Degradation Studies of LaBr3 Detector Units in High-Radiation Scenarios for Nuclear Fuel Inspection

Abstract

Nondestructive assaying (NDA) is an important step in ensuring the safe handling of spent nuclear fuel and radioactive waste. The assaying techniques require the use of ionizing radiation detectors to determine the activity of said fuel. One candidate detector for such use is the cerium-activated LaBr3 inorganic crystal scintillator. This scintillator offers excellent resolution, decay times and light yield, making for an excellent scintillator detector. During NDA the detector will be exposed to large doses of radiation. To establish whether the detector is a good candidate or not, it is important to investigate how the
detector holds up against these large doses and to what degree they cause degradation of its scintillation qualities.

In this thesis a comparison is done between three different crystal scintillators; a LaBr-scintillator irradiated with 9.8 kGy in γ- and neutron radiation, a NaI(Tl)-scintillator and a reference undamaged LaBr-scintillator. By measuring the main peaks of 137Cs, 22Na and 60Co and calculating the resolution of these peaks, the degradation in resolution and Fano
factor in LaBr γ-detection units due to large doses of radiation are discussed.

The study measures 6.193(1)% resolution peaks at 661.7 keV using the irradiated LaBr-scintillator, compared to a resolution of 3.260(1)% using the undamaged LaBr. The average relative degradation in resolution across all the measured γ energies measured to 74.1% with the peak for 60Co measuring as high as a 92.3(13)% degradation. Despite the high
dose of radiation incurred, the irradiated LaBr still outperforms the NaI(Tl)-scintillator in terms of energy resolution.

The results presented in this thesis may serve as a guide in determining how reliable the LaBr-scintillator is in use for high-radiation scenarios, as well as valuable data for improving detector performance simulation is such scenarios. Further characterization to determine the degradation of light yield and how the crystal structure is affected by the heating and cooling during the irradiation process in future studies would give greater insight of the radiation hardness of the LaBr-scintillator. Its use in NDA may be limited to scenarios with smaller effective doses to ensure the longevity of the detector.

Popular Abstract

Nuclear power is an important staple of the global power-infrastructure, offering a green alternative to fossil fuels. A major component to the use of nuclear power is the subsequent handling of spent nuclear fuel. The spent nuclear fuel remains as highly radioactive even after being "spent" to produce power, making handling and storage a very difficult topic to broach. This remaining activity can cause harm to the environment and personnel if not handled properly. One of the suggestions that has come forth in how to handle this spent nuclear fuel is a final repository deep in the bedrock, making for a combination of both natural and man-made barriers of protection between the fuel and its surroundings. Before the fuel can be placed in a final repository, steps to assure safe handling must be taken. Steps such as establishing the remaining radioactivity of the fuel-rods. To do this, techniques dubbed nondestructive assaying can be of use. These techniques utilize the ionizing radiation coming from the fuel rods, detected using different detector units, to calculate the activity, establish the composition of isotopes and other find other useful parameters in ensuring the safe handling of the spent nuclear fuel. One candidate detector unit for such scenarios is the LaBr3-scintillator detector.

LaBr3 is a so-called scintillator crystal, meaning that as ionizing radiation passes through the crystal it causes the scintillator to glow in proportion to the energy of the incoming radiation. Using different light readout sensors this glow can be measured. The LaBr3 scintillation crystal makes for a great candidate to use in nondestructive assaying, as the great time-resolution, light yield and energy-resolution of the scintillator works well in high-activity scenarios. What remains of interest is how the crystal itself reacts to being exposed to large amounts of radiation, and if these excellent detector-qualities still remain even after heavy irradiation.

• author: Nordin, Anton
• supervisor: Pavel Golubev; Linus Ros
• organization: Department of Physics; Particle and nuclear physics
• course: FYSK04 20251
• year: 2025
• type: M2 - Bachelor Degree
• subject: Physics and Astronomy
• keywords: LaBr3, LaBr, Nondestructive assaying, NDA, Spent nuclear fuel, Detectors, Scintillation detectors, Gamma-radiation, Spectroscopy, Energy-resolution, Fano factor, high-radiation scenarios, Degradation, Scintillator, Inorganic crystal, Cerium-activated, Nuclear fuel inspection, Detector units, Comparison, Lanthanum, Lanthanum Bromide, Irradiated scintillator
• language: English
• id: 9207016
• date added to LUP: 2025-07-01 08:00:36
• date last changed: 2025-07-01 08:00:36