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The accident at Fukushima Daiichi nuclear power plant on 11 March 2011 released radioactive material into the atmosphere, and contaminated land in Fukushima and several neighbouring prefectures. During rehabilitation, it is important to accurately understand and determine individual external doses to allow individuals to make informed decisions about whether or not to return to the affected areas. Personal dosimeters (D-Shuttle), used together with a global positioning system and geographic information system device, can provide realistic individual external doses and associated individual external doses, ambient doses, and activity patterns of individuals in the affected areas of Fukushima. This study involved more than 250 affected residents. The results help to determine realistic individual external doses, and corresponding time-activity patterns and airborne monitoring ambient dose rates, which can be used to predict future cumulative external doses after residents return to their homes in evacuation areas. In addition, insights gained by the study can help to explain the role of individual external dose measurements for affected residents in postaccident recovery, based mainly upon the experience gained in measuring, assessing, and communicating individual external doses. [ABSTRACT FROM AUTHOR]

Highly functionalized drugs delivered via a drug delivery system are expected to have less side effects and higher accumulation rates compared to conventional anticancer drugs. An understanding of the kinetics of drugs contained within a delivery system is necessary to obtain the maximum therapeutic effect. We performed micro-elemental analysis of human pancreatic cancer cells treated with cis-diamminedichloroplatinum(II) (CDDP)-containing polymeric micelles. The results showed that the platinum signals were distributed inside the cellular nuclei and the cytoplasm indicating that CDDP was delivered into the cells. The results from this study will be useful for designing an optimum carrier for platinum-containing anticancer drugs. [ABSTRACT FROM AUTHOR]

We performed magnetic nondestructive evaluation of degradation of nuclear pressure vessel steels due to mechanical loading as a fundamental research. We measured magnetic properties of low alloy steel samples, which were degraded due to tensile and cyclic loads. Magnetic hysteresis curves change depending on the loading conditions. The changes of the coercive force, residual magnetic flux density and permeability were obtained and analyzed in details as a function of the residual strain . Based on the above results, we performed the sensitivity analysis of magnetic property changes for the mechanical load. Finally we concluded that the incremental permeability at H = 0 is the most sensitive index for early degradation due to the mechani cal loads. The feasibility of application of this magnetic technique to the evaluation of degradation due to neutron mechanical and thermal loading is now under consideration. [ABSTRACT FROM AUTHOR]

Abstract: We are currently developing a compact monochromatic X-ray source based on laser–electron Compton scattering for the purpose of medical applications at the University of Tokyo. To realize remarkably compact-, high-intensity- and highly stable system, we adopt an X-band (11.424GHz) multi-bunch linear accelerator (linac) and reliable Q-switch Nd:YAG laser. The injector of the system consists of a 3.5-cell X-band thermionic cathode RF-gun and an alpha magnet. So far, we have continued high-power experiment and beam generation on X-band thermionic cathode RF-gun. However, breakdown was frequently occurred at coaxial structure around the thermionic cathode. In order to resolve the breakdown, we adopt a choke structure around the thermionic cathode. In this paper, the details of Compton scattering X-ray source the University of Tokyo, the experimental results of the X-ray generation, and upgrade of the X-band thermionic cathode RF-gun will be presented. [Copyright &y& Elsevier]

The chemical reactions of hot or room temperature and/or critical water in a time-range of picosecond and sub-picoseconds have been carried out by the 18 MeV S-band linac and a Mg photocathode RF gun with the irradiation of third harmonic Ti: Sapphire laser, at Nuclear Engineering Research Laboratory (NERL), the University of Tokyo. Although this short bunch and 100 fs laser light are enough to perform the experiment of radiation chemistry in the time-range of sub-picoseconds, the total time-resolution become worse by the instability of synchronization between laser and radio frequency of linac. We found that the fluctuation of room temperature causes the instability, particularly the cycle of turning on/off of the air-conditioner. When we decrease the fraction of the room temperature within 0.1 degrees, the timing drift in an hour reaches 600 fs, closed to the timing jitter of 340 fs than previous results. [ABSTRACT FROM AUTHOR]

A photon counting imaging detector system for high energy X-rays is developed for on-site non-destructive testing of thick objects. One-dimensional silicon strip (1 mm pitch) detectors are stacked to form a two-dimensional edge-on module. Each detector is connected to a 48-channel application specific integrated circuit (ASIC). The threshold-triggered events are recorded by a field programmable gate array based counter in each channel. The detector prototype is tested using 950 kV linear accelerator X-rays. The fast CR shaper (300 ns pulse width) of the ASIC makes it possible to deal with the high instant count rate during the 2 μs beam pulse. The preliminary imaging results of several metal and concrete samples are demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: Dielectric laser accelerators (DLAs) have great potential for applications, since they can generate acceleration gradients in the range of GeV/m and produce attosecond electron bunches. We described a novel reverse dual-grating dielectric accelerator structure made up of Silicon which is expected to improve beam confinement, and make fabrication easier. Numerical simulation results show that this structure effectively manipulates the laser field and generates a standing wave in the vacuum channel with a phase velocity synchronized to relativistic particles travelling through the structure. Optimum pillar height and channel width have been determined. All required laser parameters and initial particle energy have been analytically estimated and a suitable laser as an energy source is proposed. Finally, the effect of fabrication error on the acceleration gradient is discussed. [Copyright &y& Elsevier]

In proton beam therapy, changes in the proton range due to lateral heterogeneity may cause serious errors in the dose distribution. In the present study, the pencilbeam redefinition algorithm (PBRA) was applied to proton beam therapy to address the problem of lateral density heterogeneity. In the calculation, the phase-space parameters were characterized for multiple range (i.e. proton energy) bins for given pencil beams. The particles that were included in each pencil beam were transported and redefined periodically until they had stopped. The redefined beams formed a detouring path that was different from that of the non-redefined pencil beams, and the path of each redefined beam was straight. The results calculated by the PBRA were compared with measured proton dose distributions in a heterogeneous slab phantom and an anthropomorphic phantom. Through the beam redefinition process, the PBRA was able to predict the measured proton-detouring effects. Therefore, the PBRA may allow improved calculation accuracy when dealing with lateral heterogeneities in proton therapy applications. [ABSTRACT FROM AUTHOR]

The article presents research studies on the use of positron-sensitive neutron detectors (PSD) that used 6lithium (Li)-based inorganic scientillators as replacement for helium-3 (3H) for measuring neutron scattering. A candidate for an alternative to 3H detector is the Ce:LiCAF fast single crystal neutron scintillator, which is considered low sensitive to gamma rays. Ce:LiCAF scintillator was tested at various research laboratories.

A major goal in cancer research is to develop carriers that can deliver drugs effectively and without side effects. Liposomal and particulate carriers with diameters of ?100 nm have been widely used to improve the distribution and tumour accumulation of cancer drugs, but so far they have only been effective for treating highly permeable tumours. Here, we compare the accumulation and effectiveness of different sizes of long-circulating, drug-loaded polymeric micelles (with diameters of 30, 50, 70 and 100 nm) in both highly and poorly permeable tumours. All the polymer micelles penetrated highly permeable tumours in mice, but only the 30 nm micelles could penetrate poorly permeable pancreatic tumours to achieve an antitumour effect. We also showed that the penetration and efficacy of the larger micelles could be enhanced by using a transforming growth factor-? inhibitor to increase the permeability of the tumours. [ABSTRACT FROM AUTHOR]

Acceleration of plasma electrons by laser wake-filed is the most promising process to produce the next generation of compact accelerators because of its ultrahigh acceleration gradient. To achieve the efficient and stable mono-energetic acceleration of plasma electrons, we investigated the laser-plasma interaction and its correlation to electron acceleration through single shot measurements. We observed a thin laser channel when a mono-energetic spectrum was generated. [ABSTRACT FROM AUTHOR]

Efficient and fast self-injection of plasma electrons into the wake-field acceleration phase can be procured during the transverse wake-wave breaking when the wake-wave is generated by the high-intensity laser pulse propagating in a narrow plasma channel. In the strong focusing regime, when the laser pulse power exceeds critical for the self-focusing power threshold, the injected electron bunch length becomes comparable with the plasma wavelength and the bunch has the femtosecond duration. The total charge of self-injected electrons depends strongly on the laser pulse amplitude. [ABSTRACT FROM AUTHOR]

Density effects on the dynamics of a cavity produced in the wake of an ultraintense (a0=eE/mcω>1) and short (ωplτ/π<1) laser pulse and on the duration of accelerated electrons are studied via two-dimensional particle-in-cell simulation. Formation of a nonbreaking cavity is a crucial part of relativistic self-injection of plasma electrons from the front of a laser pulse and their further acceleration leading to a beam-quality femtosecond bunch. This self-injection appears in a uniform plasma when the group velocity of the pulse becomes smaller than the maximal electron velocity accelerated in the ponderomotive bias, [uppercase_phi_synonym]=mc2a02/2. However with increasing density, this mechanism starts to contend with relativistic wave breaking. Though additional injection due to the relativistic wave breaking increases the total charge of energetic electrons, the duration of the bunch increases to the picosecond range and its energy distribution becomes a Maxwellian. [ABSTRACT FROM AUTHOR]

To analyze the beam characteristics of an RF gun system, we developed a true three-dimensional beam tracking code. All forces imposed on each macrocharged particle are included in this code. Asymmetrical figures of beams and RF fields can be calculated with this code. In this paper, we describe the details of the developed code, and show comparisons between our code and PARMELA. In addition, we compare the results of our code and the experimental results of the SPring-8 S-band single-cell RF gun system. Using this code, significant differences in measured emittance values in horizontal and vertical directions resulted from an oblique incidence of a laser, that is, the difference of arrival time of the laser wavefront on the cathode. [Copyright &y& Elsevier]

In order to study the early events in radiation physics and chemistry, two kinds of new pulse radiolysis systems with higher time resolution based on pump-and-probe method have been developed at the Nuclear Engineering Research Laboratory, the University of Tokyo. The first one, a few picosecond (2 ps at FWHM) electron beam (pump) from an 18 MeV S-band Linac using a laser photocathode RF gun (BNL/KEK/SHI type: GUN IV) was operated with a femtosecond laser pulse (100 fs at FWHM), which also acted as the analyzing light (probe). The synchronization precision between the pump and the probe was 1.7 ps (rms). In a 1.0 cm sample cell, a time resolution of 12 ps was achieved. The second one, a picosecond (4 ps at FWHM) electron pulse from a 35 MeV S-band Linac employing a conventional thermionic gun with a sub-harmonic buncher, was synchronized with the femtosecond laser pulse, with a synchronization jitter of 2.8 ps (rms). A time resolution of 22 ps was obtained with 2 cm cell. This makes it possible to do the pulse radiolysis experiments in the time range from picosecond to sub-microsecond. [Copyright &y& Elsevier]

Measurements of longitudinal bunch length of subpicosecond and picosecond electron beams have been performed by three methods with three radiation sources at the 35 MeV S-band twin liner accelerators at Nuclear Engineering Research Laboratory, University of Tokyo. The methods we adopt are the femtosecond streak camera with a nondispersive reflective optics, the coherent transition radiation (CTR) Michelson interferometer and the 10 ch polychromator that detects the spectrum of CTR and coherent diffraction radiation (CDR). The measurements by the two CTR methods were independently done with the streak camera and their results were consistent with one another. As a result, the reliability of the polychromator for the diagnostics of less than picosecond electron bunch and the usefulness of the diagnostics for the single shot measurement were verified. Furthermore, perfect nondestructive diagnostics for subpicosecond bunches was performed utilizing CDR interferometry. Then the good agreement between CDR interferometry and the streak camera was obtained. [Copyright &y& Elsevier]

Abstract. For a sub-picosecond pump-and-probe-type radiation chemistry work, a new synchronized electron linac and laser system was installed in Nuclear Engineering Research Laboratory (NERL) of University of Tokyo. The new 0.3 TW laser system with a Ti:Sapphire oscillator (795 nm) and amplifiers generate 300 ps pulses at 10 Hz at first. The laser is splitted into the two beams. The first is compressed to 4 ∼ 11 ps so as to drive the RF-Gun and generate a pump-electron-beam. The second is compressed to 100 fs and used for the probe-light. The drive laser is converted to the third harmonics (265 nm, < 250 μJ). Moreover, a new 15 MW klystron was installed for the linac RF system. The RF power is divided to the gun and the accelerating section. Finally the time jitter between the pump-electron-beam and the probe-laser is designed to be 320 fs (rms). By using the new drive laser system, the charge of 7 nC per bunch was observed at the exit of the gun. Improvement of the vacuum in the gun (< 10[sup-9] Torr) is most effective to obtain such a high charge beam. After two and a half years operation of the gun, no degradation of QE has been found for the Cu photo-cathode. [ABSTRACT FROM AUTHOR]

Abstract. Measurements of longitudinal bunch length of picosecond electron bunches have been performed by the femtosecond streak camera, the interferometer and the polychromator and their results were compared with one another. As regards the radiation, transition radiation and diffraction radiation were investigated through the diagnostics. As a result, the fine agreements between them within 200 fs were obtained and the reliability of the interferometer and the polychromator for the diagnostics of less than picosecond electron bunch were verified. Furthermore, nondestructive diagnostics for subpicosecond bunches was performed utilizing coherent diffraction radiation (CDR) interferometry. [ABSTRACT FROM AUTHOR]

Abstract. The generation of an ultrashort relativistic electron bunch from a strong laser-plasma interaction have been studied by particle-in-cell simulations and observed experimentally. The electron beam was generated from the plasma created by focusing 12 TW (tera watt) laser pulse at the edge of helium gas jet expanded into the vacuum from a pulsed supersonic nozzle. The laser pulse duration was 50 fs (femtosecond). In the interaction of 50 fs, 12 TW laser pulse with plasma of density of 5 x 10[sup19]cm[sup-3], the electron generation was observed in the simulation at the very beginning of the interaction region. The plasma electrons were gaining higher energies by the huge longitudinal electric fields (created by the laser pulse) as they move through the rest of the plasma following the laser pulse. In the experiment, the electron beam transverse profile and its total charge have been measured in the forward direction (the same direction of the laser pulse) by using imaging plate and Faraday-cup, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Inverse Compton scattering has been gaining attention as a process for the generation of -ray, since it produces tunable -ray pulses with a small cone angle of radiation. A table-top tunable Compton -ray source would be realized by replacing a radio frequency (rf) linac with a laser wakefield accelerator (LWFA), which is one of the advanced accelerators. An empirical scaling law for the LWFA in the self-injection mode showed that the energy gain was inversely proportional to the plasma density. In order to effectively employ the LWFA as a Compton -ray source, its stability must be improved. For this purpose, we are developing techniques for the injection of initial electrons by a localized wavebreaking at the density ramp of a plasma. The pointing stability and acceleration efficiency of the electron beam were significantly improved by applying an axial magnetic field to the plasma channel. [Copyright &y& Elsevier]