1:45 PM - 3:15 PM
[O11-P107] Presuming the structure of school building using μ particle
Keywords:muography, Cosmic Watch, coincidence measurement
1. Background and Objectives
1-1. Background
Cosmic Rays
Cosmic rays are particles with high energy that are flying through space. Supernova explosions and nuclear fusion of the sun are the most common causes of cosmic rays. When cosmic rays collide with the Earth's atmosphere, the interaction produces a large number of particles that fall to the ground. These are called secondary cosmic rays. In this study, I used μ-particles contained in these secondary cosmic rays.
Muography
Secondary cosmic rays are natural radiation and easy to procure radiation sources. In addition, μ-particles have a strong penetrating power (=transmitting power) among secondary cosmic rays. These two points have led to the development of technology that uses μ-particles to see through large structures such as volcanoes, pyramids, and ancient tombs. This is called muography.
1-2. Previous Studies
Muography is usually used for large-scale structures, and an attempt to utilize this technique for a high school building was made in the previous study [1]. In the previous study, a μ-particle detector CosmicWatch was pointed at all four sides of a room, and the detection frequency of μ-particles was compared with the surface density of the shielding.
1-3. Purpose
The purpose of this study is to estimate the vertical thickness of this school building by comparing the frequency of arrival of μ-particles.
2. Data and analysis methods
2-1. Equipment used in this study
I used a μ-particle detector, CosmicWatch, in this study. CosmicWatch uses a plastic scintillator as a medium to detect μ-particles. A scintillator is a material that emits light when an electrically charged particle passes through it. Plastic scintillators are suitable for measuring substances that fall in large quantities, such as microparticles, because the duration of light emission is shorter than that of other types of scintillators. I collected this signal and analyzed by a personal computer.
2-2. Experimental Procedure
The experimental procedure is as follows.
(1) I set CosmicWatch particle detectors at the same vertical positions on each floor of the school building for observation. In the case of two detectors, only μ-particles that passed through two CosmicWatches at the same time were recorded.
(2) To obtain data for μ particles only, based on previous studies, I removed data with ADC values (signal strength) of 200 or less for this subsequent analysis.
(3) I examined the correlation between time and the total number of detections.
(4) I calculated the average value of the frequency of arrivals at each floor every 100 seconds.
(5) I examined The correlation between the number of floors and the number of detections.
3. Results
The results are shown in the attached image. Both measurement methods suggested that the frequency of arrival decreased as the floor went down, but it was considered difficult to estimate the thickness from the data collected this time.
4. Discussion and future issues
One drawback of this experiment is that it is difficult to estimate the thickness of the school building ceiling and floor using only this data. Therefore, I think it necessary to conduct additional basic experiments to investigate the surface density of school buildings, such as calculations based on blueprints and actual measurements of the materials and thicknesses of school buildings and the correlation between the materials and thicknesses of structures and the frequency of detection. I would also like to conduct an experiment using a different school building structure, considering the possibility that the walls of the school building set up for shielding were too thin to be appropriate for the survey.
1-1. Background
Cosmic Rays
Cosmic rays are particles with high energy that are flying through space. Supernova explosions and nuclear fusion of the sun are the most common causes of cosmic rays. When cosmic rays collide with the Earth's atmosphere, the interaction produces a large number of particles that fall to the ground. These are called secondary cosmic rays. In this study, I used μ-particles contained in these secondary cosmic rays.
Muography
Secondary cosmic rays are natural radiation and easy to procure radiation sources. In addition, μ-particles have a strong penetrating power (=transmitting power) among secondary cosmic rays. These two points have led to the development of technology that uses μ-particles to see through large structures such as volcanoes, pyramids, and ancient tombs. This is called muography.
1-2. Previous Studies
Muography is usually used for large-scale structures, and an attempt to utilize this technique for a high school building was made in the previous study [1]. In the previous study, a μ-particle detector CosmicWatch was pointed at all four sides of a room, and the detection frequency of μ-particles was compared with the surface density of the shielding.
1-3. Purpose
The purpose of this study is to estimate the vertical thickness of this school building by comparing the frequency of arrival of μ-particles.
2. Data and analysis methods
2-1. Equipment used in this study
I used a μ-particle detector, CosmicWatch, in this study. CosmicWatch uses a plastic scintillator as a medium to detect μ-particles. A scintillator is a material that emits light when an electrically charged particle passes through it. Plastic scintillators are suitable for measuring substances that fall in large quantities, such as microparticles, because the duration of light emission is shorter than that of other types of scintillators. I collected this signal and analyzed by a personal computer.
2-2. Experimental Procedure
The experimental procedure is as follows.
(1) I set CosmicWatch particle detectors at the same vertical positions on each floor of the school building for observation. In the case of two detectors, only μ-particles that passed through two CosmicWatches at the same time were recorded.
(2) To obtain data for μ particles only, based on previous studies, I removed data with ADC values (signal strength) of 200 or less for this subsequent analysis.
(3) I examined the correlation between time and the total number of detections.
(4) I calculated the average value of the frequency of arrivals at each floor every 100 seconds.
(5) I examined The correlation between the number of floors and the number of detections.
3. Results
The results are shown in the attached image. Both measurement methods suggested that the frequency of arrival decreased as the floor went down, but it was considered difficult to estimate the thickness from the data collected this time.
4. Discussion and future issues
One drawback of this experiment is that it is difficult to estimate the thickness of the school building ceiling and floor using only this data. Therefore, I think it necessary to conduct additional basic experiments to investigate the surface density of school buildings, such as calculations based on blueprints and actual measurements of the materials and thicknesses of school buildings and the correlation between the materials and thicknesses of structures and the frequency of detection. I would also like to conduct an experiment using a different school building structure, considering the possibility that the walls of the school building set up for shielding were too thin to be appropriate for the survey.