How detection works

detector-networkNew Solutions

Experts realize that scanning border and shipping traffic is an incomplete solution for interrupting the movement of nuclear material.

The 2.0 solution: building networks of detectors that can track nuclear material in larger areas.

A network can establish better background readings than a single detector, and thus can recognize smaller quantities of nuclear material.


Nuclear bomb materials—highly enriched uranium and plutonium—emit a number of radioactive particles, including gamma rays and neutrons. Gamma ray detectors and neutron detectors are used to sense the presence of nuclear material. Each has advantages and disadvantages.

Gamma Ray Detection

Many radioactive materials emit gamma rays, making gamma ray detection optimal for tracking not just nuclear bombs, but also materials for dirty bombs—including radioactive elements like Cobalt and Cesium that could be stolen from hospitals or research facilities.

Gamma ray detectors have a high rate of false-positives when searching for nuclear material: people that recently received radiation therapy (for cancer or other diseases) set off alarms, as can large shipments of bananas. False positives are expensive, and have been known to lead to inattention or even the turning off of detectors due to the high volume of false alarms.

Neutron Detection

Very few substances emit neutrons, and none are benign. This makes neutron detectors effective for isolating nuclear materials (Plutonium and Highly Enriched Uranium), as false alarm rates are significantly lower than with gamma ray detection.

However, neutron detectors are historically more expensive than gamma ray technologies. This is partly driven by the scarcity of the best-known material for detecting neutrons, Helium-3 gas (He-3). The price point of neutron detectors has limited broad deployment and use of this technology.


There are many strategies for detecting radiation, with a general correlation between complexity and cost.

Geiger Counter

At the simple end, a Geiger Counter converts the energy that comes from a gamma ray hitting the detector material into an electrical signal.


Spectroscopy is a technique by which the source of the radiation is identified. Different materials emit radioactive particles (neutrons and/or gamma rays) at different energy levels. When the particles hit the detector, it converts the amount of energy released in the collision into either a line on the readout, or a wavelength of light. Based on the line/light, the detector identifies the type of material from which the particle came.

Many detector designs rely on three basic components: detector chamber, conversion material, and wire read-outs.  Silverside’s technology illustrates one basic form of detection.


The simplest method for catching neutrons emitted by nuclear bomb materials (plutonium, highly enriched uranium) involves three components: conversion material, gas, and high-voltage wires.

How Detectors Work

  • Conversion material traps neutrons (which pass through most substances). After it is captured, the energy from the neutron forces the conversion material to release a “daughter particle.”
  • The “daughter particle” passes into the sealed detector chamber that’s filled with gas, and “ionizes” the gas particles—strips them of electrons.
  • The electrons, which carry a negative electric charge, drift toward high-voltage wires, which stretch through the detector chamber. The wires trap the charge from the electron and send out a signal to the circuit boards on the edge of the detector.