Intense X-rays signal breakthrough for non-destructive inspection

Mar 13, 2011 | X-Scan

Measurement of X-rays from FoFu-1 electron beam shows that LPP’s X-Scan application is technically feasible


New experiments this month have demonstrated for the first time that the main spin-off technology of our research, the X-Scan instrument to inspect roads, bridges, and other major infrastructure, is technically feasible with a DPF similar to our FF-1. While this is only a laboratory demonstration, far from a commercial product, the new experimental evidence indicates that such a commercial product is feasible, given adequate engineering funding. In our view, this considerably increases the chances that LPP will have a profitable product, even before the development of Focus Fusion.

Based on last month’s observation of a very powerful ion beam, the LPP research team re-positioned two of our photo multiplier tube (PMT) X-ray detectors to study the electron beam that is generated at the same time as the ion beam, but in the opposite (upward) direction. The beam creates intense X-ray radiation when it collides with the copper anode at the top of a 1.6-inch deep hole in the anode. One PMT was located so that it could view the collision point horizontally, with the radiation filtered by the 1.1-inch radius of the anode itself. A second PMT was put on top of the device, where the radiation had to penetrate 4.3 inches of copper and 1.8 inches of steel.

The ratio of the signals from these two detectors gives a good measure of the average energy of the X-rays coming from the beam, and thus of the electrons generating these X-rays. With higher energy electrons, traveling close to the speed of light, a phenomenon explained by relativity theory causes the radiation to be more and more tightly beamed along the axis as electron energy increases. At the same time, the average energy of the photons also increases, making them more penetrating. Both effects combine to increase the on-axis radiation faster than the horizontal radiation as electron beam energy rises.

In our experiments on Feb. 17, in four out of four shots that were fired by the trigger, we detected very large signals from the on-axis PMT, despite the 6” of metal that is shielding this detector. Calculations performed by Eric Lerner and LPP contractor Dr. John Guillory showed that the average energy of the electrons producing this radiation was 3-4 MeV in three of the shots and 6 MeV in a fourth. The typical X-ray photon produced by the beam was over 1 MeV.  In one shot (see Fig. 1), more radiation was actually detected vertically than horizontally, despite the much heavier shielding. This deep penetrating radiation is capable of imaging metal infrastructure to a depth of several inches and roads to a depth of a foot or more.



Figure 1. Signals showing strength of X-ray signals from PMTs on-axis and horizontally. Note that in the second horizontal peak the vertical, on-axis signal is higher. This indicates very high energy electrons compared to the first peak in horizontal signal, where electron energy is lower.

The large size of the signals, more than 1,000 times the minimum signal that the PMTs can detect, shows that even without optimizing the beam, we already have sufficient energy to create images through Compton scattering—a reflection process in which the detector and source of the X-rays can be located on the same side of the object surveyed, a necessity for large infrastructure.


Of course, this is purely a laboratory experiment, and much engineering work would have to be done to create a commercial product, including ruggedizing a DPF sufficiently to be carried by a truck. Even from an experimental standpoint, the variability in the beams will have to be greatly reduced. We expect to be studying this variability intensely in the coming months. However, the demonstration should be sufficient to attract the interest of potential partners in the inspection and non-destructive-testing markets, and we will soon be contacting these potential partners.





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