Irradiation Site Research Articles

Design of a permanent epithermal neutron irradiation site in the Syrian MNSR

A permanent epithermal neutron irradiation site was designed in the Syrian Miniature Neutron Source Reactor (MNSR) by using cadmium as a thermal neutron shielding material. This site was designed by Cd-shielding the internal surface of the outer aluminum tube of the FOIS (First Outer Irradiation Site) in the MNSR. The MCNP-4C calculations showed that, to have a permanent epithermal neutron irradiation site for the ENAA using the cadmium, it is necessary to add the top beryllium shims of the reactor to compensate for the reactivity losses due to the neutrons absorption in the cylindrical cadmium shell. The activation detectors were used to measure the thermal and epithermal neutron fluxes in the FOIS. Distribution of the thermal neutron flux along the vertical direction of the outer irradiation capsule used in the FOIS has been found using MCNP-4C code, and experimentally by irradiating five copper wires. Good agreements were obtained between the calculated and the measured results.

Determination of thermal neutron cross-section and resonance integral for the 75As (n, γ) 76As reaction by activation method using 55Mn (n, γ) 56Mn as a monitor

Nuclear constants for use in reactor activation analysis especially (n, γ) cross-sections and absolute gamma intensities, are known to show a rather large scatter in literature. Thermal and resonance cross-sections for the 75As (n, γ) 76As reaction is determined by the method of foil activation using 55Mn (n, γ) 56Mn as a reference reaction. The experimental sample with and without a cadmium cover of 1-mm wall thickness was irradiated in the isotropic neutron field of the outer irradiation sites 7 of Ghana Research Reactor-1 facility which is a miniature neutron source reactor designed by the Chinese. The irradiation channel used has a neutron spectral parameter ( α) found to be (0.037 ± 0.001). The induced activity in the sample was measured by gamma ray spectrometry with a high purity germanium detector. A standard solution of Arsenic was used for the analysis. The necessary correction for gamma attenuation, thermal neutrons and resonance neutron self-shielding effects were not taken into account during the experimental analysis because they were negligible. By defining cadmium cut-off energy of 0.55 eV, the result for 75As (n, γ) 76As reaction was found to be: thermal neutron cross-section σ 0 = (4.28 ± 0.19) b and resonance integral I 0 = (61.88 ± 1.07) b.

No Evidence for a Different RBE between Pulsed and Continuous 20 MeV Protons

To obtain greater insight into the future potential of tumor radiotherapy using proton beams generated from high-intensity lasers, it is important to characterize the ionization quality of the new beams by measuring the relative biological effectiveness (RBE) under conditions where the full dose at one irradiation site will be deposited by a few proton pulses less than 1 ns in duration. HeLa cells attached to a Mylar foil were irradiated with 70 kV X rays to obtain a reference dose-response curve or with 3 Gy of 20 MeV protons at the Munich tandem accelerator (Garching), either using a continuous mode where a cell sample was irradiated within a 100-ms time span or using a pulsed mode where radiation was given in a single proton pulse of about 1 ns. After irradiation cytochalasin B was added; 24 h later cells were fixed and stained with acridine orange and micronuclei were counted. The X-ray dose-response curve for the production of micronuclei in HeLa cells followed a linear-quadratic model. The corresponding RBE values for 20 MeV protons in pulsed and continuous irradiation modes were 1.07 +/- 0.08 and 1.06 +/- 0.10 in the first proton experiment and 1.09 +/- 0.08 and 1.05 +/- 0.11 in the second, respectively. There was no evidence for a difference in the RBE for pulsed and continuous irradiation of HeLa cells with 20 MeV protons.

Influence of LED irradiance on flexural properties and Vickers hardness of resin-based composite materials

ObjectiveTo investigate the effect of irradiance through choice of LED light-curing unit (LCU) and fiber-optic tip on the mechanical properties of methacrylate resin-based composites (RBCs). MethodsRectangular bar-shaped specimens (25mm×2mm×2mm) of four RBCs, irradiated from one side for the manufacturer's recommended times with one of two LED LCUs, and with either 8 or 13mm tip diameter, were tested in three-point bend for flexural strength and modulus of elasticity; Vickers hardness was measured on top and bottom surfaces, on overlapped and non-overlapped irradiation sites. The effects and interactions of all factors were examined by analysis of variance. ResultsWhile the materials tested differed significantly for all properties (P<1×10−6), there was no significant effect for LCU, tip, or irradiance for flexural strength or modulus of elasticity. For hardness, the only significant effect overall was due to irradiance on the bottom surface. ConclusionsBoth LCUs and both tips could be used to give adequate top surface hardness, but the recommended maximum increment thickness is too great for adequate cure at the bottom with the tested LCUs at the recommended times. An extended experimental design would be valuable to test behavior at much elevated irradiances.

Calculation and comparison of the neutron energy flux spectra in the Syrian MNSR irradiation sites using the MCNP-4C code

A 3-D neutronic model for the Syrian Miniature Neutron Source Reactor (MNSR) was developed earlier to analyze the reactor neutronic using the MCNP-4C code. This model was used in this paper to calculate the neutron energy flux spectra in the five inner and five outer irradiation sites of the MNSR reactor. The continuous energy neutron cross sections were evaluated from ENDF/B-VI library. The neutron fluxes were calculated using 69 energy groups. The neutron energy flux for each group was calculated dividing the neutron flux by the width of each energy group. The calculations showed that the distributions of the neutron energy flux spectra in the five inner irradiation sites were in good agreements. These results were noticed in the reactor outer irradiation sites as well. Using the neutron flux spectrum in the first inner irradiation site, the thermal (0.0–0.625 eV) and fast neutron fluxes (0.5–10 MeV) were calculated and found 1.035 × 10 12 and 3.022 × 10 11 cm −2 s −1 respectively. The measured fluxes in the first inner irradiation site were found previously to be (0.97 ± 0.06) × 10 12 and (2.89 ± 0.06) × 10 11 cm −2 s −1 respectively. Good agreements were noticed between the calculated and the measured results. These agreements verify the calculated neutron flux spectra in the reactor sites.

Passive nondestructive burnup monitoring of MNSR irradiated fuel by measuring photoneutrons produced within fission products

A passive nondestructive method for monitoring of Syrian miniature neutron source reactor (MNSR) fuel burnup is introduced. The inner irradiation site design inside the Be reflector was exploited to measure the generated photoneutrons induced by fission products hard gamma radiation in the subcritical state. The photoneutron flux was measured using gold foils as a function of cooling time and operation power. For cooling time ranges between 10 and 25 d, experiments show that 140Ba is the extremely dominating inducer of photoneutrons and the measured flux is proportional to the accumulated 140Ba. This result forms a new method base for MNSR fuel burnup monitoring. It might be used also as a safeguards technique to check the operator declared information.

Conceptus dose from involved-field radiotherapy for Hodgkin's lymphoma on a linear accelerator equipped with MLCs

To estimate the scattered dose to conceptus from involved-field radiotherapy for Hodgkin's lymphoma on a linear accelerator equipped with multileaf collimators. Anthropomorphic phantoms were used to simulate an average pregnant woman at the 1st, 2nd and 3rd trimesters of gestation. Conceptus dose was measured using thermoluminescent dosimeters. Phantom measurements were performed for the minimum, medium and maximum field dimensions that may be employed during radiation therapy to lymph nodes in the neck, axilla, mediastinum and neck-mediastinum. The components of the scattered dose to conceptus were determined. Phantom exposures were generated with a 6-MV photon beam. Neck irradiation with a tumor dose of 35 Gy resulted in a conceptus dose of 1.1-8.7 cGy depending upon the stage of pregnancy, the distance from treatment volume, and the field size applied. The corresponding conceptus dose ranges from radiotherapy in the regions of axilla, mediastinum and neck-mediastinum was 1.2-14.3 cGy, 3.7-57.7 cGy, and 5.1-91.8 cGy, respectively. The contribution of collimator scatter and head leakage to the total conceptus dose varied from 21% to 80% depending upon the irradiation site and gestational age. The conceptus dose associated with cervical node irradiation is below the threshold value of 10 cGy during the entire pregnancy. Radiation therapy to lymph nodes in the axilla, mediastinum and neck-mediastinum may possibly lead to a conceptus dose of > 10 cGy and, therefore, informed decisions about the pregnancy termination should be made.

New irradiation facility for biomedical applications at the RA-3 reactor thermal column

A new irradiation facility has been developed in the RA-3 reactor in order to perform trials for the treatment of liver metastases using boron neutron capture therapy (BNCT). RA-3 is a production research reactor that works continuously five days a week. It had a thermal column with a small cross section access tunnel that was not accessible during operation. The objective of the work was to perform the necessary modifications to obtain a facility for irradiating a portion of the human liver. This irradiation facility must be operated without disrupting the normal reactor schedule and requires a highly thermalized neutron spectrum, a thermal flux of around 10 10 n cm −2 s −1 that is as isotropic and uniform as possible, as well as on-line instrumentation. The main modifications consist of enlarging the access tunnel inside the thermal column to the suitable dimensions, reducing the gamma dose rate at the irradiation position, and constructing properly shielded entrance gates enabled by logical control to safely irradiate and withdraw samples with the reactor at full power. Activation foils and a neutron shielded graphite ionization chamber were used for a preliminary in-air characterization of the irradiation site. The constructed facility is very practical and easy to use. Operational authorization was obtained from radioprotection personnel after confirming radiation levels did not significantly increase after the modification. A highly thermalized and homogenous irradiation field was obtained. Measurements in the empty cavity showed a thermal flux near 10 10 n cm −2 s −1, a cadmium ratio of 4100 for gold foils and a gamma dose rate of approximately 5 Gy h −1.

Determination of zeta values for fission-track age calibration using thermal neutron irradiation at the JRR-3 reactor of JAEA, Japan

We recently determined new zeta values of zircon and apatite for fission-track dating using diallyl phthalate (DAP) detectors. Thermal neutron irradiation was performed using the pneumatic tube No.2 at the JRR-3 reactor of Japan Atomic Energy Agency (JAEA), for which the cadmium ratio for Au is 24. The resulting zeta values are 416 ± 3 (ED1) and 371 ± 3 (ED2) for zircon with Q-DAP detectors by an observer (TD), 414 ± 3 (ED1) and 391 ± 4 (ED2) for zircon with Q-DAP detectors, and 337 ± 4 (ED1) for apatite with S-DAP detectors by a second observer (HI). These values are 6-11 % higher than those obtained for the pneumatic tube at the JRR-4 reactor of JAEA, with a cadmium ratio of 3.6. The significant difference in zeta values between the two irradiation sites can be partly attributed to the effect of the fast neutron-induced fissions of 232Th and 238U in SRM612 glass at JRR-4, with its relatively poor thermalisation.

Diffuse fasciitis with eosinophilia developing after local irradiation for breast cancer

This case describes a patient who developed diffuse fasciitis with eosinophilia (DFE) after an exaggerated local response to radiation following excision of a lymph node-negative breast cancer. Our patient's fasciitis was diffuse, involving both upper and lower extremities and the trunk at sites distant from the irradiation and tumor site. The fasciitis progressed after curative excision of the breast cancer rather than concurrently with active breast cancer and persisted despite therapy; there was no tumor reoccurrence. With three published cases linking localized eosinophilic fasciitis with breast cancer, and with the literature suggesting that DFE commonly presents after a traumatic trigger, the possibility that radiation therapy for breast cancer could be one such trigger is an important insight for clinicians treating the many patients who undergo breast cancer treatment each year.

In-Beam and Off-Beam PET Measurements of Target Activation by Megavolt X-Ray Beams

In-beam positron emission tomography (in-beam PET) is a valuable in situ method for quality assurance in radiation therapy. It is well investigated for therapy with carbon ions and has been successfully implemented clinically at the Gesellschaft for Schwerionenforschung (GSI), Darmstadt, Germany. The extension of this efficient technique to other radiation treatment modalities may be worthwhile. For protons, <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> He, <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> Li, and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> O the feasibility has already been experimentally shown. Furthermore, it seems to be feasible for the case of radiotherapy with high-energy photons, since positron emitters are generated by photons with energies above ~ 20 MeV due to (gamma, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> ) photo-nuclear reactions (predominantly <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> C and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> O in tissue). In this regard, promising conclusions have been obtained by Geant4 simulations as well as by off-beam PET experiments using a conventional PET scanner. The next step was the installation of a small double head positron camera consisting of two bismuth germanate (BGO) block detectors at the irradiation site to measure the generated beta <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> activity distribution simultaneously to the irradiation. The relation between deposited dose and beta <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> activity density was quantified. The obtained results are presented and compared to that of off-beam PET experiments. Higher activities as well as an improved contrast between materials of different stoichiometry are achieved by measuring in-beam, showing the advantage of in-beam PET over off-beam PET. Thus, the application of in-beam PET to radiation therapy with high-energy photons can be useful for quality assurance, comprising monitoring of dose delivery, patient positioning and tumor response.

Influência da irradiação do laser na regeneração nervosa em diferentes locais de tratamento

OBJETIVO: Verificar a influência do laser de baixa intensidade de AsGaAl na lesão por esmagamento do nervo peroneiro de ratos através da avaliação funcional da marcha nos diferentes locais de irradiação. MÉTODOS: Foram utilizados 53 ratos, divididos em seis grupos: normal, lesado não tratado, lesado e tratado placebo, lesado e tratado na medula, lesado e tratado no nervo, lesado e tratado em ambos (nervo e medula). O esmagamento do nervo peroneiro foi realizado por meio de uma pinça e subsequente tratado com laser por 28 dias consecutivos. Na avaliação funcional foram analisadas as impressões das pegadas, registradas pela câmera de vídeo em uma passarela de acrílico, no pré-operatório e aos 14º, 21º e 28º dias de pós-operatório, e avaliadas na fórmula PFI por meio do software. RESULTADOS: Na avaliação funcional da marcha foram encontradas diferenças significantes somente no 14º dia de pós-operatório. CONCLUSÃO: A irradiação do laser AsGaAl de baixa intensidade foi capaz de acelerar e potencializar o processo de regeneração nervosa periférica de ratos no 14º dia de pós-operatório, de acordo com a avaliação funcional da marcha, tanto para o grupo tratado na medula quanto para o grupo tratado no nervo.

A Case of Radiation Retinopathy of Left Eye After Radiation Therapy of Right Brain Metastasis

A 37-year-old female, who had received modified radical mastectomy for cancer of her right breast, presented with decreased visual acuity in the left eye after radiation therapy for the management of the metastasis to her right brain 14 months ago. After ocular examination, we diagnosed her as radiation retinopathy. At the time of the first visit, the corrected best visual acuity was 0.4 in the left eye, and fundus examination revealed cotton wool spots and cystoid macular edema (CME). The findings in the right eye were normal except for cotton wool spots in the superior major arch. Fluorescein angiography (FA) showed marked telangiectasia and microaneurysms in her left eye but tiny microaneurysms in her right eye. Subsequent optical coherent tomography (OCT) showed CME. We injected intravitreal triamcinolone acetonide (TA). Two weeks after treatment, the visual acuity was improved to 0.6 and the retinal thickness was decreased. Three months later, the visual acuity in the left eye was dropped to 0.3 due to the recurrence of CME, so we injected intravitreal TA again. Five months later, visual acuity was improved to 0.5 and OCT revealed the improvement of CME. The incidence of radiation retinopathy is higher in the side nearer to radiation, but careful radiation blocking is also required on the opposite side of irradiation site considering the possibility of radiation retinopathy and careful observation is required on both sides of the eyes when performing fundus examination.

ラバーダム装着から除去後に至るまでのＮｄ：ＹＡＧレーザーによる疼痛緩和効果に関する経時的変化

The purpose of this study was to compare the pain-relieving effects of pulsed Nd:YAG laser irradiation with topical anesthetic application during placement of a rubber dam clamp.Twenty-two students, aged 22 to 31 years (mean 24.05), who had not experienced either endodontic or cervical restorative treatment of first permanent molars, participated in this study. In this study, the same tooth for the same patient was tested three times every week. The following were the conditions of each site: 1) control site: no pretreatment before placement of the rubber dam clamp, 2) topical anesthetic site: application of topical anesthetic 60 seconds before placement of the rubber dam clamp and wash-out by three-way syringe water, 3) Nd:YAG laser irradiation site: Nd:YAG laser irradiation before placement of the rubber dam clamp. The irradiation conditions were 120 mJ, 1.2 W, 10 pps, and irradiation time was 30 sec twice. The efficacy of pain-relief was assessed by visual analogue scale (VAS) at the start, before placement of the rubber dam clamp, after placement of the rubber dam clamp, and until 20 minutes at 2-minute intervals. The clamp was removed 14 minutes after the start. Pain-relieving effects were also examined by questionnaire.The VAS levels of both placement and removal of the rubber dam clamp were high for all sites. On placement of the rubber dam clamp, the VAS level with Nd:YAG laser irradiation was statistically significantly lower than with no preparation (P<0.05: Wilcoxon signed-ranks test). During placement of the rubber dam clamp, the VAS level with Nd:YAG laser irradiation and topical anesthetic application were statistically significantly lower than with no preparation (P<0.05: Wilcoxon signed-ranks test).

Development and applications of k 0 based NAA and prompt gamma-ray NAA methods at BARC

A summary of k0-based R&D work on neutron activation analysis (NAA), internal mono standard NAA (IM-NAA) and prompt gamma-ray NAA (PGNAA) is presented. The k0-based NAA was standardized by characterizing irradiation sites of research reactors, validated using reference materials and applied to samples of different origin. Recently IM-NAA method was developed, validated for small and large size samples and applied for the analysis of large size as well as non-standard geometry samples. Studies on PGNAA included characterization of neutron beam, determinations of detection efficiency and prompt k0-factors, and analytical applications.

Calculations of the thermal and fast neutron fluxes in the Syrian miniature neutron source reactor using the MCNP-4C code

The MCNP-4C code, based on the probabilistic approach, was used to model the 3D configuration of the core of the Syrian miniature neutron source reactor (MNSR). The continuous energy neutron cross sections from the ENDF/B-VI library were used to calculate the thermal and fast neutron fluxes in the inner and outer irradiation sites of MNSR. The thermal fluxes in the MNSR inner irradiation sites were also measured experimentally by the multiple foil activation method ( 197Au (n, γ) 198Au and 59Co (n, γ) 60Co). The foils were irradiated simultaneously in each of the five MNSR inner irradiation sites to measure the thermal neutron flux and the epithermal index in each site. The calculated and measured results agree well.

Four energy group neutron flux distributions in the Syrian Miniature Neutron Source Reactor using the WIMSD4 and CITATION codes

A 3-D ( R, θ, Z) neutronic model for the Miniature Neutron Source Reactor (MNSR) was developed earlier to conduct the reactor neutronic analysis. The group constants for all the reactor components were generated using the WIMSD4 code. The reactor excess reactivity and the four group neutron flux distributions were calculated using the CITATION code. This model is used in this paper to calculate the pointwise four energy group neutron flux distributions in the MNSR versus the radius, angle and reactor axial directions. Good agreement is noticed between the measured and the calculated thermal neutron flux in the inner and the outer irradiation sites with relative differences less than 7% and 5%, respectively.

Femtosecond laser nano-ablation in fixed and non-fixed cultured cells

To understand the onset and morphology of femtosecond laser submicron ablation in cells and to study physical evidence of intracellular laser irradiation, we used transmission electron microscopy (TEM). The use of partial fixation before laser irradiation provides for clear images of sub-micron intracellular laser ablation, and we observed clear evidence of bubble-type physical changes induced by femtosecond laser irradiation at pulse energies as low as 0.48 nJ in the nucleus and cytoplasm. By taking ultrathin sliced sections, we reconstructed the laser affected subcellular region, and found it to be comparable to the point spread function of the laser irradiation. Laser-induced bubbles were observed to be confined by the surrounding intracellular structure, and bubbles were only observed with the use of partial pre-fixation. Without partial pre-fixation, laser irradiation of the nucleus was found to produce observable aggregation of nanoscale electron dense material, while irradiation of cytosolic regions produced swollen mitochondria but residual local physical effects were not observed. This was attributed to the rapid collapse of bubbles and/or the diffusion of any observable physical effects from the irradiation site following the laser exposure.

A comparative neutronic study of the standard HEU core and various potential LEU alternatives for a typical MNSR system

A comparative study has been performed for neutronic analysis of highly enriched in uranium (HEU) and potential low enriched in uranium (LEU) cores for the Pakistan Research Reactor-2 (PARR-2) taken as a typical miniature neutron source reactor (MNSR) system. The group constant generation has been carried out using transport theory code WIMS-D4 and a detailed five-group RZ-model has been used in the CITATION code for multigroup diffusion theory analysis. The neutronic analysis of the 90% HEU reference and potential LEU alternative: UO 2, U 3Si 2 and U9Mo, cores has been carried out yielding 11%, 20.7% and 14.25% enrichments with corresponding values of excess reactivity: 4.33, 4.30 and 4.07 mk. These results have been found in good agreement with recently reported Monte Carlo-based transport theory calculations. The diffusion theory-based calculated values of thermal flux profiles for axial as well as for radial directions have been found to agree well with the corresponding experimental measurements. The UO 2-based LEU core has been found having flux spectrum closest to the reference core while U9Mo core has significantly harder flux spectrum at irradiation site.

Design of a permanent Cd-shielded epithermal neutron irradiation site in the Syrian Miniature Neutron Source Reactor

A Cd-shield (cylindrical shell 1 mm in thickness, 34 mm in diameter and 180 mm in length) was used to design a permanent epithermal neutron irradiation site for epithermal neutron activation analysis (ENAA) in the Syrian Miniature Neutron Source Reactor (MNSR). This site was achieved by shielding the surface of the aluminum tube of one of the outer irradiation sites. The calculated depression ratio of thermal neutron flux was 1/10. Homogeneity of the neutron flux in the first outer irradiation site has been found numerically using the WIMSD4 and CITATION codes and experimentally by irradiating five short copper wires using the outer irradiation capsule. Good agreement was obtained between the calculated and the measured results of the neutron flux distributions.