Question related to the Output using the GPS?


I have invoked GPS in place of particle gun .
and i am using this primary.mac file.
primary.txt (25.7 KB)
for this i am not getting any errors but i am getting this type of beam, why ?
Why it is not coming from all the sides as it is GPS so it should be come like that.

why i am not getting like the second one ? second one is from the example/advanced/radioprotection.
Can anyone please help me with this. it will be very helpful for me.
Thanks in advance!

Instead of

/gps/ang/mintheta 0. deg
/gps/ang/maxtheta 0.003 deg


/gps/ang/mintheta 179.007 deg
/gps/ang/maxtheta 180 deg

Thank you for your reply!
Yes, i have done this and now i am getting like this…please have a look!

now i am able to generate the GPS.
Thanks for your reply!
But i think angle is not affecting the GPS. After creation of GPS i put same angles values that i am using earlier and it is same but ya i got this. see below !

Hello sir,
can you please tell me how you suggested these above min theta and max theta values ?
if i want to calculate these for my object then how can i get this (these are used for biasing but i don’t know how it is done ).
i didn’t get any calculation information of this…like in radio-protection example max theta is 0.003 deg , how it is calculated for their object? i am not getting this exact value if i want to calculate this for the same radio-protection example.
can you please suggest me any reference for this , i will be very grateful for this.
Best Regards

Sorry. It was just a suggestion. I guess you just have to try a few things.


things like ? can you please suggest me ?

Dear Priyanshu

Are you making any progress?

What you can do to help you see what is happening is:

/tracking/verbose 2

Also, you could simply inspect/print information at each step in a stepping action.

Maybe using geantinos (non-interacting particle) would help simplify the information so you could focus on purely geometrical effects.


Thank you so much sir!
This i have done.

this is giving me information like see below

But i was just curious about theta calculation ?
for that i found something but not able to implement that on the radio-protection example , how they have written theta value according to their object ?
also i thought this could be related to cosine distribution then i read about this with this paper
cosine_distribution.pdf (111.3 KB)

but i got stuck again in the polar angle calculation , so related to this i have one question , if it is related to random number then how should i know about random number values that i can put or is it different thing, am i going wrong with this theta calculation ? is it calculated differently ?
i am really very confused with this.
if i want to calculate for my object then how can i do this ? if i know the dimensions (size) of my object ?
sorry for so many questions but if you can help , it would really grateful and appreciated.
Best Regards

Hi Priyanshu

Let’s take things a step at a time.

Question 1: Is the GPS generating particles in the way you expect?

Question 2: Every other question!


yes. GPS is generating particles like i need .

Hi Priyanshu

Looking back at primary.txt:

/gps/pos/type Surface
/gps/pos/shape Sphere
/gps/ang/type cos

That should radiate particles from the surface of a sphere with a cosine distribution (see Lambert’s cosine law)…except (I have discovered from experience) it radiates it only inwards.

primary.txt goes on to try to limit the theta angles. Why?

The second image shows particles emanating from a small source. You could get this with a point source with “uniform” distribution. Is that what you want? Look at the GPS documentation.

Sorry not to be more helpful but you have to know what you want and look at the documentation and try a few things and be in a position to see what happens.


OK. Great. So…tell me again…what is your problem?

let me tell you in detail…
i was working with a object that is in a GDML format. then i took my object and then i took examples/extended/GDML/G01 .
and i have invoked my object in this.
now next thing…
in the G01 example , by default in primary generator, particle gun is used but i wanted to use GPS (as i am working for space application).

then… i replaced particle gun to gps .
in that for the gps i used a macro that i just picked from radioprotection example.

and last my problem converted G01 example+ my object + GPS

then it was done…

now after doing all i was understanding the mac file that i used directly for my purpose that i took from radioprotection example…

so in the process of understanding the .mac file of radioprotection example , i got stuck in the command line /gps/ang/maxtheta 0.003 deg
how this maxtheta value is written ? otherwise i understood all the things in the mac file except thi one.
that is the problem.

You are right to be puzzled by the max/minTheta statements. So am I. You will have to ask the authors of the radioprotection example. Please do this (their names should be in the README and/or the code). We may all learn from this.

Good luck

yes, i sent them this query personally from this forum but didn’t get any reply on particularly this.
By the way thanks for the help.