RE: Defining a radioactive isotope as source

From: Thomas Otto <>
Date: Wed, 25 Apr 2012 12:29:39 +0000

Dear Mina& List,

Further to Joachim's reply, replacing the two individual photos with two
of the average energy (approx. 1250 keV) will not give the same results,
because cross sections and conversion coefficients are energy dependent.
However, in this specific case the two photon energies are so close that it
does not make a lot of difference, and the error induced by this simplification
may well be smaller than the Monte-Carlo uncertainties.

Regards, Thomas

Thomas Otto
Safety Officer, Technology Department

-----Original Message-----
From: [] On Behalf Of Joachim Vollaire
Sent: 24 April 2012 22:24
To: Mina Nozar;
Subject: RE: Defining a radioactive isotope as source

Dear Mina,

Here are some answers to your questions :

1) Does the first method, i.e. using the HI-PROPE option, do the same, i.e.
use isotropic and mono-energetic gammas with energy as the average energy
of (1332.5 keV and 1173.2 keV)?

Yes in theory both approach should be the same if you are careful with the
normalization. Using the built-in source is however more straightforward, especially
for isotopes with many gamma lines... In the case of Co you could do one photon
run with one energy and another one with the other line. As the results are normalized
per primary, you would need to add the scored quantity of the two runs and
then multiply per the Co60 activity as one disintegration leads to the
production of two photons....

2) Can the activity of the radioisotope be incorporated in the source definition?
If you use the built-in source, the results are normalized to one disintegration.
This mean than when you post process the results you have to normalize to the activity,
as for a "prompt" calculation where results are normalized to one primary particle....

3) Is it possible to define multiple radioisotopes as sources, taking into account
activities of each?

The best is to run independent calculations for each isotopes, then normalize to
the corresponding activity (see 2) above) and add the results....

More general comment, you must not forget to call the particle decay with RADDECAy
for ISOTOPE used with the BEAM card. I have attached below some cards taken from
a calculations where I was looking at the dose rate from Ar41 decay in air
in a 300 X 300 X 300 cm3 room. The specific activity in the air was equal to
70 kBq/m3, thus to get the results in microSv/h the normalization factor I
was using is the following :


BEAMPOS 0.0 300.0 0.0 300.0 0.0 300.0CART-VOL
BEAMPOS 0.0 0.0 0.0
HI-PROPE 18. 41.

DCYSCORE -1.0 0. 0. DR-001 DR-001 USRBIN
USRBIN 10.0 DOSE-EQ -45.0 200.0 20.0 200.0DR-001
USRBIN -200.0 -20.0 -200.0 100.0 1.0 100.0&

Hoping this help

Received on Wed Apr 25 2012 - 23:28:40 CEST

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