Development of detectors and electronics for "neutron in, gamma out" technique

"Neutron in, gamma out" technique, and especially its powerful APT/NNA variety, requires state-of-the art alpha-particle and gamma-ray detectors.

The challenge of having a fast and reliable detector of associated alpha-particles inside sealed vacuum of a portable neutron generator has been the major reason for a slow progress of APT/NNA in the past.

Special requirements to a built-in position-sensitive a-detector:
• close to 100% intrinsic efficiency to 3 MeV alpha-particles;
• ability to handle extremely high count rates (up to 10⁷ a/s);
• compatibility with high static vacuum;
• stability to neutron and a-radiation (must operate for the whole life time of the neutron generator);
• insensitivity to "parasitic" radiation (x-rays, electrons, deuterons, light).

APSTEC has developed several varieties of position-sensitive alpha-detectors, which have been installed into different types of portable neutron generators.

Another important component of the APT/NNA device is a detector of secondary gamma-rays, which must possess high efficiency, good energy resolution and good timing properties. Since time resolution of the alpha-detector/gamma-detector pair is directly responsible for "in-depth" position resolution of the device, having time resolution below or around 2 ns is of major importance.

Detectors must be equipped with appropriate electronics and followed by an adequate data acquisition system, which is ultimately responsible for the performance of the ATP/NNA device. The major challenge here is to preserve the parameters of alpha-particle detectors and gamma-ray detectors at very high counting rate. Typically, the counting rate of an alpha-particle detector installed into a 5x10⁷ n/s neutron generator will be over one million alpha-particles per second. Counting rate of each of the gamma-ray detectors in the device is around 100,000 gamma-rays per second, about 10% of which are correlated it time with one of the million alpha-particles.

Traditional analogue electronics falls short of fulfilling theses demands. That is why APSTEC has developed and built a completely new set of digital data acquisition and control electronics, which ensures unprecedented speed and spectra quality.