Neutron spectrum and doses in a 18 MV LINAC

Bonner sphere spectrometer with TLDs pairs has been utilized to measure the neutron spectrum 100 cm from isocenter of a 18 MV LINAC, simultaneously the ambient dose equivalent due to neutrons and photons was measured in the control room area with neutron and gamma-ray area monitors. Measurements were carried out when the LINAC was delivering a dose of 600 MU at the isocentre that was located at 5 cm depth of a head phantom. Undesired neutron field in the treatment room produce activation reactions with nuclei in different materials of LINAC, couch, air, and phantom. To determine the dose due to decay of activation nuclei the ambient dose due to gamma-rays was measured inside the treatment room immediately after dose was delivered. Measured spectrum has two peaks, one between 0.1–1 MeV and other in the thermal region, the ambient dose equivalent in the control room are 3.1 and 0.93 μSv h⁻¹ for photons and neutrons, respectively. In the treatment room the ambient dose equivalent due to photons produced during decay of activation nuclei varies from 6 to 26.1 μSv h⁻¹.     

Measurements of the photonuclear neutron yield of 15 MV medical linear accelerator

High energy medical linear accelerators (>10 MV) are increasingly used in radiotherapy. At such high photon energies neutron production via photonuclear reactions in the heavy elements which compose the linac head is inevitable. Neutrons from linacs can contribute to an additional dose to staff, patients and the general public. Our intention is two-fold; to provide shielding against the neutron contamination and to establish the depthdose curve of thermal neutrons within human tissue, with an aim to utilise linacs in boron neuron capture therapy (BNCT). In our studies neutron measurements were undertaken, with a Varian Clinac 2100C/D linear accelerator operating at 15 MV nominal energy, by irradiating 18 cm thick 30×30 cm² block of tissue equivalent material. Measurements were taken using indium and aluminum activation foil at the centre of the block. Our results show that by leaving the linac jaws open neutron production is increased compared to the case when these are shut, for one minute exposure at 400MU. In this work we present a comparison between our results and existing literature and attempt to explore some sharp contrasts.     

Measurement of photoneutrons in the output of 15 MV varian clinac 2100C LINAC using bubble detectors

Photoneutron contamination in the output of Varian Clinac 2100C medical linear accelerator (LINAC) operated at 15 MV photon beam energy has been investigated using bubble detectors. Photoneutrons are produced from the photo-disintegration reaction of photons with materials of the head components with threshold energy of approximately 8 MeV. Measurements were conducted in the patient plane at 100 cm source-to-detector distance on beam axis and at stipulated distances outside the irradiated field for 5×5 cm² to 40×40 cm² field sizes for in-air and 5×5 cm² to 20×20 cm² for water phantom measurements. Neutron dose equivalent of 1.57±0.10 mSv·Gy⁻¹ was measured for 10×10 cm² field size for in-air. For in phantom, neutron dose equivalent of 1.42 mSv·Gy⁻¹ was measured for 10×10 cm² field size on the beam axis at a depth of 1 cm but independent of field size at depth >5 cm.     

Neutron flux distribution around the disk-shaped source of accelerator type neutron generators

The neutron flux distribution around the disk-shaped sources of accelerator type fast neutron generators has been calculated theoretically and compared with experimental data. It has been shown that the observed sharp flux gradients are inherent in the system and not due to non-ideal behaviour of the experimental parameters.     

Simultaneous determination of three components by X-ray spectrometry after neutron activation

A method is described for the simultaneous determination of cadmium, antimony and praseodymium by 14-MeV neutron activation analysis based on characteristic X-ray spectrometry. The results of analysis show a relative error not higher than ±5%, when diluted with H₃BO₃ /90%/ and utilizing the internal standard method to minimize the interelement effects.     

Neutron activation analysis and inductively coupled plasma-mass spectrometry for the determination of elements in tree stems

Mn, Zn and Al concentrations of ume, sakura and sugi stems determined by ICP-MS using a simple pretreatment were compared with those determined by INAA. We obtained a considerably good agreement between the two methods. ICP-MS using simple pretreatment was found to be useful in analyzing the elements in tree stems.     

The determination of carbon,nitrogen and oxygen in gases by neutron time-of-flight spectrometry

Carbon, nitrogen and oxygen were determined in gases by time-of-flight spectrometry of prompt neutrons from the respective reactions¹²C(d, n)¹³N,¹⁴N(d, n)¹⁵O and¹⁶O(d, n)¹⁷F, produced by a pulsed beam of deuterons of 2 MeV (for nitrogen) or 3 MeV. The analysis is non-destructive and requires about 15 min. per sample. The relative standard deviation for all three elements was about ±3%. Detection limits, using a total irradiation current of 20 millicoulombs, for carbon, nitrogen and oxygen, respectively, were 6·10⁻⁸ g, 2·10⁻⁷ g and 1.7·10⁻⁷ g per cm² cross-sectional area of irradiating beam.     

The determination of boron in biological materials by neutron irradiation and prompt gamma-ray spectrometry

A prompt-gamma neutron activation technique has been developed using the (n, ) apparatus situated at the O degree through-tube of the Imperial College CONSORT II Reactor with a thermal neutron flux at the target position of approximately 2×10⁶ n cm^–2 sec^–1, and a Compton-suppression system involving a lithium-drifted germanium (Ge(Li)) detector and a sodium iodide anti-Compton shield. Boron levels of 1–5 g g^–1 (detection limit 0.05 g B for 10,000 sec period of measurement) can be attained using the Compton-suppression system with graphical inter-polation correction for the 472 keV sodium-ray peak contribution to the Doppler-broadened 478 keV boron gamma-ray peak resulting from the¹⁰B(n, )⁷Li reaction. Very good agreement is reached for boron levels compared using this system for various Standard Reference Materials and other published values. Measurement of the boron content of bone and tooth samples from rheumatoid arthritis individuals shows lower levels, (p<0.05); 16.13±7.53 g g^–1, when compared with a control population; 19.79±4.18 g g^–1. A positive correlation existed between the boron content of bone and tooth material for each study group. Results indicate that boron availability may be associated with rheumatoid arthritis.     

基于中子活化瞬发伽马能谱确定地层元素含量的方法

中子技术能够利用中子与物质的相互作用确定其组成等性质,广泛应用于医学、环境科学、核反应堆建设、金属矿产勘查及石油工业中。在石油天然气领域,中子探测技术主要被用于确定井孔中的孔隙度、密度和流体饱和度等参数。随着测井技术的不断发展,基于瞬发伽马射线的中子活化分析技术也已应用于井下确定地层元素含量,并成为复杂岩性和非常规油气储层获得矿物含量的唯一手段。本文阐述了地层元素伽马能谱测井的方法,利用蒙特卡罗方法模拟了不同地层条件下的伽马能谱,构建了地层元素的标准谱库,研究了奇异值分解和极大似然估计能谱数据处理方法,并利用得到的元素产额及氧闭合模型实现地层元素含量的确定。利用蒙特卡罗方法构建已知地层的伽马能谱,采用上述数据处理方法得到元素含量与地层真实元素含量误差均在4%之内,Si元素误差最大为2.8%,Ca元素最大误差为3.3%,研究结果为井下确定地层元素成分及含量提供了有效的技术支持。     

Non-destructive determination of niobium in steel by neutron activation followed by X-ray spectrometry

Neutron activation followed by X-ray spectrometry and magnetic deflection of interfering β particles is applied to the non-destructive determination of niobium in steels. AMS 5643 (17-4PH) and B.C.S. No. 320–330 steel samples containing Nb in the range of 0.02–0.3% were analyzed. By using Nb₂O₅ in cellulose as standard, an overall error of ±20% was obtained.     

Simultaneous determination of four components by X-ray spectrometry after 14 MeV neutron activation

14 MeV neutron activation followed by X-ray spectrometry was applied to the simultaneous nondestructive determination of cadmium, antimony and bromine, utilizing praseodymium as an internal standard. The results of analysis show a relative error not higher than ±5%, when the samples were diluted with H₃BO₃ -5% to minimize the interelement effects.     

Application of radiochemical neutron activation and flame atomic absorption spectrometry for the determination of manganese in blood

The triplet-triplet absorption spectra of various aromatic compounds in benzene solution were studied by pulse radiolysis. It has been found that methylation of naphthalene characteristic absorption band in this group of compounds at 430±10 nm (naphthalene, 2-methylnaphthalene, 2,6-dimethylaphthalene, anthracene, phenanthrene, pyrene and fluorene); new bands appeared with phenanthrene and pyrene at 495 and 525 nm respectively. The decay remains of the first order in the whole group with similar rate constant values. Diphenyl and 1,1-dinaphthyl show significant changes in their T-T spectra in comparison with the preceding group of compounds. T-T spectrum of o-terphenyl differs significanly from those of p-and m-isomers, which can be caused by greater overlapping of electron orbitals in o-isomer molecule. Aromatic ketones show a complex picture both in spectra and decay kinetics.     

Precise determination of low isotopic nitrogen-15 abundances by emission spectrometry

Improvements in the determination of low nitrogen-15 abundances by emission spectrometry are described. Stronger emission is observed if a capillary constriction is formed at the centre of the discharge tube, and the background under the ¹⁴N¹⁵N peak is greatly reduced. The relative error normally caused by problems in estimating the background is thus decreased. The overall precision is better than 1% in the range from natural abundance to 1.0 atom-% nitrogen-15.     

Rare earth element determination in silicate rocks using neutron activation analysis and mass spectrometry

A pre-irradiation group separation procedure for the quantification of 11 to 13 rare earth elements (REE) in geological materials by neutron activation analysis, with yield determination by mass spectrometry isotope dilution analysis of Sm and Nd, is described. Utilization of the shorterlived isotopes of the REE allow sufficient data for most geochemical studies to be obtained within one day of irradiation, although where necessary additional information may be obtained following a decay period of three to four weeks. Analysis of selected USGS rock standards shows the method to be both accurate and precise.     

The determination of boron in sedimentary rocks by neutron irradiation and prompt γ-ray spectrometry

Prompt γ-rays following the (n_th, α) reaction on¹⁰B have been measured to determine the boron content of sedimentary rocks. Employing an external reactor neutron beam with only modest flux, it is possible to assay boron at concentrations typically encountered in this material (>5 μg/g). The technique relies on the use of chemical standards and the values obtained for 9 North American shales are compared with measurements performed by emission spectrography. Detection limits and statistical errors as a function of beam time are also discussed. Department of Geology, Mcmaster University, Hamilton, Ontario (Canada)     

The determination of selenium in biological material by thermal neutron activation analysis and atomic absorption spectrometry

Neutron activation analysis and atomic absorption spectrometry (graphite furnace) methods for the analysis of selenium in human tissue are described. The sensitivity (10–30 ng/sample), accuracy and precision are of the same order for both techniques and the choice can only be made on grounds of urgency or convenience. AAS should be chosen for the analysis of wet tissue or the urgent analysis of small numbers of dry tissue. NAA should be chosen for the analysis of large numbers of dry tissue samples where time is not important. The selenium concentration of human liver is shown to be in the region of 1 to 2 ppm (dry weight). Selenium may be lost from tissue during freeze drying if the samples are not maintained at −35°C.     

Non-destructive neutron activation determination of silver and antimony in bismuth byγ.γ-coincidence spectrometry

A non-destructive neutron activation method was developed for the determination of silver and antimony in high-purity bismuth ; γ,γ-coincidence counting of ^110mAg or ¹²⁴Sb was applied. The activity of the matrix or other impurities did not interfere. When 1-g samples were irradiated at a neutron flux of 4·10¹¹ n cm^-2 sec^-1 for 25 days, the sensitivity of the method was in the p.p.b. region.     

Epithermal instrumental neutron activation analysis with Compton suppression spectrometry for the determination of iodine in food samples

Epithermal instrumental neutron activation analysis (EINAA) together with Compton suppression system were optimized and used to analyze several food samples for the determination of low levels of iodine. The method involved the irradiation of samples in the outer epi-cadmium site of the Dalhousie University Slowpoke-2 reactor facility. The samples were then counted directly without any chemical treatment on an anticoincidence counting system. This system comprised a 25 cm³ hyperpure Ge detector, a guard detector consisting of a 10"×10" NaI(Tl) annulus with five photomultiplier tubes (PMTs) and a 3"×3" NaI(Tl) plug with one PMT. Iodine was quantitatively analyzed using the 443 keV photopeak of ¹²⁸I. The precision and accuracy of the method were evaluated using real samples and biological reference materials, respectively. The precision of the method was calculated as percent relative standard deviation and in all cases was within ±5%. The agreement between our iodine values and those of the certified values was generally within ±10%, suggesting an excellent accuracy of the method. The detection limits of the various samples calculated, with the lowest value of 20 ppb. The values of iodine determined ranged between 24 to 3080 ppb. The methods and results are presented.     

液相色谱-串联质谱法检测水产品中15种喹诺酮类药物残留量

建立了液相色谱-串联质谱技术同时检测水产品中15种喹诺酮类药物(氟罗沙星、氧氟沙星、依诺沙星、诺氟沙星、环丙沙星、恩诺沙星、洛关沙星、单诺沙星、奥比沙星、双氟沙星、沙拉沙星、司帕沙星、口恶喹酸、萘啶酸、氟甲喹)残留量的方法.试样中残留的喹诺酮类药物采用乙腈提取,提取液经正已烷液液分配脱脂后,以强阳离子固相萃取小柱净化,液相色谱.串联质谱法测定.对液/质分离条件与样品前处理条件进行了优化,并对喹诺酮类药物在分析过程的稳定性进行了研究.15种喹诺酮类药物在1.0～100 μg/L范围内线性关系良好,相关系数为0.9924～0.9992.在0.002～0.04 mg/kg浓度范围内,平均加标回收率在79.9%～93.8%;相对标准偏差为4.8%～14.6%.方法可满足水产品中喹诺酮类药物多残留检测与确证的需要.