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A mathematical simulation approach based on the general purpose Monte Carlo N-particle transport code MCNP was developed to predict the response of the XRF branch of the hybrid K-edge/K-XRF densitometer (HKED). The respective MCNP models for two different versions of HKED instruments currently in use were set up and experimentally validated. The setting up of the models involved comprehensive simulations of a bremsstrahlung photon source, the examination of different particle transport models, as well as the examination of different photon attenuation and X-ray fluorescence data libraries. The computation speed was significantly increased through the extensive use of the variance reduction techniques. The models were validated through the series of benchmarking experiments performed with a representative set of uranium, plutonium and mixed U/Pu reference solutions. The models and simulation approach developed are intended for: (i) establishing a consistent mathematical calibration approach for the XRF branch of the HKED instruments, which will require minimum calibration effort and time, (ii) extending the applicability of the HKED method to non-standard samples (e.g. U/Pu mixtures with unusual element ratios) and non-standard sample matrices (e.g. HM matrices from the pyro-processing of irradiated nuclear fuel) without investing a great deal of extra calibration work, and (iii) improving the accuracy of the measurements through the modelling of special measurement effects (e.g. the secondary excitation effect, the interference with X-ray escape peaks, the inconsistent unfolding of the overlapping peaks and peak background delineation in the measured XRF spectrum), which are difficult or sometimes impossible to account for experimentally.

In the last decade or so, an evolution in experimental relativistic laser-plasma physics has led to highly sophisticated lasers which are now capable of generating ultra-short pulses and can be focused to intensities in excess of 1021 W cm-2. The laser interaction with solid or gas targets can generate collimated beams of highly energetic electrons, protons and ions. These high-intensity laser systems, therefore, turn out to be versatile and powerful sources of radiation and high-energy particles, without recourse to large-scale facilities such as nuclear reactors or particle accelerators. The potential to induce various kinds of nuclear reactions with laser-induced radiation fields has been demonstrated at several laboratories in recent years. The present paper lays out a comprehensive overview of nuclear reactions induced by high-intensity laser matter interactions. Mechanisms for electron, proton and ion acceleration, in addition to secondary bremsstrahlung, positron and neutron production, are addressed, with a focus on the types of nuclear reactions that are possible and potential applications. Discussion of the extrapolation of these processes and applications to the next generation of table-top lasers under construction is also presented.

The β--decay of 147Cs to 147Ba has been studied by means of γ- and X-ray spectroscopy. A new level scheme of 147Ba is significantly modified and extended in comparison to the one previously reported. The Advanced Time-Delayed βγγ(t) method has been applied to measure half-lives of the 46.2 and 85.4 keV levels in 147Ba yielding T 1/2 of 510(80) ps and 370(100) ps, respectively. The lifetime results combined with the deduced internal conversion coefficients allowed to assign M1 multipolarity to three γ transitions. The B(M1) values obtained for the 39.2, 46.2 and 85.4 keV transitions range from 0.017 to 0.043 W.u. and represent typical B(M1) strength in the Ba-Er region. Model calculations using a shell correction approach with the axially deformed Woods-Saxon potential predict for 147Ba an octupole deformed ground state with β3 = 0.11.

A relativistic electron beam, generated by relativistic self-focusing of an ultra-high-intensity laser pulse in a He gas jet, was targeted onto high-Z materials for conversion to high-energy bremsstrahlung. Nuclear reactions in the primary converter materials as well as in secondary and tertiary targets placed directly behind the converter were analyzed with time-resolved γ-spectroscopy. The electron-jet temperature of more than 35 MeV, matching the giant dipole resonances of heavy nuclei, enabled us to efficiently generate photo-induced nuclear reactions. The measured temperatures are significantly higher than suggested by ponderomotive scaling. We supplemented our earlier measurement of the (γ, n) reaction cross section of 129I with a method solely based on nuclear reactions. The photo-induced transmutation yields were increased by two orders of magnitude compared to earlier experiments. Simulations with the Monte Carlo code MCNPX confirm the experimental results .

Tabletop Ti : sapphire lasers, such as the Jena multi-Terawatt laser, can nowadays reach focused intensities of up to 1020 W cm−2. The interaction of this intense light field with a solid target—in our case tantalum—leads to the production of energetic bremsstrahlung x-rays. These are used to induce (γ,n)- and (γ,f)-reactions in 181Ta, 129I, 232Th, 238U and 9Be. The results are discussed in the context of laser plasma diagnostics and photo transmutation studies on radioactive material.We also report on fusion experiments in low-Z targets where the fusion neutrons are utilized to characterize ion acceleration processes.

We report the first successful laser-induced transmutation of 129I, one of the key radionuclides in the nuclear fuel cycle. 129I with a half-life of 15.7 million years is transmuted into 128I with a half-life of 25 min through a (γ, n) reaction using laser-generated Bremsstrahlung. The integral cross-section value for the (γ, n) reaction is determined. These experiments offer a new approach to studying transmutation reactions with neutral and charged particles without resource to nuclear reactors or particle accelerators.

One can design a critical system with fissile material in the form of a thin layer on the inner surface of a cylindrical neutron moderator such as graphite or beryllium. Recently, we have investigated the properties of critical and near critical systems based on the use of thin actinide layers of uranium, plutonium and americium. The thickness of the required fissile layer depends on the type of fissile material, its concentration in the layer and on the geometrical arrangement, but is typically in the μm–mm range. The resulting total mass of fissile material can be as low as 100 g. Thin fissile layers have a variety of applications in nuclear technology—for example in the design neutron amplifiers for medical applications and “fast” islands in thermal reactors for waste incineration. In the present paper, we investigate the properties of a neutron booster unit for spallation sources and isotope production. In those applications a layer of fissile material surrounds the spallation source. Such a module could be developed for spallation targets foreseen in the MYRRHA (L. Van Den Durpel, H. Ait Abderrahim, P. D’hondt, G. Minsart, J.L. Bellefontaine, S. Bodart, B. Ponsard, F. Vermeersch, W. Wacquier. A prototype accelerator driven system in Belgium: the Myrrha project, Technical Committee Meeting on Feasibility and Motivation for Hybrid concepts for Nuclear Energy generation and Transmutation, Madrid, Spain, September 17–19, 1997 [1]). or MEGAPIE (M. Salvatores, G.S. Bauer, G. Heusener. The MEGAPIE initiative: executive outline and status as per November 1999, MPO-1-GB-6/0_GB, 1999 [2]) projects. With a neutron multiplication factor of the booster unit in the range 10–20 (i.e. with a k eff of 0.9–0.95), considerably less powerful accelerators would be required to obtain the desired neutron flux. Instead of the powerful accelerators with proton energies of 1 GeV and currents of 10 mA foreseen for accelerator driven systems, similar neutron fluxes can be obtained with a medical cyclotron with proton energies of 350 MeV and currents of 2 mA. A basic limitation of such booster units is of course the limited lifetime of the thin fissile layer due to burn up and fission product poisoning. Nevertheless, for initial investigations of full power ADS systems, such units would allow the generation of the full neutron flux without the use of ADS class accelerators. The properties of the neutron booster have been intensively studied through systematic investigations of the different parameters (thickness, Hohlraum, reflector, etc.) of the concept. The calculations were performed with deterministic codes solving the neutron transport equation, and those results have been partially verified with the probabilistic code MCNP (Monte Carlo N-Particle Transport Code System). Layer of pure 235 U and 242m Am fuel have been initially investigated, but non-proliferation concerns led to the use of more conventional fuel layer. A specific geometry of a booster spallation source is presented. The effects of layer-burn up and lifetime are discussed.

A comprehensive study has been carried out of the yield pattern of fission products formed in fast neutron-induced fission of 233U. The isotope separator on-line facility at Studsvik to the R2-0 nuclear reactor was used for rapid separation of the fission products. At a target temperature of 2250°C fission products of the elements from zinc (Z = 30) to barium (Z = 56) are released, with the exception of yttrium, zirconium, niobium, molybdenum, technetium, ruthenium and rhodium. The individual isotopes are then available for study, implying that an almost complete mapping of the yield distribution can be made. In the analysis, the delay between production and measurement and the overall separator efficiency for three consecutive elements (the one under study and its parent and grand parent) are taken into account. Independent and/or cumulative yields have been obtained for 203 nuclear species, among them 59 isomeric states.

The VUV spectroscopic study of -particle-excited neon-krypton mixtures showed the occurrence of intense energy transfers from neon to krypton. The spectra of mixtures containing a few per cent krypton are similar to those of pure krypton. They are dominated by krypton's second continuum centred at 148 nm, its intensity increasing with the krypton concentration and the total pressure. Furthermore, a low-intensity emission due to the heteronuclear ion situated at 166.5 nm was also observed. The kinetic study of the second continuum of krypton revealed that heteronuclear reactions play an important role in the formation of at low krypton partial pressures. Their reaction constants were found to be for the state and for . Under high krypton pressures, homonuclear reactions were dominant, the reaction constant being for the state and for .

In two-component Xe/HCl mixtures irradiated with alpha -particles, emissions centred at 308, 345 and 470 nm are observed; they correspond to the (B to X) and (C to A) transitions of XeCl* and to the transition (42 Gamma to 12 Gamma ) of Xe2Cl*, respectively. The Xe2Cl* emission was only seen when HCl was present as traces and Xe was at a pressure of over 200 Torr. The experiments showed the simultaneous presence of the emissions of the third continuum of xenon (290 and 390 mm) which compete with those of XeCl*. This implies that the Xe2+* ions and their precursors, which participate in the reactions of XeCl (B, C) formation are also at the origin of the third continuum. By means of intensity measurements, the energy gap between states B and C of XeCl was estimated at 118+or-40 cm-1.

For pt.I see ibid., vol.25, no.23, p.5141-8 (1992). In Ne-Xe mixtures molecular states responsible for the second continuum of xenon ( lambda =170 nm) are shown to be created by homonuclear and heteronuclear reactions from the 3P1 and 3P2 states of xenon. In Ar-Xe mixtures, at lambda =826 nm, two lines of argon and xenon are superimposed; it is observed that the atomic states responsible for the two transitions undergo decay (for argon) or creation (for xenon). The creation of the 2p10 xenon state is measured from the transition at lambda =980 nm which it produces. In the Ne-Xe mixture, at lambda =882 nm, it is the decay, through homonuclear and heteronuclear mechanisms, of the precursor 2p8 state of xenon which is demonstrated. In each case, the rate constants of the corresponding reactions are reported.

In a recent experiment [1] a high efficiency regime of stable electron acceleration to kinetic energies ranging from 10 to 40 MeV has been achieved. The main parameters of the electron bunches are comparable with those of bunches provided by commercial Radio‐Frequency based Linacs currently used in Hospitals for Intra‐Operative Radiation Therapy (IORT). IORT is an emerging technique applied in operating theaters during the surgical treatment of tumors. Performances and structure of a potential laser‐driven Hospital accelerator are compared in detail with the ones of several commercial devices. A number of possible advantages of the laser based technique are also discussed.

High-energy electrons can be produced in interactions of intense, ultra-short laser pulses with plasmas. Experiments conducted in the regime of moderate laser power (a few terawatts [TW]) are attracting increasing attention for their possibility of optimizing the acceleration process. Here we report the successful production of several-MeV electron bunches in interactions of femtosecond laser pulses from a 10 TW tabletop laser with supersonic gas-jets. The laser–plasma interaction and the obtained electron bunches have been characterized in detail, and conditions for stable and reproducible acceleration have been found. The accelerated electron bunches have been characterized by means of the measurement of the induced photo-activation of a gold sample via bremsstrahlung-generation of photons with suitable energy. The obtained result opens up a wide range of possible applications of the compact electron source for the concerns of nuclear physics studies. Some of them are briefly considered in this paper.

At wavelengths lower than 550 nm, addition of argon or neon to xenon gives rise to the emission of continua produced by heteronuclear processes (ArXe, Ne+Xe and NeXe+) indicating large energy transfers from the preponderant and lighter gas. Above 550 nm the transitions observed were all produced by atomic processes. Addition of argon to xenon causes an enhancement of certain xenon emissions ( lambda =770 nm in particular): this does not occur in Ne-Xe mixtures. These processes involve, above all, high energy states of xenon (configuration 5d). The kinetic study of certain emissions is dealt with in paper II (Galy et al., 1993).

At low pressures, excitation is due to the absorption of three photons and causes emission of the resonance line and the related first continuum ( lambda approximately 125 nm). At higher pressures, excitation mainly arises from a photon of the third harmonic of the laser wave and the second continuum ( lambda approximately 148 nm) is detected. Luminescence attenuations in the excitation spectra can be explained by the absorption of a fourth photon. The natural lifetime of the 3P1 is determined using Holstein's theory. The role of two and three-body collisions is demonstrated in the decay of the 3P1 state as in the role of three-body collisions for the 3P2 state. The corresponding rate constants are determined and the lifetime of the 1u(3P2) state evaluated.

A gamma-ray source with an intense component around the giant dipole resonance for photonuclear absorption has been obtained via bremsstrahlung of electron bunches driven by a 10-TW tabletop laser. 3D particle-in-cell simulation proves the achievement of a nonlinear regime leading to efficient acceleration of several sequential electron bunches per each laser pulse. The rate of the gamma-ray yield in the giant dipole resonance region (8

Neutron production rates using laser-accelerated protons from high-energy single-shot laser (giant pulse laser) and low-energy high-repetition tabletop laser systems are compared. With the VULCAN giant pulse laser, more than 10 9 neutrons per shot were produced in a nanosecond pulse through (p,m) reactions with lead. In contrast, a current state-of-the-art tabletop laser theoretically can produce 10 6 to 10 7 neutrons per second in repetitional nanosecond pulses. It is estimated that next-generation tabletop lasers currently under construction will be capable of producing nanosecond neutron pulses at a rate of 10 10 neutrons per second.

Electron and proton beams were investigated using a compact laser with intensities up to 2times1019 W/cm2 irradiating thin targets. For the direction of the electron beam theory and experiment disagree

A beam of MeV protons, accelerated by ultraintense laser-pulse interactions with a thin target foil, is used to investigate nuclear reactions of interest for spallation physics. The laser-generated proton beam is shown (protons were measured) to have a broad energy distribution, which closely resembles the expected energy spectrum of evaporative protons (below 50 MeV) produced in GeV-proton-induced spallation reactions. The protons are used to quantify the distribution of residual radioisotopes produced in a representative spallation target (Pb), and the results are compared with calculated predictions based on spectra modeled with nuclear Monte Carlo codes. Laser-plasma particle accelerators are shown to provide data relevant to the design and development of accelerator driven systems. © 2005 The American Physical Society.

Neutron production capabilities of table-top laser accelerated protons based on data from a high-energy single-shot large laser are addressed. Recently, McKenna et al (2005 Phys. Rev. Lett. 94 084801) have analysed the energy spectrum for a beam of protons accelerated on the VULCAN laser. In this paper, we present a new analysis of the same experiment which demonstrates, for the first time, production levels in excess of 109 neutrons per laser shot within a nanosecond pulse through (p,xn) reactions on lead targets. We have used this natPb(p,xn) conversion analysis approach to make predictions on the neutron production capabilities of table-top laser systems. Neutron spectra for current state-of-the-art table-top lasers have been calculated, and we have estimated that current systems are capable of producing 106 neutrons per second in nanosecond pulses. Furthermore, we have found that nanosecond neutron pulses at a rate of 5 × 109 neutrons per second are possible with the next generation of table-top lasers currently under construction., JRC.E.4-Nuclear fuels

Excited states in the 134Sb nucleus, populated in the β−-decay of 134Sn, have been studied at the mass separator OSIRIS. The 134Sn activity was produced via fast neutron-induced fission of 238U target. A main result was the discovery of a very low-lying first-excited state of 134Sb, at 13 keV, which has led to a strong revision of the level scheme. The new results are compared with different theoretical calculations and with the known data for the analogous neutron and proton two-particle nucleus in the 208Pb region. On the basis of this comparison, the energy of the (πg 7/2νf 7/2)7− isomer is estimated to be about 250 keV, some 100 keV lower than previously reported.

In the last decade an evolution of experimental relativistic laser-plasma physics has led to highly sophisticated lasers, which are now able to generate ultra short pulses and can be focused to intensities in excess of 10(21) W cm(-2), with more than 500 J on target. In the intense electric field of the laser focus, plasma with temperatures greater than 10 billion degrees can be generated. The laser interactions with solid or gas targets can generate collimated beams of highly energetic electrons and ions. Experiments utilizing high-intensity laser systems turn out to be an interesting and versatile source for radiation, high-energy particles and nuclear reactions, without recourse to large-scale facilities such as nuclear reactors or particle accelerators. The possibility of accelerating electrons to energies over 200 MeV in such early experiments led to the utilization of high-energy bremsstrahlung radiation in order to investigate laser-induced gamma reactions. Many experiments of this type have been reported in several laboratories worldwide. However, to our knowledge, no dedicated investigations have been reported with respect to the characterization of the generated bremsstrahlung in such experiments. As it is not experimentally feasible to measure directly a bremsstrahlung spectrum, we report in the present paper on a dedicated series of calculations on the generated bremsstrahlung distributions from two experimental electron spectra measured using the giant pulse VULCAN laser and a gas jet target. Potential applications are also investigated.

An inexpensive, high capacity counting device has been made for time analysis of light pulses by time-amplitude conversion. In order to allow for particularly long storage times, it has two channels with a capacity of 10 12 pulses. The result is protected from power cuts. The total recording time is measured by a quartz clock.

The authors have studied the excitation of the B2 Sigma u+ state of N2+ by energy transfer from neon in Ne-N2 mixtures at total pressures of several hundred torr. The decay of the light pulse corresponding to the transition nu '=O, nu "=O( lambda =391.4 nm) was reconstituted by means of the time-amplitude conversion method. The curves decrease exponentially. The variations of the decay time constant with the partial pressures of Ne and N2 enabled the kinetic scheme of the transfer process which uses Ne+ ions to be deduced.

The emission spectra of KrXe mixtures were plotted at different total pressures and at xenon concentrations varying from 0.5 to 99%. A characteristic emission of the mixture was seen at 490 nm, it appeared as soon as possible as the mixture contained 0.5% xenon. The emission at 490 nm has a maximum intensity at a xenon concentration of 20%. The shape of the light pulses obtained for this transition is described by an exponential decay with a time constant corresponding to the formation of the radiative state. The KrXe+ ion involved is the IV1/2 state; the kinetic scheme given defines the role and the value of the various reaction rate constants.

Selective excitation of the 6s'(1/2)1(1P1) state of xenon by three-photon absorption produces, in the VUV range, three characteristic emissions of xenon at 129, 147 and 173 nm. For pressures above 1 Torr, the excitation spectra are obtained for laser excitation wavelengths lower than the wavelength corresponding to three-photon resonant excitation of the 1P1 state in accordance with the negative dispersion wavelength zone where third harmonic generation is possible. The sharp drops in these excitation spectra are explained by a four-photon absorption process. From the temporal analysis of the emission at 129 nm, it is reasonable to infer that an ionisation phenomenon is involved which leads to the formation of an upper atomic state responsible for the formation of radiative molecular states by three-body collisions.

In the VUV range, the spectra of krypton, at pressures of a few hundred torr, consist of continuous emissions that are characteristic of Kr2* molecules. A time resolved study of the second continuum of krypton ( lambda =145 nm) has allowed the authors to establish a scheme of the formation and decay kinetics of the excited species that is responsible for this emission. The radiative molecular state has a lifetime of tau 2=250+or-20 ns, it is formed by two- and three-body collisions from an intermediate molecular state at a frequency 1/ tau 3=18.6 p2+3.9*103 p s-1 (p in torr).

The VUV luminescence spectra of argon excited by alpha particles at a few hundred Torr present two continua, at 180 and 127 nm. The 127 nm emission is very intense, it corresponds to transitions from the lowest vibrational levels of the A 1y(3 Sigma u+) and B Ou+(1 Sigma u+) states of Ar2 towards the dissociative X Og+(1 Sigma g+) ground state. The shape of the pulse corresponding to the emission of the second continuum was reconstituted by time amplitude conversion. Three exponential terms can be seen. The variation of the time constants with pressure allows a kinetic scheme for the formation and decay of the radiative molecule species to be established. The excited states of the argon molecule are created by three-body collisions, from the (1)()J=1 and (1)()J=2 states of the 3p54s configuration, the collision constants being 1.6 and 13.8 Torr-2 s-1 respectively. The radiative lifetime of the A 1u(3 Sigma u+) state is 2.86 mu s.

For pt.I see ibid., vol.15, p.2935 (1982). Spectroscopic and kinetic study of ultraviolet emissions from argon-xenon mixtures brings to light very large energy transfers from argon and xenon. When small amounts of xenon (a few ppm) are added to argon, the argon continua disappear and simultaneously Xe resonance lines can be seen. At higher Xe concentrations (of the order of a few per cent), the spectra of mixtures are similar to those obtained in pure xenon. Kinetic analysis of the main VUV emissions of the two gases allows a complete kinetic scheme of the transfer phenomena to be established. Excited radiative xenon states are created from Ar2* molecules and atomic precursor states. The 1P1 state of xenon is excited by two-body collisions with the excimer Ar2*(3 Sigma u+) which is responsible for the second argon continuum (k=1.5*107 Torr-1 s-1). The transfer is also observed from the Ar*(3P1) state towards highly excited xenon levels (configuration 5f) (k=2.4*107 Torr-1 s-1). Both these paths lead, directly or indirectly, to the production of the 3P1 and 3P2 states of xenon which, through three-body heteronuclear collisions, are involved in the formation of the radiative Xe2* states responsible for the emission of the second continuum at 173 nm. The lifetime of this state, tau =106 ns, is not modified by the presence of argon.

The experiment demonstrates at low pressure the resonant excitation of the 3P1 atomic state of xenon by three-photon absorption; as the pressure increases the xenon molecules in the ground state intervene in the absorption process. The emission spectra present the VUV continua characteristic of the excimer. In the same experimental conditions but with observation along the excitation axis, the frequency tripling phenomenon is seen close to the resonance line at 147 nm and the authors have measured new values of the phase matching parameter CXe between 145 and 147 nm.

A characteristic emission in the spectra of argon krypton mixtures can be seen at 640 nm. It reaches a maximum for krypton concentrations of about 30%. In argon xenon mixtures two emissions with the same origin are seen at 328 and 500 nm. The variation of their intensity with partial pressures is similar; a maximum is reached at a 10% Xe concentration. The shapes of the light pulses obtained at 640 nm in ArKR and at 328 nm in ArXe are described by an exponential decay relationship corresponding to the formation of the radiative state. In both cases the kinetic study shows that the emissions correspond to radiative transitions arising from the IV1/2 state of the heteronuclear ion which dissociates to the Ar(2P1.2) state; the various two- and three-body reaction constants relative to the atomic ion are calculated.

The results obtained in a xenon multiphoton excitation experiment using a pulsed dye laser are presented. At low pressures, the 3P1 resonant state of xenon is created by 3-photon resonant absorption. At higher pressures (> 20 torr), the excitation spectrum presents 2 components situated on either side of the resonance line. Spectral analysis in this region showed that they were continually originating from the molecular states A \( 1u\left( {{}^3\sum\nolimits_u^ + {} } \right)\) and B \( O_u^1\left( {{}^1\sum\nolimits_u^ + {} } \right)\) which are themselves related to the atomic 3P1 state. In the zone of negative dispersion of the medium we demonstrated the existence of a phenomenon of frequency tripling of the excitation laser beam. The light obtained in the direction of incidence is intense, the frequency can be tuned, and the band width is very narrow.