Geesthacht Neutron Facility Research Articles

SU‐E‐T‐195: Commissioning the Neutron Production of a Varian TrueBeam Linac

Purpose:The purpose of this work is the characterization of a new Varian TrueBeam™ facility in terms of neutron production, in order to estimate neutron equivalent dose in organs during radiotherapy treatments.Methods:The existing methodology [1] was used with the reference SRAMnd detector, calibrated in terms of thermal neutron fluence at the reference field operated by PTB (Physikalisch‐Technische‐Bundesanstalt) at the GeNF (Geesthacht‐Neutron‐Facility) with the GKSS reactor FRG‐1 [2]. Thermal neutron fluence for the 5 available possibilities was evaluated: 15 MV and 10&6 MV with and without Flattening Filter (FF and FFF, respectively). Irradiation conditions are as described in [3]. In addition, three different collimator‐MLC configurations were studied for 15 MV: (a) collimator of 10×10 cm2 and MLC fully retracted (reference), (b) field sizes of 20×20 cm2 and 10×10 cm2 for collimator and MLC respectively, and (c) collimator and MLC aperture of 10×10 cm2.Results:Thermal fluence rate at the “reference point” [3], as a consequence of the neutron production, obtained for (a) conformation in 15 MV is (1.45±0.11) x10⁴ n•cm2/MU. Configurations (b) and (c) gave fluences of 96.6% and 97.8% of the reference (a). Neutron production decreases up to 8.6% and 5.7% for the 10 MV FF and FFF beams, respectively. Finally, it decreases up to 2.8% and 0.1% for the 6 MV FF and FFF modes, respectively.Conclusion:This work evaluates thermal neutron production of Varian TrueBeam™ system for organ equivalent dose estimation. The small difference in collimator‐MLC configuration shows the universality of the methodology [3]. A decrease in this production is shown when decreasing energy from 15 to 10 MV and an almost negligible production was found for 6 MV. Moreover, a lower neutron contribution is observed for the FFF modes.[1]Phys Med Biol,2012;57:6167–6191.[2]Radiat Meas,2010;45:1513–1517.[3]Med Phys,2015;42:276–281.

Dinosaur and Crocodile Fossils from the Mesozoic of Portugal: Neutron Tomography and Synchrotron-Radiation Based Micro-Computed Tomography

ABSTRACTPortugal is ranked within the 10 countries with the most dinosaur taxa and the Lourinhã Formation is known by the Late Jurassic findings of dinosaurs and other fossils. In many cases, studies of the external morphological characteristics of the fossils are not sufficient to extract all the information for a paleontological study and, thus, observations of internal structures, using non-destructive techniques, are required. The fossils studied in the present work belong to the Museum of Lourinhã. The access to the Geesthacht Neutron Facility in Germany allowed us to characterize a jaw of the dinosaur Baryonyx walkeri specimen and the jaw of a crocodile (possibly a Tomistomidae) by Neutron Tomography. The study allowed us to detect the presence of teeth inside the jaws and it provides valuable information about the development of its dental characteristics. Synchrotron radiation based micro-computed tomography studies on tiny samples have been performed at the beamline HARWI II operated by the Helmholtz-Zentrum Geesthacht at the storage ring DORIS III at the Deutsches Elektronen–Synchrotron DESY in Hamburg, Germany. The first data recorded for eggshells collected in the Lourinhã Formation is shown. It allowed us to visualize the morphology of the pores and their connectivity in the eggshells, providing information that is either exceedingly difficult or impossible to obtain by traditional methods based on section cutting.

Monte Carlo simulations of the new small-angle neutron scattering instrument SANS-1 at the Heinz Maier-Leibnitz Forschungsneutronenquelle

A new small-angle scattering instrument SANS-1 will be installed on beamline NL 4a at the Heinz Maier-Leibnitz Forschungsneutronenquelle (FRM II). It is a joint venture between the Technische Universität München and the Geesthacht Neutron Facility (GENF). SANS-1 has been optimized to be one of the most intense and versatile small-angle scattering instruments within the boundaries of available space and interaction with neighbouring instruments. Using the program McStas, the dimensions and the features of the different optical components were investigated and compared for the final selection. A vertical S-shaped neutron guide, a tower with two possible selectors, one for medium resolution at high intensity and one for high resolution, and two optimized transmission polarizers are the main advantages of SANS-1 compared with traditional instruments at other facilities.

Application of different TL detectors for the photon dosimetry in mixed radiation fields used for BNCT

Different approaches for the measurement of a relatively small gamma dose in strong fields of thermal and epithermal neutrons as used for Boron Neutron Capture Therapy (BNCT) have been studied with various thermoluminescence detectors (TLDs). CaF(2):Tm detectors are insensitive to thermal neutrons but not tissue-equivalent. A disadvantage of applying tissue-equivalent (7)LiF detectors is a strong neutron signal resulting from the unavoidable presence of (6)Li traces. To overcome this problem it is usual to apply pairs of LiF detectors with different (6)Li content. The experimental determination of the thermal neutron response ratio of such a pair at the Geesthacht Neutron Facility (GeNF) operated by PTB enables measurement of the photon dose. In the experimental mixed field of thermal neutrons and photons of the TRIGA reactor at Mainz the photon dose measured with different types of (7)LiF/(nat)LiF TLD pairs agree within a standard uncertainty of 6% whereas the CaF(2):Tm detectors exhibit a photon dose by more than a factor of 2 higher. It is proposed to determine suitable photon energy correction factors for CaF(2):Tm detectors with the help of the (7)LiF/(nat)LiF TLD pairs in the radiation field of interest.

Two-dimensional position-sensitive gaseous detectors for high-resolution neutron and X-ray diffraction

Two-dimensional position-sensitive gaseous detectors have been developed at the Geesthacht Neutron Facility (GeNF) for high-resolution neutron and X-ray diffractometry. They are multi-wire proportional counters with delay-line readout and sensitive areas of 300 mm×300 mm or 500 mm×500 mm. For detecting X-rays, neutrons and hard X-rays the counters are filled with Ar/CO2, 3He/CF4 and Xe/CO2, respectively. One neutron detector is used at the ARES diffractometer at GKSS, which is dedicated to the analysis of residual stresses. Further ones are used for analysing textures and residual stresses at the hard-X-ray beamline PETRA-2 at HASYLAB, and one detector is being developed for the neutron reflectometer REFSANS at the research reactor FRM-II in Munich, Germany.

USANS investigation of early stages of metal foam formation

Metallic foams are on the verge of being used in industrial applications. However, the mechanism of foam creation, especially the early stages, are still unexplored. Ultra small-angle neutron scattering (USANS), performed with the double-crystal diffractometer (DCD) at the Geesthacht Neutron Facility (GeNF), is a promising method for obtaining a three-dimensional average of a pore size distribution in a wide size range from about 100 nm to about 20 μm. Analysis of the neutron scattering curves yielded pore size distributions which conformed with the results obtained by microscopy.

Two-dimensional position-sensitive detectors for high resolution diffraction with neutrons and high energy synchrotron radiation

A two dimensional position-sensitive neutron detector has been developed at the Geesthacht Neutron Facility (GeNF) for the new diffractometer ARES which is dedicated to the analysis of residual stresses. The detector is a 3He and CF 4 filled multiwire proportional counter with delay line readout and has a sensitive area of 300 mm×300 mm.The detector was tested at different 3He and CF 4 partial pressures with a well collimated neutron beam. Excellent linearity and homogeneity of the detection probability combined with a spatial resolution of about 2 mm×2 mm were found.

Properties of a Cold-Neutron Irradiation Facility for in Vitro Research on Boron Neutron Capture Therapy at the Geesthacht Neutron Facility

A new irradiation facility, GBET (basic research on boron neutron capture therapy), especially designed for in vitro experiments on boron neutron capture therapy was put into operation at the Geesthacht Neutron Facility of the GKSS Research Center. Its location at a cold-neutron guide without direct view of the reactor core has two advantages: First, contamination of the primary beam with fast neutrons or photons is negligible. Second, GBET yields a high cold-neutron flux of 1.4 × 108/(cm2·s) over an area of 3 × 4 cm. As a result of the energy dependence of the neutron absorption cross section of boron, this corresponds to a higher effective thermal flux of 4.7 × 108/(cm2·s). This effect is used to reduce the irradiation times by a factor of 3.32.The effective flux is sufficient for irradiation of thin samples like cell monolayers in conventional culture flasks. For such in vitro irradiations, a survival fraction of 1% is achieved at a homogeneous boron concentration of 100 ppm 10B within ~20 min. Furthermore, the beam can be used for boron radiography. The respective experimental conditions are discussed, especially the neutron flux distribution, available for these different types of samples.

Two-dimensional position-sensitive [formula omitted]-neutron detector for reflectometry and high-resolution diffractometry

A two-dimensional position-sensitive neutron detector has been developed at the Geesthacht Neutron Facility (GeNF). The detector is a 3 He and CF 4 filled multiwire proportional counter with delay line readout and has a sensitive area of 300 mm ×300 mm and a high detection efficiency for wavelengths λ>0.15 nm. It is an important component of the new diffractometer ARES at GeNF which is dedicated to the analysis of residual stresses. The detector design to achieve excellent linearity, detection homogeneity and a spatial resolution of about 2 mm ×2 mm has been described.

Performance of a double crystal diffractometer with different channel-cut perfect Si crystals

The double crystal diffractometer (DCD) at the Geesthacht Neutron Facility (GeNF) is equipped with triple-bounce channel-cut perfect Si(111) crystals. In this way the intrinsic background of DCD, i.e. given by the rocking-curve wings, has been decreased dramatically. Its former dependence on the scattering vector q of q −2 was changed to q −6. An observed deviation from the q −6 behaviour is possibly attributed to neutrons propagating and diffracting inside the walls of the channel-cut crystals. In order to reduce this parasitic intensity and for further improvement of DCD with respect to higher sensitivity to weak sample scattering quintuple-bounce side grooved channel-cut crystals have been used. The change in the rocking curves without and with inserting cadmium in the grooves of the walls is pointed out. The efficiency of DCD is shown in the case of neutron scattering from Latex spheres with radii of about 2200 nm.

User-friendly software for SANS data reduction

At the Geesthacht Neutron Facility (GeNF) we have developed new software for the reduction of two-dimensional small-angle neutron scattering (SANS) data. The main motivation for this work was to create software for users of our SANS facilities that is easy to use. Another motivation was to provide users with software they can also use at their home institute. Therefore, the software is implemented on a personal computer running Windows. The program reads raw data from an area detector in binary or text format and produces text files containing the scattering curve. The cross section can be averaged over the whole area of the detector or over sectors only. Scripts can be used for the processing of large numbers of files.

Elastic neutron-scattering experiments at the Geesthacht Neutron Facility (GeNF)

The Geesthacht Neutron Facility (GeNF) comprises experimental facilities for elastic neutron scattering for materials research and engineering problems as well as for environmental research purposes at the research reactor FRG-1. The experimental facilities for elastic neutron-scattering experiments at GeNF, most of which can be optimally used with polarized neutrons, will be presented. They are open to national and international users from universities and other research institutes at no cost.

Improvement of the double crystal diffractometer at the Geesthacht Neutron Facility (GeNF) by means of perfect channel-cut silicon crystals

High resolution small-angle neutron scattering (HR-SANS) investigations have been performed by means of the double crystal diffractometer (DCD) at the Geesthacht Neutron Facility (GeNF). The two single perfect silicon crystals of the instrument have recently been replaced by channel-cut ones in the non-dispersive (1, −1) setting to reduce the intensity of the rocking curve in its wings by three-fold reflections. Thereby a very strong decrease of this intensity has been achieved, whereby its former dependence on the scattering vector q of q −2 has been changed to q −6. This improvement of the rocking curve leading to a reduction of the inherent background is presented, and a new perspective for future HR-SANS investigations is pointed out.

Characterization of microstructures with sizes from the sub-nm to the μm-range by extended small-angle neutron scattering

Conventional SANS facilities cover scattering vectors q between about 0.01 and 3 nm −1 and are well suited for analyzing microstructures in materials with sizes from 1 to about 100 nm. At the Geesthacht neutron facility (GeNF), this range has been greatly extended. Larger values of q (up to 25 nm −1) are made accessible at the pin-hole facility SANS-2 by means of a second area detector, which can be rotated around the sample. Smaller q-values down to 10 −3 nm −1 can be covered at the SANS-2 by means of the beam broadening (BB) technique. With the use of a double-crystal diffractometer (DCD) still smaller q-values down to 10 −4 nm −1 become accessible. Investigations of extremely small structures (cluster with radii of only 0.3 nm), and extremely large ones (creep pores in ceramics with size up to some μm) are presented.