Sci-Fri PM: Topics - 01: A monte carlo model of a miniature low-energy x-ray tube using EGSnrc

2014 ◽  
Vol 41 (8Part3) ◽  
pp. 24-24 ◽  
Author(s):  
P Watson ◽  
J Seuntjens
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Model ◽  
Low Energy ◽  
X Ray

A Theoretical Study of the Effects of Dead Layers on Low Energy X-Ray Detectors

1977 ◽  
Vol 21 ◽  
pp. 207-215
Author(s):  
R. Hight ◽  
C. N. Inskeep
Keyword(s):  
Monte Carlo ◽  
Theoretical Study ◽  
Monte Carlo Model ◽  
Counting Efficiency ◽  
Spectral Shape ◽  
Low Energy ◽  
Semiconductor Detectors ◽  
X Ray

A Monte-Carlo model has been developed to calculate the effect entrance windows, or dead layers, have on the spectral shape and the counting efficiency of semiconductor detectors used in the low energy x-ray region (1 – 5 KeV).

scholarly journals Glimpses of the past activity of Sgr A★ inferred from X-ray echoes in Sgr C

2018 ◽  
Vol 610 ◽  
pp. A34 ◽  
Author(s):  
D. Chuard ◽  
R. Terrier ◽  
A. Goldwurm ◽  
M. Clavel ◽  
S. Soldi ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Black Hole ◽  
Monte Carlo Model ◽  
Line Of Sight ◽  
X Rays ◽  
X Ray ◽  
Supermassive Black Hole ◽  
The Past ◽  
Sgr A ◽  
Past Activity

Context. For a decade now, evidence has accumulated that giant molecular clouds located within the central molecular zone of our Galaxy reflect X-rays coming from past outbursts of the Galactic supermassive black hole. However, the number of illuminating events as well as their ages and durations are still unresolved questions. Aims. We aim to reconstruct parts of the history of the supermassive black hole Sgr A★ by studying this reflection phenomenon in the molecular complex Sgr C and by determining the line-of-sight positions of its main bright substructures. Methods. Using observations made with the X-ray observatories XMM-Newton and Chandra and between 2000 and 2014, we investigated the variability of the reflected emission, which consists of a Fe Kα line at 6.4 keV and a Compton continuum. We carried out an imaging and a spectral analysis. We also used a Monte Carlo model of the reflected spectra to constrain the line-of-sight positions of the brightest clumps, and hence to assign an approximate date to the associated illuminating events. Results. We show that the Fe Kα emission from Sgr C exhibits significant variability in both space and time, which confirms its reflection origin. The most likely illuminating source is Sgr A★. On the one hand, we report two distinct variability timescales, as one clump undergoes a sudden rise and fall in about 2005, while two others vary smoothly throughout the whole 2000–2014 period. On the other hand, by fitting the Monte Carlo model to the data, we are able to place tight constraints on the 3D positions of the clumps. These two independent approaches provide a consistent picture of the past activity of Sgr A★, since the two slowly varying clumps are located on the same wavefront, while the third (rapidly varying) clump corresponds to a different wavefront, that is, to a different illuminating event. Conclusions. This work shows that Sgr A★ experienced at least two powerful outbursts in the past 300 yrs, and for the first time, we provide an estimation of their age. Extending this approach to other molecular complexes, such as Sgr A, will allow this two-event scenario to be tested further.

X-ray diffuse scattering from HMTA: analysis via a Monte Carlo model

2008 ◽  
Vol 64 (4) ◽  
pp. 456-465 ◽  
Author(s):  
D. J. Goossens ◽  
A. P. Heerdegen ◽  
T. R. Welberry
Keyword(s):  
Monte Carlo ◽  
Azelaic Acid ◽  
Diffuse Scattering ◽  
Cross Correlation ◽  
Monte Carlo Model ◽  
Limited Range ◽  
Thermally Induced ◽  
X Ray ◽  
Zero Correlation ◽  
Average Position

Hexamethylenetetramine (HMT, C6H12N4, also referred to as urotropin) and azelaic acid [A, HOOC—(CH2)7—COOH] form a co-crystal or adduct (HMTA, also referred to as urotropin azelate) which exhibits several structural phases as a function of temperature. At room temperature, the structure is orthorhombic, but shows substantial disorder. Here, this disorder is explored by analyzing the diffuse scattering from single crystals of HMTA via Monte Carlo simulation. The disorder is in part occupational, with two orientations of azelaic acid occurring, and in part thermally induced, which is to say dynamic. The occupational disorder can be thought of as a combination of limited-range in-plane (bc plane) negative correlations combined with effectively zero correlation between planes (along a), rather like stacking faults. Size effect, the cross-correlation between molecular orientation and displacement from average position, is required to reproduce the observed diffuse scattering.

X-RAY COLLIMATOR DESIGN USING MONTE CARLO SIMULATIONS

2013 ◽  
Vol 25 (06) ◽  
pp. 1350054
Author(s):  
Eun Young Han ◽  
Richard Clarkson ◽  
Sunil Sharma ◽  
Peter M. Corry ◽  
Eduardo G. Moros ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Small Animal ◽  
Low Energy ◽  
Aperture Size ◽  
Beam Size ◽  
Dose Distributions ◽  
X Ray ◽  
Collimation System ◽  
Acceptable Agreement ◽  
Ebt2 Film

The purpose of this study was to apply Monte Carlo (MC) based simulations to design a new collimation system to achieve a larger beam size (2 ± 0.1 cm) and tight penumbra (< 1 mm) with a kV X-ray small animal irradiator. The BEAMnrc and DOSXYZnrc MC-based programs were adapted to simulate the system. First the aperture of the primary collimator was expanded until the desired size of the beam was obtained. Subsequently, the beam was trimmed by reducing the aperture size of the secondary collimator in order to eliminate low energy scattered photons and sharpen the penumbra. Finally, the new collimator was constructed and the resultant dose distributions were evaluated with EBT2 film measurements. From the MC computed dose profiles, a 2.1 cm FWHM (1.9 cm width at 95% of the dose) and a sharp penumbra (< 1.0 mm) at 1.0 cm depth in water were obtained. Dose distribution comparisons between the EBT2 film measurements and the MC calculations showed acceptable agreement. MC-based calculation is an effective tool to expedite the creation of new collimator designs and avoid costly machining.

Monte Carlo simulation of Boron diffusion during low energy implantation and high temperature annealing

1997 ◽  
Vol 469 ◽  
Author(s):  
M.-J. Caturla ◽  
T. Diaz de la Rubia ◽  
J. Zhu ◽  
M. Johnson
Keyword(s):  
Monte Carlo ◽  
High Temperature ◽  
Kinetic Monte Carlo ◽  
Monte Carlo Model ◽  
Low Energy ◽  
High Temperature Annealing ◽  
Boron Diffusion ◽  
Enhanced Diffusion ◽  
Diffusion Enhancement ◽  
High Doses

ABSTRACTWe use a kinetic Monte Carlo model to simulate the implantation of low energy Boron in Silicon, from 0.5 to 1 keV, at high doses, 1015 ions/cm2. The damage produced by each ion is calculated using UT-Marlowe, based on a binary collision approximation. During implantation at room temperature,, silicon self-interstitials, vacancies and boron interstitials are allowed to migrate and interact. The diffusion kinetics of these defects and dopants has been obtained by ab initio calculations as well as Stillinger Weber molecular dynamics. Clustering of both self-interstitials, vacancies and boron atoms is included. We also model the diffusion of the implanted dopants after a high temperature annealing in order to understand the transient enhanced diffusion (TED) phenomenon. We observe two different stages of TED During the first stage vacancies are present in the lattice together with interstitials and the diffusion enhancement is small. The second stage starts after all the vacancies disappear and gives rise to most of the final TED.

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