Comparative tissue uptake and cellular deposition of three different plutonium chemical forms in rats

PURPOSE

To evaluate the influence of the chemical form of plutonium (Pu) on its distribution in tissues and within liver cells populations.

MATERIALS AND METHODS

Groups of male Sprague-Dawley rats were contaminated by intravenous injection of either Pu citrate, Pu nitrate or Pu phytate. Pu content was determined in various tissues at different times after injection. Pu liver distribution was analysed by autoradiography and after cellular separation.

RESULTS

Biokinetic studies indicate that Pu citrate and Pu nitrate predominantly retained in the skeleton within the first hours after injection, whereas most of the Pu was in the liver after injection of Pu phytate. Autoradiographs showed that Pu citrate was homogeneously distributed in the liver, while Pu nitrate accumulated into 'hot points'. Pu phytate showed an intermediate distribution pattern. Hepatic cell separation revealed a difference of uptake between the two cell types depending on the chemical form of injected Pu, and on the time after contamination.

CONCLUSIONS

Distinct Pu behaviour was observed for biokinetics, retention and liver distribution. The large differences noted between citrate, nitrate and phytate might be explained by differences in systemic and hepatic transport.

Direct lung delivery of a dry powder formulation of DTPA with improved aerosolization properties: Effect on lung and systemic decorporation of plutonium

DTPA, an actinide chelating agent, has demonstrated its ability to complex plutonium (Pu) and to facilitate its urinary excretion after internal contamination. This process, known as decorporation is crucial to diminish the burden of Pu in the body. The ability to deliver a chelating agent directly to the alveolar region may increase its local concentration as compared to systemic delivery and therefore increase the extent of decorporation. Second, inhalation offers the potential for needle-free, systemic delivery of small molecules and would be convenient in case of nuclear accident as a first pass emergency treatment. To benefit from the improvement of inhalation technology, we have formulated DTPA into porous particles by spray-drying with dl-Leucine, DPPC and ammonium bicarbonate. The optimized particles possess a volume mean geometric diameter around 4.5 mum and crumpled paper morphology. The in vitro aerodynamic evaluation shows that about 56% of the powder should deposits in the lungs, with about 27% in the alveolar region, an improvement as compared with the micronized powder available with the Spinhaler. After pulmonary administration to rats contaminated with PuO(2), a 3-fold increase of the Pu urinary excretion was observed, but the dissolution of PuO(2) in the lungs was not enhanced.

Decorporation of plutonium by pulmonary administration of Ca-DTPA dry powder: a study in rat after lung contamination with different plutonium forms

This study evaluates the decorporation efficacy of a pulmonary administration of a new Ca-DTPA (diethylenetriaminepentaacetic acid) dry powder (18 micromol kg(-1) of body mass) after pulmonary contamination of rats with different Pu compounds. After inhalation of PuO2, a delayed intratracheal administration of DTPA cannot reduce significantly the retention of Pu in the lungs but limits its transfer in liver and skeleton. After pulmonary contamination by Pu nitrate, early insufflation of the DTPA powder appears twice as more efficient than an i.v injection of DTPA (30 micromol kg(-1)) to reduce Pu retention in the lungs and is as effective as i.v. injection to limit the extrapulmonary deposit. In contrast, a delayed administration of DTPA cannot reduce the lung or extrapulmonary retention. In conclusion, the improvement of aerodynamic properties of DTPA powder leads to an increase of DTPA amount deposited in the lungs and enhances the body decorporation.

Influence of initial lung deposit on pulmonary clearance after plutonium oxide inhalation in rat

Alveolar macrophages are a key element in the clearance of inhaled particles after phagocytosis, and thus participate actively in lung dose distribution and in the risk of tumour formation. We studied the influence of initial lung deposit (ILD) on lung clearance and distribution of activity from 3 d to 3 months after inhalation of two forms of PuO2 (97% 239Pu and 70% 239Pu) in rats. ILDs ranging from 2.1 to 17 kBq were used. The total activity measured using X-ray spectrometry 3 months post-inhalation, relative to the ILD, showed a similar decrease in all groups, with the remaining activity representing approximately 30% of the ILD. The total activity recovered in bronchoalveolar lavages represented approximately 60% of the total lung activity. This ratio remained stable over time for the lowest ILD tested but decreased for higher ILD. In addition, the percentage of macrophages associated with particles decreased faster with time in rats with the highest ILD. Under our experimental conditions, there were no marked differences in lung clearance between groups. However, the distribution of the activity seems to vary with the time post-exposure between low and high ILD.

Enhanced decorporation of plutonium by DTPA encapsulated in small PEG-coated liposomes

The aim of the study was to demonstrate that decorporation of 238Pu is achieved more efficiently by an optimized liposomal formulation of diethylene triamine pentaacetic acid (DTPA) than by the usual free DTPA treatment. The optimized formulation consisted of polyethylene glycol-coated stealth liposomes with a mean diameter of 100 nm (SL-100 nm). Rats were intravenously injected with various Pu-phytate salt solutions in order to test different contamination conditions (activity and salt concentration) impacting liver kinetics and skeletal uptake of Pu. All treatments were given intravenously 1 h after contamination. Efficiency was evaluated 24 h, 7, 16 or 30 days later through their ability to promote Pu elimination and to reduce Pu burden in the skeleton and liver, the main organs of Pu deposition and radiotoxicological effects. Whatever the conditions of contaminations, a single injection of SL-100 nm (3.2 micromol kg(-1) DTPA) boosted urinary elimination of Pu to above 90% of the injected dose. In addition, liposomes strongly and significantly reduced the Pu burden of the liver and skeleton even 30 days after a single treatment: a dose of 0.3 micromol kg(-1) induced the same skeletal Pu reduction as four injections of free DTPA (30 micromol kg(-1)). A log dose-effect relation was found with SL-100 nm DTPA and Pu excretion in urine or Pu burden in the studied organs (liver, femurs, spleen and kidneys). This efficacy was attributed to an optimized targeting of DTPA to the main Pu retention organs and especially the liver.

Imaging and quality assessment of high-harmonic focal spots

We present a direct method of studying the focusability of an intense, short-pulse extreme-ultraviolet (XUV) beam obtained by high-harmonic generation. We perform near-field imaging of the focal spot of five high-harmonic orders strongly focused by a broadband toroidal mirror. To visualize the focal spot directly, we image the fluorescence induced by an XUV beam on a cerium-doped YAG crystal on a visible CCD camera. We can thus measure the harmonic spot size on a single image, together with the Strehl ratio, to evaluate the quality of focusing. Such techniques should become instrumental in optimizing the focusing conditions and reaching intensities required for exploring attosecond nonlinear optics in the XUV range.

Global optimization of high harmonic generation

We investigate the relevance of the absorption limit concept in the optimization of high harmonic generation. Thanks to the first direct observation of the coherence length of the process from high-contrast Maker fringes, we unravel experimental conditions for which the harmonic dipole response is enhanced when phase matching is realized within the absorption limit, leading to record conversion efficiencies in argon. Moreover, we show that harmonic generation in guided or freely propagating geometries are equivalent in the loose focusing regime. This analysis is generalized to other advanced phase-matching schemes, thereby predicting the possibility to boost the conversion efficiencies using light noble gases.

In vivo measurement of Pu dissolution parameters of MOX aerosols and related uncertainties in the values of the dose per unit intake

The aim of this study was to compare dissolution parameter values for Pu from industrial MOX with different Pu contents. For this purpose, preliminary results obtained after inhalation exposure of rats to MOX containing 2.5% Pu are reported and compared to those obtained previously with MOX containing 5% Pu. Dissolution parameter values appear to increase when the amount of Pu decreases. Rapid fractions, f(r), of 4 x 10(-3) (s.d. = 2 x 10(-3)) and 1 x 10(-3) (s.d. = 6 x 10(-4)) and slow dissolution rates, s(s) of 2 x 10(-4) d(-1) (standard deviation, sigma = 5 x 10(-5)) and 5 x 10(-5) d(-1) (sigma = 1 x 10(-5)) were derived for MOX containing 2.5 and 5% of Pu, respectively. Simulations were performed to assess uncertainties on dose due to experimental errors. The relative standard deviations of the dose per unit intake (DPUI) due to f(r) (4-8%), are far less than those due to s(s) (about 20%), which is the main parameter altering the dose. Although quite different dissolution parameter values were derived, similar DPUIs were obtained for MOX aerosols containing 2.5 and 5% Pu which appear close to that for default Type S values.

Comparative decorporation efficacy of 3,4,3-LIHOPO, 4,4,4-LIHOPO and DTPA after contamination of rats with soluble forms of 238Pu and 233U

The aim of this study was to compare the efficacies of DTPA, 3,4,3-LIHOPO and a newly synthesised molecule, 4,4,4-LIHOPO, in removing 233U and 238Pu after internal contamination by soluble forms of those nuclides. For this purpose, intravenous injections of DTPA (30 micromol kg(-1)) or 3,4,3-LIHOPO or 4,4,4-LIHOPO at dosages of 0.3 or 30 micromol kg(-1) were performed 1, 6 and 24 h after contamination of rats by intravenously injected 238Pu citrate and 1 h after intravenous injection of 233U nitrate. Actinide content in the main retention organs and cumulated excretion were measured 48 h after contamination. These experiments show similar decorporation efficacies of 4,4,4-LIHOPO and 3,4,3-LIHOPO for Pu, which are much higher than that of DTPA. At a dosage of 0.3 micromol kg(-1), the two LIHOPO analogues were as efficient as DTPA at a dosage of 30 micromol kg(-1). After U contamination, a 20% decorporation efficacy was obtained for either 3,4,3-LIHOPO or 4,4,4-LIHOPO at a dosage of 30 micromol kg(-1).

Demonstration of a Ni-like Kr optical-field-ionization collisional soft x-ray laser at 32.8 nm

We report the first experimental demonstration of a Ni-like optical-field ionization collisional soft x-ray laser. The amplifying medium is generated by focusing a circularly polarized 760 mJ, 30 fs, 10-Hz Ti:sapphire laser beam in a few mm cell filled with krypton. We have measured a gain coefficient of 78 cm(-1) on the 3d(9)4d 1S0-3d(9)4p(1)P1 transition at 32.8 nm, which is here amplified for the first time. This radiation source represents the shortest wavelength optical-field ionization collisional soft x-ray laser ever produced. The influence of the gas pressure and the pumping energy on the lasing output are also presented.

Relativistic electron generation in interactions of a 30 TW laser pulse with a thin foil target

Energy and angular distributions of the fast outgoing electron beam induced by the interaction of a 1 J, 30 fs, 2 x 10(19) W/cm(2), 10 Hz laser with a thin foil target are characterized by electron energy spectroscopy and photonuclear reactions. We have investigated the effect of the target thickness and the intensity contrast ratio level on the electron production. Using a 6-microm polyethylene target, up to 4 x 10(8) electrons with energies between 5 and 60 MeV were produced per laser pulse and converted to gamma rays by bremsstrahlung in a Ta secondary target. The rates of photofission of U as well as photonuclear reactions in Cu, Au, and C samples have been measured. In optimal focusing conditions, about 0.06% of the laser energy has been converted to outgoing electrons with energies above 5 MeV. Such electrons leave the target in the laser direction with an opening angle of 2.5 degrees.

Deuterium-deuterium fusion dynamics in low-density molecular-cluster jets irradiated by intense ultrafast laser pulses

Following the interaction of superintense, short pulse lasers and plasmas, ions can be accelerated to velocities sufficient to drive nuclear fusion reactions, in particular, by the process of Coulomb explosion of clusters [T. Ditmire, Nature (London) 398, 491 (1999)]]. We show here how short bursts of neutrons can be produced using a jet of low-density deuterated methane clusters. Ion velocity distributions were simultaneously measured by a Thomson parabola mass spectrometer, demonstrating deuteron energies up to 120 keV. We show that, in such conditions, nuclear fusion will occur not only in the hot plasma core, but also in the cold outer region by collision processes.

[Specific parameters for the calculation of dose after aerosol inhalation of transuranium elements]

A review on specific parameter measurements to calculate doses per unit of incorporation according to recommendations of the International Commission of Radiological Protection has been performed for inhaled actinide oxides. Alpha activity distribution of the particles can be obtained by autoradiography analysis using aerosol sampling filters at the work places. This allows us to characterize granulometric parameters of "pure" actinide oxides, but complementary analysis by scanning electron microscopy is needed for complex aerosols. Dissolution parameters with their standard deviation are obtained after rat inhalation exposure, taking into account both mechanical lung clearance and actinide transfer to the blood estimated from bone retention. In vitro experiments suggest that the slow dissolution rate might decrease as a function of time following exposure. Dose calculation software packages have been developed to take into account granulometry and dissolution parameters as well as specific physiological parameters of exposed individuals. In the case of poorly soluble actinide oxides, granulometry and physiology appear as the main parameters controlling dose value, whereas dissolution only alters dose distribution. Validation of these software packages are in progress.

Saturated amplification of a collisionally pumped optical-field-ionization soft X-ray laser at 41.8 nm

We report the first saturated amplification of an optical-field-ionization soft x-ray laser. The amplifying medium is generated by focusing a circularly polarized 330-mJ, 35-fs, 10-Hz Ti:sapphire laser system in a few-mm cell filled with xenon. A gain of 67 cm(-1) on the 4d(9)5p-4d(9)5d transition at 41.8 nm in Pd-like xenon and a gain-length product of 15 have been inferred at saturation. This source delivers about 5 x 10(9) photons per pulse. The influence of the pumping energy and the laser polarization on the lasing output are also presented.

Non-thermal melting in semiconductors measured at femtosecond resolution

Ultrafast time-resolved optical spectroscopy has revealed new classes of physical, chemical and biological reactions, in which directed, deterministic motions of atoms have a key role. This contrasts with the random, diffusive motion of atoms across activation barriers that typically determines kinetic rates on slower timescales. An example of these new processes is the ultrafast melting of semiconductors, which is believed to arise from a strong modification of the inter-atomic forces owing to laser-induced promotion of a large fraction (10% or more) of the valence electrons to the conduction band. The atoms immediately begin to move and rapidly gain sufficient kinetic energy to induce melting--much faster than the several picoseconds required to convert the electronic energy into thermal motions. Here we present measurements of the characteristic melting time of InSb with a recently developed technique of ultrafast time-resolved X-ray diffraction that, in contrast to optical spectroscopy, provides a direct probe of the changing atomic structure. The data establish unambiguously a loss of long-range order up to 900 A inside the crystal, with time constants as short as 350 femtoseconds. This ability to obtain the quantitative structural characterization of non-thermal processes should find widespread application in the study of ultrafast dynamics in other physical, chemical and biological systems.

Dosimetric measurements of electron and photon yields from solid targets irradiated with 30 fs pulses from a 14 TW laser

A 14 TW Ti:Sa laser furnishing pulses with a duration of 30 fs (full width at half maximum) at a repetition rate of 10 Hz was used to expose solid targets to intensities of up to 3x10(18) W/cm(2). Dosimetric techniques were employed to study the total x-ray yield, the spectral and angular distribution of the x-ray photons and the energy distribution of high-energy electrons injected into the solid target and emitted into the vacuum. Scans of laser pulse energy and duration were carried out to study the dependence of the x-ray generation efficiency on these parameters. The radiation transport processes in the target were modeled using the Monte Carlo method. The results of these calculations were used to interpret the measurement results and to critically discuss the applicability of dosimetric methods to the investigation of photon and electron emission from laser-produced plasmas.

Comparative biokinetics of plutonium and americium after inhalation of PuO2 and mixed oxides (U, Pu)O2 in rat

PURPOSE

To compare the biokinetics of Pu and Am in rat after inhalation of PuO2 and two (U, Pu) mixed oxides (MOX), referred to as MIMAS and SOLGEL.

MATERIALS AND METHODS

Lung clearance was measured in vivo by X-and y-ray spectrometry. Retention of Pu and Am in femurs, liver and kidneys was measured by alpha-spectrometry.

RESULTS

Observed lung clearance was in the same range for all three powders. Extra-pulmonary transfers were expressed as the percent of the initial deep lung deposit (IDLD) measured 7 days after inhalation. After PuO2 exposure, bone retention remained nearly constant throughout the 270-day experiment. It was approximately 0.7% of the IDLD for Pu and Am. By contrast, a gradual increase was observed for the two MOX. After 7 days, bone retention of Pu and Am was respectively 0.05 and 0.08% for MIMAS, and 0.2 and 0.6% for SOLGEL. The retention reached maximal values between 180 and 270 days post-exposure, which were 0.2 and 0.3% for MIMAS, and 1.2 and 2.8% for SOLGEL for Pu and Am respectively.

CONCLUSIONS

Different transfer rates of Pu and Am from the lung were observed depending on the chemical composition of the oxides and/or the method of their preparation.

Hot-electron distribution functions in a subpicosecond laser interaction with solid targets of varying initial gradient scale lengths

We have studied the distribution function of the hot electrons produced during the interaction of a 120-fs, 60-mJ, 800-nm wavelength and a p-polarized laser pulse with bilayered Al/Fe targets. The main pulse interacts with a preformed plasma, obtained with a controlled prepulse, whose density gradient scale length has been measured. The electron distribution function is characterized by means of the Kalpha emission of the two materials of the target as a function of the Al-layer thickness. The low-energy region (<50 keV) of the hot-electron distribution function shows no dependency in shape on the gradient scale length, but only a variation in the total number of the generated electrons. The comparison between the experimental results and the particle-in-cell and Monte Carlo calculations of the electron distribution function and the Kalpha emission is gratifying.

Anomalous long-range propagation of femtosecond laser pulses through air: moving focus or pulse self-guiding?

Self-guided propagation of femtosecond laser pulses is studied for a converging-beam configuration. Channeling of the pulse energy through various gases is observed over distances well beyond the lens focal point, a fact that cannot be explained by the moving-focus model. The results are in good agreement with three-dimensional numerical simulations.

Conical emission from self-guided femtosecond pulses in air

Conical emission in the forward direction is observed from intense femtosecond light pulses propagating through air over long distances. The conical emission is attributed to Cerenkov radiation from a dynamic self-guiding structure consisting of a weakly ionized core surrounded by Kerr cladding.

Efficacy of 3,4,3-LIHOPO for enhancing the excretion of plutonium from rat after simulated wound contamination as a tributyl-n-phosphate complex

The siderophone analogue 3,4,3-LIHOPO, referred to hereafter as LIHOPO, has been examined for its ability to remove 238Pu in a tributyl-n-phosphate (TBP) complex from rat after intramuscular (i.m.) or subcutaneous (s.c.) contamination. The chelating agent was administered at a dosage of 30 mumol.kg-1, 30 min after the contamination, either by intravenous (i.v.) or local injection. By day 7 after exposure, local (i.m.) administration of LIHOPO reduced the amounts of i.m.-injected 238Pu in the would site, skeleton and liver to 75, 20 and 25% respectively of those in untreated animals. At the i.m. Pu would site, local treatment was superior to i.v. treatment; both ligands were equally effective. At the s.c. Pu would site, local and systemic treatments were equally effective and LIHOPO was superior to DTPA. After translocation, LIHOPO was the most effective treatment for enhancing Pu excretion, whatever the route of contamination and treatment: the administration of LIHOPO and DTPA reduced whole-body Pu retention by a factor of 1.8 and 1.4 respectively. All these results are encouraging for the use of LIHOPO in the future but more studies are needed, concerning both the toxicity of the compound and its use in man.

Subcellular and intranuclear localization of neptunium-237 (V) in rat liver

The present investigation was aimed at establishing the distribution of 237Np within the different structures of hepatocytes. Rats were contaminated experimentally by intravenous injection of 237Np (V) and the subcellular structures of the liver were separated by ultracentrifugation. Twenty-four hours after contamination, the nuclear and cytosolic fractions bound 54 and 32%, respectively, of the total radionuclide. Purification of the nuclei followed by dissociation of the protein components in medium of increasing ionic strength showed a specific binding of neptunium to the structural proteins of the nuclear matrix.

Age-dependent variation of selenium-75 biokinetics in rat

Substantial levels of selenium-79 (79Se) in radioactive waste from the nuclear fuel cycle, may result in a significant collective dose commitment following release into the environment. Few data are available from which the effective dose equivalent among subgroups of the general population can be made. Accordingly, whole body retention and organ content were studied in neonate, adult and pregnant rat following oral contamination with 75Se. The results for whole-body retention conformed to a two-component exponential with terminal biological half-time of about 40, 30 and 20 days in adult male, neonate and pregnant rat, respectively. The highest concentrations of Se occurred in the liver, kidney, and testis. Influence of Se kinetics as a function of age and physiological development on dose estimates are discussed. Results were consistent with current dosimetric models but suggested that the testis should also be included.

Compact and efficient multipass Ti:sapphire system for femtosecond chirped-pulse amplification at the terawatt level

We have developed efficient multipass Ti:sapphire amplifiers for femtosecond chirped-pulse amplification. With only two of these devices we get an amplification factor of 10(8), which corresponds to a peak power of ~0.5 TW after compression. We present a detailed analysis of such a system and its advantages in terms of its high quantum yield (0.3), flexibility, optical quality, and potential for tunability.

Electronic nonlinear optical susceptibilities of silicate glasses

Femtosecond techniques have been used to measure the electronic contribution to the nonlinear susceptibility of several standard glasses. The relation between their nonlinear efficiency and the content of network-modifying cations has been determined.

Relaxation of mammalian heart muscle during chronic cardiac overload

Cardiac relaxation was studied in rat papillary muscle during hypertrophy induced by different chronic volume and/or pressure overload (aortic insufficiency, aorto-caval fistula, aortic stenosis, spontaneously hypertensive rat). Maximum velocity of lengthening did not depend upon the degree of cardiac hypertrophy, but rather on the type of chronic overload. Cardiac hypertrophy did not modify the load sensitivity of relaxation, whatever the type and stage of chronic overload, although, during acute hypoxia, the load sensitivity disappeared both in normal and in hypertrophied heart muscle.

[Cardiac relaxation in experimental chronic myocardial hypertrophy: role of the sarcoplasmic reticulum]

The relaxation phase was studied in normal rat hearts submitted to chronic myocardial pressure and/or volume overload (stenosis of the abdominal aorta, aortic regurgitation, aorto-caval fistula) and in spontaneously hypertensive rats, some of which also had aorto-caval fistulae. Four indices were chosen to quantify the relaxation phase: maximal velocity of relaxation during contraction with preload alone, the negative peak of the derivative of isometric tension, and two other indices testing the sensitivity of the relaxation phase to other conditions of load. The first two indices were found to be depressed during chronic myocardial overload, especially with aorto-caval fistulae and mixed overload. On the other hand, the other two indices of the degree of sensitivity to the relaxation load by two different methods showed no significant difference between chronically overloaded and control hearts, though changes were observed after acute hypoxia. These two indices are related to morphological development and to the functional state of the sarcoplasmic reticulum. These results suggest that the rate of calcium uptake by the sarcoplasmic reticulum is reduced during chronic myocardial overload but that the myocardium retains its ability to regulate the relaxation phase with respect to time and the degree of total load. This property disappears temporarily after hypoxia when the heart behaves like frog myocardium which has practically no sarcoplasmic reticulum.

[The use of lasers in the study of cardiac mechanics]

Cardiac and skeletal muscles exhibit regularly spaced light and dark transverse striations (the I and A bands respectively). Consequently, when they are illuminated by a laser beam, they behave like diffraction gratings. The diffraction line spacing varies inversely with the sarcomere length. Real-time kinetics of sarcomere can be measured with a high accuracy. The analysis of the diffraction pattern indicates a high degree of synchronization of sarcomere movements (contraction and relaxation). This technique represents a powerful method to analyse the mechanical behaviour of heart muscle at subcellular level.