Fluence Conditions Research Articles

Workshop 4 – Experimental Techniques

• This workshop had an attendance of about 15 participants. • On calculation discrepancies of gamma heating and DPA in stainless steel or low carbon steel with high depth inside EPR, a question was raised on how to benchmark TRIPOLI with experimental heating techniques. The experiences with heating measurements at Cadarache with special differential calorimeters were discussed. The importance of these measurements concerning JHR (need to define) was mentioned. • On the implementation of mass spectrometric techniques in measuring stable products in dosimeters, experience in precisely carrying out the measurements was addressed. One of the issues is that the initial sample needs a careful characterization to make sure that transmuted isotopes exceed the level of the starting impurities. In general, stable isotopes can be measured reliably. As an example, the production of helium due to the transmutation of 58Ni to 59Ni (which has a high thermal neutron (n, ) cross section) and 10B has been cited, a phenomenon that is famous within the fusion community due to the high production of helium similar to fusion reactor conditions. Although these transmutations were very well studied, some discrepancies were noticed under very high fluence conditions. An ongoing experiment at Cadarache to address high Helium production in the VVER’s has been cited. • Difficulties related to mixed neutron/gamma field measurements, especially owing to the lack of measured photon spectra, were discussed. New techniques are needed to reliably measure the gamma spectra in reactors separately from the neutron spectra. • On the issue of modeling secondary gammas, the capability of the newest MCNP version in taking this effect into account was addressed. • On the issue of availability of alloyed dosimeters for high temperature applications (Co-V alloys for instance), the participants agreed upon looking out for a manufacturer who could deliver such products. This is a general problem since many useful dosimeters are no longer being produced such as depleted uranium and 237Np fission monitors. The reactor dosimetry community needs to push this issue with potential sources of such materials, such as Oak Ridge National Lab in the US or IRMM, Geel. It is also nearly impossible to obtain 252Cf which is very useful for testing of reactor dosimetry reactions, as cited in recent work by the IAEA in the validation of the IRDFF evaluated cross section library for reactor dosimetry. • On the issue of fluorescence effects in the measurement of the reaction product 93mNb, the filter paper technique, coupled to x-ray measurements, is deemed to provide good results while

Interface effect in pentacene field-effect transistors from high energy proton beam irradiation

We report the effect of irradiation using 10 MeV high energy proton beams on pentacene organic field-effect transistors (OFETs). The electrical characteristics of the pentacene OFETs were measured before and after proton beam irradiation with fluence (dose) conditions of 1012, 1013, and 1014 cm−2. After proton beam irradiation with fluences of 1012 or 1013 cm−2, the threshold voltage of the OFET devices shifted to the positive gate voltage direction with an increase in the current level and mobility. In contrast, for a high proton beam fluence condition of 1014 cm−2, the threshold voltage shifted to the negative gate voltage direction with a decrease in the current level and mobility. It is evident from the electrical characteristics of the pentacene OFETs treated with a self-assembled monolayer that these experimental observations can be attributed to the trapped charges in the dielectric layer and pentacene/SiO2 interface. Our study will enhance the understanding of the influence of high energy particles on organic field-effect transistors.

Low-level red laser therapy alters effects of ultraviolet C radiation on Escherichia coli cells.

Low-level lasers are used at low power densities and doses according to clinical protocols supplied with laser devices or based on professional practice. Although use of these lasers is increasing in many countries, the molecular mechanisms involved in effects of low-level lasers, mainly on DNA, are controversial. In this study, we evaluated the effects of low-level red lasers on survival, filamentation, and morphology of Escherichia colicells that were exposed to ultraviolet C (UVC) radiation. Exponential and stationary wild-type and uvrA-deficientE. coli cells were exposed to a low-level red laser and in sequence to UVC radiation. Bacterial survival was evaluated to determine the laser protection factor (ratio between the number of viable cells after exposure to the red laser and UVC and the number of viable cells after exposure to UVC). Bacterial filaments were counted to obtain the percentage of filamentation. Area-perimeter ratios were calculated for evaluation of cellular morphology. Experiments were carried out in duplicate and the results are reported as the means of three independent assays. Pre-exposure to a red laser protected wild-type and uvrA-deficient E. coli cells against the lethal effect of UVC radiation, and increased the percentage of filamentation and the area-perimeter ratio, depending on UVC fluence and physiological conditions in the cells. Therapeutic, low-level red laser radiation can induce DNA lesions at a sub-lethal level. Consequences to cells and tissues should be considered when clinical protocols based on this laser are carried out.

Analysis of epidermal/dermal temperature changes according to the different cryogen spray cooling conditions.

This study measured epidermal and dermal temperatures under different cryogen spray cooling (CSC) conditions to determine the optimum cooling conditions for skin rejuvenation. For this purpose, CSC conditions were applied before a laser transmission for varying spurt times of 50, 150, and 200 ms with delay times of 150 and 200 ms. A long-pulsed 1,064 nm Nd:YAG laser irradiated the skin surface of a pig with a condition of fluence of 26 J/cm2 and a spot diameter of 8 mm. The pulse duration was set to 30 ms during all experiments. This study found that all employed CSC conditions significantly decreased internal-external skin temperatures. Moreover, skin temperatures were influenced more by variations in spurt time of CSC compared with the delay times. Based on these experimental results, two spurt times were selected as the optimum CSC conditions for skin rejuvenation: 50 ms with delay time of 150 and 200 ms and 150 ms with a delay time of 150 and 200 ms.

Analysis of epidermal/dermal temperature changes according to the different cryogen spray cooling conditions.

This study measured epidermal and dermal temperatures under different cryogen spray cooling (CSC) conditions to determine the optimum cooling conditions for skin rejuvenation. For this purpose, CSC conditions were applied before a laser transmission for varying spurt times of 50, 150, and 200 ms with delay times of 150 and 200 ms. A long-pulsed 1,064 nm Nd:YAG laser irradiated the skin surface of a pig with a condition of fluence of 26 J/cm2 and a spot diameter of 8 mm. The pulse duration was set to 30 ms during all experiments. This study found that all employed CSC conditions significantly decreased internal-external skin temperatures. Moreover, skin temperatures were influenced more by variations in spurt time of CSC compared with the delay times. Based on these experimental results, two spurt times were selected as the optimum CSC conditions for skin rejuvenation: 50 ms with delay time of 150 and 200 ms and 150 ms with a delay time of 150 and 200 ms.

Pulsed laser ablation of Germanium under vacuum and hydrogen environments at various fluences

Laser fluence and ambient environment play a significant role for the formation and development of the micro/nano-structures on the laser irradiated targets. Single crystal (100) Germanium (Ge) has been ablated under two environments of vacuum (10−3Torr) and hydrogen (100Torr) at various fluences ranging from 4.5Jcm−2 to 6Jcm−2. For this purpose KrF Excimer laser with wavelength of 248nm, pulse duration of 18ns and repetition rate of 20Hz has been employed. Surface morphology has been observed by Scanning Electron Microscope (SEM). Whereas, structural modification of irradiated targets was explored by Fourier Transform Infrared Spectroscopy (FTIR) and Raman spectroscopy. Electrical conductivity of the irradiated Ge is measured by four probe method. SEM analysis exhibits the formation of laser-induced periodic surface structures (LIPSS), cones and micro-bumps in both ambient environments (vacuum and hydrogen). The formation as well as development of these structures is strongly dependent upon the laser fluence and environmental conditions. The periodicity of LIPSS or ripples varies from 38μm to 60μm in case of vacuum whereas in case of hydrogen environment, the periodicity varies from 20μm to 45μm. The difference in number of ripples and periodicity as well as in shape and size of cones and bumps in vacuum and hydrogen is explained on the basis of confinement and shielding effect of plasma. FTIR spectroscopy reveals that no new bands are formed for laser ablated Ge under vacuum, whereas CH stretching vibration band is formed for two moderate fluences (5Jcm−2 and 5.5Jcm−2) in case of ablation in hydrogen. Raman spectroscopy shows that no new bands are formed in case of ablation in both environments; however a slight Raman shift is observed which is attributed to laser-induced stresses. The electrical conductivity of the irradiated Ge increases with increasing fluence and is also dependent upon the environment as well as grown structures.

Gold-based nucleation in implanted silica studied by x-ray absorption spectroscopy

Ion implantation into silica is used to produce Au subnanometer metal clusters, whose size can be finely tuned from few-atom to about 1nm by acting on the implantation fluence and post-implantation annealing conditions. The structural analyses rely basically on x-ray absorption spectroscopy that can investigate the metal site independently from long range order considerations. Besides the signal from the intermetallic coordination, a correlation of the dopant with oxygen atoms from the matrix is found, especially upon implantation at low fluence. The possibility of promoting the formation of subnanometer AuAg clusters by sequential ion implantation is also explored, with promising preliminary results. The control of the metal cluster nucleation, composition and first steps of growth have relevant consequences on the interpretation of the optical emission spectra of these molecule-like clusters and on their sensitizing action towards nearby rare-earth ions embedded in the same matrix.

Elastic properties of sub-stoichiometric nitrogen ion implanted silicon

Elastic properties of sub-stoichiometric nitrogen implanted silicon were measured with nanometer-resolution using contact resonance atomic force microscopy (CR-AFM) as function of ion fluence and post-annealing conditions. The determined range of indentation moduli was between 100 and 180GPa depending on the annealing duration and nitrogen content. The high indentation moduli can be explained by formation of Si–N bonds, as verified by X-ray photoelectron spectroscopy.

Characterizing low fluence thresholds for in vitro photodynamic therapy.

The translation of photodynamic therapy (PDT) to the clinic has mostly been limited to superficial diseases where traditional light delivery is noninvasive. To overcome this limitation, a variety of mechanisms have been suggested to noninvasively deliver light to deep tissues. This work explores the minimum amount of light required by these methods to produce a meaningful PDT effect in the in vitro setting under representative low fluence and wavelength conditions. This threshold was found to be around 192 mJ/cm(2) using the clinically approved photosensitizer aminolevulinic acid and 12 mJ/cm(2) for the more efficient, second generation photosensitizer TPPS2a.

Experimental characterization of the excitation state of picosecond laser-induced Tungsten plasmas

In order to quantitatively determine the retention of light atoms by plasma facing components (mainly tungsten) used in fusion reactors, the Laser-Induced Breakdown Spectroscopy (LIBS) technique can be used. The nanosecond laser regimes classically used for LIBS present major limitations mainly due to the conditions of the laser-matter interaction process itself and cannot be used in the present context. Picosecond laser pulses are more appropriate. To validate the diagnostic based on picosecond laser pulses, preliminary characterizations of the produced plasmas have to be performed. Some related results are reported in the present communication. The study is focused on (1) the ablation of tungsten under two laser (low and high) fluence conditions and (2) the excitation equilibrium of the plasma from the nanosecond to microsecond time scales.

Dynamics of charge clouds ejected from laser-induced warm dense gold nanofilms.

We report a systematic study of the ejected charge dynamics surrounding laser-produced 30-nm warm dense gold films using single-shot femtosecond electron shadow imaging and deflectometry. The results reveal a two-step dynamical process of the ejected electrons under high pump fluence conditions: an initial emission and accumulation of a large amount of electrons near the pumped surface region, followed by the formation of hemispherical clouds of electrons on both sides of the film, which escape into the vacuum at a nearly isotropic and constant velocity with an unusually high kinetic energy of more than 300 eV. We also developed a model of the escaping charge distribution that not only reproduces the main features of the observed charge expansion dynamics but also allows us to extract the number of ejected electrons remaining in the cloud.

Advances in multi-megawatt lower hybrid technology in support of steady-state tokamak operation

It has been demonstrated that lower hybrid current drive (LHCD) systems play a crucial role for steady-state tokamak operation, owing to their high current drive (CD) efficiency and hence their capability to reduce flux consumption. This paper describes the extensive technology programmes developed for the Tore Supra (France) and the KSTAR (Korea) tokamaks in order to bring continuous wave (CW) LHCD systems into operation. The Tore Supra LHCD generator at 3.7 GHz is fully CW compatible, with RF power PRF = 9.2 MW available at the generator to feed two actively water-cooled launchers. On Tore Supra, the most recent and novel passive active multijunction (PAM) launcher has sustained 2.7 MW (corresponding to its design value of 25 MW m−2 at the launcher mouth) for a 78 s flat-top discharge, with low reflected power even at large plasma-launcher gaps. The fully active multijunction (FAM) launcher has reached 3.8 MW of coupled power (24 MW m−2 at the launcher mouth) with the new TH2103C klystrons. By combining both the PAM and FAM launchers, 950 MJ of energy, using 5.2 MW of LHCD and 1 MW of ICRH (ion cyclotron resonance heating), was injected for 160 s in 2011. The 3.7 GHz CW LHCD system will be a key element within the W (for tungsten) environment in steady-state Tokamak (WEST) project, where the aim is to test ITER technologies for high heat flux components in relevant heat flux density and particle fluence conditions. On KSTAR, a 2 MW LHCD system operating at 5 GHz is under development. Recently the 5 GHz prototype klystron has reached 500 kW/600 s on a matched load, and studies are ongoing to design a PAM launcher. In addition to the studies of technology, a combination of ray-tracing and Fokker–Planck calculations have been performed to evaluate the driven current and the power deposition due to LH waves, and to optimize the N∥ spectrum for the future launcher design. Furthermore, an LHCD system at 5 GHz is being considered for a future upgrade of the ITER Heating and Current Drive systems, with a power capability of 20 MW coupled to the plasma using a PAM launcher. An R&D programme is being conducted at CEA/IRFM to develop a BeO vacuum window which is a safety critical component of the transmission line. In addition, a mock-up of a TE10–TE30 mode converter at 5 GHz, designed for a rectangular transmission line, has been manufactured and successfully tested on Tore Supra at low RF power.

Fabrication of silicon molds with multi-level, non-planar, micro- and nano-scale features

A method for single-step fabrication of arbitrary, complex, three-dimensional (3D) silicon structures from the nano- to millimeter-scale at multiple levels on non-planar, curved, or domed surfaces is reported. The fabrication is based on focused or masked ion beam irradiation of p-type silicon followed by electrochemical anodization. The process allows fabrication of a wide range of surface features at multiple heights and with arbitrary orientations by varying the irradiated feature width, ion type, energy fluence, and subsequent anodization conditions. The technology has achieved depth resolution of 10 nm as step heights and is capable of creating lateral features down to 7 nm at high aspect ratios of up to 40, with surface roughness down to 1 nm scaled up to full wafer areas. The single-step ability has seamlessly interfaced a network of complex, integrated micro- to nano-structures in 3D orientations with no alignment required. The final template has been converted to a master copy for nano-imprinting lithography of 3D fluidic structures and optical components.

Irradiation Effects of High-Energy Proton Beams on MoS2Field Effect Transistors

We investigated the effect of irradiation on molybdenum disulfide (MoS2) field effect transistors with 10 MeV high-energy proton beams. The electrical characteristics of the devices were measured before and after proton irradiation with fluence conditions of 10(12), 10(13), and 10(14) cm(-2). For a low proton beam fluence condition of 10(12) cm(-2), the electrical properties of the devices were nearly unchanged in response to proton irradiation. In contrast, for proton beam fluence conditions of 10(13) or 10(14) cm(-2), the current level and conductance of the devices significantly decreased following proton irradiation. The electrical changes originated from proton-irradiation-induced traps, including positive oxide-charge traps in the SiO2 layer and trap states at the interface between the MoS2 channel and the SiO2 layer. Our study will enhance the understanding of the influence of high-energy particles on MoS2-based nanoelectronic devices.

Ablation behaviour of allanites during U–Th–Pb dating using a quadrupole ICP-MS coupled to a 193 nm excimer laser

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been employed for U–Th–Pb geochronology of allanite, using various analytical parameters. Opinions diverge on analytical protocols and data reduction, and particularly, on the possibility of using non-matrix-matched standards and samples to obtain accurate and precise ages. In this study, ablation experiments were carried out in spot mode using an ArF 193nm excimer laser coupled to a quadrupole ICP-MS, in order to characterise the ablation behaviour of allanite under various fluence (4, 7.8 and 12J/cm2) and ablation rate conditions (4, 8 and 12Hz). The U–Th–Pb data were compared to the Plešovice zircon (337.13±0.37Ma) in order to investigate the effects of the different matrices. The ratio-of-the-mean intensities method was used for data reduction. Analyses in spot mode at low frequency and fluence provide accurate and precise allanite 206Pb/238U and 208Pb/232Th ages, using a matrix-matched external standard. Matrix effects between allanites with different ages (30.1 to 417Ma), common 208Pb (0.5–33%) and 206Pb (5.8–90%) proportions, and FeOtotal (11.5–16.1%) and REE+Th (0.52–0.90apfu) compositions do not affect the age accuracy. The difference of mass bias correction coefficients between allanites and zircon shows evidence of matrix effects, which are often responsible for systematic errors on ages. Matrix-matched standardisation with an allanite standard is required for precise U–Th–Pb allanite ages. Even though laser-induced elemental fractionation can be minimised for non-matrix-matched standards and samples, other sources of matrix effects still affect age accuracy and precision.

ANALYSIS OF THE THERAPEUTIC EFFECTS ON SKIN REJUVENATION FOR THE DIFFERENT TREATMENT CONDITIONS OF 1064 nmNd:YAG LASER: SIMULATION AND PHANTOM STUDY

In this study, we analyzed internal and external skin temperatures as well as penetration depths for the different treatment conditions regarding the 1064 nm Nd :YAG laser to find the optimum treatment condition for skin rejuvenation. We transmitted the laser into a skin mimicking phantom with laser fluence conditions of 26, 30 and 36 J/cm2, and spot diameter conditions of 8 and 10 mm. We also selected the pulse duration as 30 ms, and measured internal–external skin temperatures and penetration depths. To examine the distribution of internal–external skin temperatures, we performed a heat transfer analysis based on the finite element method. Skin layers were designed as three-dimensional models to predict skin temperatures more accurately. We employed the same laser conditions of fluence and spot diameter while performing actual and simulation analyses. Consequently, we found that laser conditions for a spot diameter of 8 mm with a fluence of 36 J/cm2 and a spot diameter of 10 mm with a fluence of 26 and 30 J/cm2 demonstrate the greatest effectiveness toward skin rejuvenation. Moreover, the penetration depths and the range of thermal distribution increased as the fluence and spot diameter increased. In particular, the spot diameter influenced the therapeutic effects more seriously than the fluence.

On the infrared fluorescence of monolayer 13CO:NaCl(100)

Computations are presented to describe and analyze the high levels of infrared laser induced vibrational excitation of a monolayer of absorbed (13)CO on a NaCl(100) surface. Extending the vibrational site-to-site surface hopping technique of Corcelli and Tully, kinetic Monte Carlo computations are used to incorporate single-quantum vibrational pooling and depooling of the (13)CO by phonon excitation to allow up to the n = 45 vibrational state under different lasing conditions. Previously unpredicted pooling peaks at n > 16 are calculated and, under the highest fluence conditions, pooling up to the n = 32 state is found in the calculation. These results lead to the prediction of a secondary local maximum in the dispersed fluorescence of monolayer CO:NaCl(100) under sufficiently high fluence excitation conditions. At times on the order of ms, we recover similar behavior for both high and low fluence results. The calculations confirm that, for situations where the Debye frequency limited n domain restriction approximately holds, the vibrational state population deviates from a Boltzmann population linearly in n, a result that we have derived earlier theoretically for a domain of n restricted to one-phonon transfers. This theoretically understood term, linear in n, dominates the Boltzmann term and is responsible for the inversion of the population of vibrational states, Pn.

Reactor pressure vessel integrity assessment by probabilistic fracture mechanics – A plant specific analysis

The probabilistic fracture mechanics method is widely adopted in nuclear power plant industry, especially for the structural integrity assessment of reactor pressure vessels. In this work, the plant specific analyses of Taiwan's boiling water reactors, BWR/4 and BWR/6, under the design transients were performed by the FAVOR (Fracture Analysis of Vessel – Oak Ridge) code. The difference of reactor pressure vessel geometry, alloying elements, neutron fluence, and loading conditions were taken into account in the probabilistic fracture mechanics analyses. The failure probabilities of the axial welds at 64 effective full-power year (EFPY) for the analyzed BWR/4 and BWR/6 are less than 2.8 × 10−10/year and 1.5 × 10−4/year, respectively. Furthermore, the circumferential welds present much smaller failure probabilities. The results of this work are useful for the subsequent aging management of the operating reactor pressure vessels.

A thousand-fold enhancement of photoluminescence in porous silicon using ion irradiation

A large increase in the porosity of highly doped p-type silicon is observed at the end-of-range depth of high-energy ions after subsequent electrochemical anodization. This occurs under certain conditions of irradiation geometry and fluence, owing to the dual effects of increased wafer resistivity and a locally increased current density during anodization. This results in the creation of highly porous, sub-surface zones which emit photoluminescence with an intensity of more than three orders of magnitude greater than the surrounding mesoporous silicon, comparable to that produced by microporous silicon. This provides means of selectively enhancing and patterning the photoluminescence emission from micron-sized areas of porous silicon over a wide range of intensity.

Laser-Induced Silver Nanojoining of Gold Nanoparticles

Gold nanoparticles have been silver-joined to fabricate nanowires by irradiating gold nanospheres of 25 nm in diameter and silver nanospheres of 8 nm in diameter held together on a carbon-coated copper grid with a 30 ps laser pulse of 532 nm for 20 min at a fluence of 3.0 mJ/cm2. Laser-induced nanojoining of silver nanoparticles as well as that of gold nanoparticles has also been carried out by varying the wavelength and fluence of irradiation laser pulses. Irradiation at an optimum condition of laser fluence is essential for the proper silver nanojoining of gold nanospheres to produce gold@silver core-shell composite nanowires. The excitation of the surface plasmon resonances of the base-metallic gold nanospheres rather than the filler-metallic silver nanospheres paves the way for the silver nanojoining of gold nanoparticles.