Bonino Valentina, Torsello Daniele, Prestipino Carmelo, Mino Lorenzo, Truccato Marco
ESRF - The European Synchrotron, 71 Avenue des Martyrs, 38000 Grenoble, France.
Istituto Nazionale di Fisica Nucleare, Sezione di Torino I, 10125 Torino, Italy.
J Synchrotron Radiat. 2020 Nov 1;27(Pt 6):1662-1673. doi: 10.1107/S1600577520010553. Epub 2020 Sep 16.
X-ray synchrotron sources, possessing high power density, nanometric spot size and short pulse duration, are extending their application frontiers up to the exploration of direct matter modification. In this field, the use of atomistic and continuum models is now becoming fundamental in the simulation of the photoinduced excitation states and eventually in the phase transition triggered by intense X-rays. In this work, the X-ray heating phenomenon is studied by coupling the Monte Carlo method (MC) with the Fourier heat equation, to first calculate the distribution of the energy absorbed by the systems and finally to predict the heating distribution and evolution. The results of the proposed model are also compared with those obtained removing the explicit definition of the energy distribution, as calculated by the MC. A good approximation of experimental thermal measurements produced irradiating a millimetric glass bead is found for both of the proposed models. A further step towards more complex systems is carried out, including in the models the different time patterns of the source, as determined by the filling modes of the synchrotron storage ring. The two models are applied in three prediction cases, in which the heating produced in BiSrCaCuO microcrystals by means of nanopatterning experiments with intense hard X-ray nanobeams is calculated. It is demonstrated that the temperature evolution is strictly connected to the filling mode of the storage ring. By coupling the MC with the heat equation, X-ray pulses that are 48 ps long, possessing an instantaneous photon flux of ∼44 × 10 photons s, were found to be able to induce a maximum temperature increase of 42 K, after a time of 350 ps. Inversely, by ignoring the energy redistribution calculated with the MC, peaks temperatures up to hundreds of degrees higher were found. These results highlight the importance of the energy redistribution operated by primary and secondary electrons in the theoretical simulation of the X-ray heating effects.
X射线同步辐射源具有高功率密度、纳米级光斑尺寸和短脉冲持续时间，其应用前沿正在扩展到直接物质改性探索领域。在该领域，原子模型和连续介质模型的使用在光致激发态模拟以及最终由强X射线引发的相变模拟中变得至关重要。在这项工作中，通过将蒙特卡罗方法（MC）与傅里叶热方程相结合来研究X射线加热现象，首先计算系统吸收的能量分布，最终预测加热分布和演化。还将所提出模型的结果与通过MC计算去除能量分布的明确定义后获得的结果进行了比较。对于所提出的两种模型，在照射毫米级玻璃珠时都能很好地近似实验热测量结果。朝着更复杂系统迈出了进一步的一步，在模型中纳入了由同步加速器储存环的填充模式决定的源的不同时间模式。这两种模型应用于三个预测案例，计算了通过用强硬X射线纳米束进行纳米图案化实验在BiSrCaCuO微晶中产生的加热情况。结果表明，温度演化与储存环的填充模式密切相关。通过将MC与热方程耦合，发现长度为48 ps、瞬时光子通量约为44×10光子/秒的X射线脉冲在350 ps时间后能够诱导最高42 K的温度升高。相反，忽略用MC计算的能量重新分布时，发现峰值温度高达数百摄氏度更高。这些结果突出了初级和次级电子进行的能量重新分布在X射线加热效应理论模拟中的重要性。
