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Question cold neutron spin tracking 

Keywords: spin, neutrons, magnetic field
Forum: Fields: Magnetic and Otherwise
Date: 22 Nov, 2005
From: Emil Frlez <Emil Frlez>

 Dear GEANT-ers,

 I would appreciate if people who have a better insight
 into the GEANT4 tracking could help me increase my productivity ;8-)

 My problem is the cold neutron spin tracking in the non-homogeneous
 magnetic field. I am using geant4.6.2.p01. Reading the exchange
 between Bertalan and Peter it appeared to me (at the first sight)
 that this problem is (basically) solved in G4.

 So I used the Peter's recipe with "G4Mag_SpinEqRhs.cc". First thing
 I notice is that the anomaly is hard-wired for muons. Second issue,
 the code will only change the spin of the charged particles
 because dSpin is multiplied by particle charge. I checked 
 that code compiles and works for electrons, it does run, and
 does the spin procession, though I have not checked that 
 the results are OK.

 So, I thought that for cold neutrons only thing necessary is
 to copy and rename "G4Mag_SpinEqRhs.cc" into, say,
 "G4Mag_Neutron_SpinEqRhs.cc", change "anomaly = 1.165923e-3;"
 into  "anomaly = 2.913;" and set "ParticleCharge = -1;"
 to reflect the negative neutron magnetic moment and get non-zero
 dSpin ...

 But then I noticed that my "GetFieldValue" is not called at 
 all for neutron, so there will be no tracking for (presumably)
 any neutral particle. Does that means that the G4 FieldManager
 checks the charge of the tracked particle and quits if it is dealing
 with neutral particle? Can this behavior be changed in an elegant
 way? And are the simple changes I was thinking of, outlined above, 
 only ones necessary for the neutron spin tracking?
 (With a rush of cold neutron experiments I find google-ing
 that a number of people are working on the spin tracking
 simulations. If the full machinery already exists in G4
 and an experienced C++ programmer can make the fixes in 10 mins,
 what are those people working on ...;8-?) Or is the whole problem
 more complicated and I am missing something?

                                        Best Regards, Emil Frlez

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1 Feedback: Re: cold neutron spin tracking   (Peter Gumplinger - 22 Nov, 2005)
3 Question: Re: cold neutron spin tracking   (Emil Frlez - 11 Jan, 2006)
1 Note: Re: cold neutron spin tracking   (Emil Frlez - 03 Feb, 2006)
3 None: Re: cold neutron spin tracking   (Kosta Kliakhandler - 23 Jun, 2010)
1 Idea: Re: cold neutron spin tracking   (Gumplinger Peter - 24 Jun, 2010)
... 2 Message(s)
2 None: Re: cold neutron spin tracking   (John Apostolakis - 24 Jun, 2010)
... 3 Message(s)
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