Micro-spot gamma-ray generation based on laser wakefield acceleration

Abstract

The radiography of gamma-ray is one of the most important non-destructive testing in many fields. However, the spot size is always in millimeter scale for the generation of gamma-ray by conventional way. As the development of laser wakefield acceleration, the electron beam with small divergence and spot size can be generated easily in the experiment by tens of terawatt ultra-short laser pulse. Based on this electron beam, gamma-ray with micro spot size is generated and the properties are measured and tested in detail experimentally. The experiment demonstrates that the spot size of this gamma-ray is always smaller than 200 μm, no matter the conversion target thickness, and can be as small as about 40 μm when the conversion target thickness of 0.2 mm is used. The spatial resolution of this gamma-ray is much better than 2.5 LP/mm, the fitting temperature (which is relative to the average energy of gamma-ray) is between 5 MeV and 8 MeV, and the maximum yield per shot of the gamma-ray can be up to 9.1 × 109 photons (energy higher than 1 MeV). High-resolution radiography shows that the areal density of the gamma-ray radiography can be up to 51.3 g/cm2 (stainless steel thickness equivalent is about 6.5 cm). Such micro-spot gamma-ray can play an important role in the high-resolution radiography of high areal density objects.

Towards high-energy, high-resolution computed tomography via a laser driven micro-spot gamma-ray source

“…In the experiment, the conditions of the micro-spot gamma-ray generation were chosen according to our previous research 26 . A 0.8 J, 28 fs laser pulse was focused on a gas jet with an outlet diameter of 0.7 mm to generate low emittance electron beams with energies of tens of MeV (see Fig.…”

“…The spot size was reduced with decreasing convertor thickness, and provided higher spatial resolution, however, the source intensity was also reduced. To balance the photon yield and spot size, a 0.5 mm-thick copper convertor was used to supports a 100 µm spot size 26 . A filter stack spectrometer (FSS) 27 , 28 could be inserted into the gamma-ray beam before the object to measure the gamma-ray spectra and photon yields.…”

“…According to the absolute gamma-ray spectrum, the radiation dose could be obtained from using flux-to-dose conversion factors 46 . Before the CT demonstration, a projection image of a 2D resolution test object, used in our previous experiment 26 , was obtained to check the spatial resolution of the imaging system. (Supplementary Fig.…”

“…Since 2012, we started our research on this subject 25 . In 2016, the properties and conditions of micro-spot gamma-ray source were detailed investigated 26 to have a spot size is also as small as 40 μm by using a 5mrad electron beam. Two-dimensional (2D) radiography demonstrations with this gamma-ray source have high spatial resolution and penetration for high-area density objects.…”

Development of control mechanisms for a laser wakefield accelerator-driven bremsstrahlung x-ray source for advanced radiographic imaging

“…Compact X-ray sources for imaging have also been demonstrated using bremsstrahlung radiation [8,[17][18][19][20][21], which is produced by the deceleration of charged particles in the nuclear field. Electrons incident on a high-Z material produce a cone of radiation with a broad energy spread extending up to the maximum electron energy.…”