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Question Radioactive decay in flight 

Forum: Hadronic Processes
Re: Question Why must an unstable ion decay when at rest ? (Andrea Conti)
Re: None Re: Why must an unstable ion decay when at rest ? (michel maire)
Date: 03 Feb, 2015
From: Andrea Conti <Andrea Conti>

I have modified TrackingAction::PreUserTrackingAction of the extended example rdecay01 like this:

[...]
  //fFullChain: stop ion and print decay chain (this comment was already in the original)
  //
  std::ofstream TestOutput;
  if (ID == 1) TestOutput.open("TestOutput.txt",std::ios::out);
  else TestOutput.open("TestOutput.txt",std::ios::app);
  if (fCharge > 2.) {
    G4Track* tr = (G4Track*) track;
	TestOutput << "\n A: " << name << ", status = " << tr->GetTrackStatus() << ", kinetic energy = " << tr->GetKineticEnergy();
    if (fFullChain) tr->SetTrackStatus(fStopButAlive); (this statement was already in the original)
	TestOutput << "\n B: " << name << ", status = " << tr->GetTrackStatus() << ", kinetic energy = " << tr->GetKineticEnergy();
    if (ID == 1) fEvent->AddDecayChain(name);
      else       fEvent->AddDecayChain(" ---> " + name); 
  }
  TestOutput.close();
[...]

Then I ran it and gave the following command lines:

/gun/particle ion

/gun/ion 92 238

/rdecay01/fullChain true

/run/beamOn 1

and here is the output file (status=0 means fAlive, status=1 means fStopButAlive):

 A: U238, status = 1, kinetic energy = 0
 B: U238, status = 1, kinetic energy = 0
 A: Th234, status = 0, kinetic energy = 0.0725359
 B: Th234, status = 1, kinetic energy = 0.0725359
 A: Pa234[78.920], status = 0, kinetic energy = 0.0726698
 B: Pa234[78.920], status = 1, kinetic energy = 0.0726698
 A: Pa234, status = 0, kinetic energy = 0.0726698
 B: Pa234, status = 1, kinetic energy = 0.0726698
 A: U234[1958.770], status = 0, kinetic energy = 0.0727266
 B: U234[1958.770], status = 1, kinetic energy = 0.0727266
 A: U234[1022.969], status = 0, kinetic energy = 0.0727263
 B: U234[1022.969], status = 1, kinetic energy = 0.0727263
 A: U234[142.469], status = 0, kinetic energy = 0.072726
 B: U234[142.469], status = 1, kinetic energy = 0.072726
 A: U234[42.616], status = 0, kinetic energy = 0.072726
 B: U234[42.616], status = 1, kinetic energy = 0.072726
 A: U234, status = 0, kinetic energy = 0.072726
 B: U234, status = 1, kinetic energy = 0.072726
 A: Th230, status = 0, kinetic energy = 0.184498
 B: Th230, status = 1, kinetic energy = 0.184498
 A: Ra226[67.670], status = 0, kinetic energy = 0.343662
 B: Ra226[67.670], status = 1, kinetic energy = 0.343662
 A: Ra226, status = 0, kinetic energy = 0.343662
 B: Ra226, status = 1, kinetic energy = 0.343662
 A: Rn222, status = 0, kinetic energy = 0.469452
 B: Rn222, status = 1, kinetic energy = 0.469452
 A: Po218, status = 0, kinetic energy = 0.744178
 B: Po218, status = 1, kinetic energy = 0.744178
 A: Pb214, status = 0, kinetic energy = 1.31339
 B: Pb214, status = 1, kinetic energy = 1.31339
 A: Bi214[351.932], status = 0, kinetic energy = 1.31261
 B: Bi214[351.932], status = 1, kinetic energy = 1.31261
 A: Bi214, status = 0, kinetic energy = 1.31261
 B: Bi214, status = 1, kinetic energy = 1.31261
 A: Po214[1377.678], status = 0, kinetic energy = 1.31658
 B: Po214[1377.678], status = 1, kinetic energy = 1.31658
 A: Po214[609.318], status = 0, kinetic energy = 1.31657
 B: Po214[609.318], status = 1, kinetic energy = 1.31657
 A: Po214, status = 0, kinetic energy = 1.31657
 B: Po214, status = 1, kinetic energy = 1.31657
 A: Pb210, status = 0, kinetic energy = 1.41345
 B: Pb210, status = 1, kinetic energy = 1.41345
 A: Bi210[46.539], status = 0, kinetic energy = 1.41356
 B: Bi210[46.539], status = 1, kinetic energy = 1.41356
 A: Bi210, status = 0, kinetic energy = 1.41356
 B: Bi210, status = 1, kinetic energy = 1.41356
 A: Po210, status = 0, kinetic energy = 1.41431
 B: Po210, status = 1, kinetic energy = 1.41431
 A: Pb206, status = 0, kinetic energy = 1.20364
 B: Pb206, status = 1, kinetic energy = 1.20364

So they decay also if their kinetic energy is > 0, t.i. in flight. What matters seems to be exclusively the status: if status is fStopButAlive then they decay. If I repeat the experiment using:

/rdecay01/fullChain false

then here is the output:

 A: U238, status = 1, kinetic energy = 0
 B: U238, status = 1, kinetic energy = 0
 A: Th234, status = 0, kinetic energy = 0.0725359
 B: Th234, status = 0, kinetic energy = 0.0725359

So, if the ion is in status=0=fAlive then it doesn't decay. It decays only if it is in status fStopButAlive, independently from its kinetik energy. Why this ? What is the sense of this?

Andrea Conti

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1 None: Re: Radioactive decay in flight   (michel maire - 05 Feb, 2015)
(_ Ok: Example rdecay01   (Andrea Conti - 05 Feb, 2015)
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