Gamma-ray Spectroscopy - Principle, Parts, Applications
Gamma rays are electromagnetic radiation and are part of photon radiation. They are produced when transitions between excited nuclear levels of a nucleus occur. Delayed gamma rays are emitted during the decay of the parent nucleus and often follow a Beta decay. There can be many transitions between energy levels of a nucleus, resulting in many gamma‐ray lines. The typical wavelength is 10-7 to 10-13 m, corresponding to an energy range of 0.01–10 MeV. Gamma rays can be detected through their interaction with matter. There are three main processes: photoelectric absorption, Compton scattering and pair production. The photoelectric effect occurs when a gamma ray interacts with an electron of an inner shell of an atom and a photoelectron is emitted. This is the most important effect for the detection of gamma rays with semiconductor detectors. The effect of Compton scattering describes the interaction of a gamma ray with matter when some of its energy is transferred to the recoil electron. The energy transmitted is a function of the scattering angle. Therefore, the Compton effect results in a broad range of gamma‐ray energies, which gives a continuous background in the gamma spectrum. Pair production is the third effect when a gamma ray is absorbed by matter and loses energy to produce an electron/positron pair. This effect only occurs when gamma rays have more than 1.02 MeV energy, twice the rest mass energy of an electron (0.551 MeV)
Gamma-ray (γ-ray) spectroscopy is a quick and nondestructive
analytical technique that can be used to identify various radioactive isotopes
in a sample. In gamma-ray spectroscopy, the energy of incident gamma-rays is
measured by a detector. By comparing the measured energy to the known energy of
gamma-rays produced by radioisotopes, the identity of the emitter can be
determined. This technique has many applications, particularly in situations
where rapid nondestructive analysis is required. Gamma rays are an
ultrahigh-frequency of light that is emitted by radioactive elements, energetic
celestial bodies such as black holes and neutron stars, and high energy events
such as nuclear explosions and supernovae.
What is Gamma-ray (γ-ray) Spectroscopy?
- Gamma-ray (γ-ray) spectroscopy is a quick and nondestructive analytical technique that can be used to identify various radioactive isotopes in a sample.
- A gamma-ray spectrometer (GRS) is an instrument for measuring the distribution of the intensity of gamma radiation versus the energy of each photon.
Principle of Gamma-ray (γ-ray) spectroscopy
- Most radioactive sources produce gamma rays, which are of various energies and intensities.
- When these emissions are detected and analyzed with a spectroscopy system, a gamma-ray energy spectrum can be produced.
- In gamma-ray spectroscopy, the energy of incident gamma-rays is measured by a detector.
- By comparing the measured energy to the known energy of gamma-rays produced by radioisotopes, the identity of the emitter can be determined.
- A detailed analysis of this spectrum is typically used to determine the identity and quantity of gamma emitters present in a gamma source and is a vital tool in the radiometric assay.
- The gamma spectrum is characteristic of the gamma-emitting nuclides contained in the source.
Instrumentation of Gamma-ray (γ-ray) spectroscopy
The equipment used in gamma spectroscopy includes:
- An energy-sensitive radiation detector
- The commonly used detectors may be any among the two:
Scintillation detector
- Scintillation is the process by which some material, be it a solid, liquid, or gas, emits light in response to incident ionizing radiation.
- In practice, this is used in the form of a single crystal of sodium iodide that is doped with a small amount of thallium, referred to as NaI(Tl).
- This crystal is coupled to a photomultiplier tube which converts the small flash of light into an electrical signal through the photoelectric effect.
- This electrical signal can then be detected by a computer.
Semiconductor detector
- A semiconductor accomplishes the same effect as a scintillation detector, conversion of gamma radiation into electrical pulses, except through a different route.
- In a semiconductor, there is a small energy gap between the valence band of electrons and the conduction band.
- When a semiconductor is hit with gamma-rays, the energy imparted by the gamma-ray is enough to promote electrons to the conduction band. T
- his change in conductivity can be detected and a signal can be generated correspondingly.
- Germanium crystals doped with lithium, Ge(Li), and high-purity germanium (HPGe) detectors are among the most common types.
Electronics
- It processes detector signals produced by the detector.
- For example. A pulse sorter (i.e., multichannel analyzer)
- Associated amplifiers and data readout devices
Applications of Gamma-ray (γ-ray) spectroscopy
They are used extensively in the studies of:
- Nuclear structure
- Nuclear transitions and
- Nuclear reactions
- In space research such as water detection on planets
- Used for the elemental and isotopic analysis of airless bodies in the solar system, especially the moon and mars.
- GRS instruments supply data on the distribution and abundance of chemical elements
References
https://en.wikipedia.org/wiki/Gamma_spectroscopy
https://www.physlab.org/wp-content/uploads/2016/04/GammaExp-min.pdf
https://archive.cnx.org/contents/686b9c8b-1656-49ec-a969-84da62a60eca@1/principles-of-gamma-ray-spectroscopy-and-applications-in-nuclear-forensics
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