An active galactic nuclei (AGN) refers to the central region of a galaxy with special activity, whose brightness is much brighter than a typical galaxy. The galaxies in which these active nuclei exist are called active galaxies. At the center of the active nuclei is a supermassive black hole with millions to billions of times the mass of the sun. This black hole emits a lot of energy as the temperature rises while pulling surrounding materials into gravity to form an accretion disk. In this process, some materials are rapidly ejected in a direction perpendicular to the disk around the rotation axis of the black hole, which is called a jet. The materials in this jet erupt close to the relativistic velocity, that is, the velocity of light. The activity is classified according to the radiation characteristics of these jets.

Coronal mass ejection refers to plasma and magnetic fields in the form of clouds of gas exploding from the Sun into interplanetary space. It mainly occurs with solar flares and eruptions of prominence (or filaments). It is known as a phenomenon in which magnetic energy accumulated in the solar magnetic field is rapidly converted into heat or kinetic energy, and magnetic force lines and plasma are ejected.

A charged particle or a charged particle is a particle that has an electric charge. An electric field and a magnetic field are formed around the charged particle to exchange electromagnetic force with other charged particles. In the normal state, atoms or molecules are all neutral by themselves, but they can lose or gain electrons to become an ionic state. If it loses electrons, it is called an anion.

It is a generic term for high-energy particles and radiation pouring from space to Earth. It can be divided into primary cosmic rays before colliding with atmospheric molecules and secondary cosmic rays occurring after colliding with atmospheric molecules. Particles corresponding to secondary cosmic rays are observed near the Earth's surface.

Dose Equivalent

It refers to the amount of radiation in terms of effects on the human body. When radiation is irradiated to an organism, even if the absorbed dose of the organism is the same, the effect on the human body is different depending on the type of radiation. In other words, RBE (Relative Biological Effectiveness) is different. Sv(Sivert) is expressed as absorbed dose considering RBE. However, RBE is determined for the effects of living organisms, and individual differences occur. Therefore, in the field of radiation protection, it is expressed as a quality coefficient Q related to a physical quantity instead of RBE, which is an experimental value.

Sv=Quality coefficient (Q)×Gy

This is called dose equivalent and is used in fields related to the biological effects of radiation. In radiation management measurement, the effective dose equivalent is H*( 10) is expressed. The unit is sievert (Sv) or rem (rem).

Atmosphere is the layer of air that surrounds the Earth in which we live. It can be classified according to several criteria. Except for carbon dioxide and ozone, it can be divided into a homosphere, in which the distribution of gases according to altitude is approximately constant, and a heterosphere, in which the distribution of gases is uneven. Alternatively, it can be divided into the atmosphere, stratosphere, mesosphere, and thermosphere according to the temperature change with altitude.

Earth's own magnetic field is called the Earth's magnetic field. Without the earth's magnetic field to protect the earth, the solar wind blows from the sun hits the atmosphere, and living things on the earth are directly exposed to strong energy. There is Van Allen radiation belt inside Earth’s magnetosphere.

When various tissues of the human body are exposed to radiation, the effect of radiation on tissues in the human body is relative to each tissue. In this way, the dose that evaluates the biological effect by reflecting the different risk levels for each tissue is called the effective dose. The effective dose can be obtained as the sum of the products of the equivalent dose for each tissue and the tissue weighting factor, and it is impossible to obtain this value from actual measurement. Therefore, it can be compared indirectly through methods such as dose equivalent. The unit is sievert (Sv) or rem (rem).

The flux of particles as function of particle energy

Fluence-to-Dose conversion coefficient

It is a coefficient that changes the particle fluence to the required dose. It was first proposed in ICRP Publication 74 and revised in Publication 116. However, as problems with the proposed coefficients have been raised, certain researchers have applied particle transport codes to 3D voxel graphic phantom to continuously modify and publish coefficients.

Flux means the rate at which a specific physical quantity is transported per unit time through a unit area. A unit solid angle is additionally taken into account to specify the direction.

Geostationary orbiting satellites orbit in a circular orbit located 35,786 km above the equator, and orbit according to the direction of the Earth's rotation. They appear stationary at one point when observed from the ground because the orbital period of the satellite and the rotation period of the Earth are the same. This orbit is also called GeoSynchronous Orbit (GSO) because it is always located in the same position when viewed from the ground, thus, most commercial communication satellites, broadcasting satellites, and weather satellites operate in geostationary orbit.

Geomagnetic Cutoff Rigidity

Geomagnetic Cutoff Rigidity refers to the shielding effects of the Earth's magnetic field against incident charged particles. In other words, it means the maximum energy of an incident charged particle depending on the geographic location of the Earth. These energies are not limited to one, but rather to a range. This range can be expressed as a single value is called effective cutoff rigidity. Cutoff rigidity is generally low in the magnetic north pole region and high in the magnetic equator region. Therefore, it is relatively vulnerable to the incidence of particles in the polar region.

Great Circle Route

The shortest route between two points on Earth. The Great Circle means that an arc created with the center of the sphere and two points on the surface of a sphere.

The heliosphere is a space dominated by the solar wind (plasma from the sun) and the sun's magnetic field. A portion of galactic cosmic rays (GCRs) entering the heliosphere's interstellar space are blocked by the this magnetic field. Therefore, the amount of galactic cosmic rays inside the heliosphere is less than that of the outside, and it changes according to the sunspot cycle. The outer part of the heliosphere is called the heliopause, and it was confirmed by Voyager 1 and Voyager 2 to be about 120 AU away from the Sun.

High Energy Particle

In general, it refers to particles with high energy of more than 1 million eV (1MeV), and is often detected in cosmic ray such as solar wind. They are accelerated and created by phenomena such as the explosion of supernovae and the activities of the solar flares. There are various high-energy particles in space, such as electrons, protons, and helium nuclei, and they have electric charges.

An international organization that recommends and advises on radiation protection. It was founded in 1928 by the International Society of Radiology (ISR). At the time of its establishment, it was named the International X-ray and Radium Protection Committee, but was changed to the current name in 1950. The ICRP is a sister organisation to the International Commission on Radiation Units and Measurements (ICRU). In general terms ICRU defines the units, and ICRP recommends, develops and maintains the International system of radiological protection which uses these units.

The interplanetary magnetic field refers to the magnetic field observed in the solar wind. The interplanetary magnetic field is a magnetic field rooted in the sun and is carried by the solar wind to sweep the interplanetary space and move away from the sun, so the overall shape is like a ballerina's skirt. Like the solar magnetic field, the interplanetary magnetic field changes according to the sunspot cycle, and the direction of the magnetic dipole changes at a 22-year cycle. When the direction of the interplanetary magnetic field is opposite to the direction of the Earth's magnetic field, that is, when a southward magnetic field hits the magnetosphere, a powerful geomagnetic storm occurs.

A neutron stars are a very dense celestial bodies made up of only neutrons. It is the core part that remains after a massive star with more than 10 times the mass of the Sun explodes as a supernova.

A code that tracks and calculates the phenomena that occur as particles progress under specific physical conditions. In general, there are many codes based on Monte Carlo simulation that obtain integrated probabilistic results by injecting particles one by one very many times (typically more than one million times). There are codes such as Geant4, MCNP, and FLUKA.

Secondary cosmic rays are created by the collision of primary cosmic rays (i.e. atomic nuclei without electrons) and atomic nuclei in atmospheric gas. High-energy protons in the primary cosmic rays collide with atomic nuclei of oxygen or nitrogen in the atmosphere, where they make protons or neutrons. Some of these secondary nucleons are bounced off in the direction of movement of the primary particles with a high energy (not significantly different from those of the primary nucleons), thereby continuously making nucleons. When the primary particle has sufficiently high energy, the nucleon component proliferates stepwise to create a nucleon cascade (stepwise multiplication of particles).

The number of sunspots, which is an index indicating the activity of the sun, increases and decreases in a cycle of about 11 years is called the solar cycle. The period when the number of sunspots is maximum during a period is called the solar maximum, and the period when the number of sunspots is the minimum is called the solar minimum.

These are particles that have been accelerated by solar magnetic activity and have high energy. It is known that the generation of solar high-energy particles is closely related to not only strong flares but also very large and rapidly ejecting coronal mass ejections. Due to the strong solar high-energy particle, astronauts performing space exploration activities, and crew members and passengers using polar routes may be exposed to radiation from the particles.

A solar flare is a phenomenon in which magnetic energy accumulated in the atmosphere near sunspots is released explosively in a short time due to magnetic reconnection, and shines intensely. When a flare occurs, the surrounding plasma heats up to tens of millions of degrees and shines brightly. For a period of approximately 10 minutes, the flare emits a large amount of X-rays and ultraviolet rays. Since flares emit electromagnetic waves in virtually all wavelength bands, flare observations are made in various wavelength bands such as radio waves, visible light, ultraviolet rays, extreme ultraviolet rays, and X-rays.

A sunspot is a black spot that appears on a photosphere when its viewed with white light. Because sunspots have a strong magnetic field that binds the gas, it interferes with the movement of the fluid, making convection difficult. Therefore, it does not receive enough heat from the inside, and the temperature is lower than the surrounding area, so it looks black. Sunspots and surrounding areas are called ‘Active region’ because of their active magnetic activity, and the main activities of the sun occur in this area.

A supernova remnant is a collective term for the remnants of a star that exploded in a supernova and surrounding matter swept away by a supernova blast wave. When a star reaches its end and explodes into a supernova, the material that makes up the star is ejected at a speed of thousands of kilometers per second or more. The supersonic-expanding jet drives powerful shock waves, accelerating and heating surrounding matter. As radiation emitted by accelerated and heated gas, supernova remnants glow in all wavelength ranges, including radio, infrared, optical, and X-rays. About 300 supernova remnants are known in our galaxy.