Beginner at geant4

i am beginner at geant4
i have installed all geant4 and execute all examples of geant4.
Now what should i do next to learn geant 4 .
Please guide me to learn geant4.
thanks in advance


A good first step is to copy one of the basic examples and just play with it. Change an input file according to what the README says you can do, run it and see how the output changes. When you understand (roughly) how it works, modify the code to do something different that is of interest to you, recompile it and run it. For example, change the geometry and/or materials and see how the outputs change. Modify the readout mechanism, be it in stepping action or a sensitive detector to output a different quantity than the one(s) it presently provides.

When you get confident enough with that, you can start writing code for your own projects.

To use Geant4 successfully, you need to know C++. If you already do, that is great. If not, there are many introductory and advanced resources on line that can help you with that. For example, (currently down, but it was up a day ago) (covers C++ and C)

There are lots of others. If you are having a particular problem with some piece of C++ code, always remember that Google and Stack Overflow are your friends. For stuff related to Geant4, as you obviously already know, this forum is your friend.

To make sense of the examples, to be able to modify them, and to write your own fresh simulations, you will need to read the Geant4 documentation. The latest version (Geant4 11.0) is at

Most of what you’ll need at first is in Users Guide for Application Developers.

You don’t have to read it cover to cover at first, but you should skim it to find where the major topics are. Eventually, working on your own simulations will have led you to read most or all of it and the other reference manuals, as well.

All of this may seem a little daunting, but if you take it slow and methodically you will do OK.

Good luck.
P.S. There are training courses available, both introductory and advanced. Look for ‘Training courses and materials’ in the side bar of Geant4 Getting Started. I do not know who to talk to to find out what, when and where is coming up next.


sir i have done change input in example and see their output geometery.
but now i do not know ,how can i modify code?

you have to open the code in a text editor or programming environment and change the code properly to your needs and according to Geant4.

The code can mostly be found in .cc and .hh files.

Cmakelists.txt (377 Bytes) (352 Bytes)
this is a code which i want to run but i face error in cmake

guide me about error
thanks in advance

is there any basics tutorials to learn the basics of geant4, it is very difficult for me to learn geant4. please guide me how to learn their basics

Here is an installation guide Installation Guide — Geant4 Installation Guide 11.0 documentation

Does this help? Ah, sorry, you installed it already, right?
I’m starting my application as follows:

cmake -S C:\geant4\sim -B C:\geant4\build -G “Visual Studio 17 2022”


cmake --build C:\geant4\build --config RelWithDebInfo

but this is on Windows, so you would probably exchange Visual Studio with something else.

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CMake requires the script to be named “CMakeLists.txt”, note the capitalised “L”.

The earlier post Beginner at geant4 - #2 by John_McFee points to all of the basics here - see in particular the Application Developer Guide and especially the section that walks through the implementation of a minimal example.


after correction on CMakeLists.txt , i did cmake ,but but still there is another error

Please, have a read through the section: How to Make an Executable Program — Book For Application Developers 11.0 documentation in the linked guide. This will cover the basics of CMake - in this case the error is that the package name to be passed to find_package is “Geant4” not “GEANT4”.

there is an error, please guide me how to resolve it
thanks in advance

Spell the names of your files correctly.

we make our coding but we face an error
please guide me .
thanks in advance

It’s impossible to tell as the output doesn’t show the line(s) and code triggering the error. Fixing compiler errors should always start from the first error message as that will reference the actual line of code causing the problem. That in itself may lead to a quick fix as the source of the error may be obvious, or point to something to look up in relevant documentation.

here is my , which i want to run but i face some error in line 14,16,18

here is error which i am facing ,
please guide where should i declare worldMat and logicWorld in line no. 16 and 18 respectively.
there is an other error in line 14 G4Box

there is G4Box in line 14 and also G4BOX, one is right and one is wrong :slight_smile:

Spell your variable names correctly. Use the same name for the same variable. Read the error messages and think about what they are telling you. Start with the first message. Fix that and recompile. Then fix the new first one. Repeat until you have fixed everything. Maybe read some tutorials or documentation about C++ programming online to learn the basics.

you can search “geant4 tutorial” in youtube. there is a very useful tutorial by Mustafa Schmidt

Screenshot from 2022-12-06 18-56-39 (1.7 KB)

i am facing error ,but do not know how can i resolve it?
i attach file coding which i do?
please guide what should i do to resolve it.