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At ELI-NP, high-power lasers together with a very brilliant γ beam are the main research tools. The high-power laser system (HPLS) and the γ beam system (GBS) of ELI-NP are presented. The expected performance of the electron accelerator and production lasers of the GBS, and the targeted operational parameters of the γ beam are described. Possible laser-induced fission and γ beam photofission experiments which are under preparation at ELI-NP, and the different set-ups and instrumentation, are designed for these experiments, are presented. [ABSTRACT FROM AUTHOR]

We determine the isomeric ratios of Xe in the photo-fission of Th and U induced by end-point bremsstrahlung energy of 13.5 MeV. The isomeric ratios were determined from the characteristic gamma ray activities of the isomeric and ground states of Xe. The induced gamma ray spectra of Xe were measured by a spectroscopic system, which consists of a HPGe detector connected to a PC based multichannel analyzer. In order to improve the accuracy of the experimental results, the method of inert gaseous flow was used to carry the fission product from the reaction camera to the collector. The isomeric ratios of Xe from the present work are the first time measurements. The present results were analyzed, discussed and compared with the similar data from literature to examine the role of excitation energy, energy separated in fission process and effect of reaction channels. [ABSTRACT FROM AUTHOR]

The Extreme Light Infrastructure Nuclear Physics (ELI-NP) Facility in Magurele is a European research centre for ultrahigh intensity lasers, laser-matter interaction, nuclear science and material science using laser-driven radiation beams. It is the first project within the European Strategic Forum for Research Infrastructure (ESFRI) agenda financed by the European Regional Development Fund. The nuclear physics research programme of the facility is focussed on studies with brilliant narrow-width γ-beams and experiments in extreme laser fields. [ABSTRACT FROM AUTHOR]

U photofission is studied in the region of nuclear excitation energies that extends up to 20 MeV. Independent photofission-fragment yields and cumulative photofission-fragment yields after the emission of fast neutrons are measured by gamma-spectroscopy methods. The mass distributions of photofission fragments are obtained at the endpoint bremsstrahlung energies of 19.5, 29.1, 48.3, and 67.7 MeV. A comparative analysis of the behavior of the symmetric and asymmetric modes of photoninduced fission as a function of the average excitation energy of the fissioning nucleus is performed. The integrated yield of U photofission is calculated, and the evaluated cross sections for photofission and for photoneutron reactions are discussed. [ABSTRACT FROM AUTHOR]

Data on cross sections for the reaction U( γ,F) in the giant-resonance region were analyzed in connection with the preparation of new experiments aimed at studying U photofission-in particular, in beams of photons from in-flight positron annihilation on internal targets of positron storage rings. These data were taken from measurements also performed with annihilation photons but from positron beams external to the accelerators used. The procedures applied in such measurements and based both on processing the multiplicity of detected neutrons and on detecting fission fragments were also analyzed. [ABSTRACT FROM AUTHOR]

The mass distribution of the 238U photofission fragments formed under γ-quanta action is analyzed in the range of excitation energies of a fissile nucleus from 5 to 20 MeV. The influence on the ratio of asymmetric and symmetric photofission of the 238U structure and excitation energy of a fissile nucleus is discussed. A combined analysis and the comparison of the behavior of the asymmetric and symmetric modes of photofission were conducted for the first time. The results we obtained are compared with the prediction of the multimode model of the dependence of fission modes on the nuclear excitation energy. [ABSTRACT FROM AUTHOR]

Photofission of U by bremsstrahlung photons is studied at four energies of an electron accelerator: 19.5, 29.1, 48.3, and 67.7 MeV. The yields of the fission fragments after the emission of prompt neutrons are obtained using the gamma-ray spectroscopic technique. The mass distributions of photofission are obtained at different upper energies of the bremsstrahlung spectrum. The ratio the symmetric-fission mode to the asymmetric mode is obtained from the mass distribution. The symmetric mode becomes 3-4 times greater than the asymmetric as the excitation energy of the U nucleus increases from 12 to 16 MeV. [ABSTRACT FROM AUTHOR]

The ratio of the probabilities of population of the isomeric and ground states, so called the isomeric ratio is closely connected to the angular momentum of the initial fission fragments that is dissipated at the later stages of gamma ray cascade. This ratio also provides important information on the nuclear level structure as well as the nuclear reaction mechanism involved. In this work, the isomeric ratio in fission fragment Xe from photofission of U induced by 23.5 MeV bremsstrahlung has been determined by the method that uses inert gaseous flow. The results have been discussed and compared with that of other authors. [ABSTRACT FROM AUTHOR]

Yields of fragments originating from 232Th photofission were measured at bremsstrahlungphoton endpoint energies of 50 and 3500 MeV. Charge and mass distributions of fission fragments were analyzed. On the basis of the model of multimode fission, symmetric and asymmetric channels are singled out in 232Th photofission at intermediate energies. This decomposition made it possible to estimate the contributions of various fission components and the fissility of 232Th. [ABSTRACT FROM AUTHOR]

A theoretical analysis of the most detailed experimental data on the subbarrier fission of 232Th is performed. The energy dependences of the components of the cross sections for photofission through specific channels characterized by the quantum numbers J π K are obtained on the basis of previously measured total photofission cross sections and angular distributions of fission fragments. A theoretical analysis of the subbarrier photofission of 232Th is performed on the basis of the results obtained for these components. This analysis relies on the one-dimensional fission model within which one assumes a three-humped structure of the fission barrier and introduces damping in the second and third wells by including an imaginary part in the potential used. Values are selected for the parameters of the fission barriers and are compared with similar data from other studies. It is shown that the energy dependences of the photofission cross sections in question can be described adequately. [ABSTRACT FROM AUTHOR]

A method for determining the quadrupole deformation parameter of transuranium nuclei is presented. This method is based on giant dipole resonance splitting in the photofission cross section. The experimental setup containing an avalanche counter of fission fragments, as well as a method for reconstructing the cross section from the measured dependence of the photofission reaction yield on the endpoint energy of the bremsstrahlung spectrum, are described. The setup was tested on the bremsstrahlung beam of the MT-25 microtron at the Flerov Laboratory for Nuclear Reactions of the Joint Institute for Nuclear Research. The test results—in particular, the measured excitation function of the uranium photofission reaction—are presented. [ABSTRACT FROM AUTHOR]

Statistical distributions of the coefficients measured for the angular distribution of fragments originating from the fission of 235U oriented nuclei that was induced by resonance neutrons obtained by using booster targets at the electron accelerator in Harwell and at a pulsed reactor in Dubna were approximated by a curve that was calculated under the assumption of a normal distribution of partial-wave fission amplitudes. A cutoff from below at a level of one-half of the average partial-wave width was introduced in this distribution. The calculation was performed with allowance for the K = 0, 1 and 2 channels for J = 3 and the K = 1 and 2 channels for J =4. The contributions of the K channels to the total probability were in the ratio 0.15 : 0.53 : 0.32 for J = 3 and in the ratio 0.625 : 0.375 for J = 4. A strong suppression of the K = 0 channel in the J = 3 spin subsystem in contrast to the situation observed in photofission can be interpreted as an indication of the possible partial conservation of K in resonance states formed from the entrance channel, which features only maximum values of K equal to J and J − 1. [ABSTRACT FROM AUTHOR]

The yields of products originating from 238U photofission are measured at the bremsstrahlung endpoint energies of 50 and 3500 MeV. Charge and mass distributions of fission fragments are obtained. Symmetric and asymmetric channels in 238U photofission are singled out on the basis of the model of multimode fission. This decomposition makes it possible to estimate the contributions of various fission components and to calculate the fissilities of 238U in the photon-energy regions under study. [ABSTRACT FROM AUTHOR]

Nuclear waste management cost at CEA is a heavy budget share. Therefore, it is important, in order to minimize that cost, to select the most suitable repository for the waste. Significant cost savings are obtained, for example, whenever a medium activity waste drum initially filed to end up in a geological repository can be measured accurately enough to be accepted by the Centre de Stockage de l’Aube (CSA). Photofission can be used as a non-destructive technique to measure the actinide content embedded in a nuclear waste drum. It can even be applied when the waste is packaged in its heavy concrete shielding. It is equally sensitive to non-fissile nuclear material. However, the present state of art suffers from a lack of sensitivity to be able to help redirecting the waste to the proper repository. A new program called INPHO is proposed at CEA Saclay aiming at enhancing the sensitivity sufficiently to be applicable for waste characterization. [ABSTRACT FROM AUTHOR]

Results are presented that were obtained by measuring the independent yields of Kr (A = 89 – 93) and Xe (A = 135 – 142) appearing as fragments in the photofission of 237Np and 243Am odd nuclei. The respective experiments were performed in a beam of bremsstrahlung photons from electrons accelerated to an energy of 25 MeV at the microtron of the Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research (JINR, Dubna). Use was made of the procedure involving the transportation of fragments emitted from the target by a gas flow along a capillary and the condensation of inert gases in a cryostat at liquid-nitrogen temperature. The identification of Kr and Xe appearing as fragments was performed by the gamma spectra of their daughter products. The mass-number distributions of the independent yields of Kr and Xe isotopes were obtained, along with those for the complementary fragments (Y and La in the fission of 237Np and Nb and Pr in the fission of 243Am). © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Within quantum-mechanical fission theory, the angular distributions of fragments originating from the subthreshold photofission of the even–even nuclei 232Th, 234U, 236U, 238U, 238Pu, 240Pu, and 242Pu are analyzed for photon energies below 7 MeV. Special features of various fission channels are assessed under the assumption that the fission barrier has a two-humped shape. It is shown that the maximum value of the relative orbital angular momentum Lm of fission fragments can be found upon taking into account deviations from the predictions of A. Bohr’s formula for the angular distributions of fission fragments. The result is Lm ≈ 30. The existence of an “isomeric shelf” for the angular distributions of fragments from 236U and 238U photofission in the low-energy region is confirmed. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Reasons behind the known systematic discrepancies between the results of photonuclear experiments performed with different photon beams are investigated in detail. Information about the cross sections obtained for the reactions 63Cu(γ, n)62Cu and 197Au(γ, xn) at all stages of experiments with quasimonoenergetic photons from relativistic positrons annihilating in flight is studied, and a comparison with the data of experiments with beams of bremsstrahlung gamma radiation is performed. Data obtained in experiments of both types for the reaction 16O(γ, xn) are used in the present analysis. It is shown that the difference procedure typically used experiments with quasimonoenergetic annihilation photons hinders the estimation of the actual energy resolution substantially, thus leading to a considerable distortion of information about the structure of cross sections for photonuclear reactions.© 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Results of an experiment performed to study 238U photofission with the aid of the initial section of the GAMMA channel of the Siberia-2 storage ring at the Kurchatov Institute are presented. These results are predominantly of a methodological value, because a photonuclear experiment was conducted for the first time in this channel. However, the data obtained in this way allowed us to evaluate an upper limit on the probability of the fast fission (fragmentation) of 238U nuclei that was induced by photons of energy up to 2.5 GeV. This is pertinent to the problem of the deviations of the total photoabsorption cross sections for actinide nuclei from a “universal curve.”© 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

In order to probe neutron-rich radioactive noble gases produced by photofission, a PARRNe 1 experiment (Production d’Atomes Radioactifs Riches en Neutrons) has been carried out at CERN. The incident electron beam of 50 MeV was delivered by the LIL machine (LEP Injector Linac). The experiment allowed one to compare under the same conditions two production methods of radioactive noble gases: fission induced by fast neutrons and photofission. The obtained results show that the use of the electrons is a promising mode to obtain intense neutron-rich ion beams. Thereafter, with the success of this photofission experiment, a conceptual design for the installation at IPN Orsay of a 50-MeV electron accelerator close to the PARRNe 2 device has been worked out: the ALTO project. This work has started within a collaboration between IPNO, LAL, and CERN groups.© 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The yields of Kr (A = 87-93) and Xe (A = 138-143) primary fission fragments produced in [sup 232]Th, [sup 238]U, and [sup 244]Pu photofission upon the scission of a target nucleus and neutron emission were measured in an experiment with bremsstrahlung from electrons accelerated to 25 MeV by a microtron, and the results of these measurements are presented. The experimental procedure used involved the transportation of fragments that escaped from the target by a gas flow through a capillary and the condensation of Kr and Xe inert gases in a cryostat at liquid-nitrogen temperature. The fragments of all other elements were retained with a filter at the capillary inlet. The isotopes of Kr and Xe were identified by the γ spectra of their daughter products. The mass-number distributions of the independent yields of Kr and Xe isotopes are obtained and compared with similar data on fission induced by thermal and fast neutrons; the shifts of the fragment charges with respect to the undistorted charge distribution are determined. Prospects for using photofission fragments in studying the structure of highly neutron-rich nuclei are discussed. [ABSTRACT FROM AUTHOR]

The relative method was used to measure the photofission cross sections for [sup 243]Cm and [sup 249]Cf isotopes in the energy range from 6 to 12 MeV, for [sup 245]Cm in the energy range from 5 to 10 MeV, and for [sup 249]Bk in the energy range from 5.5 to 10 MeV. The measurements were performed with an energy step of 50 to 200 keV by using the microtron installed at the Institute of Physics and Power Engineering (Obninsk). The cross section for [sup 238]U photofission was used as a reference in these measurements. Data on the cross sections for [sup 243]Cm, [sup 245]Cm, and [sup 249]Bk photofission were obtained for the first time, while data on the cross section for [sup 249]Cf photofission were obtained for the first time only in the energy region E < 10 MeV. The data on the [sup 245]Cm nucleus suggest that, in the energy region around 6 MeV, the cross section for its photofission has a maximum, which is likely to be due to the low-energy resonance structure of the dipole-photoabsorption cross section. For [sup 249]Cf, an anomalously large value of the photofission cross section is observed in the region of the first maximum of the giant dipole resonance (E approx. 11 MeV). By comparing the energy dependences obtained for the fissilities of the [sup 243]Cm and [sup 249]Bk isotopes from photofission data with the fissilities from direct-reaction data, it is found that the observed fission thresholds agree and that there is a plateau-like dependence at energies above 7.5 MeV. For the [sup 245]Cm and [sup 249]Cf nuclei, there are no similar data for performing such a comparison. Data on the fissilities as obtained from the present series of relative measurements that employ the microtron bremsstrahlung spectrum are analyzed.© 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The cross sections for the photofission of plutonium isotopes [sup 238]Pu, [sup 240]Pu, and [sup 242]Pu in the energy range 5-10 MeV have been measured by using a beam of bremsstrahlung photons from the microtron installed at the Institute of Physics and Power Engineering (Obninsk). The energy regions below the fission barrier and above 6 MeV have been scanned with pitches of 0.05 and 0.1 MeV, respectively. In deriving the absolute cross section for [sup 238]Pu photofission, [sup 238]U photofission has been employed as a reference reaction. In measurements involving [sup 240]Pu and [sup 242]Pu nuclei, the neptunium isotope [sup 237]Np, which is characterized by a more regular dependence of the photofission cross section on excitation energy than [sup 238]U, has been chosen for the first time as a reference nucleus. The measured cross sections as functions of energy show resonance structures in the vicinity of the fission threshold that are consistent with those previously observed in the energy dependences of fissilities for corresponding direct reactions. The partial-wave cross sections for the J[sup π]K = 1[sup -]0, 1[sup -]1, and 2[sup +]0 photofission channels have been determined as functions of energy. At energies below some 5.5 MeV, the total cross section for photofission of each plutonium isotope being studied receives a significant contribution from quadrupole interaction. Within the one-dimensional model of a two-humped fission barrier, the parameters of the barriers for [sup 238]Pu, [sup 240]Pu, and [sup 242]Pu have been extracted from data and have then been compared with estimates based on previous measurements. [ABSTRACT FROM AUTHOR]

A new approach to describe the compound nucleus formation process, where clustering aspects of the nucleus are taken into account, is worked out. It is shown that quantitative differences between the compound nucleus cross-section ofTh andU, as observed in recent photofission experiments, could be due to the different cluster preformation probabilities of these nuclei. [ABSTRACT FROM AUTHOR]

The photofission and photoneutron cross-sections ofU have been measured by using monochromatic and discrete photons produced by thermal neutron capture gamma-rays in several targets placed at the core of the IEA-R1 reactor in the energy interval from 5.43 MeV to 9.72 MeV. The evaluation of the total photoabsorption cross-sections and the parameters: single fission barrier, relative fissionability, fission probability, neutron emission/fission competition, nuclear temperature are also presented. [ABSTRACT FROM AUTHOR]

The yields of the photofission reactions induced inBi andPb by quasi-monochromatic photon beam of 226 MeV maximum energy have been measured by using makrofol plates as solid-state detector of fission tracks and found to be (1.1±0.4) mb and (0.8±0.4) mb, respectively. The measured yields are compared with data of fission induced in the same targets by different photon beams. [ABSTRACT FROM AUTHOR]

Nuclear emulsion plates Ilford-K0 exposed to (1.0÷5.5) GeV bremsstrahlung beams in order to study photoinduced break-up of Ar, Br nuclei have been processed to produce visible fission tracks for track analysis with optical microscope. Track-length distributions, angular distributions and angular correlations of the produced fragments obtained at six end-point bremsstrahlung energies are presented and discussed. The analysis of the data shows that the recorded events are produced by two different reaction mechanisms, namely fission and fragmentation. The absolute mean cross-sections per photon for fragmentation, binary and ternay fission of Ag, Br targets in the energy range investigated have been measured. Absolute mean cross-sections per photon and corresponding fissilities have been evaluated for binary fission of Ag and Br and compared with literature data. [ABSTRACT FROM AUTHOR]

The yields of ternary fission ofNb andAg nuclei induced by bremsstrahlung photons of 0.8, 1.0, 1.4 and 1.8 GeV end-point energies have been measured by using the 2π-forward geometry with thick target metal foils in contact with makrofol polycarbonate sheets as fission-track detectors. Absolute mean cross-sections per photon in the range (0.8÷1.8) GeV have been obtained as (0.3±0.3) μb and (0.5±0.4) μb, respectively, forNb andAg nuclei. These correspond to a probability of ternary fission of ≈10 for both nuclei. Results are discussed and compared with previous ternary fission data obtained by us for nuclei of A≲90. [ABSTRACT FROM AUTHOR]

Copyright of Il Nuovo Cimento: A is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Il Nuovo Cimento: A is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Magnetic moment measurements of isomeric states in neutron-rich isotopes populated in photofission using γ-beam facility at the Extreme Light Infrastructure−Nuclear Physics (ELI-NP) laboratory aim at addressing many open questions related to the structure of the nuclei in A around 100 and 130 mass regions. The possibility of such measurements at ELI-NP is briefly discussed here using Geant4 Monte Carlo simulations. The present paper report the estimates of γ-beam profile at the target, fission fragment production rates and the possible target geometry. [ABSTRACT FROM AUTHOR]