Learn how to define dependent sources in mcnp

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Learn how to define dependent sources in mcnp

In Dependent source, Depending on the source parameter, the value of one parameter is different for different particles. For example, if the source emits 2 different radiation and each of these two radiations has a specific energy spectrum. It is called a dependent source because the value of energy depends on the type of particle (radiation).

1) How to define dependent sources in MCNP

To define dependent sources in mcnp code, we link the value of one parameter to the desired independent parameter. This is done by writing the command in fDep format. As an example, if we want to make the amount of energy-dependent on the type of particle, we shoud write

sdef  par=d1   erg=fpar=d2
si1 L 1  2
sp1 1  1
DS2 S  21  22
SI21  0   1
SP21  0    1
SI22  0   1
SP22 0    1

Here, the SDEF card is first told that the particle parameter value is not a specific value but has a distribution, ie it takes more than one input. Then in distribution number 1, it is said that the amount of PAR card inputs is equal to 1 and 2.

But the amount of energy in these two types of radiation is not the same, so we can not define a specific value for the energy card or enter a specific distribution, but the amount of this card depends on the type of particle.

To solve this problem, we link the amount of the energy card to the PAR card. We do this using the command erg = fpar = d2.

1-1) How does the code figure out what distribution to use for each particle?

In the previous sections, we learned how we can link the value of one card to another card. But the unanswered question is, how does the code communicate?

In the definition of the energy card, it is said that the value of the energy card depends on the particle type card (erg = fpar). Then next part was added (= d2).  

This part means that the relationship between the energy card and the particle type is determined by distribution number 2. So, distribution number 2 is to relate the energy card of each particle to the type of particle. This type of communication is always done using a DS card and an S type.

 1-2) What is the relationship between distributions?

After defining the DS card to the number of independent variable parameters (here par particle type card) we must enter the distribution number. We have two types of particles, so we enter two numbers. Each number represents a distribution that follows. Therefore

Here is the distribution 21 for particle number 1 and the distribution 22 for particle number 2.

2) Define a photon source with two different energies

 In this example, we define a source that emits two neutron and photon particles and the energy of both is equal.

sdef  par=d1   erg=14
si1 L 1  2
sp1 1  1

Here,  photon and neutron particles with an energy of 14 MeV are emitted.

 

3) Define a neutron and photon source with different energy spectra

In this example, a source that emits two neutron and photon particles have different energies.

sdef  par=d1   erg=fpar=d2
si1 L 1  2
sp1 1  1
DS2 S  21  22
SI21  0   10
SP21  0    1
SI22  0   2
SP22 0    1

 

Here, neutron radiation with an energy spectrum between 0-10 MV and photon radiation with an energy spectrum between 0-2 MV is produced.

4) Can all parameters be linked together?

The important point to note is that it is not possible to link all parameters to each other. To view the parameters that can be linked to each other, you must refer to the manual version of the code.

 

 

 

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