Van Allen Radiation Belt

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What is the Van Allen Belt?

The Van Allen radiation belt is an area in the Earth's magnetosphere that contains doughnut-shaped zones of highly charged particles. The magnetosphere is a level in the Earth's atmosphere that is placed at high altitudes, and which interacts with solar winds that cause distortions in the shape of the belts. In 1958, an American physicist by the name of James A. Van Allen discovered the radiation belts using data sent by the US Explore satellite. The naming of these radiation belts is done in honor of the physicist who discovered them. In this article, we will discuss the Van Allen belt and learn more about this phenomenon. 


Understanding the Location of the Van Allen Belts 

The Van Allen radiation belt is placed in such a way that it is most densely present over the Equator and absent near the poles. The shape of the belt is such that it appears to be divided into two zones: an inner belt and an outer belt. In reality, there is no actual gap between the zones and they in fact merge with each other. 

The inner and outer belts appear so due to the changing flux of the charged particles which look like two regions of maximum density. The inner region lies about three thousand kilometers above the Earth's surface. The outer region of the Van Allen belt is found at an altitude of fifteen thousand to twenty thousand kilometers, however, according to some estimates, it is placed as far away as six Earth radii (which is about thirty-eight thousand kilometers). 


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The Inner Van Allen Belt

The inner Van Allen belt is an area of densely packed protons in high-energy states. The energy of the charged particles in this region exceeds 30,000,000 electron volts. The protons travel in this area of the belt with high intensity, peaking at approximately 20,000 particles per second crossing a spherical region of one square centimeter. The origin of the charged particles in this inner region of the Van Allen belt is an interesting concept. Scientists explain that in the magnetosphere, the atoms in the Earth's atmosphere collide with high-intensity cosmic rays from out of the solar system which causes neutrons to decay. These decaying neutrons are responsible for the release of high-energy protons which are abundant in the inner belt. 

Some neutrons in the belt are ejected away from the atmosphere, while some of them undergo decay. These independently charged particles travel in spirals along the lines of Earth's magnetic field. As the particles reach near the polar caps, the strength of the magnetic fields deflects the charged particles off their course. This phenomenon causes the particles to travel back and forth between the poles, forming a sort of magnetic mirror. These particles finally move out of the belt when they collide with atoms in the atmosphere. 


The Outer Van Allen Belt 

The composition of the outer Van Allen belt largely consists of highly charged particles originating from the Earth's atmosphere and also from heavy streams of charged particles (mainly helium) flowing from the sun, which are known as solar winds. The particles in this region have comparatively lower energies as opposed to the inner belt. However, they experience a much greater flux. The electrons in this region are the most energetically abundant, with values reaching up to several hundred million electron volts. 

A lot of cosmic activity, often caused by the sun, such as coronal mass ejection can negatively affect the outer Van Allen radiation belt. These forces can cause the belt to deplete, resulting in a third feeble belt between the outer and inner regions. Interaction between solar forces and the belts is also responsible for atmospheric phenomena such as auroras and magnetic storms. 


Solved Examples 

1. Briefly State the Cause Behind the Formation of a Van Allen Radiation Belt. 

Answer: The Van Allen belt is a region of energetically charged particles that are brought along by cosmic rays and solar winds and get attracted to the Earth's magnetic field. 


2. How Many Satellites are Present in the Region of the Van Allen Belt?

Answer: Since this region of the Earth's atmosphere is dense in charged particles, we use this region to support our communication and navigation systems. There are approximately 800 satellites present in the region of the belt. 

FAQs (Frequently Asked Questions)

1. Briefly Discuss the Outer and Inner Van Allen Belts.

Answer: The Van Allen belt is divided into two regions, namely, the inner and outer belts. The inner region of the belt is characterized by a high density of energetically charged protons. These positively charged particles are formed when solar winds from the Sun hit atmospheric atoms and molecules and lead to the decay of neutrons. These protons travel across the magnetic fields of the earth with high energies and form the inner belt of the Van Allen region. Conversely, the outer region of the belt is more abundant in electrons. The particles here are mostly ones carried along by cosmic rays or solar winds. All the charged particles form a belt around the earth in the region of the magnetosphere attracted by the magnetic field of the planet. 

2. Can Astronauts Survive in the Van Allen Radiation Belt?

Answer: The Van Allen belt is a region characterized by intense forces of radiation. When satellites or spaceships pass through this region of the planet's atmosphere, there is a certain degree of risk of the spacecraft being affected by the radiation. Especially on manned missions such as that of the Apollo, there were numerous threats faced by the crew members. However modern technology is such that we can build our spacecraft to withstand strong cosmic forces such as solar wind and cosmic rays. Due to such technological progress, not a single astronaut was affected in the Apollo mission while passing through the Van Allen belt. 

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