What is Gamma-ray Spectroscopy?

• Gamma-ray spectroscopy is an effective method for analyzing and identifying radioactive isotopes in a sample. Gamma rays are a type of high-frequency electromagnetic radiation released by a variety of sources such as radioactive materials, astronomical bodies such as black holes and neutron stars, and intense events such as nuclear explosions and supernovae.
• Gamma-ray spectroscopy is accomplished through the use of a gamma-ray spectrometer (GRS), which is a device designed to quantify the distribution of gamma radiation intensity as a function of photon energy. The GRS detects and records gamma rays released by a sample, resulting in the creation of an energy spectrum.
• The gamma-ray spectroscopy energy spectrum gives vital information about the radioactive isotopes contained in the sample. Gamma rays of varying energy and intensities are emitted by many radioactive sources. Scientists can identify the identity and quantity of gamma-emitting nuclides in a sample by studying the energy spectrum. This study is critical for applications such as nuclear radiometric assay, geological studies, and astrophysics research.
• A gamma-ray spectrometer, similar to how an optical spectrometer exposes the distinctive optical spectrum of a substance, displays the characteristic gamma spectrum of a gamma source. The gamma spectrum is specific to the source’s gamma-emitting nuclides. Researchers can identify certain isotopes and measure their presence in the sample by carefully examining the energy spectrum.
• Gamma-ray spectroscopy is a rapid and nondestructive analytical technique that is extremely useful in a variety of scientific domains. Its capacity to offer extensive information on gamma-ray energy spectra has made it a vital instrument for understanding radioactive materials, researching cosmic phenomena, and guaranteeing radiation safety in a variety of applications.

Gamma-ray (γ-ray) spectroscopy Principle

The basic idea behind gamma-ray spectroscopy is to detect and analyze the energy of incident gamma rays. Gamma rays of varying energy and intensities are emitted by radioactive sources. A gamma-ray energy spectrum is produced when these gamma rays are detected and examined using a spectroscopic instrument.

The initial stage in gamma-ray spectroscopy is to detect gamma rays using an appropriate detector. The detector captures and measures the energy of incoming gamma rays. Scintillation detectors, semiconductor detectors, and gas-filled detectors are among the detectors used in gamma-ray spectroscopy. The energy of the incoming gamma rays is converted into electrical signals that may be processed and studied by these detectors.

The spectroscopic system measures and records the energy of gamma rays when they are detected. The derived energy spectrum depicts the distribution of gamma-ray intensity as a function of energy. The spectrum is a visual depiction of the various energy levels found in gamma-ray emissions.

The observed energy levels are compared to the known energies associated with various gamma rays emitted by radioisotopes to identify the identification of the gamma-ray emitter. Each radioactive isotope releases gamma rays at different energies that are unique to that nuclide. Scientists can identify the individual nuclide responsible for gamma-ray emissions by comparing observed energies to known energy values.

Furthermore, a thorough examination of the gamma-ray spectrum reveals not only the identification but also the number of gamma emitters present in a gamma source. The strength of the peaks in the spectrum correlates to the abundance of gamma-emitting nuclides. This quantitative data is critical in radiometric assay, where precise measurement of radioactive elements is required for a variety of applications.

In summary, gamma-ray spectroscopy works by measuring the energy of incoming gamma rays using a detector. The identification of the gamma-ray emitter can be identified by comparing the recorded energy levels to known energies associated with radioisotopes. The resultant gamma spectrum is typical of the gamma-emitting nuclides present in the source, and comprehensive study of the spectrum enables identification and quantification of the gamma emitters.

Characteristics of Gamma ray 

Gamma rays have numerous distinguishing features that set them different from other types of electromagnetic radiation:

• Highest Energy: Gamma rays are the most energetic kind of electromagnetic radiation. While X-rays, visible light, infrared, and radio waves are physically identical, gamma rays contain more photon energy due to their shorter wavelength.
• Individual Resolution: Because of the high energy of gamma-ray photons, they may be resolved individually. The energy of individual gamma-ray photons can be detected and measured by a gamma-ray spectrometer. The capacity to determine the energy of each photon is critical for evaluating gamma-ray spectra.
• Radioactive Nuclei Emission: Gamma rays are frequently emitted by radioactive nuclei, also known as radionuclides. These nuclei generate gamma rays with energies ranging from a few kiloelectron volts (keV) to roughly ten million electron volts (MeV). These gamma rays’ energy levels match to the typical energy levels seen in nuclei with relatively extended lives.
• Line Spectra: Gamma-ray emissions from radioactive sources frequently display “line spectra.” This means that photons are released at discrete energy, resulting in separate gamma-ray peaks in the spectrum. These line spectra reveal important information about the radionuclides present in the source.
• Continuum Spectra: Gamma-ray spectra may display continuum spectra in specific circumstances, such as astrophysics and basic particle physics. This indicates that the spectrum encompasses a wide range of energy, up to one teraelectron volt (TeV). These high-energy gamma rays are frequently related with phenomena such as astrophysical sources and elementary particle interactions.
• Difference from X-rays: The difference between gamma and X-rays might be hazy. However, there are several key distinctions between them. Gamma rays are monochromatic or have distinct energies because of electronic emission within atoms. X-rays, on the other hand, are often produced electrically, such as through X-ray tubes or linear accelerators, and have a wider energy range.

Understanding the distinct properties of gamma rays helps scientists to identify them from other types of radiation and efficiently use gamma-ray spectroscopy techniques. The capacity to resolve individual photon energies and examine line or continuum spectra allows for radionuclide identification, investigation of astrophysical events, and advances in elementary particle physics research.

Objectives of Gamma-ray (γ-ray) Spectroscopy

• To introduce students to the most basic techniques for measuring Gamma Rays.
• To gain experience in energy calibration and analysis of gamma ray spectrums to identify the isotopes emitting gamma radiation.

Equipment Needed for Gamma-ray (γ-ray) Spectroscopy

Several main pieces of equipment are necessary to accomplish gamma-ray spectroscopy. These are some examples:

1. Radioactive Source: A cobalt-60 (60Co) radioactive source, such as the one offered by PASCO, is a popular alternative. This source generates precise energies of gamma rays, which are used to calibrate and validate the gamma-ray spectrometer.
2. Scintillation Detector: For detecting and converting gamma-ray photons into electrical signals, a NaI(Tl) scintillation detector with a photomultiplier tube, such as the one offered from REXON Components Inc., is required. The scintillation detector is made up of a thallium-doped sodium iodide crystal (NaI(Tl)), which creates flashes of light (scintillations) when gamma rays interact with it.
3. Gamma-Ray Spectrometer: The SPEC TECH UCS30 Universal Computer Spectrometer is an example of a gamma-ray spectrometer used to analyze the energy spectra of gamma-ray emissions. The purpose of this spectrometer is to detect, measure, and evaluate the energy levels of gamma-ray photons.
4. Position Stand and Sample Tray: A position stand with a sample tray is used to hold the radioactive source and the samples being evaluated safely. It ensures that the source, detector, and shielding are properly aligned, allowing for precise readings while reducing background radiation.
5. Lead Shield: A lead shield is used to reduce background radiation and protect the detector from gamma rays from outside sources. It reduces interference and increases measurement accuracy by attenuating undesired gamma rays from the environment.
6. Signal and High Voltage Cables: Advanced Digital Cables, Inc.’s BNC-6 Signal Cable and CAROL’s MHV-6 High Voltage Cable are used to link the scintillation detector to the spectrometer. The signal cable transports the electrical signals created by the detector to the spectrometer for analysis, whilst the high voltage cable feeds the detector with the high voltage required for operation.

These equipment components give the tools needed to conduct gamma-ray spectroscopy studies. A radioactive source, a scintillation detector, a gamma-ray spectrometer, a position stand with sample tray, lead shielding, and appropriate cables are used to detect, measure, and analyze gamma-ray emissions, allowing for the identification and quantification of radioactive isotopes in a sample.

Instrumentation of Gamma-ray (γ-ray) spectroscopy

The equipment used for the gamma spectrum comprises:

1. An energy-sensitive radiation detector

An energy-sensitive radiation detector is an essential component of gamma-ray spectroscopy systems. There are two commonly used types of detectors: scintillation detectors and semiconductor detectors.

1. Scintillation detector: Scintillation detectors operate based on the scintillation process, in which certain materials emit light when exposed to ionizing radiation. One popular scintillation detector is a single crystal of sodium iodide (NaI) doped with a small amount of thallium (Tl), known as NaI(Tl). When gamma radiation interacts with the crystal, it produces scintillations or flashes of light. This light is then detected by a photomultiplier tube (PMT) coupled to the crystal, which converts the light flashes into electrical signals through the photoelectric effect. These electrical signals can be further processed and analyzed by a computer or data acquisition system.
2. Semiconductor detector: On the other hand, semiconductor detectors achieve the same objective of converting gamma radiation into electrical signals but through a different mechanism. Semiconductors, such as germanium, have a small energy gap between the valence band and the conduction band. When gamma rays interact with the semiconductor material, the energy from the gamma rays can promote electrons from the valence band to the conduction band. This change in conductivity within the semiconductor can be detected and measured, generating an electrical signal proportional to the energy of the incident gamma rays. Common types of semiconductor detectors used in gamma-ray spectroscopy include germanium crystals doped with lithium (Ge(Li)) and high-purity germanium (HPGe) detectors.

Both scintillation and semiconductor detectors are energy-sensitive, meaning they can differentiate between gamma rays of different energies. This capability allows for the construction of gamma-ray energy spectra, where the intensity of gamma-ray emissions is plotted as a function of energy. By analyzing these energy spectra, scientists can identify the radioactive isotopes present in a sample and quantify their abundance.

In summary, energy-sensitive radiation detectors, such as scintillation and semiconductor detectors, play a critical role in gamma-ray spectroscopy. These detectors convert the energy of gamma rays into electrical signals that can be processed and analyzed to determine the energy levels and intensities of gamma-ray emissions. The choice of detector depends on factors such as the specific application, energy range of interest, and desired sensitivity.

2. Electronics

• It is responsible for processing signals from the detector produced from the device. For instance. A pulse sorter (i.e., multichannel analyzer)

3. Associated amplifiers and data readout devices

• They assist in the creation, display and storage of the spectrum.

Features of Gamma spectrum 

There are a variety of distinctive aspects that are visible in the Gamma spectrum. The main feature that will be noticed will be the photopeak. The photopeak occurs when a gamma-ray has been completely absorption into the detector. Larger and more dense detector sizes enhance the chance of absorbing the gamma-ray.

The other major aspect to be observed is The Compton edge, and the distribution. The Compton edge occurs due to Compton Effect which is where some energy of the gamma ray is transfered to the detector for semiconductors or scintillator. This happens when the high energy gamma ray is struck by an electron that is relatively low in energy. There is a sharp edge that is a Compton edge that represents the highest amount of energetic energy transferable to an electron through this kind of scattering. 

The broad peak with lower energies than that of it is the Compton edge is known as the Compton distribution. It is a reflection of the energy levels generated by a range different scattering angle. A characteristic of Compton distributions includes that of the peak in backscatter. This peak is the outcome of the exact phenomenon however it is the smallest energy quantity of energy transferred. A sum of energy that are reflected by both the Compton edge as well as the peak of backscatter ought to give that energy as the photopeak.

Another set of characteristics in an gamma spectrum include high-frequency peaks associated with pair production. This is the process through the gamma ray with sufficient energies (>1.022 MeV) can create the electron and positron pairs. The electron and the positron could be annihilated and create two 0.511 MeV photons called gamma. If all three gamma-rays that are the original, with its energy diminished by 1.022 MeV, as well as the two annihilation gamma-rays are simultaneously detected the full energy peak can be observed. In the event that one of annihilation-gamma rays are not absorbed into the detection system, an energy peak equal to the full energy but less 0.511 MeV is observed. This is referred to as an escape peak. If both annihilation gamma radiations escape, then a complete energy peak of less than 1.022 MeV is observed. This is referred to as an escape peak with double-escape.

Applications of Gamma-ray (γ-ray) spectroscopy

Gamma-ray (γ-ray) spectroscopy finds a wide range of applications across various scientific disciplines. Some notable applications include:

1. Nuclear Structure Studies: Gamma-ray spectroscopy is extensively used in the study of nuclear structure. By analyzing the energy spectra of gamma-ray emissions from atomic nuclei, scientists can gain insights into the energy levels, excited states, and nuclear configurations. This information helps in understanding the fundamental properties and behavior of atomic nuclei.
2. Nuclear Transitions and Reactions: Gamma-ray spectroscopy plays a crucial role in investigating nuclear transitions and reactions. It provides valuable data on the energies, lifetimes, and branching ratios of gamma-ray transitions occurring within atomic nuclei. These studies contribute to our understanding of nuclear decay processes, particle interactions, and the dynamics of nuclear reactions.
3. Space Research: Gamma-ray spectroscopy has significant applications in space research. For example, it is used for the detection of water and other elemental compositions on planets and celestial bodies. By analyzing the gamma-ray emissions from these objects, scientists can infer the presence of certain elements and isotopes, helping to unravel the geological and chemical characteristics of planetary bodies. The elemental and isotopic analysis of airless bodies in the solar system, such as the Moon and Mars, is one of the primary applications of gamma-ray spectroscopy in space research.
4. Elemental and Isotopic Analysis: Gamma-ray spectroscopy is employed for elemental and isotopic analysis in various fields. It can determine the abundance and distribution of chemical elements in a sample or source. This analysis is vital in areas such as environmental monitoring, geological exploration, and forensic investigations. Gamma-ray spectroscopy enables the identification and quantification of specific isotopes, aiding in studies related to radiation safety, nuclear power generation, and materials analysis.

Overall, gamma-ray spectroscopy serves as a powerful tool for investigating nuclear phenomena, understanding the composition of celestial bodies, and conducting elemental and isotopic analysis. Its applications span diverse fields including nuclear physics, astrophysics, space exploration, environmental science, and materials research, among others. The ability to detect and analyze gamma-ray emissions provides valuable insights into the nature of matter, energy levels within atomic nuclei, and the composition of the universe.

FAQ

References

• https://www.intechopen.com/chapters/53780
• https://www.physlab.org/wp-content/uploads/2016/04/GammaExp-min.pdf
• https://stfc.ukri.org/files/a-bruce-gamma-spectroscopy/
• https://en.wikipedia.org/wiki/Gamma_spectroscopy
• https://archive.cnx.org/contents/686b9c8b-1656-49ec-a969-84da62a60eca@1/principles-of-gamma-ray-spectroscopy-and-applications-in-nuclear-forensics
• https://owlcation.com/stem/Gamma-Ray-Spectroscopy
• https://www.slideshare.net/Moinkhan444/gammaray-spectroscopy