Residual radioactivity - metastable vs ground states

From: George Kharashvili <georgek_at_jlab.org>
Date: Tue, 04 May 2010 11:13:46 -0400

Dear FLUKA experts,

According to the manual and some comments on the discussion board, when
predicting residual radioactivity using RESNUCLE card all the residuals
are scored in ground state and FLUKA does not distinguish between ground
states and isomeric states. However, when I try to predict residual
radioactivity in a 5-cm radius 10-cm long gold cylinder exposed to 1 GeV
electrons (same is true at lower energies), I get 2 different Au-196
isomers, which decay with half-lives that correspond to Au-196m (8.1
sec) and Au-196m2 (9.7 hours). Even though the second isomer should be
decaying to the first one 100% of the time (and establish equilibrium)
and both of these isomers should be decaying to the ground state of
Au-196 (half-life=6.2 days), the first isomer disappears several minutes
after the end of the irradiation (as if it wasn't generated by decay of
the second isomer) and the ground state is never scored. Could you
please explain what is going on, or tell me where this subject might be
discussed?
I saw the same when I ran this example with copper target: residual
radionuclides decay with half-lives that correspond to metastable states
and I never see ground states (of Co-60 for example).
Does this mean that if I calculate dose rates from the activated target
only the prompt radiation from those isomers will be contributing and
radiation coming from the decay of the ground states will be ignored?

Thank you very much for your time
 - George

-- 
George Kharashvili
RadCon, ESH&Q
Thomas Jefferson National Accelerator Facility
12050 Jefferson Avenue, MS 6B
Newport News, Virginia 23606
Tel: 757-269-6435

* ..+....1....+....2....+....3....+....4....+....5....+....6....+....7...
TITLE
Simple gold activation problem
*
DEFAULTS NEW-DEFA
*
* beam definitions
BEAM -1.0 0.0 0.0 0.0 0.0 1.0ELECTRON
BEAMPOS 0.0 0.0 -0.1 0.0 0.0
GEOBEGIN COMBNAME
    0 0 Cylindrical Target
*
* Bodies
* ------
*
* General definitions:
* blackhole to include geometry
  SPH BLK 0.0 0.0 0.0 10000.0
* void
  RPP VOI -1000.0 1000.0 -1000.0 1000.0 -1000.0 1000.0
*
* Tungsten target:
* cylinder to contain target
  ZCC TARG 0.0 0.0 5.0
* planes limiting the target
  XYP ZTL 0.0
  XYP ZTH 10.0
  END
*
* Regions
* -------
*
* Blackhole
  BLKHOLE 5 +BLK -VOI
* Vacuum
  VAC 5 +VOI -(+TARG -ZTL +ZTH)
* Target
  TARGET 5 +TARG -ZTL +ZTH
  END
GEOEND
*
* material definitions
* ..+....1....+....2....+....3....+....4....+....5....+....6....+....7...
ASSIGNMA BLCKHOLE BLKHOLE
ASSIGNMA VACUUM VAC
ASSIGNMA GOLD TARGET
EMFCUT -5.0E-3 5.0E-3 0.0 GOLD PROD-CUT
*
* ..+....1....+....2....+....3....+....4....+....5....+....6....+....7...
*
* scoring
*
USRBIN 10.0 ALL-PART 40.0 100.0 100.0 50.0flu
USRBIN -100.0 -100.0 -50.0 100.0 100.0 100.0&
EVENTYPE 0.0 0.0 2.0 0.0 0.0 0.0DPMJET
PHYSICS 3.0 0.0 0.0 0.0 0.0 0.0EVAPORAT
PHOTONUC 1.0 0.0 0.0 GOLD 0.0 0.0
* residual nuclei in target
RESNUCLE 3.0 60.0 TARGET 785.4Activity
*
* ..+....1....+....2....+....3....+....4....+....5....+....6....+....7....+....8
RADDECAY 1.0 3.0 0.0
IRRPROFI 3600.0 1.0E13
* 1sec 1min 1hour 12hours 1day 10days
DCYTIMES 1.0 60.0 3600.0 43200.0 86400.0 864000.0
* 30days
DCYTIMES 2592000.0
*
DCYSCORE 1.0 Au-1s RESNUCLE
RESNUCLE 3.0 61.0 TARGET 785.4Au-1s
DCYSCORE 2.0 Au-1m RESNUCLE
RESNUCLE 3.0 61.0 TARGET 785.4Au-1m
DCYSCORE 3.0 Au-1h RESNUCLE
RESNUCLE 3.0 61.0 TARGET 785.4Au-1h
DCYSCORE 4.0 Au-12h RESNUCLE
RESNUCLE 3.0 61.0 TARGET 785.4Au-12h
DCYSCORE 5.0 Au-1d RESNUCLE
RESNUCLE 3.0 61.0 TARGET 785.4Au-1d
DCYSCORE 6.0 Au-10d RESNUCLE
RESNUCLE 3.0 61.0 TARGET 785.4Au-10d
DCYSCORE 7.0 Au-30d RESNUCLE
RESNUCLE 3.0 61.0 TARGET 785.4Au-30d
RANDOMIZ 1.0 0.0 0.0 0.0 0.0 0.0 0.0
START 1.0E7
STOP
* ..+....1....+....2....+....3....+....4....+....5....+....6....+....7....+....8
Received on Tue May 04 2010 - 17:55:11 CEST

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