用于硼中子俘获治疗的超热中子束理论设计

目的 设计用于硼中子俘获治疗(BNCT)的超热中子束理论方案。方法 基于清华大学试验核反应堆,以其1号孔道为材料布放孔道,设计了由慢化材料、热中子吸收材料、γ屏蔽材料组成,但材料布放位置具有差异的5种理论方案;利用蒙特卡罗(MC)模拟方法,分别计算5种方案束出口处的中子注量率、剂量率及γ剂量率值,通过与BNCT技术指标对比,从5种方案中选择一种合适的方案。结果 得到了一个符合BNCT各项技术指标的超热中子束理论方案,其慢化材料厚度为53.5 cm、热中子吸收材料厚度为2 mm、γ屏蔽材料厚度为9 cm。结论 本研究给出的超热中子束理论方案为基于反应堆实现BNCT提供一定的理论参考。     

Bone structure investigation using X-ray and neutron radiography techniques.

In this paper we report a study of the periodic variation of bone tissue humidity immediately after death using both neutron and X-ray radiography techniques. After death, bone tissue experiences sequential change over time. This change consists of organic and inorganic phase variations of the bone structure, as well as gradual reduction of the bone's water content. These variations are investigated by periodically imaging dead bone using X-ray and neutron radiography. Chemical separation techniques such as calcification and decalcification were used to separate the organic and inorganic phases of the bone. Comparison between X-ray and neutron radiographs of bone following phase separation can be potentially used to investigate the bone disease or to determine a cause of death. In our experiments, we use adult rat femur bones, and the interpretations of these results are presented based on our understanding of bone structure and images produced by neutron and X-ray photon interactions.     

中子剂量测量及估算方法

随着科技的发展,中子在许多行业得到越来越广泛的应用,在医疗上应用最广泛的是硼中子俘获治疗.但在使用中子辐射的过程中,操作人员可能会受到中子辐射,因此中子剂量的测量和估算问题也就变得重要起来.目前,国内关于中子剂量的研究在有些方面还不是很深人,因此对中子剂量的测量和估算方法进行了归纳和阐述.     

Image enhancement using MCNP5 code and MATLAB in neutron radiography

This work presents a method that can be used to enhance the neutron radiography (NR) image for objects with high scattering materials like hydrogen, carbon and other light materials. This method used Monte Carlo code, MCNP5, to simulate the NR process and get the flux distribution for each pixel of the image and determines the scattered neutron distribution that caused image blur, and then uses MATLAB to subtract this scattered neutron distribution from the initial image to improve its quality.This work was performed before the commissioning of digital NR system in Jan. 2013. The MATLAB enhancement method is quite a good technique in the case of static based film neutron radiography, while in neutron imaging (NI) technique, image enhancement and quantitative measurement were efficient by using ImageJ software. The enhanced image quality and quantitative measurements were presented in this work.     

Unfolding the neutron spectrum of a NE213 scintillator using artificial neural networks

Artificial neural networks technology has been applied to unfold the neutron spectra from the pulse height distribution measured with NE213 liquid scintillator. Here, both the single and multi-layer perceptron neural network models have been implemented to unfold the neutron spectrum from an Am–Be neutron source. The activation function and the connectivity of the neurons have been investigated and the results have been analyzed in terms of the network's performance. The simulation results show that the neural network that utilizes the Satlins transfer function has the best performance. In addition, omitting the bias connection of the neurons improve the performance of the network. Also, the SCINFUL code is used for generating the response functions in the training phase of the process. Finally, the results of the neural network simulation have been compared with those of the FORIST unfolding code for both ²⁴¹Am–Be and ²⁵²Cf neutron sources. The results of neural network are in good agreement with FORIST code.     

Determination of neutron absorbed doses in lithium aluminates.

Lithium-based ceramics have been proposed as tritium breeders for fusion reactors. The lithium aluminate (gamma phase) seems to be thermally and structurally stable, the damages produced by neutron irradiation depend on the absorbed dose. A method based on the measurement of neutron activation of foils through neutron capture has been developed to obtain the neutron absorbed dose in lithium aluminates irradiated in the thermal column facility and in the fixed irradiation system of a Triga Mark III Nuclear Reactor.     

Towards a laser neutron driver

During the last few years, important experimental investigations have been made concerning the possibility of induced nuclear fission of high-Z elements by electromagnetic interaction (photofission, electron fission, neutron fission). Fast ions, neutrons and fission fragments from such interactions can be used to pump a laser medium, to produce energy from the ²³²Th–²³³U nuclear fission cycle. The main aim of the present work is to study a three-step process, in a relatively new experimental scheme, in order to improve the number of both neutrons and fast ions. In the proposed scheme, high-energy particles and photons are produced by high-intensity laser beam interaction with a solid or gas target, which are utilized later on to trigger the nuclear reactions for the production of (photo) neutrons. These neutrons can give rise to fission of ²³²Th that leads through a cascade of decays to ²³³U —a highly fissionable material. Such a process will enhance, by an important factor, the final neutron flux and the energetic fission fragments. The use of a high intensity pulsed laser beam will control the turn-on and turn-off of the nuclear reactions and allow one to ensure the security of the whole operation. Finally, the produced neutrons are used to accomplish a major population inversion in an appropriate gas medium for the last stage of amplification of a high-contrast ultra-short laser seed pulse.     

Advances in neutron radiographic techniques and applications: a method for nondestructive testing.

A brief history of neutron radiography is presented to set the stage for a discussion of significant neutron radiographic developments and an assessment of future directions for neutron radiography. Specific advances are seen in the use of modern, high dynamic range imaging methods (image plates and flat panels) and for high contrast techniques such as phase contrast, and phase-sensitive imaging. Competition for neutron radiographic inspection may develop as these techniques offer application prospects for X-ray methods.     

Development of real-time thermal neutron monitor using boron-loaded plastic scintillator with optical fiber for boron neutron capture therapy.

A new thermal neutron monitor for boron neutron capture therapy was developed in this study. We called this monitor equipped boron-loaded plastic scintillator that uses optical fiber for signal transmission as an [scintillator with optical fiber] SOF detector. A water phantom experiment was performed to verify how the SOF detector compared with conventional method of measuring thermal neutron fluence. Measurements with a single SOF detector yielded indistinguishable signals for thermal neutrons and gamma rays. To account for the gamma ray contribution in the signal recorded by the SOF detector, a paired SOF detector system was employed. This was composed of an SOF detector with boron-loaded scintillator and an SOF detector with a boron-free scintillator. The difference between the recorded counts of these paired SOF detectors was used as the measure of the gamma ray contribution in the measured neutron fluence. The paired SOF detectors were ascertained to be effective in measuring thermal neutron flux in the range above 10(6)(n/cm(2)/s). Clinical trials using paired SOF to measure thermal neutron flux during therapy confirmed that paired SOF detectors were effective as a real-time thermal neutron flux monitor.     

Thermal neutron reflection method for measurement of total hydrogen contents in Ghanaian petroleum products.

A fast and non-destructive technique based on thermal neutron reflection was used to determine total hydrogen contents in petroleum products available in Ghana. A source holder consisting of an 241Am-Be neutron source and 3He neutron probe designed for detection of liquid levels was used to measure reflection parameter as a function of hydrogen contents in liquid hydrocarbons which served as standards. The measured data were fitted to two linear equations for two different geometrical arrangements. The trend of data was found to be consistent with theoretical analysis based on neutron moderation. The calibration lines were used to determine hydrogen contents in 10 petroleum products. The results agree favourably with those obtained using different experimental set-ups with other neutron sources and probes. The technique was also used to determine the quality of diluted petrol with aviation fuel.     

A review of boron neutron capture therapy (BNCT) and the design and dosimetry of a high-intensity, 24 keV, neutron beam for BNCT research

This paper reviews the development of boron neutron capture therapy (BNCT) and describes the design and dosimetry of an intermediate energy neutron beam, developed at the Harwell Laboratory, principally for BNCT research. Boron neutron capture therapy is a technique for the treatment of gliomas (a fatal form of brain tumour). The technique involves preferentially attaching 10B atoms to tumour cells and irradiating them with thermal neutrons. The thermal neutron capture products of 10B are short range and highly damaging, so they kill the tumour cells, but healthy tissue is relatively undamaged. Early trials required extensive neurosurgery to exposure the tumour to the thermal neutrons used and were unsuccessful. It is thought that intermediate-energy neutrons will overcome many of the problems encountered in the early trials, because they have greater penetration prior to thermalization, so that surgery will not be required. An intermediate-energy neutron beam has been developed at the Harwell Laboratory for research into BNCT. Neutrons from the core of a high-flux nuclear reactor are filtered with a combination of iron, aluminium and sulphur. Dosimetry measurements have been made to determine the neutron and gamma-ray characteristics of this beam, and to monitor them throughout the four cycles used for BNCT research. The beam is of high intensity (approximately 2 x 10(7) neutrons cm-2 s-1, equivalent to a neutron kerma rate in water of 205 mGy h-1) and nearly monoenergetic (93% of the neutrons have energies approximately 24 keV, corresponding to 79% of the neutron kerma rate).     

Results of neutron radiosurgery for inoperable arteriovenous malformations of the brain

Twenty patients with inoperable arteriovenous malformations (AVMs) of the brain were treated with neutron radiosurgery. A 50 MeV cyclotron was used to deliver 9 Gy in a single fraction through 7 to 14 isocentric portals. The size and shape of the portals were customized to each treatment site. Nineteen patients have been followed for a median duration of 24 months following neutron radiosurgery. A radiographically demonstrable partial response was seen in 8 patients (42%). No complete responses were observed. There has been one post-treatment hemorrhage, no fatalities, and no evidence of radiation toxicity. The low response rate and absence of toxicity suggest that the appropriate dose for neutron radiosurgical treatment of AVMs is higher than the dose of 9 Gy at isocenter used in this initial study.     

In-phantom characterisation studies at the Birmingham Accelerator-Generated epIthermal Neutron Source (BAGINS) BNCT facility.

A broad experimental campaign to validate the final epithermal neutron beam design for the BNCT facility constructed at the University of Birmingham concluded in November 2003. The final moderator and facility designs are overviewed briefly, followed by a summary of the dosimetric methods and presentation of a small subset of the results from this campaign. The dual ionisation chamber technique was used together with foil activation to quantify the fast neutron, photon, and thermal neutron beam dose components in a large rectangular phantom exposed to the beam with a 12 cm diameter beam delimiter in place. After application of a normalisation factor, dose measurements agree with in-phantom MCNP4C predictions within 10% for the photon dose, within 10% for thermal neutron dose, and within 25% for the proton recoil dose along the main beam axis.     

Neutron phase contrast imaging beamline at CIRUS, reactor, India

This paper presents the development of neutron phase contrast imaging facility at medium flux research reactor, CIRUS, India. The approach adopted for this study is innovative in the sense that both conventional and phase contrast imaging can be performed within same experiment hutch without any major modification in the experimental hutch or collimator.     

Neutron flux density profiling during iridium irradiation

Using the perturbation method, the dependence of the specific activity of ¹⁹²Ir on the variation of neutron flux density is investigated. It has been shown that sensitivity of the specific activity of ¹⁹²Ir value at a given irradiation time depends on the time-point of neutron flux perturbation, being greater if perturbation is introduced at the end of the irradiation cycle. Practical realisation of a proposed scheme will allow an increase in ¹⁹²Ir specific activity together with savings in reactor fuel, due to the lower level of reactor power at the beginning of the cycle.     

Analysis of epithermal neutron production by near-threshold (p,n) reactions

A recent advance in portable accelerator neutron source development was research on production of epithermal neutrons by near-threshold charged-particle reactions. When the projectile energy is accurately controlled at an energy close to the reaction threshold, the neutrons produced will have energies less than or around 100 keV and can be used with little or no moderation or filtration in neutron capture therapy. Although the total neutron yield is lower than at higher proton energies, the epithermal neutron flux may be sufficiently intense because of the softer energy spectrum and the requirement for less neutron moderation. This paper presents an analysis of the main characteristics of epithermal neutron production by this method using the Li (p,n) reaction as an example. The energy, yield and angular characteristics of neutron emission are discussed. The achievable epithermal fluxes are computed from experimental data. The results are used to assess the feasibility of near-threshold production of epithermal neutrons for neutron capture therapy with compact accelerators such as a RFQ proton acceelerator. The results indicated that, using a Li₃N target, 1 mA of 2 MeV protons will produce 10⁹ n/cm²/s with an average energy of 83 keV while 5.6 mA of 1.91 MeV protons can produce 10⁹ n/cm²/s with an average energy of 45 keV.     

Comparison of neutron spectrum measurement methods used for the epithermal beam of the LVR-15 research reactor

The LVR-15 research reactor's horizontal channel with its epithermal neutron beam is used mainly for boron neutron capture therapy. Neutrons from the reactor core pass through a special filter before the collimator and the beam outlet. Neutron fluence and spectrum are the basic characteristics of an epithermal neutron beam. Three methods used to measure the beam's neutron spectrum are described: the activation method, a Bonner sphere spectrometer with gold activation detectors and a Bonner sphere spectrometer with LiI(Eu) scintillation detector. Examples of results are compared and discussed.     

Spatial and spectral characteristics of a compact system neutron beam designed for BNCT facility

The development of suitable neutron sources and neutron beam is critical to the success of Boron Neutron Capture Therapy (BNCT). In this work a compact system designed for BNCT is presented. The system consists of ²⁵²Cf fission neutron source and a moderator/reflector/filter/shield assembly. The moderator/reflector/filter arrangement has been optimized to maximize the epithermal neutron component which is useful for BNCT treatment of deep seated tumors with the suitably low level of beam contamination. The MCMP5 code has been used to calculate the different components of neutrons, secondary gamma rays originating from ²⁵²Cf source and the primary gamma rays emitted directly by this source at the exit face of the compact system. The fluence rate distributions of such particles were also computed along the central axis of a human head phantom.     

Neuron source energy on resonance absorption

Four different methods are used to study the neutron slowing down and to evaluate the neutron resonance escape probability in an infinite homogeneous medium containing a heavy resonant nuclide [U238] and a light moderator nuclide [H]. Two statistical methods use the Monte Carlo simulation and two deterministic methods are based on the numerical solutions of the neutron slowing down equation and a corresponding adjoint equation with an appropriate adjoint source.This study has been done for several dilutions and for two neutron source energies (E_s = 676.45 eV and E_s = 2 MeV). The cut-off energy is placed at 2.77 eV.We have found that the direct numerical solution of the neutron slowing down equation does not agree with the other three methods. In order to eliminate this disagreement, we have taken account of some corrections concerning the hydrogen cross-section in the thermal region.     

MCNP study for epithermal neutron irradiation of an isolated liver at the Finnish BNCT facility.

A successful boron neutron capture treatment (BNCT) of a patient with multiple liver metastases has been first given in Italy, by placing the removed organ into the thermal neutron column of the Triga research reactor of the University of Pavia. In Finland, FiR 1 Triga reactor with an epithermal neutron beam well suited for BNCT has been extensively used to irradiate patients with brain tumors such as glioblastoma and recently also head and neck tumors. In this work we have studied by MCNP Monte Carlo simulations, whether it would be beneficial to treat an isolated liver with epithermal neutrons instead of thermal ones. The results show, that the epithermal field penetrates deeper into the liver and creates a build-up distribution of the boron dose. Our results strongly encourage further studying of irradiation arrangement of an isolated liver with epithermal neutron fields.