Instrumentation for radioactivity
Instrumentation for radioactivity is of many types, due to different applications (e.g., analysis vs. safety), needs for portability, and the intensity and types of expected radiation. Military policy defines the survey function as needing to analyze ionizing radiation present from" [1]
While alpha particle emitters such as those in depleted uranium(DU) (i.e., uranium 238) are not a hazard at a distance, alpha particle measurements are necessary for safe handling of projectile dust, or of damaged vehicles with DU armor.
Survey of Environments that can be Monitored by Humans
No single type of instrumentation for radioactivity meets all military requirements, even at the tactical level. Different types are needed, variously, for:
- Health risk to individuals
- Analysis of nuclear materials that emit alpha particles
- Tritium survey
The basic field survey instrument that can detect alpha particles is an scintillometer, such as the AN/PDR-77, which comes with a set of probes variously intended for alpha, beta/gamma, and low-energy X-ray radiation. The X-ray probe allows detection of plutonium and americium contamination. "Knowing the original assay and the age of the weapon, the ratio of plutonium to americium may be computed accurately and so the total plutonium contamination may be determined. [2]
Different instruments, such as the AN/PDR-73 or AN/PDR-74, are used for tritium survey.
Yet another set of instruments are used to measure health risks to individuals. These include portable ionization chambers, film badges, and thermoluminescent personal dosimeters.
There are limits to what can be determined with portable equipment. For more complex analysis, either a transportable laboratory needs to be brought to the site, or, if safety permits, to have representative samples taken to a laboratory. Analysis of radioactive trace elements, for example, can help identify the source of fuel for a given contamination incident. Some of the less portable,, but powerful instrumentation includes gamma spectroscopy, [[low background alpha and beta counting and liquid scintillation counters for extremely low energy beta emitters such as tritium.
The DoD directive makes the distinction clear that detection is harder than measurement, and the latter is necessary for MASINT:
Nuclear radiation is not easy to detect. Radiation detection is always a multistep, highly indirect process. For example, in a scintillation detector, incident radiation excites a fluorescent material that de-excites by emitting photons of light. ... the quantitative relationship between the amount of radiation actually emitted and the reading on the meter is a complex function of many factors. Since those factors may only be controlled well within a laboratory. Such a laboratory either must be moved to the field, or samples brought to a fixed laboratory.[2]
Detectors based on semiconductors, such as germanium, have better intrinsic energy resolution than scintillators, and are preferred where feasible for gamma-ray spectrometry. Neutron detection is improved by using hydrogen-rich scintillation counters, such those using a liquid rather than a crystal scintillation source.
Surveying High-Level Radioactive Areas
Some reactor accidents have left extremely high levels, such as at Chernobyl or the Idaho SL-1. In the case of Chernobyl, many brave rescue and mitigation workers, some knowingly and some not, doomed themselves. The very careful cleanup of the SL-1, in a remote area and where the containment retained its integrity, minimized hazards.
Since those incidents and others, remotely operated or autonomous vehicle technology has improved.
References
- ↑ Office of the Assistant to the Secretary of Defense for Nuclear and Chemical and Biological Defense Programs (February 22, 2005). Nuclear Weapon Accident Response Procedures (NARP).
- ↑ 2.0 2.1 United States Department of Defense, DoD 3150.8-M, "Nuclear Weapon Accident Response Procedures (NARP)"