Can Someone explain Why we integrate over 4[tex]\pi[/tex]? What allows

In summary, we integrate over 4π in order to encompass all directions and orientations in 3D. This is equivalent to 2π in 2D. The solid angle, represented by 4π, is the 3D analog to 2π radians in 2D. When referring to the angular flux, integrating over the solid angle gives the scalar flux. This integration assumes that neutrons are produced and move uniformly. It is not necessary to convert it to scalar format.
  • #1
candice_84
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Can Someone explain Why we integrate over 4[tex]\pi[/tex]? What allows us to get rid of Omega?
 

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  • #2


One is simply integration over all 'directions'. 4π is just the total solid angle, which represents all directions/orientations.
 
  • #3


2pi = 360 which is enough.
 
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  • #4


candice_84 said:
2pi = 360 which is enough.

2 pi in 2D, not 3D.

In 3D, 2 pi is half the solid angle encompassed by a sphere, i.e. hemisphere.

Think - the area of a sphere is 4pi r2, where r is the radius.

Note, when one refers to
[tex]\phi(r,E,\vec{\Omega})[/tex]
one is referring to the angular flux in n/cm2-s-(unit E)-steradian.

Integrating over the solid angle gives the 'scalar' flux.

http://en.wikipedia.org/wiki/Neutron_transport
 
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  • #5


solid angle is a volume?
 
  • #6


candice_84 said:
solid angle is a volume?
No solid angle is the solid angle, like angle is angle in 2D. The 4π (steradians) solid angle is the 3D analog to 2π radians in 2D.

The total solid angle would be the area of a sphere divided by r2, i.e. A/r2 = 4πr2/r2 = 4π, just like 2π = circumference (2π r) of the circle divided by r.

http://en.wikipedia.org/wiki/Steradian
http://en.wikipedia.org/wiki/Solid_angle

http://mathworld.wolfram.com/SolidAngle.html
http://mathworld.wolfram.com/Radian.html
http://mathworld.wolfram.com/Angle.html
 
  • #7


This integration is only correct if we assume neutrons are produce and move uniformly. Its better to not convert it to scalar format, am i right?
 

What is integration over 4π?

Integration over 4π refers to the process of summing up or calculating the area under a curve that extends over 4π units on the x-axis. This is typically done in calculus or physics to find the total value of a function over a specific range.

Why do we integrate over 4π?

Integrating over 4π allows us to find the total value of a function over a larger range than just 2π, which is the standard range for trigonometric functions. This can be useful in various applications, such as calculating the total displacement or velocity of an object in circular motion.

What is the significance of 4π in integration?

The number 4π represents the circumference of a full circle in radians, which is equivalent to 360 degrees. By integrating over this range, we are essentially calculating the value of a function over a complete rotation, which can have practical applications in physics and engineering.

Is it necessary to integrate over 4π?

The need to integrate over 4π depends on the specific problem at hand. In some cases, integrating over 2π may be sufficient, but there are situations where a larger range is necessary to accurately represent the behavior of a function. It is important to carefully consider the problem and choose the appropriate integration range.

What is the difference between integrating over 4π and 2π?

Integrating over 4π covers a larger range and allows for a more comprehensive calculation of a function's total value. Integrating over 2π is typically used for trigonometric functions and represents one full cycle. In some cases, integrating over 4π may yield a different result than integrating over 2π, depending on the behavior of the function.

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