Genetic effects induced by neutrons in Drosophila melanogaster I. Determination of absorbed dose

A method to obtain the absorbed dose in Drosophila melanogaster irradiated in the thermal column facility of the Triga Mark III Reactor has been developed. The method is based on the measurements of neutron activation of gold foils produced by neutron capture to obtain the neutron fluxes. These fluxes, combined with the calculations of kinetic energy released per unit mass, enables one to obtain the absorbed doses in Drosophila melanogaster.     

A model calculation of coherence effects in the elastic backscattering of very low energy electrons (1–20 eV) from amorphous ice

Abstract

Purpose: Backscattering of very low energy electrons in thin layers of amorphous ice is known to provide experimental data for the elastic and inelastic cross sections and indicates values to be expected in liquid water. The extraction of cross sections was based on a transport analysis consistent with Monte Carlo simulation of electron trajectories. However, at electron energies below 20 eV, quantum coherence effects may be important and trajectory-based methods may be in significant error. This possibility is here investigated by calculating quantum multiple elastic scattering of electrons in a simple model of a very small, thin foil of amorphous ice.

Method: The average quantum multiple elastic scattering of electrons is calculated for a large number of simulated foils, using a point-scatterer model for the water molecule and taking inelastic absorption into account. The calculation is compared with a corresponding trajectory simulation.

Results: The difference between average quantum scattering and trajectory simulation at energies below about 20 eV is large, in particular in the forward scattering direction, and is found to be almost entirely due to coherence effects associated with the short-range order in the amorphous ice. For electrons backscattered at the experimental detection angle (45° relative to the surface normal) the difference is however small except at electron energies below about 10 eV.

Conclusion: Although coherence effects are in general found to be strong, the mean free path values derived by trajectory-based analysis may actually be in fair agreement with the result of an analysis based on quantum scattering, at least for electron energies larger than about 10 eV.     

High-contrast radiographs for field control and field documentation in radiotherapy with high-energy photons

In ambitious radiotherapy with individually shaped irradiation fields, high-contrast field radiography is necessary for fine adjustment, control and field documentation. If intensification foils made of materials with medium or high atomic numbers such as copper, iron and lead are used, the film lying between the foils is mainly darkened by the secondary electrons released from the material of the front foil. Within the range of 1 MeV to 15 MeV, high-contrast radiographs are produced by means of copper or steel foils which are clearly superior to lead foils. Steel foils are to be preferred to copper foils because of their rigidity and the firmness of the polished surface. Usual X-ray diagnosis films with steep graduation can be used as film material for field control radiography performed in double exposure technique. A new insensitive film not applied hitherto in X-ray diagnosis allows to prepare field documentation images of high quality which are exposed during the whole irradiation time. This is also important for perpetuation of evidence.     

Half-life measurements of lutetium-176 using underground HPGe-detectors

The half-life of ¹⁷⁶Lu was determined by measuring the ¹⁷⁶Lu activity in metallic lutetium foils. Three different HPGe-detectors located 225 m underground were employed for the study. Measurements using the sum-peak method were performed and resulted in an average massic activity of (52.61±0.36) Bq g⁻¹. The foils were of natural isotopic abundance so using the massic activity and the value of the natural isotopic abundance of (2.59±0.01)%, a half-life of (3.722±0.029)×10¹⁰a could be calculated.     

Excitation functions of natZn(p,x) nuclear reactions with proton beam energy below 18 MeV

We measured the excitation functions of ^natZn (p,x) reactions up to 17.6 MeV, using the stacked-foils activation technique. High-purity natural zinc (and copper) foils were irradiated with proton beams generated by an 18 MeV isochronous cyclotron. Activated foils were measured using high-purity Ge gamma spectroscopy to quantify the radionuclides ⁶¹Cu, ⁶⁶Ga, ⁶⁷Ga, and ⁶⁵Zn produced from the reactions. Thick-target integral yields were also deduced from the measured excitation functions of the produced radioisotopes. These results were compared with the published literature and were found to be in good agreement with most reports, particularly those most recently compiled.     

Multi-layer 235UF4–6LiF–Au targets for high-resolution fission fragment measurements

Multi-layer ²³⁵UF₄–⁶LiF–Au targets have been produced by vacuum deposition on thin polyimide foils with an areal density, measured by spectrophotometry, of about 33 µg cm⁻². The foils were first covered with an Au-layer and then, with a second layer of ⁶LiF, both by vapour deposition. The ²³⁵UF₄ layer was prepared by fluoride sublimation. Each deposited mass was characterized separately by means of differential weighing for the Au and ⁶LiF layers and by low-geometry alpha-particle counting for the ²³⁵UF₄ layer. The atomic abundances of the uranium base material have been measured by thermal ionization mass spectrometry. The targets were prepared for measuring fission-fragment emission yields with high mass-resolution.     

The use of radiochromic films to measure and analyze the beam profile of charged particle accelerators

The use of radiochromic films as a simple and inexpensive tool to accurately measure and analyze the beam profile of charged particle accelerators is described. In this study, metallic foils of different materials and thicknesses were irradiated with 17.8 MeV protons and autoradiographic images of the beam strike were acquired by exposing pieces of RCF in direct contact with the irradiated foils. The films were digitalized using a conventional scanner and images were analyzed using DoseLab. Beam intensity distributions, isodose curves and linear beam profiles of the digitalized images were acquired.     

基于蒙特卡罗方法的脑转移瘤术中放疗施照器设计及剂量学评估

目的 设计适用脑转移瘤术中放疗的施照器并评估其剂量学特征。方法 施照器设计首先通过模拟计算电子束经过一系列不同厚度散射箔后的散射角和剂量率,确定散射箔厚度;其次,建立散射箔位于不同高度的位置评估模型,通过计算模型表面平均能量方差,确定散射箔位置;最后,建立调节层几何结构特征与施照器表面剂量之间的关系,确定调制器的内表面特征。使用蒙特卡罗（MC）EGSnrc/BEAMnrc和EGS4/DOSXYZ程序完成Mobetron加速器、位置评估模型、调节层、施照器建模和剂量学分析。结果 半球囊状施照器的限光筒直径为2.5 cm、筒壁厚0.5 cm,材料为0.2 cm厚水等效材料加0.3 cm厚不锈钢;散射箔厚度0.14 cm,材料为金属钨,位置高度为0.5 cm;调制器为月牙形,材料为水等效材料。该施照器能够使Mobetron 12 MeV的电子束产生半球面剂量分布,剂量率为160 cGy/min,治疗深度为0.85 cm。结论 采用MC模拟设计的适用于高能电子束的半球囊状施照器,能产生半球面剂量分布。     

A solid target system with remote handling of irradiated targets for PET cyclotrons

A solid target system was developed for a PET cyclotron. The system is compatible with many different target materials in the form of foils and electroplated/sputtered targets which makes it useful for production of a wide variety of different PET radionuclides. The target material is manually loaded into the system. Remote handling of irradiated target material is managed with a pneumatic piston and a vacuum technique which allows the targets to be dropped into a shielded transport container. To test the target performance, proton irradiations (12.8 MeV, 45 μA) of monoisotopic yttrium foils (0.64 mm, direct water cooling) were performed to produce ⁸⁹Zr. The yields were 2200±200 MBq (1 h, n=13) and 6300±65 MBq (3 h, n=3).     

Brain iron detected by SWI high pass filtered phase calibrated with synchrotron X‐ray fluorescence

Purpose:

To test the ability of susceptibility weighted images (SWI) and high pass filtered phase images to localize and quantify brain iron.

Materials and Methods:

Magnetic resonance (MR) images of human cadaver brain hemispheres were collected using a gradient echo based SWI sequence at 1.5T. For X‐ray fluorescence (XRF) mapping, each brain was cut to obtain slices that reasonably matched the MR images and iron was mapped at the iron K‐edge at 50 or 100 μm resolution. Iron was quantified using XRF calibration foils. Phase and iron XRF were averaged within anatomic regions of one slice, chosen for its range of iron concentrations and nearly perfect anatomic correspondence. X‐ray absorption spectroscopy (XAS) was used to determine if the chemical form of iron was different in regions with poorer correspondence between iron and phase.

Results:

Iron XRF maps, SWI, and high pass filtered phase data in nine brain slices from five subjects were visually very similar, particularly in high iron regions. The chemical form of iron could not explain poor matches. The correlation between the concentration of iron and phase in the cadaver brain was estimated as c_Fe [μg/g tissue] = 850Δ? + 110.

Conclusion:

The phase shift Δ? was found to vary linearly with iron concentration with the best correspondence found in regions with high iron content. J. Magn. Reson. Imaging 2010;31:1346–1354. © 2010 Wiley‐Liss, Inc.

     

Investigation of production of the therapeutic radioisotope 165Er by proton induced reactions on erbium in comparison with other production routes

The excitation function of the ^natEr(p,xn)¹⁶⁵Tm reaction resulting in production of ¹⁶⁵Er was measured up to 70 MeV by activation of stacked foils practically for the first time. The theoretical interpretation is based on the results of the ALICE-IPPE and EMPIRE-II codes. From the measured experimental cross section data integral production yield was calculated and compared with experimental integral yield data reported in the literature. Different production routes of the therapeutic radioisotope ¹⁶⁵Er were compared.     

A simple method for determining the activity of large-area beta sources constructed from anodized aluminum foils

A simple method has been developed for determining the activity of large-area beta reference sources in anodized aluminum foils. It is based on the modeling of the transmission of beta rays through thin foils in planar geometry using Monte Carlo simulation. The method was checked experimentally and measurement results show that the activity of large-area beta reference sources in anodized aluminum foils can be measured with standard uncertainties smaller than the limit of 10% required by ISO 8769.     

The effects of cognitive loading on balance control in patients with multiple sclerosis

The aim of this study was to compare the effects of concurrent cognitive task (silent backward counting) on balance performance between two groups of multiple sclerosis (MS) (n = 23) and healthy (n = 23) participates. Three levels of postural difficulty were studied on a force platform, i.e. rigid surface with eyes open, rigid surface with eyes closed, and foam surface with eyes closed. A mixed model analysis of variance showed that under difficult sensory condition of foam surface with eyes closed, execution of concurrent cognitive task caused a significant decrement in variability of sway velocity in anteroposterior direction for the patient group (P < 0.01) while this was not the case for healthy participants (P = 0.22). Also, the variability of sway velocity in mediolateral direction was significantly decreased during concurrent execution of cognitive task in patient group (P < 0.01) and not in healthy participants (P = 0.39). Furthermore, in contrast to single tasking, dual tasking had the ability to discriminate between the 2 groups in all conditions of postural difficulty. In conclusion, findings of variability in sway velocity seem to confirm the different response to cognitive loading between two groups of MS and healthy participants.     

Evaluation of reconstructed orbital wall fractures: high-resolution MRI using a microscopy surface coil versus 16-slice MSCT

We evaluated high-resolution magnetic resonance imaging (MR) using a 47-mm microscopy surface coil in comparison to 16-slice multislice CT (MSCT) for postsurgical imaging of reconstructed orbital walls. Twenty-five patients with 27 internal orbital wall fractures were imaged prospectively after reconstruction with resorbable polydioxanone sulfate (PDS) sheets. Coronal high-quality T1- and T2-weighted MR images were obtained with an in-plane resolution of 350 m within a measure time of 6–7 min for each sequence. Nineteen symptomatic patients underwent MSCT as the current gold standard. In MRI the PDS foil appears in T1- and T2-weighted images as a thin, low-signal-intensity linear structure. In CT it appears hyperdense in comparison to soft tissue and slightly hypodense in comparison to cortical bone. PDS foils could be clearly depicted in 20 out of 25 patients (80%) with MRI and in 13 out of 19 patients (68%) with MSCT. An inadequate foil position or size could be diagnosed in eight patients with MRI and in only three patients with MSCT. In ten symptomatic patients secondary surgery could be avoided because of regular MRI findings except mild hematoma and muscle edema. High-resolution MRI of the orbit using a 47-mm microscopy coil is a promising method to accurately demonstrate normal and pathologic conditions in symptomatic patients after orbital wall reconstruction with PDS foils.     

Distribution of spatial photoneutrons inside a 70 kg water phantom via neutron activation analysis

This study evaluated spatial Φ_th inside a 70 kg water phantom using the NAA method. Fifty indium foils were placed inside the water phantom and exposed under 15 MV LINAC for 2.5 min to yield the 10 Gy X-ray dose. The Φ_th value at the isocenter of the water was 1.03×10⁶ n cm^?2/Gy-X, and the maximum quantity of Φ_th appeared at the water surface along the z-axis, 3.99×10⁶ n cm^?2/Gy-X. The thermal neutron dose at isocenter of the water phantom occupied approximately 0.151% of the whole photo and neutron dose.     

Production of 38K via the 35Cl(α, n)- process at a compact cyclotron

Excitation functions were measured by the stacked-foil technique for the reactions ³⁵Cl(α, n)³⁸K and ³⁵Cl(α, αn) ^34mCl up to E_α = 26 MeV. Thin foils of poly(1,1-dichloroethene) sandwiched between thin Al foils were used as targets for cross section measurements. The chlorine content of the polymer foil was determined via neutron activation analysis. Cross section data and calculated thick target yields of ³⁸K and ^34mCl show that the optimum energy range for the production of ³⁸K is E_α = 22.5→7 MeV; the thick target yield of ³⁸K amounts to 5.5 mCi/μA·15 min and the level of ^34mCl is < 0.2%. Thick target yields were also measured experimentally under high current production conditions using NaCl as target material; the result (1.8 mCi ³⁸K/μA·15 min) agrees with the published data. ³⁸K is produced in 10 mCi quantities for applications in humans. Results of quality control are given.     

A 81Rb/81mKr generator made by ion implantation

Isotopically pure ⁸¹Rb was implanted in plastic foils, and the daughter-^81mKr was eluted quantitatively by air or by a 0.9% NaCl solution. The elution yield, the purity of the ^81mKr, and the washing-out losses of ⁸¹Rb were studied as functions of the implantation density. It was seen that the densities below 5 × 10¹² Rb atoms/cm² provide a high yield for elution both by liquid and air. The first 100 MBq implantation-type generator was tested by making a lung-ventilation study in man.     

Production of the mercury-197 through proton induced reaction on gold

The excitation function of the proton exchange reactions on gold was investigated in the energy range from threshold up to 20 MeV. We presented our experimental results upto 14 MeV stacked-foil technique was used, the target was of high purity gold foils (99.99%.) Reactions cross-sections and excitation functions were studied. Both isomeric level cross sections of ¹⁹⁷Hg were measured and calculated theoretically using the DDHMS routine of the EMPIRE-II (v2.19) code. Isomeric cross-section ratios for the pair ^197m,gHg were calculated and presented as a function of proton energy.     

Excitation functions of proton-induced reactions in natCu in the energy range 7–17 MeV

Elemental production cross sections were measured for (p,x) reactions on natural Cu targets, leading to the formation of ^62,63,65Zn. These reactions are generally used for monitoring the proton beam intensity and energy e.g. in isotope production facilities. Cross sections were obtained by activation of stacked foils and subsequent gamma spectroscopy. The production data for ^62,63,65Zn between 7 and 16.5 MeV proton energy are presented as well as comparisons with literature values. Good agreement with the evaluated values was found for most of the cross-section values.     

Design and construction of a thermal neutron beam for BNCT at Tehran Research Reactor

An irradiation facility has been designed and constructed at Tehran Research Reactor (TRR) for the treatment of shallow tumors using Boron Neutron Capture Therapy (BNCT). TRR has a thermal column which is about 3 m in length with a wide square cross section of 1.2×1.2 m². This facility is filled with removable graphite blocks. The aim of this work is to perform the necessary modifications in the thermal column structure to meet thermal BNCT beam criteria recommended by International Atomic Energy Agency. The main modifications consist of rearranging graphite blocks and reducing the gamma dose rate at the beam exit. Activation foils and TLD700 dosimeter have been used to measure in-air characteristics of the neutron beam. According to the measurements, a thermal flux is 5.6×10⁸ (n cm⁻² s⁻¹), a cadmium ratio is 186 for gold foils and a gamma dose rate is 0.57 Gy h⁻¹.