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Forum: Event and Track Management
Re: Question Number of initial events and Statistic (Kim Tuyet)
Date: 18 Sep, 2013
From: Michael H. Kelsey <Michael H. Kelsey>

On Tue, 17 Sep 2013 07:12:41 GMT, Kim Tuyet wrote:
> Hello all. My name is Kim Tuyet Tran. I am currently a technician of a
> Nuclear Techniques Laboratory, University of Science - Ho Chi Minh city,
> Viet Nam.
> 
> In a research of Compton Scattering, because of the big geometry of lead
> collimator, the detected event is very low.

You probably want to look into the various biasing options available to you, so that you only generate events which reflect the physics you care about.

If you choose to do biasing, you need to be aware that the event rate will (obviously) not reflect the underlying physics, and you will have to apply scaling factors to convert your observed events to true physical distributions.

> Initial events is 2E+09 but detected events is 3E+02. Thus, this
> detected events number is not good for statistic.
> I have two solutions and I hope you can review and give me some advices:
>  1. The initial events in Geant4 is limited by 2E+09.
>     I run 4E+09 but the initial events stop at 2.2E+09.

The number of events is a regular int (not unsigned), and so is limited to 2^31-1.

> Is this any possible way to increase the initial events?

To increase the number of events in your job, you can run multiple /run/beamOn commands in your macro file.

>  2. The second solution is run the input file many times (maybe 3 or 4
> times) and then combine (integrate) the result files.

This won't work in the default configuration, because the same random seed is used at the start of every job (so all of your file would end up with exactly the same events). You can change the random seed, for example by using the system time, to get a different sequence for each run.

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