Direct Observation of Sub-Poissonian Temporal Statistics in a Continuous Free-Electron Beam with Subpicosecond Resolution.

We present a novel method to measure the arrival time statistics of continuous electron beams with subpicosecond resolution, based on the combination of an rf deflection cavity and fast single electron imaging. We observe Poissonian statistics within time bins from 100 to 2 ns and increasingly pronounced sub-Poissonian statistics as the time bin decreases from 2 ps to 340 fs. This 2D streak camera, in principle, enables femtosecond-level arrival time measurements, paving the way to observing Pauli blocking effects in electron beams and thus serving as an essential diagnostic tool toward degenerate electron beam sources for free-electron quantum optics.

RF acceleration of ultracold electron bunches.

The ultrafast and ultracold electron source, based on laser cooling and trapping of atomic gas and its subsequent near-threshold two-step photoionization, is capable of generating electron bunches with a high transverse brightness at energies of roughly 10 keV. This paper investigates the possibility of increasing the range of applications of this source by accelerating the bunch using radio frequency electromagnetic fields. Bunch energies up to 35 keV are measured by analyzing the diffraction patterns generated from a mono-crystalline gold sample. It is found that the normalized transverse emittance is largely preserved during acceleration.

Photodiode-based time zero determination for ultrafast electron microscopy.

Pump-probe experiments in ultrafast electron microscopy require temporal overlap between the pump and probe pulses. Accurate measurements of the time delay between them allows for the determination of the time zero, the moment in time where both pulses perfectly overlap. In this work, we present the use of a photodiode-based alignment method for these time zero measurements. The cheap and easy-to-use device consists of a photodiode in a sample holder and enables us to temporally align individual, single-electron pulses with femtosecond laser pulses. In a first device, a temporal resolution of 24 ps is obtained, limited by the photodiode design. Future work will utilize a smaller photodiode with a lower capacitance, which will increase the temporal resolution and add spatial resolution as well. This upgrade will bring the method toward the micrometer and picosecond spatiotemporal resolution.

Phase-space manipulation of ultracold ion bunches with time-dependent fields.

All applications of high brightness ion beams depend on the possibility to precisely manipulate the trajectories of the ions or, more generally, to control their phase-space distribution. We show that the combination of a laser-cooled ion source and time-dependent acceleration fields gives new possibilities to perform precise phase-space control. We demonstrate reduction of the longitudinal energy spread and realization of a lens with control over its focal length and sign, as well as the sign of the spherical aberrations. This creates new possibilities to correct for the spherical and chromatic aberrations which are presently limiting the spatial resolution.

Design and characterization of dielectric filled TM110 microwave cavities for ultrafast electron microscopy.

Microwave cavities oscillating in the TM110 mode can be used as dynamic electron-optical elements inside an electron microscope. By filling the cavity with a dielectric material, it becomes more compact and power efficient, facilitating the implementation in an electron microscope. However, the incorporation of the dielectric material makes the manufacturing process more difficult. Presented here are the steps taken to characterize the dielectric material and to reproducibly fabricate dielectric filled cavities. Also presented are two versions with improved capabilities. The first, called a dual-mode cavity, is designed to support two modes simultaneously. The second has been optimized for low power consumption. With this optimized cavity, a magnetic field strength of 2.84 ± 0.07 mT was generated at an input power of 14.2 ± 0.2 W. Due to the low input powers and small dimensions, these dielectric cavities are ideal as electron-optical elements for electron microscopy setups.

Measurements of the energy distribution of a high brightness rubidium ion beam.

The energy distribution of a high brightness rubidium ion beam, which is intended to be used as the source for a focused ion beam instrument, is measured with a retarding field analyzer. The ions are created from a laser-cooled and compressed atomic beam by two-step photoionization in which the ionization laser power is enhanced in a build-up cavity. Particle tracing simulations are performed to ensure the analyzer is able to resolve the distribution. The lowest achieved full width 50% energy spread is (0.205 ±â€¯0.006) eV, which is measured at a beam current of 9 pA. The energy spread originates from the variation in the ionization position of the ions which are created inside an extraction electric field. This extraction field is essential to limit disorder-induced heating which can decrease the ion beam brightness. The ionization position distribution is limited by a tightly focused excitation laser beam. Energy distributions are measured for various ionization and excitation laser intensities and compared with calculations based on numerical solutions of the optical Bloch equations including ionization. A good agreement is found between measurements and calculations.

High quality ultrafast transmission electron microscopy using resonant microwave cavities.

Ultrashort, low-emittance electron pulses can be created at a high repetition rate by using a TM110 deflection cavity to sweep a continuous beam across an aperture. These pulses can be used for time-resolved electron microscopy with atomic spatial and temporal resolution at relatively large average currents. In order to demonstrate this, a cavity has been inserted in a transmission electron microscope, and picosecond pulses have been created. No significant increase of either emittance or energy spread has been measured for these pulses. At a peak current of 814 ±â€¯2 pA, the root-mean-square transverse normalized emittance of the electron pulses is ɛn,x=(2.7±0.1)·10-12 m rad in the direction parallel to the streak of the cavity, and ɛn,y=(2.5±0.1)·10-12 m rad in the perpendicular direction for pulses with a pulse length of 1.1-1.3 ps. Under the same conditions, the emittance of the continuous beam is ɛn,x=ɛn,y=(2.5±0.1)·10-12 m rad. Furthermore, for both the pulsed and the continuous beam a full width at half maximum energy spread of 0.95 ±â€¯0.05 eV has been measured.

Time-of-flight electron energy loss spectroscopy by longitudinal phase space manipulation with microwave cavities.

The possibility to perform high-resolution time-resolved electron energy loss spectroscopy has the potential to impact a broad range of research fields. Resolving small energy losses with ultrashort electron pulses, however, is an enormous challenge due to the low average brightness of a pulsed beam. In this paper, we propose to use time-of-flight measurements combined with longitudinal phase space manipulation using resonant microwave cavities. This allows for both an accurate detection of energy losses with a high current throughput and efficient monochromation. First, a proof-of-principle experiment is presented, showing that with the incorporation of a compression cavity the flight time resolution can be improved significantly. Then, it is shown through simulations that by adding a cavity-based monochromation technique, a full-width-at-half-maximum energy resolution of 22 meV can be achieved with 3.1 ps pulses at a beam energy of 30 keV with currently available technology. By combining state-of-the-art energy resolutions with a pulsed electron beam, the technique proposed here opens up the way to detecting short-lived excitations within the regime of highly collective physics.

Theory and particle tracking simulations of a resonant radiofrequency deflection cavity in TM110 mode for ultrafast electron microscopy.

We present a theoretical description of resonant radiofrequency (RF) deflecting cavities in TM110 mode as dynamic optical elements for ultrafast electron microscopy. We first derive the optical transfer matrix of an ideal pillbox cavity and use a Courant-Snyder formalism to calculate the 6D phase space propagation of a Gaussian electron distribution through the cavity. We derive closed, analytic expressions for the increase in transverse emittance and energy spread of the electron distribution. We demonstrate that for the special case of a beam focused in the center of the cavity, the low emittance and low energy spread of a high quality beam can be maintained, which allows high-repetition rate, ultrafast electron microscopy with 100 fs temporal resolution combined with the atomic resolution of a high-end TEM. This is confirmed by charged particle tracking simulations using a realistic cavity geometry, including fringe fields at the cavity entrance and exit apertures.

Direct diffusion of cis-diamminedichloroplatinum(II) in intraperitoneal rat tumors after intraperitoneal chemotherapy: a comparison with systemic chemotherapy.

Chemotherapy i.p. is increasingly being tested as a treatment modality for cancer limited to the peritoneal cavity. We have developed a rat tumor model in which penetration and distribution of cis-diamminedichloroplatinum(II) into intraperitoneal tumors have been studied. The platinum concentration in intraperitoneal tumor nodules, measured by two techniques, flameless atomic absorption spectroscopy and proton-induced X-ray emission, was always higher after i.p. treatment than i.v. Further, platinum concentrations were higher at the periphery of the tumor after i.p. administration than after i.v., while platinum concentrations in the center of the tumor nodules were identical. No difference was detected in platinum concentrations in s.c. tumors nor in the total area under the curve (plasma) after i.p. and i.v. administration of cis-diamminedichloroplatinum(II), suggesting that the higher drug concentration measured in peritoneal tumors after i.p. administration is due to direct diffusion of the drug from the peritoneal cavity.

Time-of-flight electron energy loss spectroscopy using TM110 deflection cavities.

We demonstrate the use of two TM110 resonant cavities to generate ultrashort electron pulses and subsequently measure electron energy losses in a time-of-flight type of setup. The method utilizes two synchronized microwave cavities separated by a drift space of 1.45 m. The setup has an energy resolution of 12 ± 2 eV FWHM at 30 keV, with an upper limit for the temporal resolution of 2.7 ± 0.4 ps. Both the time and energy resolution are currently limited by the brightness of the tungsten filament electron gun used. Through simulations, it is shown that an energy resolution of 0.95 eV and a temporal resolution of 110 fs can be achieved using an electron gun with a higher brightness. With this, a new method is provided for time-resolved electron spectroscopy without the need for elaborate laser setups or expensive magnetic spectrometers.

Optimisation of intraperitoneal cisplatin therapy with regional hyperthermia in rats.

The purpose of this study was to optimise intraperitoneal chemotherapy by combining this modality with regional hyperthermia. In vitro data demonstrated that both the uptake of cisplatin into CC531 tumour cells and cytotoxicity were increased at temperatures of 40 degrees C (factor 4) and 43 degrees C (factor 6) compared to 37 degrees C. The increase of intracellular platinum concentration correlated well with the decrease in survival of these cells. In vivo, rats were treated intraperitoneally with cisplatin (5 mg/kg) in combination with regional hyperthermia of the abdomen (41.5 degrees C, 1 h). The mean (S.D.) temperature in the peritoneal cavity was 41.5 (0.3) degrees C and outside the peritoneal cavity 40.5 (0.3) degrees C. Enhanced platinum concentrations were found in peritoneal tumours (factor 4.1) and kidney, liver, spleen and lung (all around a factor 2.0), after combined cisplatin-hyperthermia treatment. The platinum distribution in peritoneal tumours was more homogeneous after the combined treatment than after cisplatin alone, possibly due to increased penetration of cisplatin into peritoneal tumours. Pharmacokinetic data demonstrated an increased tumour exposure for unfiltered platinum in the peritoneal cavity (area under the curve [AUC] increased from 339 mumol/l/min to 486 mumol/l/min at 37 degrees C and 41.5 degrees C, respectively), and for total and ultrafiltered platinum in the blood. The AUC for total platinum increased from 97.9 to 325.8 mumol/min and for ultrafiltered platinum from 22.2 to 107 mumol/l/min at 37 degrees C and 41.5 degrees C respectively. The latter might be due to a slower elimination of platinum from the blood. The combined treatment, intraperitoneal cisplatin and regional hyperthermia, also increased toxicity. The thermal enhancement ratio (TER) using lethality as endpoint was 1.8.

The use of oxaliplatin versus cisplatin in intraperitoneal chemotherapy in cancers restricted to the peritoneal cavity in the rat.

Pharmacokinetic studies demonstrated the advantage of intraperitoneal oxaliplatin (1-OHP) for cancers restricted to the peritoneal cavity. The area under the concentration X time curve (AUC) in the peritoneal cavity for both total and ultrafiltered drug was almost 2 times higher for 1-OHP than cisplatin (cDDP). The AUC for ultrafiltered 1-OHP in plasma was also a factor 4 higher than cDDP, indicating that peritoneal tumors received a higher exposure from 1-OHP than cDDP directly in the peritoneal cavity and indirectly via the systemic circulation. Total platinum concentrations in peritoneal tumors of rats were determined after i.p. administration of equimolar doses of 1-OHP and cDDP. In spite of the pharmacological advantages, no significant difference in platinum concentration was demonstrated. In addition, no difference in the distribution of platinum within peritoneal tumors was detected after i.p. treatment with equimolar doses, i.e., platinum concentrations were comparable both in the periphery, 29 +/- 4 ppm for cDDP and 22 +/- 8 for 1-OHP and in the center of the tumor, 18 +/- 3 for both drugs. When CC531 tumor cells were incubated in vitro with equimolar concentrations of 1-DHP and cDDP in vitro, 2 to 4 times less platinum was found in cells treated with 1-OHP, indicating that the uptake of 1-OHP differed from that of cDDP. Oxaliplatin was not cross resistant for cDDP in CC531.RL4 tumor cells, a cDDP resistant cell line, which may indicate its value in ovarian cancer patients who did not respond to earlier cDDP treatment.

Penetration of carboplatin and cisplatin into rat peritoneal tumor nodules after intraperitoneal chemotherapy.

Platinum distribution was studied in rat peritoneal tumors after i.p. treatment with equimolar doses of carboplatin and cisplatin. Low platinum concentrations (4 ppm) were detected in the periphery of the tumor after carboplatin treatment, whereas no platinum was detected 0.5 mm in from the periphery. In contrast, after cisplatin treatment, high platinum concentrations (29 ppm) were measured in the periphery of the tumor and moderate concentrations (14 ppm) were measured in the center. Only following increased carboplatin doses were low platinum concentrations detectable in the tumor. The total platinum concentration in the tumors was determined after equimolar administration of both drugs. In all, 7 times more platinum was detected after cisplatin treatment than after carboplatin treatment, and 10 times more carboplatin than cisplatin had to be injected to obtain comparable platinum concentrations in the tumors. When single cells were incubated with equimolar concentrations of carboplatin and cisplatin, 6-7 times more platinum was found in cells treated with cisplatin. However, pharmacokinetic studies favored i.p. administration of carboplatin because the clearance of this compound from the peritoneal cavity, expressed as t1/2 beta, was lower than that of cisplatin (239 vs 78 min), resulting in an AUC in the peritoneal cavity for both total and ultrafiltered drug that was almost 3 times higher for carboplatin than cisplatin. The AUC for ultrafiltered carboplatin in plasma was 2-fold that for cisplatin (2,801 +/- 210 vs 1,334 +/- 431 microM m). The present study demonstrated that in spite of the pharmacological advantages of carboplatin, its capacity to penetrate into peritoneal tumors and tumor cells is far lower than that of cisplatin.

Platinum distribution in intraperitoneal tumors after intraperitoneal cisplatin treatment.

The spatial distribution of platinum (Pt) in the kidney was studied by an autoradiographic technique, in which cisplatin (CDDP) was replaced by 195mPt-labeled CDDP, and by proton-induced X-ray emission (PIXE). Although both studies demonstrated comparable spatial distribution patterns, PIXE had the advantage that Pt concentrations could be determined quantitatively, in contrast to the relative information obtained by the autoradiographic technique. Using PIXE, the distribution of Pt in i.p. tumors was studied after i.p. administration of CDDP. The highest Pt concentrations were always found on the periphery of tumors, indicating that the periphery was exposed to a higher drug concentration than the center. Dose was correlated to the concentration of CDDP at both the center and the periphery (r = 0.99). The Pt concentration in the periphery was usually higher by a factor of 2-3 after i.p. administration than after i.v. treatment, whereas in the center of the tumor no concentration difference could be detected. The penetration depth of CDDP lay between 1 and 2 mm and was calculated from the differences in Pt concentration after i.p. and i.v. treatment. This indicates that the effective advantage of i.p. chemotherapy with CDDP in cases of cancers limited to the peritoneal cavity is accentuated at the periphery of the tumor.

Compact, low power radio frequency cavity for femtosecond electron microscopy.

Reported here is the design, construction, and characterization of a small, power efficient, tunable dielectric filled cavity for the creation of femtosecond electron bunches in an existing electron microscope without the mandatory use of femtosecond lasers. A 3 GHz pillbox cavity operating in the TM(110) mode was specially designed for chopping the beam of a 30 keV scanning electron microscope. The dielectric material used is ZrTiO(4), chosen for the high relative permittivity (ε(r) = 37 at 10 GHz) and low loss tangent (tan δ = 2 × 10(-4)). This allows the cavity radius to be reduced by a factor of six, while the power consumption is reduced by an order of magnitude compared to a vacuum pillbox cavity. These features make this cavity ideal as a module for existing electron microscopes, and an alternative to femtosecond laser systems integrated with electron microscopes.

Low-energy-spread ion bunches from a trapped atomic gas.

We present time-of-flight measurements of the longitudinal energy spread of pulsed ultracold ion beams, produced by near-threshold ionization of rubidium atoms captured in a magneto-optical atom trap. Well-defined pulsed beams have been produced with energies of only 1 eV and a root-mean-square energy spread as low as 0.02 eV, 2 orders of magnitude lower than the state-of-the-art gallium liquid-metal ion source. The low energy spread is important for focused ion beam technology because it enables milling and ion-beam-induced deposition at sub-nm length scales with many ionic species, both light and heavy. In addition, we show that the slowly moving, low-energy-spread ion bunches are ideal for studying intricate space charge effects in pulsed beams. As an example, we present a detailed study of the transition from space charge dominated dynamics to ballistic motion.

Purification and biochemical characterization of a putative [6Fe-6S] prismane-cluster-containing protein from Desulfovibrio vulgaris (Hildenborough).

A novel iron-sulfur protein has been isolated from the sulfate-reducing bacterium Desulfovibrio vulgaris (Hildenborough). It is a stable monomeric protein, which has a molecular mass of 52 kDa, as determined by sedimentation-equilibrium centrifugation. Analysis of the metal and acid-labile sulfur content of the protein revealed the presence of 6.3 +/- 0.4 Fe/polypeptide and 6.2 +/- 0.7 S2-/polypeptide. Non-iron transition metals, heme, flavin and selenium were absent. Combining these data with the observation of a very anisotropic S = 1/2 [6Fe-6S]3+ prismane-like EPR signal in the dithionite-reduced protein, we believe that we have encountered the first example of a prismane-cluster-containing protein. The prismane protein has a slightly acidic amino acid composition and isoelectric point (pI = 4.9). The ultraviolet/visible spectrum is relatively featureless (epsilon 280 = 81 mM-1.cm-1, epsilon 400 = 25 mM-1.cm-1, epsilon 400,red = 14 mM-1.cm-1). The shape of the protein is approximately globular (S20.w = 4.18 S). The N-terminal amino acid sequence is MFS/CFQS/C QETAKNTG. Polyclonal antibodies against the protein were raised. Cytoplasmic localization was inferred from subcellular fractionation studies. Cross-reactivity of antibodies against this protein indicated the occurrence of a similar protein in D. vulgaris (Monticello) and Desulfovibrio desulfuricans (ATCC 27774). We have not yet identified a physiological function for the prismane protein despite trials for some relevant enzyme activities.

Pixe microanalysis of trace elements of normoxic, ischemic and reperfused rat hearts.

With a 3 x 3 mu m(2) proton microbeam spatial distributions of Na, Mg, P, S, K, Ca and Fe were measured via PIXE in 50 x 50 mu m(2) areas of rat heart, sliced into 10-15 mu m thick cryosections. The isolated rat hearts were subjected to normal perfusion, ischemia and reperfusion. Substantial changes in the elemental distribution were found in tissue after 40 min. of reperfusion, particularly indicated by locally elevated Ca and decreased K levels. Electron microscopic examination was used for assessment of artefacts due to sample preparation and handling. Results of stained cryosections analyzed via STIM demonstrated that this latter technique can be employed prior to PIXE analysis to localize individual cells in freeze-dried cryosections.

Redox properties of the iron-sulfur clusters in activated Fe-hydrogenase from Desulfovibrio vulgaris (Hildenborough).

The periplasmic Fe-hydrogenase from Desulfovibrio vulgaris (Hildenborough) contains three iron-sulfur prosthetic groups: two putative electron transferring [4Fe-4S] ferredoxin-like cubanes (two F-clusters), and one putative Fe/S supercluster redox catalyst (one H-cluster). Combined elemental analysis by proton-induced X-ray emission, inductively coupled plasma mass spectrometry, instrumental neutron activation analysis, atomic absorption spectroscopy and colorimetry establishes that elements with Z > 21 (except for 12-15 Fe) are present in 0.001-0.1 mol/mol quantities, not correlating with activity. Isoelectric focussing reveals the existence of multiple charge conformers with pI in the range 5.7-6.4. Repeated re-chromatography results in small amounts of enzyme of very high H2-production activity determined under standardized conditions (approximately 7000 U/mg). The enzyme exists in two different catalytic forms: as isolated the protein is 'resting' and O2-insensitive; upon reduction the protein becomes active and O2-sensitive. EPR-monitored redox titrations have been carried out of both the resting and the activated enzyme. In the course of a reductive titration, the resting protein becomes activated and begins to produce molecular hydrogen at the expense of reduced titrant. Therefore, equilibrium potentials are undefined, and previously reported apparent Em and n values [Patil, D. S., Moura, J. J. G., He, S. H., Teixeira, M, Prickril, B. C., DerVartanian, D. V., Peck, H. D. Jr, LeGall, J. & Huynh, B.-H. (1988) J. Biol. Chem. 263, 18,732-18,738] are not thermodynamic quantities. In the activated enzyme an S = 1/2 signal (g = 2.11, 2.05, 2.00; 0.4 spin/protein molecule), attributed to the oxidized H cluster, exhibits a single reduction potential, Em,7 = -307 mV, just above the onset potential of H2 production. The midpoint potential of the two F clusters (2.0 spins/protein molecule) has been determined either by titrating active enzyme with the H2/H+ couple (E,m = -330 mV) or by dithionite-titrating a recombinant protein that lacks the H-cluster active site (Em,7.5 = -340 mV). There is no significant redox interaction between the two F clusters (n approximately 1).