• NS Group Leader
  Steve Wender
• Deputy Group Leader
  To Be Announced
• Office Administrator
  Julie Quintana-Valdez
• User Office Support
• Program Administrator
  Theresa Chavez
  505-665-6466
• Group Office Location
  TA-53, Building 31
  505-667-5377

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The ICE House

The ICE House (Irradiation of Chips and Electronics ) is located on the 30º flight path of WNR. At this angle, the shape of the neutron spectrum here is very similar to that of neutrons produced in the atmosphere by cosmic rays but with a neutron flux a million times higher, depending on altitude. This large flux allows testing of semiconductor devices at greatly accelerated rates. Companies from around the world can use the WNR high-energy-neutron source to characterize components and study various failure modes caused by neutron radiation.

Single Event Upsets

When cosmic rays collide with nuclei in the upper atmosphere, they create a shower of subatomic particles. By the time the cosmic-ray shower reaches aircraft altitudes and below, the uncharged neutrons present are the dominant source of errors in electronics. These neutrons pose little health hazard because the radiation dose is relatively low, but each neutron can interact with silicon and other elements in integrated circuits to deposit a charge in localized regions, with potentially disastrous impact on memory and chip function. Such disruptions, potentially caused by a single neutron, are collectively known as single-event upsets (SEUs), and their rate is the largest single contributor to the soft-error rate of modern electronic integrated circuits. Hardware is said to experience soft errors if it malfunctions temporarily and hard errors if it is damaged permanently.

What are the effects that can be so disastrous to electronics? The simplest SEU occurs when a memory or logic location changes its state because of charge deposited by an energetic particle. Sometimes more than one memory location can be affected by a single particle. Latchup is another frequently encountered, although much more serious, soft error, whereby an electrical current arises in an unintended area. The device stops functioning until it is turned off and then on again. Finally, hard errors can permanently damage or even destroy devices by causing them to draw large currents.

Origins of an SEU

High-energy cosmic rays impacting the upper atmosphere generate a cascade of secondary particles that reach lower altitudes. In general, these high-energy particles are very penetrating and do not stop in exposed electronic devices. Since the energy deposited in the host device is small, the excess charge (electron-hole pairs) generated by electronic ionization is insufficient to cause soft errors. Even though the probability of a collision is very small, these secondary particles can collide with a silicon nucleus in the semiconductor device. When neutrons collide with a silicon nucleus, many different nuclear reactions can occur. Scattering reactions, elastic and inelastic, leave the silicon nucleus intact, but they cause it to recoil. The recoiling nucleus leaves an intense local ionization trail. In high-energy cases, the collision may lead to a series of direct reactions (intranuclear cascade), whereby individual nucleons (protons or neutrons) or small groups of nucleons (say, an alpha particle) are ejected from the silicon nucleus or the silicon nucleus may fragment. As the available energy becomes less, a compound nucleus (a neutron may be captured by a nucleus) may be formed that will “boil off” nucleons to reach stability. When the total number of ionization electron-hole pairs collected in a sensitive region of the device exceeds a critical value (which is a characteristic of the device), an SEU is born.