Study on the optimal incident proton energy of ^(7)Li(p,n)^(7)Be neutron source for boron neutron capture therapy

Boron neutron capture therapy(BNCT)is recognized as a precise binary targeted radiotherapy technique that effectively eliminates tumors through the^(10)B(n,α)^(7)Li nuclear reaction.Among various neutron sources,accelerator-based sources have emerged as particularly promising for BNCT applications.The^(7)Li(p,n)^(7)Be reaction is highly regarded as a potential neutron source for BNCT,owing to its low threshold energy for the reaction,significant neutron yield,appropriate average neutron energy,and additional benefits.This study utilized Monte Carlo simulations to model the physical interactions within a lithium target subjected to proton bombardment,including neutron moderation by an MgF_(2)moderator and subsequent BNCT dose analysis using a Snyder head phantom.The study focused on calculating the yields of epithermal neutrons for various incident proton energies,finding an optimal energy at 2.7 MeV.Furthermore,the Snyder head phantom was employed in dose simulations to validate the effectiveness of this specific incident energy when utilizing a^(7)Li(p,n)^(7)Be neutron source for BNCT purposes.

Evaluation of the fraction of delayed photoneutrons for TMSR-SF1

The 10 MW_(th) solid-fueled thorium molten salt reactor(TMSR-SF1) is a FLi Be salt-cooled pebble bed reactor to be deployed in 5–10 years, designed by the TMSR group. Due to a large amount of beryllium in the core, the photoneutrons are produced via(γ , n) reactions.Some of them are generated a long time after the fission event and therefore are considered as delayed neutrons. In this paper, we redefine the effective delayed neutrons into two fractions: the delayed fission neutron fraction and the delayed photoneutron fraction. With some reasonable assumptions, the inner product method and the k-ratio method are adopted for studying the effective delayed photoneutron fraction. In the k-ratio method, the Monte Carlo code MCNP6 is used to evaluate the effective photoneutron fraction as the ratio between the multiplication factors with and without contribution of the delayed neutrons and photoneutrons. In the inner product method, with the Monte Carlo and deterministic codes together, we use the adjoint neutron flux as a weighting function for the neutrons and photoneutrons generated in the core. Results of the two methods agree well with each other, but the k-ratio method requires much more computing time for the same precision.

Study on neutronics design of ordered-pebble-bed fluoride-salt- cooled high-temperature experimental reactor

This paper presents a neutronics design of a 10 MW ordered-pebble-bed fluoride-salt-cooled high-temperature experimental reactor. Through delicate layout, a core with ordered arranged pebble bed can be formed,which can keep core stability and meet the space requirements for thermal hydraulics and neutronics measurements.Overall, objectives of the core include inherent safety and sufficient excess reactivity providing 120 effective full power days for experiments. Considering the requirements above, the reactive control system is designed to consist of 16 control rods distributed in the graphite reflector. Combining the large control rods worth about 18000–20000 pcm, molten salt drain supplementary means(-6980 to -3651 pcm) and negative temperature coefficient(-6.32 to -3.80 pcm/K) feedback of the whole core, the reactor can realize sufficient shutdown margin and safety under steady state. Besides, some main physical properties, such as reactivity control, neutron spectrum and flux, power density distribution, and reactivity coefficient,have been calculated and analyzed in this study. In addition, some special problems in molten salt coolant are also considered, including ~6Li depletion and tritium production.

Neutronics analysis for MSR cell with different fuel salt channel geometries

The neutronic properties of molten salt reactors(MSRs)differ from those of traditional solid fuel reactors owing to their nuclear fuel particularity.Based on the Monte-Carlo N particle transport code,the effects of the size and shape of the fuel salt channel on the neutron physics of an MSR cell are investigated systematically in this study.The results show that the infinite multiplication factor(k?)first increases and then decreases with the change in the graphite cell size under certain fuel volume fraction(FVF)conditions.For the same FVF and average chord length,when the average chord length is relatively small,the k?values for different fuel salt channel shapes agree well.When the average chord length is relatively large,the k?values for different fuel salt channel shapes differ significantly.In addition,some examples of practical applications of this study are presented,including cell selection for the core and thermal expansion displacement analysis of the cell.

Research on the effect of the heavy nuclei amount on the temperature reactivity coefficient in a small modular molten salt reactor

Small modular thorium-based graphite-moderated molten salt reactors (smTMSRs), which combine the advantages of small modular reactors and molten salt reactors, are regarded as a wise development path to speed deployment time. In a smTMSR, low enriched uranium and thorium fuels are used in once-through mode, which makes a marked difference in their neutronic properties compared with the case when a conventional molten salt breeder reactor is used. This study investigated the temperature reactivity coefficient (TRC) in a smTMSR, which is mainly affected by the molten salt volume fraction (VF) and the heavy nuclei concentration in the fuel salt (HN). The fourfactor formula method and the reaction rate method were used to indicate the reasons for the TRC change, including the fuel density effect, the fuel Doppler effect, and the graphite thermal scattering effect. The results indicate that only the fuel density has a positive effect on the TRC in the undermoderated region. Thermal scattering from both salt and graphite has a significant negative influence on the TRC in the overmoderated region. The maximal effective multiplication factor, which shows the highest fuel utilization, is located at 10% VF and 12 mol% HN and is still located in the negative TRC region. In addition, on increasing the heavy nuclei amount from 2 mol% HN to 12 mol% HN (VF = 10%), the total TRC undergoes an obvious change from - 11 to - 3 pcm/K, which implies that the change in the HN caused by the fuel feed online should be small to avoid potential trouble in the reactivity control scheme.

Development of a dynamics model for graphite-moderated channel-type molten salt reactor

A molten salt reactor(MSR) is one of the six advanced reactor concepts selected by the generation Ⅳ international forum because of its advantages of inherent safety, and the promising capabilities of Th-U breeding and transuranics transmutation. A dynamics model for the channel-type MSR is developed in this work based on a three-dimensional thermal–hydraulic model(3DTH) and a point reactor model. The 3DTH couples a three-dimensional heat conduction model and a one-dimensional single-phase flow model that can accurately consider the heat conduction between different assemblies. The 3DTH is validated by the RELAP5 code in terms of the temperature and mass flow distribution calculation. A point reactor model considering the drift of delayed neutron precursors is adopted in the dynamics model. To verify the dynamics model, three experiments from the molten salt reactor experiment are simulated. The agreement of the experimental data and simulation results was excellent.With the aid of this model, the unprotected step reactivity addition and unprotected loss of flow of the 2 MWt experimental MSR are modeled, and the reactor power and temperature evolution are analyzed.

Application of global variance reduction method to calculate a high-resolution fast neutron flux distribution for TMSR-SF1

The solid fuel thorium molten salt reactor(TMSR-SF1) is a 10-MWth fluoride-cooled pebble bed reactor. As a new reactor concept, one of the major limiting factors to reactor lifetime is radiation-induced material damage. The fast neutron flux(E > 0.1 MeV) can be used to assess possible radiation damage. Hence, a method for calculating high-resolution fast neutron flux distribution of the full-scale TMSR-SF1 reactor is required. In this study,a two-step subsection approach based on MCNP5 involving a global variance reduction method, referred to as forward-weighted consistent adjoint-driven importance sampling, was implemented to provide fast neutron flux distribution throughout the TMSR-SF1 facility. In addition,instead of using the general source specification cards, the user-provided SOURCE subroutine in MCNP5 source code was employed to implement a source biasing technique specialized for TMSR-SF1. In contrast to the one-step analog approach, the two-step subsection approach eliminates zero-scored mesh tally cells and obtains tally results with extremely uniform and low relative uncertainties.Furthermore, the maximum fast neutron fluxes of the main components in TMSR-SF1 are provided, which can be used for radiation damage assessment of the structural materials.

Burnup optimization of once-through molten salt reactors using enriched uranium and thorium

The advantages of once-through molten salt reactors include readily available fuel,low nuclear proliferation risk,and low technical difficulty.It is potentially the most easily commercialized fuel cycle mode for molten salt reactors.However,there are some problems in the parameter selection of once-through molten salt reactors,and the relevant burnup optimization work requires further analysis.This study examined once-through graphitemoderated molten salt reactor using enriched uranium and thorium.The fuel volume fraction(VF),initial heavy nuclei concentration(HN_(0)),feeding uranium enrichment(E_(FU)),volume of the reactor core,and fuel type were changed to obtain the optimal conditions for burnup.We found an optimal region for VF and HN_(0) in each scheme,and the location and size of the optimal region changed with the degree of E_(FU),core volume,and fuel type.The recommended core schemes provide a reference for the core design of a once-through molten salt reactor.

Changes in corneal curvature and aberrations after cataract surgery

Background:Surgically induced astigmatism(SIA)and corneal high-order aberrations(HOAs)are the two main causes of poor visual quality after cataract surgery.Changes in the parameters of corneal HOAs after cataract surgery and their effects on and relationships with changes in corneal curvature have not yet been reported.This study aimed to explore changes in anterior,posterior and total corneal curvature,astigmatism and HOAs after microincision cataract surgery.Methods:Sixty-one age-related cataract patients(61 eyes)were included in this prospective study.The total,anterior and posterior corneal astigmatism and corneal HOAs were analyzed by anterior segment optical coherence tomography(AS-OCT)and iTrace before,one day,one week and three months after 2.2 mm temporal microincision coaxial phacoemulsification to evaluate the changes in anterior,posterior and total corneal curvature,astigmatism and corneal HOAs.Results:The mean J0 and J45 values of anterior,posterior and total corneal curvature obtained by ASOCT showed no statistically significant difference between preoperatively and any postoperative followup.SIA occurred on the anterior,posterior and total corneal surfaces and showed no statistically significant difference at any postoperative follow-up.No significant changes in 3rd-order oblique trefoil,vertical coma or 4th-order spherical aberrations were observed after surgery except for a significant increase in horizontal coma at postoperative day 1(POD1).Conclusions:There were no significant changes in corneal curvature after 2.2 mm temporal microincision coaxial phacoemulsification,and the corneal HOAs were not changed significantly except for the increase in horizontal coma at POD1,which may be one of the main reasons of poor visual quality at POD1 in some cataract patients who have good uncorrected or corrected distance vision.

Changes in crystalline lens parameters during accommodation evaluated using swept source anterior segment optical coherence tomography

Backgrounds:To assess changes in anterior segment biometry during accommodation using a swept source anterior segment optical coherence tomography(SS-OCT).Methods:One hundred-forty participants were consecutively recruited in the current study.Each participant underwent SS-OCT scanning at 0 and−3 diopter(D)accommodative stress after refractive compensation,and ocular parameters including anterior chamber depth(ACD),anterior and posterior lens curvature,lens thickness(LT)and lens diameter were recorded.Anterior segment length(ASL)was defined as ACD plus LT.Lens central point(LCP)was defined as ACD plus half of the LT.The accommodative response was calculated as changes in total optical power during accommodation.Results:Compared to non-accommodative status,ACD(2.952±0.402 vs.2.904±0.382 mm,P<0.001),anterior(10.771±1.801 vs.10.086±1.571 mm,P<0.001)and posterior lens curvature(5.894±0.435 vs.5.767±0.420 mm,P<0.001),lens diameter(9.829±0.338 vs.9.695±0.358 mm,P<0.001)and LCP(4.925±0.274 vs.4.900±0.259 mm,P=0.010)tended to decreased and LT thickened(9.829±0.338 vs.9.695±0.358 mm,P<0.001),while ASL(6.903±0.279 vs.6.898±0.268 mm,P=0.568)did not change significantly during accommodation.Younger age(β=0.029,95%CI:0.020 to 0.038,P<0.001)and larger anterior lens curvature(β=−0.071,95%CI:−0.138 to−0.003,P=0.040)were associated with accommodation induced greater steeping amplitude of anterior lens curvature.The optical eye power at 0 and−3 D accommodative stress was 62.486±2.284 and 63.274±2.290 D,respectively(P<0.001).Age was an independent factor of accommodative response(β=−0.027,95%CI:−0.038 to−0.016,P<0.001).Conclusions:During−3 D accommodative stress,the anterior and posterior lens curvature steepened,followed by thickened LT,fronted LCP and shallowed ACD.The accommodative response of−3 D stimulus is age-dependent.

Review of key technologies of climbing robots

In recent years,the robot industry has developed rapidly,and researchers and enterprises have begun to pay more attention to this industry.People are barely familiar with climbing robots,a kind of special robot.However,from their practical value and scientific research value,climbing robots should studied further.This paper analyzes and summarizes the key technologies of climbing robots,introduces various kinds of climbing robots,and examines their advantages and disadvantages to provide a reference for future researchers.Many countries have studied climbing robots and made some achievements.However,due to the complexity of climbing robots,their climbing efficiency and accuracy need to be further improved.The new structure can improve the climbing efficiency.This paper analyzes climbing robots such as mechanical arms,magnetic attraction,and claws.Optimization methods and path planning can improve the accuracy of work.This paper involves some control methods,including complex intelligent control methods such as behavior-based robot control.This paper also investigates various kinematic planning methods and expounds and summarizes various path planning algorithms,including machine learning and reinforcement learning of artificial intelligence,ant colony algorithm,and other algorithms.Therefore,by analyzing the research status of climbing robots at home and abroad,this paper summarizes three important aspects of climbing robots,namely,structural design,control methods,and climbing strategies,elaborates on the achievements and existing problems of these key technologies,and looks forward to the future development trend and research direction of climbing robots.

Generation of femtosecond dual pulses by a transverse standing wave in a volume holographic grating

Based on Kogelnik’s coupled-wave theory, it is found that when a femtosecond pulse is incident on a transmitted volume holographic grating, two transverse standing waves along the grating vector direction will be generated inside the volume holographic grating(VHG). Due to field localization of two standing waves, they have two different velocities along the propagation depth. On the output plane of the VHG, femtosecond dual pulses are generated in both the diffracted and transmitted directions. Results show that the pulse interval is determined by the refractive index modulation and thickness of the grating, while the waveform of the dual pulses is independent of the grating parameters.

Effect of spatio-temporal coupling on ultrafast laser direct writing in glass

Spatio-temporal coupling characteristics of ultrafast laser pulses are quantitatively tailored. An asymmetric microstructure is induced in the focal volume when the laser scans perpendicularly to the direction of the spatial chirp in fused silica. The tilted direction reverses when adding a Dove prism into the light path. The sign of the pulse front tilt can be turned from positive to negative by changing the group delay dispersion by steps. We reveal that the tilted direction of a microstructure depends on spatial chirp, and the interplay between spatiotemporal chirp leads to the change of tilted angles.