# Semi-analogue mode for dose rate and spectum caculation

Good day,
Fluka is used to a radiation protecting tool for me, such as shielding design, spectra caculation, dose rate caculation, etc.
Some questions disturb me about the non-analogue mode, whose instruction is too short to understand.

1. The results of Userbin/Userdbx with DCYCORE is unit by per weight. How could I translate them to dose rate\flunce rate,etc. If the unit result represent per Bq?
When I got a result from the Userbin Dose-eq(Do= 8.6272E-5), is it correct to use this method to get the 1Ci(3.7E10) result ，per hour（3600s）:
D(1Ci dose rate)= 8.6272E-5 × 3.7E10 × 1E-12 × 3600=0.0115 Sv/h?

2.As we know ,USERDBX could show you the sprectrum(fluence) betwen the bounry. When E=1.17E-3 Gev the fluence is 9.918E+04/(4pi100100)=0.789 cm-1? Why not 1/ 4pi100100=7.9577E-6 cm-1, as scource is Co60 ?

3.Here is an flair used for test my work method,which is used to caculate the sprectum and dose rate, could you find any error for me?

Thank you! Happy new year!

TESTCo6020201227_03 (copy).flair (2.4 KB)

Hello Jane,

I limit myself to answer your question 1.
Your reasoning is correct if every decay of the isotope results in emission of a photon or electron, particles capable to transmit energy to the target. The fraction of decays leading to emission of photons or electrons is indicated by the branching ratio. If the sum of branching ratios leading to photons and electrons is e.g. 25 %, then only every 4th decay leads to an energy deposit and the dose per Bq is 4 times smaller.

Best regards and Happy New Year as well, Thomas

Hello Otto,
Thanks for your answer. So I want to ensure the question again.
What you mean is that all of the result(include dose rate,flux,etc) is normalized by Bq in semi-analogue mode, instead of per particle?
For example Cobalt 60： 1.173（100%）1.332（100%）
A.When normalized by Bq(per decay) , it is not necessary to plus 2（total peak） to get the result for dose rate per Bq.
B.When normalized by particle(per decay) , it is necessary to plus 2（total peak） to get the result for dose rate per Bq.
So which one is correct? A?
Best regards, Arvin.

Hi Arvin,

yes A is correct.

There is a fundamental difference in the units of the results between “prompt” and “decay” calculations.

For “prompt” calculations where you have a particle source (e.g. an accelerator) all results are reported “per primary unit weight”. A bit simplified that basically means per primary particle. So for example the dose rate will be reported as “pSv per primary”. If you scale that with your beam intensity, for example the number of particles per hour, then you have your results in pSv per hour.

For “decay” calculations this changes and everything is reported “per second”. Now you can have 2 different kinds of “decay” calculations. The first one is for example residual activity or residual dose originating from some particle beam that hit an object. In that case the dose rate is to be understood as “pSv per second” because for these kind of calculations you had to define a beam intensity already via the IRRPROFI card.

Then there is the second way of “decay” calculation which in FLUKA jargon is called “semi-analogue”. In this case your particle beam is an isotope and in accordance with the previous explanations also here the units are reported as “per second” which is equivalent to “per Bq = per decay”.
As Thomas already mentioned one decay can have some branching ratios and these are already taken into account. Thus, in your example the result per Bq already reflects the fact that Co-60 emits two photons for one single decay.

Regarding the value of 9E4 that you find between 1.17 and 1.18 MeV: please keep in mind that values of USRBDX and USRTRACK are normally reported as differential quantities. Thus, this is 9E4 cm-1 GeV-1. So if you multiply it with the bin width 1E-5 you find 0.9 which is what you expected.

Cheers
Chris

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