Category: Improvised Explosive Devices

  • All the X Ray Info You Need from A-C Shot

    All the X Ray Info You Need from A-C Shot

    The best practice when x-raying a suspect item is to get all the angles: back to front (A-C), side to side (B-D), top to bottom (E-F) shots. Sometimes these shots are hard or impossible to get safely and it is important to ask: what information can we get if we stick to only an A-C shot? Is it enough to get spatial resolution inside the item? Spoiler: yes.

    Here is the constraint for this scenario: you have an item that for whatever reason you can only get one angle on. You can move the x-ray panel or source in between shots, but only in the same plane. For the purposes of this scenario, I will be moving the source rather than the panel.

    An x-ray image is a 2D representation of the object but it does actually have part of the 3D information because the distance between the panel and the object creates magnification. The magnification factor is equal to the source-imager (or panel) distance (SID) divided by the source-object distance (SOD):

    \( M = \frac{\text{Relative Size}}{\text{Actual Size}} = \frac{\text{SID}}{\text{SOD}} \)

    If we are trying to figure out where along the length of that axis an item like a 9V battery is, we can use the known actual size and the magnification factor to determine where inside the item the 9V battery is. This should be relatively clear to people who have played around with x-rays: things that appear larger than they should be are further away from the panel (and closer to the x-ray source).

    The bit that may be more surprising is that we can also figure out where an item is when we do not know what the actual size is by moving the source and hence changing the magnification factor. The derivation is a little bit messy but the process is simple for taking the x-ray. First, take an image where the source is closer than you would normally take it and the panel is in a typical position. Note this source-image distance down. Move the source back a set distance (we will call it y) and take another image.

    Diagram of our x-ray setup with the source on the left and a box (blue) with our hidden object (pink) a distance x away from the image plate.

    The two images you have will have different magnification factors for the object we are trying to locate along the axis of the shot. Measure these in your x-ray software. We can then use the expression we had before for magnification factors and take the ratio, noting that our SID and SOD are changing by the distance y:

    \( \frac{M_{2}}{M_{1}} = \frac{\frac{\text{SID}+y}{\text{SOD}+y}}{\frac{\text{SID}}{\text{SOD}}}\)

    We could solve this expression for SOD to find where the object we are looking for is inside the item, but a more useful value x will be easier to work with, where x is the distance from the panel to the object. Given that the panel will typically be right next to the object, x is an easier distance to measure. Noting that \(\text{SID} = \text{SOD} + x \), we can re-arrange the expression above as:

    \( \frac{M_{2}}{M_{1}} = 1 – \frac{xy}{\text{SID} (\text{SID}-x+y)}\)

    With a bit more rearranging of equations, and using the relative size we measured earlier in images 1, 2 (\(\text{Rel}_{1,2}\)):

    \( x = \frac{(\text{SID}+y)(1-\frac{\text{Rel}_{2}}{\text{Rel}_{1}})}{\frac{y}{\text{SID}}+(1-\frac{\text{Rel}_{2}}{\text{Rel}_{1}})} \)

    This is a somewhat ugly expression, but it is important to note that all the values on the right hand side of the equation are knowns: the source-image distance (SID) was measured for the first image, the distance the source was brought back (y) was measured, and the relative sizes of the object (\(\text{Rel}\)) are measured on the images. If your x-ray tablet is like mine, you could make a quick Excel spreadsheet to do this calculation for you with the measured values and get depth perception to your item.

    There are, of course, limitations: if some element in the x-ray image completely blocks another thing, then naturally there is no way to see it from that angle. For this technique to work we need at least enough x-ray penetration to see through to the panel. It is also a more cumbersome and unclear way than getting alternate angles. However, in a pinch, depth perception for known and unknown sized objects is possible from a single axis shot.

  • All Improvised Explosives Have Power Sources

    All Improvised Explosives Have Power Sources

    Given that improvised explosive devices can be made in as many ways as the bomb maker can imagine, it is useful to try and breakdown what components make up an IED. A few acronyms get used regularly: PIES, SPICE, and PIECES are the most common ones.1 They are broken down as:

    • PIES: Power Source, Initiator, Explosives, Switching
    • SPICE: Switching, Power Source, Initiator, Container, Explosives
    • PIECES: Power Source, Initiator, Explosives, Container, Enhancements, Switching

    The bare minimum is given by PIES since containers are not strictly necessary and not all IEDs have enhancements. What is needed for an IED is an explosive as the main charge (or it is not really an explosive device), an initiator for that explosive (or it cannot initiate), a switch that triggers said initiation, and a power source to give the initiator the energy needed to fire.

    Whilst most IEDs are electrically initiated and hence the power source is often a battery, sometimes people say that power sources are not strictly necessary because non-electric initiation is possible. Whilst it is true that power source and battery often gets used interchangeably, the power source is whatever gives the initiator the required energy to commence the explosive train and function the device.

    This means that to understand what a power source can be, we need to understand what kinds of initiators are available to the would-be IED maker. Again, the majority of IEDs are electric, so the power source is going to provide some kind of electricity, such as a battery, solar panel, capacitor, or mains power.

    But not all IEDs are electrically initiated. In the realm of non-electric initiators, there exist flame/spark initiators (like the classic safety fuze non-electric detonators), impact based ones (for instance, slapper detonators), friction based (like matches), stab (used in cocked striker fuzes), and percussion initiators (most commonly percussion primers for small arms rounds).

    Importantly, all these kinds of initiators need some kind of energy to initiate. In conventional munitions the energy for stab detonators can be stored in the form of a striker spring and the reason that cocked striker fuzes are so dangerous is that the power source (mechanical tension in a spring) can so easily fire the detonator if set free.

    Mechanical spring tension in a spring is probably the most obvious non-electric power source, but sometimes there really does not appear to be a power source in a device. For instance, below are so-called “gingerbread” mines seen in Ukraine. It consists of a 3D printer container with some plasticised explosive, a screw and a detonator. When the victim steps on the mine, it flattens the container, making the screw hit the detonator and functioning the device.

    The explosive and initiator are obvious. The switch is the screw pushing into the detonator. Where is the power source? The answer is that the victim is the power source. If nothing pushes that screw into the detonator capsule, there is no detonation. In other words, unlike other kinds of devices where the power source is integral to the device, the victim gives it the energy to function.

    The point that makes this whole description make sense is that initiators cannot function by themselves. They need an activation energy to function. Something has to give it that energy. For some improvised devices and munitions, this energy comes from the target exerting a force.

    This is different to a pressure plate where the victim is merely connecting the power source (typically a battery) to the initiator. Not all victim operated devices have the victim as the power source since most of them use the victim to function the switch, which in turn connects a separate power source to the initiator to initiate the device.

    If you tried to argue that the gingerbread mine does not have a power source because it is not part of the device, then you would also have to concede that the device is neutralised by design since it cannot function by itself. Similar to if a long command wire IED was designed to fire by connecting a battery to loose ends a the firing point, you would say that the power source was not connected, but you would concede that there is a power source as part of the whole functioning device.

    For some conventional munitions with impact fuzes functioned by hitting the target, the power source is the kinetic energy built up by being dropped/launched and the energy is imparted to the initiator when the munition impacts the target. If for whatever reason the impact fuze did not hit a target, then it would revert to needing some external power source to function it. This is why movement is a hazard for impact munitions: movement can supply energy.

    To conclude on the main point: all initiators need energy to function and that energy has to come from a power source. All IEDs are designed to function, so all IEDs have some kind of power source by design. If that energy comes from the victim, the victim is the power source.

    1. See for instance: https://counteriedreport.com/a-journey-through-pieces-of-spice-pies-what-components-make-up-an-ied-technical-component-classification/ ↩︎