Development of a simple neutron irradiation facility utilizing the stray neutron field of a medical cyclotron

During the routine isotope production schedule at the Australian National Medical Cyclotron thick copper plates, electroplated with enriched target materials, are bombarded with 30 MeV protons with an average beam current of 200 μA. As a result an intense high-energy, prompt neutron flux of the order of 1.72 × 10¹³ neutrons·cm⁻²·2⁻¹ is generated in the immediate vicinity of the target. The stray fast neutrons were moderated using a water-filled PVC bucket placed on the target station. A maximum thermal neutron flux of 3.88 × 10⁹ neutrons·cm⁻²·s⁻¹ was measured in the bucket using cobalt activation discs. The thermal neutrons from this irradiation facility has been used for the neutron activation analysis of trace elements in archaeological artefacts. It has also been planned to utilize the fast neutron flux by varying the geometry of the water moderator in order to estimate oxygen concentration in high-temperature superconductors and aluminium and silicon in ceramics.     

Neutron flux characterization of a peripheral target position in the High Flux Isotope Reactor.

The High Flux Isotope Reactor at the Oak Ridge National Laboratory provides the highest steady-state thermal neutron flux in the western world for a wide range of experiments and for isotope production. The highest available fluxes are located in a flux trap region created inside the nested fuel elements. The experimentally determined thermal and the empirically obtained epithermal flux values along the vertical axis of the peripheral target position were fit to cosine curves, with the thermal flux ranging from 1.1 x 10(15)ns(-1)cm(-2) at outer positions to 1.5 x 10(15)ns(-1)cm(-2) at the center. The corresponding epithermal flux ranged from 3.5 x 10(13) to 7.5 x 10(13)ns(-1)cm(-2), respectively. The fast neutron flux (En > or = 0.32 MeV in two positions and En > or = 1.5 MeV in two other positions) was approximately 6 x 10(14)ns(-1)cm(-2), corresponding to a fast to thermal ratio of approximately 0.4.     

Performance tests of external moderators of a PGNAA setup.

Performance tests of external cylindrical moderators of an accelerator-based prompt gamma ray neutron activation analysis (PGNAA) setup have been carried out through thermal neutrons and prompt gamma-ray yield measurements. The PGNAA setup is to be used for analysis of cement samples. This study was conducted to investigate the effects of geometry of cylindrical moderator on yield of thermal neutrons and prompt gamma-rays for two different types of moderator assemblies. One of the moderators was to be used with a small sample and the other to be used with a large sample. Fast and thermal neutron yield was measured inside the sample volume as a function of the front moderator thickness as well as sample length. Neutron yield measurement was carried out at the King Fahd University of Petroleum and Minerals 350 keV pulsed beam accelerator using nuclear track detectors. The pulsed 200 keV deuteron beam with 5 ns pulse width and 31.25 kHz frequency was used to produce 2.8 MeV neutrons via D(d,n) reaction. Neutron yield measurements showed that the large sample moderator has a smaller yield of thermal neutrons as compared to the small sample moderator, which is in complete agreement with the results of Monte Carlo yield calculations of the thermal and fast neutrons from both the moderators. Finally, the prompt gamma-ray yield from a Portland cement sample was measured using the two moderators and was compared with each other. As predicted by Monte Carlo simulations, in spite of a smaller yield of thermal neutrons, the large sample moderator has a higher yield of prompt gamma-rays.     

Recognition of internal structure of unknown objects with simultaneous neutron and gamma radiography.

Generally speaking in customary industrial and medical radiography, there is no tendency to reveal the nature of the samples. Ordinarily, the main objective of taking a radiograph is to show the position and dimension of unknown parts, inside the test object and to determine cracks, defects, etc. Whereas in radiography many important factors such as material cross-sections and build-up factors are also involved. In this paper, by using both neutron and gamma radiography techniques, some mathematical relations were successfully generated, in order to calculate the neutron and gamma total macroscopic cross-sections of some unknown elements in the presence of the other elements. For this work, some test pieces were defined and made of lead, silver, copper, Nickel, tin, graphite and polyethylene. The neutron radiography facility at Tehran Research Reactor (TRR) was used as mixed neutron and gamma radiography source (Proceedings of the Second World Conference on Neutron Radiography, Paris, France, pp. 25-32). On testing of a correction of the above-mentioned generated relations, a new technique of simultaneous neutron and gamma radiography was also investigated.     

Evaluation of neutron sources for ISAGE—in-situ-NAA for a future lunar mission

For a future Moon landing, a concept for an in-situ NAA involving age determination using the ⁴⁰Ar–³⁹Ar method is developed. A neutron source ²⁵²Cf is chosen for sample irradiation on the Moon. A special sample-in-source irradiation geometry is designed to provide a homogeneous distribution of neutron flux at the irradiation position. Using reflector, the neutron flux is likely to increase by almost 200%. Sample age of 1 Ga could be determined. Elemental analysis using INAA is discussed.     

Effect of chronic exposure to low doses of ionized radiation on embryonal development of the Japanese quail

Experiments on Japanese quail embryogenesis on a background of chronic exposure to gamma- and neutron doses comparable with the doses of ionized radiation inside the orbital space stations Mir and ISS, and exploration vehicles gave evidence that permanent absorption of low gamma-doses (0,15 cgy/d) did not impact development of the Japanese quail embryos. On the contrary, the neutron dose of 200 microgy/d imparted by the neutron flux of 30 particles/cm2s was hazardous to embryos as it caused morphological disorders in 12% of embryos.     

A processing circuit for overlapped pulse signals for a thermal neutron coincidence counter

We have developed a processing circuit for overlapped pulse signals. The overlapped pulse signals are generated when the pulse signals of a He-3 detector, by using a neutron coincidence counter, are connected to shift register coincidence electronics by an OR gate device. The developed circuit detects the overlapped pulse signals from among four input signals and produces new 50 ns pulse wide signals. We considered a case where two pulse signals are simultaneously overlapped among four signals. This circuit was tested with an ACP safeguards neutron counter (ASNC) for an advanced spent fuel conditioning process (ACP) and a ²⁵²Cf neutron source at high rates. The loss rate of the output signal was reduced by 1.27% for singles and 4.75% for doubles when compared with the OR gate device. Also the variation for the triples was much bigger.     

Results of measuring neutron dose inside the Russian segment of the International Space Station using bubble detectors in experiment Matreshka-R

Distribution of neutron equivalent dose both inside and outside the spherical phantom (experiment Matryeshka-R) was determined with the help of dedicated research equipment "Bubble-dosimeter". Equipment is built up from an automatic bubbles counter and 8 bubble detectors of neutrons with energy ranging from approximately 200 keV to 15 MeV. Measurements inside the ISS were made in several 7-day sessions in the period from April 2006 till October 2007 (ISS increments 13-15). According to the bubble detectors on the outside of the phantom, ambient neutron dose H*(10) was equal to 0.1 mSv/d or approximately 20% of the dose from charged particles inside the ISS. In the tissue-equivalent phantom, neutron dose was 1.2 +/- 0.2 times less as compared with the phantom surface which characterized the degree of dose attenuation in cosmonaut's body.     

148g,mPm: Evaluation of the decay schemes for two important reactor poisons

During reactor operation ^148gPm and ^148mPm are formed in large quantities from thermal neutron capture on the fission product ¹⁴⁷Pm. Subsequent neutron capture reactions, on the ¹⁴⁸Pm ground state and isomer, have cross sections differing by a factor of 5 and so precise knowledge of their decay properties is vitally important. New decay scheme evaluations using the DDEP methodology for ^148gPm and ^148mPm are presented. The complete data tables and detailed evaluator comments are available through the DDEP website.     

Neutron radiography using neutron imaging plate

The aims of this research are to study properties of a neutron imaging plate (NIP) and to test it for use in nondestructive testing (NDT) of materials. The experiments were carried out by using a BAS-ND 2040 Fuji NIP and a neutron beam from the Thai Research Reactor TRR-1/M1. The neutron intensity and Cd ratio at the specimen position were approximately 9×10⁵ ns/cm² s and 100 respectively. It was found that the photostimulated luminescence (PSL) readout of the imaging plate was directly proportional to the exposure time and approximately 40 times faster than the conventional NR using Gd converter screen/X-ray film technique. The sensitivities of the imaging plate to slow neutron and to Ir-192 gamma-rays were found to be approximately 4.2×10^?3 PSL/mm² per neutron and 6.7×10^?5 PSL/mm² per gamma-ray photon respectively. Finally, some specimens containing light elements were selected to be radiographed with neutrons using the NIP and the Gd converter screen/X-ray film technique. The image quality obtained from the two recording media was found to be comparable.     

The use of associated particle timing based on the D + D reaction for imaging a solid object.

Associated particle timing based on the D + D reaction has been applied for imaging a bulk sample, namely an aluminium box. The relatively low neutron energy, 2.8 MeV, allows a better spatial resolution from time-of-flight measurements. A combination of a Si detector for charged particles and an NaI(Tl) scintillator for inelastic-scatter gamma rays yielded an overall time resolution of 0.4 ns, giving a spatial resolution of better than 1 cm. A new reconstruction program was developed, yielding an image free from major artefacts.     

The HYDAD-D antipersonnel landmine detector

HYDAD (HYdrogen Density Anomaly Detection) systems have been developed to detect small (>200 g) antipersonnel landmines (APM) of plastic construction. The HYDAD-D detector is based on the earlier HYDAD designs HYDAD-H and HYDAD-VM. It consists of a neutron source and two identical slow neutron detectors. The difference between the responses of the two detectors is monitored as a function of position in the minefield and APM detection is based on an analysis of this difference. Laboratory tests and Monte Carlo simulations demonstrate that HYDAD-D is capable of detecting the IAEA standard dummy landmine DLM2 at burial depths up to 23 cm in dry sand and at burial depths up to 7 cm in damp sand containing 12% (by mass) water.     

Calibration of semiconductor detectors in the 200-8500 keV range at VNIIM

At the ionising radiation department of the D.I. Mendeleyev Institute for Metrology, a semiconductor detector was calibrated in the energy range 200-8500 keV using (n,2γ) and (n,γ) reactions. Separate cylindrical targets (77 mm diameter and 10mm height) were made from mercuric sulphate, sodium chloride and metallic titanium. A (252)Cf spontaneous fission neutron source, placed in 150 mm diameter polyethylene ball, was used to generate thermal neutrons. The optimal target dimensions were determined taking into account the thermal neutron cross-sections and gamma-radiation attenuations in the target materials. The influence of the background radiation induced by neutrons from the walls, floors and ceilings was also taken into account. The shapes of the efficiency curves for point and volume sources in the 200-8500 keV range have been investigated. The experimental results are in good agreement with Monte-Carlo calculations. The emission rate of the 6.13 MeV photons from a (238)Pu-(13)C source was determined with an expanded uncertainty, U(c), of 10% (k=2).     

Advances in treatment planning dosimetry for a high energy neutron beam

Before starting the clinical programme, a series of physical measurements were made using the Clatterbridge high energy neutron facility. These consisted of measurements made under standard conditions, e.g. with square fields, full scatter conditions and perpendicular beam incidence. Further measurements have now been performed to include various clinically relevant non-standard conditions. These included the effects of field shape, backscatter, oblique incidence, bolus and beam blocking on dose distributions.     

Neutron irradiation and post annealing effect on sapphire by positron annihilation

Sapphire single crystals grown by an improved Kyropoulos-like method are irradiated by fast neutron flux. The irradiated doses of neutron are 10¹⁸ and 10¹⁹ n/cm². The infrared transmission spectra of sapphire were studied before and after irradiation. The irradiated samples were annealed at 200, 400, 600, 800 and 1000 °C for 10 min in ambient atmosphere. Positron annihilation studies have been carried out before and after neutron irradiation. The experimentally measured positron lifetime in the pristine specimen is 143 ps. There were aluminum vacancies produced in sapphire crystals after neutron irradiation. The positron lifetime increased with the dose of neutron flux. A longer value τ₂ was found after annealing at 600 °C, which indicated vacancies were aggregated with each other. The second long-time component τ₂ has been found to increase with the annealing temperature. There was almost no change in peak position of the CDB spectra after neutron irradiation and isothermal annealing. The chemical environment of core in sapphire did not change greatly after neutron irradiation.     

Monte Carlo N-particle simulation of neutron-based sterilisation of anthrax contamination

Objective To simulate the neutron-based sterilisation of anthrax contamination by Monte Carlo N-particle (MCNP) 4C code. Methods Neutrons are elementary particles that have no charge. They are 20 times more effective than electrons or γ-rays in killing anthrax spores on surfaces and inside closed containers. Neutrons emitted from a (252)Cf neutron source are in the 100 keV to 2 MeV energy range. A 2.5 MeV D-D neutron generator can create neutrons at up to 10(13) n s(-1) with current technology. All these enable an effective and low-cost method of killing anthrax spores. Results There is no effect on neutron energy deposition on the anthrax sample when using a reflector that is thicker than its saturation thickness. Among all three reflecting materials tested in the MCNP simulation, paraffin is the best because it has the thinnest saturation thickness and is easy to machine. The MCNP radiation dose and fluence simulation calculation also showed that the MCNP-simulated neutron fluence that is needed to kill the anthrax spores agrees with previous analytical estimations very well. Conclusion The MCNP simulation indicates that a 10 min neutron irradiation from a 0.5 g (252)Cf neutron source or a 1 min neutron irradiation from a 2.5 MeV D-D neutron generator may kill all anthrax spores in a sample. This is a promising result because a 2.5 MeV D-D neutron generator output >10(13) n s(-1) should be attainable in the near future. This indicates that we could use a D-D neutron generator to sterilise anthrax contamination within several seconds.     

Gadolinium-loaded chitosan nanoparticles for neutron-capture therapy: Influence of micrometric properties of the nanoparticles on tumor-killing effect

As a nanoparticulate device for controlled delivery of Gd in NCT, the authors have developed gadolinium-loaded chitosan nanoparticles (Gd-nanoCPs). In the present study, influence of micrometric properties such as particle size, particle-surface charge and Gd content of Gd-nanoCPs on tumor-killing effect by Gd-NCT was investigated with Gd-nanoCPs. Two types of Gd-nanoCPs with different mean particle size, zeta potential and Gd-content (Gd-nanoCP-400; 391 nm, 28 mV, 9 wt% and Gd-nanoCP-200; 214 nm, 19 mV, 24 wt%) could be prepared by using chitosans with different molecular weights. Gd-nanoCPs incorporating 1.2 mg of natural Gd were injected intratumorally once or twice to mice subcutaneously-bearing B16F10 melanoma. Eight hours after the last administration, thermal neutron was irradiated to tumor region of the mice. Remarkable tumor-growth was observed in both hot and cold control groups. In contrast, Gd-NCT groups showed significant tumor-growth suppression effect, though their efficacy was found to depend on the micrometric properties of Gd-nanoCPs. In particular, the Gd-nanoCP-200 exhibited stronger tumor-killing effect than the Gd-nanoCP-400 at the same Gd dose and it was still similar to Gd-nanoCP-400 in tumor-growth suppressing effect even at the half of Gd dose of Gd-nanoCP-400. This significance in tumor-killing effect would be ascribed from a higher Gd retention in the tumor tissue and an improved distribution of Gd with intratumorally administered Gd-nanoCP-200. Indeed, the Gd concentration in tumor tissue at the time corresponding to the onset of thermal neutron irradiation was determined to be significantly higher in Gd-nanoCP-200, compared with Gd-nanoCP-400. These results demonstrated that appropriate modification of Gd-nanoCPs in micrometric properties would be an effective way to improve the retention of Gd in the tumor tissue after intratumoral injection, leading to the enhanced tumor-killing effect in Gd-NCT.     

APE1RNA干扰提高骨肉瘤中子放疗敏感性的研究

目的应用pSilence APE1“敲低”HOS细胞APE1的表达，观察pSilence APE1联合中子放疗对HOS细胞生长抑制的协同作用并探讨其机制。方法用脂质体将pSilence APEI质粒导人HOS细胞，“敲低”HOS细胞中APE1的表达，同时给予^252Cf中子射线照射，MTT法绘出细胞存活曲线，克隆形成分析测算D37值和剂量修饰系数（DMF），彗星分析法检测照射后细胞的DNA损伤情况，并用流式细胞仪检测细胞凋亡。结果由克隆形成分析得到对照质粒与转染pSilence APE1质粒的HOS细胞经^257Cf中子照射后的D37值为3．02和2．42，DMF值为1．43。以上2组HOS细胞以200、500和1000cGy3个剂量^252Cf子射线照射后，碱性彗星尾力矩分别是6．146±0．741、19．918±1．574、31．885±1．192和7．997±0．542、25．238±1．185、39．191±1．052（P〈0．01）；细胞凋亡率是4．00、5．91、9．63和5．68、7．55、13．51（P〈0．05）。结论pSilence APE1能显著提高HOS细胞对中子射线的敏感性，促进DNA损伤和细胞凋亡。pSilence APE1基因联合中子放疗可能成为今后骨肉瘤治疗的新方法。     

Characterization of ultra high energy neutron beam generated by 500 MeV proton beam

An ultra high energy neutron facility was constructed at PARMS, University of Tsukuba, to produce a neutron beam superior to an X-ray beam generated by a modern linac in terms of dose distribution. This has been achieved using the reaction on a thick uranium target struck by 500 MeV proton beam from the booster-synchrotron of High Energy Physics Laboratory. The percentage depth dose of this neutron beam is nearly equivalent to that of X-rays at around 20 MV and the dose rate of 15 cGy per minute. Relative biological effectiveness of this neutron beam has been estimated on the cell killing effect by the use of HMV-I cell line. Resultant survival curve of cells after the neutron irradiation shows the shoulder with n and Dq of 8 and 2.3 Gy, respectively. RBE value at 10(-2) survival level for the present neutron, compared with 137Cs gamma-rays is 1.24. The result suggests that the biological effects of high energy neutrons are not practically large enough whenever the depth dose distribution of neutrons becomes superior to high energy linac X-rays.     

Non-destructive 10B analysis in neutron transmission experiments.

Boron alloyed stainless-steel sheets are predominantly used in nuclear engineering as neutron shielding for radioactive waste disposal equipment. The neutron absorption depends strongly on the amount and the distribution of the 10B isotope. A systematic transmission study of 10B enriched steel plates by means of neutron time-of-flight and neutron radiography experiments was performed. The 10B content was analyzed with accuracy up to 5 x 10(-3) wt% using monochromatic beams and a linear increase of the macroscopic cross section with the 10B content was found even for strong absorbers. Then we extended the transmission analysis to "white" thermal neutron beams where large deviations from the exponential transmission law are observed. The influence of the spectral width is discussed in more detail because beam hardening causes an elevation of the effective transmission through strong absorbing materials, an effect which is crucial for the design of neutron shielding.