factor by pulsing the ion source rf-power. A first-generation coaxial gamma source has been built for low duty factor experiments and testing.

We use a combination of crossed laser-molecular beam scattering experiments and velocity map imaging experiments to investigate the three primary photodissociation channels of chloroacetone at 193 nm: C-Cl bond photofission yielding CH3C(O)CH2 radicals, C-C bond photofission yielding CH3CO and CH2Cl products, and C-CH3 bond photofission resulting in CH3 and C(O)CH2Cl products. Improved analysis of data previously reported by our group quantitatively identifies the contribution of this latter photodissociation channel. We introduce a forward convolution procedure to identify the portion of the signal, derived from the methyl image, which results from a two-step process in which C-Cl bond photofission is followed by the dissociation of the vibrationally excited CH3C(O)CH2 radicals to CH3 + COCH2. Subtracting this from the total methyl signal identifies the methyl photofragments that result from the CH3 + C(O)CH2Cl photofission channel. We find that about 89% of the chloroacetone molecules undergo C-Cl bond photofission to yield CH3C(O)CH2 and Cl products; approximately 8% result in C-C bond photofission to yield CH3CO and CH2Cl products, and the remaining 2.6% undergo C-CH3 bond photofission to yield CH3 and C(O)CH2Cl products. [ABSTRACT FROM AUTHOR]

This study initially characterizes the primary photodissociation processes of epichlorohydrin, c-(H2COCH)CH2Cl. The three dominant photoproduct channels analyzed are c-(H2COCH)CH2+Cl, c-(H2COCH)+CH2Cl, and C3H4O+HCl. In the second channel, the c-(H2COCH) photofission product is a higher energy intermediate on C2H3O global potential energy surface and has a small isomerization barrier to vinoxy. The resulting highly vibrationally excited vinoxy radicals likely dissociate to give the observed signal at the mass corresponding to ketene, H2CCO. The final primary photodissociation pathway HCl+C3H4O evidences a recoil kinetic energy distribution similar to that of four-center HCl elimination in chlorinated alkenes, so is assigned to production of c-(H2COC)=CH2; the epoxide product is formed with enough vibrational energy to isomerize to acrolein and dissociate. The paper then analyzes the dynamics of the C3H5O radical produced from C–Cl bond photofission. When the epoxide radical photoproduct undergoes facile ring opening, it is the radical intermediate formed in the O(3P)+allyl bimolecular reaction when the O atom adds to an end C atom. We focus on the HCO+C2H4 and H2CO+C2H3 product channels from this radical intermediate in this report. Analysis of the velocity distribution of the momentum-matched signals from the HCO+C2H4 products at m/e=29 and 28 shows that the dissociation of the radical intermediate imparts a high relative kinetic energy, peaking near 20 kcal/mol, between the products. Similarly, the energy imparted to relative kinetic energy in the H2CO+C2H3 product channel of the O(3P)+allyl radical intermediate also peaks at high-recoil kinetic energies, near 18 kcal/mol. The strongly forward-backward peaked angular distributions and the high kinetic energy release result from tangential recoil during the dissociation of highly rotationally excited nascent radicals formed photolytically in this experiment. The data also reveal substantial branching to an HCCH+H3CO product channel. We present a detailed statistical prediction for the dissociation of the radical intermediate on the C3H5O potential energy surface calculated with coupled cluster theory, accounting for the rotational and vibrational energy imparted to the radical intermediate and the resulting competition between the H+acrolein, HCO+C2H4, and H2CO+C2H3 product channels. We compare the results of the theoretical prediction with our measured branching ratios. We also report photoionization efficiency (PIE) curves extending from 9.25 to 12.75 eV for the signal from the HCO+C2H4 and H2CO+C2H3 product channels. Using the C2H4 bandwidth-averaged absolute photoionization cross section at 11.27 eV and our measured relative photoion signals of C2H4 and HCO yields a value of 11.6+1/-3 Mb for the photoionization cross section of HCO at 11.27 eV. This determination puts the PIE curve of HCO measured here on an absolute scale, allowing us to report the absolute photoionization efficiency of HCO over the entire range of photoionization energies. [ABSTRACT FROM AUTHOR]

In experiments for photofission of 238U with bremsstrahlung, the isomeric yield ratios for 133Xe at the end-point energies Ee = 6.25, 14.5 and 18 MeV and for 135Xe at Ee = 6.25, 12.5 and 14.5 MeV were measured. Isomeric yield ratios were obtained taking into account the contribution from beta-decay of isobaric nuclei to the yields of investigated isotopes. Average angular moments of investigated fission fragments were determined using the statistical model of decay. [ABSTRACT FROM AUTHOR]

Abstract The role of active-interrogation systems for nuclear security is to detect the presence of special nuclear material inside an object by observing the radiation emitted by that object when it has been exposed to known sources of external radiation. Because of the cost, complexity, and the need to avoid irradiating occupants, active-interrogation systems are intended for cargo applications where shielding can prevent detection by passive radiation detection systems. To ensure that active-interrogation systems for detection of special nuclear material are designed and tested to a consistent level of performance, technical standards are needed for evaluating such systems. This paper addresses the testing standards needed for active-interrogation systems to detect high atomic number materials, fissionable materials, and specific special nuclear materials. Because the use of special nuclear material for a testing standard is not practical, this work focuses on the determination of materials that could be used as surrogates in that they provide a similar response as targets of special nuclear materials. The results of this paper, determined through analytic calculations and radiation transport modeling, are based upon scenarios constructed and applied to specific active-interrogation modalities. [ABSTRACT FROM AUTHOR]

The detection of special nuclear materials (SNM) in commercial cargoes is a major objective in the field of nuclear security. In this work we investigate the use of two-neutron time-correlations from photo-fission using the Prompt Neutrons from Photofission (PNPF) detectors in Passport Systems Inc.'s (PSI) Shielded Nuclear Alarm Resolution (SNAR) platform for the purpose of detecting ∼5 kg quantities of fissionable materials in seconds. The goal of this effort was to extend the secondary scan mode of this system to differentiate fissile materials, such as highly enriched uranium, from fissionable materials, such as low enriched and depleted uranium (LEU and DU). Experiments were performed using a variety of material samples, and data were analyzed using the variance-over-mean technique referred to as Y2F or Feynman-α. Results were compared to computational models to improve our ability to predict system performance for distinguishing fissile materials. Simulations were then combined with empirical formulas to generate receiver operating characteristics (ROC) curves for a variety of shielding scenarios. We show that a 10 second screening with a 200 μA 9 MeV X-ray beam is sufficient to differentiate kilogram quantities of HEU from DU in various shielding scenarios in a standard cargo container. [ABSTRACT FROM AUTHOR]

A radioactive isotope (RI) separator named ERIS (electron-beam-driven RI separator for SCRIT) was constructed at the SCRIT (Self-Confining Radioactive isotope Ion Target) electron scattering facility at RIKEN RI Beam Factory and has been in operation since 2013. Recently, ion stacking and pulse extraction were developed at ERIS to improve the dc-to-pulse conversion efficiency of a radio-frequency quadrupole cooler buncher. Using a surface-ionization ion source, long-time stacking inside ERIS was realized and a dc-to-pulse conversion efficiency of more than 50% was achieved with a relatively small amount of buffer gas. [ABSTRACT FROM AUTHOR]

Isomeric yield ratios for the fragments of photofission of 235U, 237Np and 239Pu by bremsstrahlung with end-point energy of 18 MeV are measured. New data for isomeric yield ratios of the fragments 84Se, 90Br, 131Te, 132Sb, 132I, 133Te, 134I, 135Xe are determined. The contributions to the isomeric yield ratios from β-decay of the nuclei of parent isobaric chains were removed. Mean angular momenta of studied nuclei are estimated within the framework of an extended Huizenga-Vandenbosh statistical model with using EMPIRE 3.2 code.