Absolutely correct! Sorry I forgot to mention it.
Alfredo
+----------------------------------------------------------------------+
| Alfredo Ferrari || Tel.: +41.22.76.76119 |
| CERN-EN/STI || Fax.: +41.22.76.69474 |
| 1211 Geneva 23 || e-mail: Alfredo.Ferrari_at_cern.ch |
| Switzerland || |
+----------------------------------------------------------------------+
On Fri, 27 Apr 2018, paola sala wrote:
> Dear Shirley, Alfredo,
> if I may add something: one should add in the balance the residual nucleus
> recoil energy, available in the RESNUC common. Target and redisual masses are
> available as well in the common
> Regards
> Paola
> On 04/27/2018 08:43 AM, Alfredo Ferrari wrote:
>> Dear Shirley
>>
>> the Fluka interaction models assures energy and momentum conservation down
>> to (almost) the computer precision. Typically the "errors" on
>> energy/momentum conservation are of the order of 1E-13 or less wrt the
>> initial state (total) energy (including target mass).
>>
>> In order to properly cross check energy conservation you should consider
>> the "exact" mass of each individual isotope (initial and final state),
>> which are in general different from A x atomic mass unit.
>>
>> Two things to be careful about:
>>
>> a) "nuclear" masses must be considered and not atomic ones, that is
>> atomic electron masses and their binding must be undone from the
>> atomic mass
>> b) as already mentioned above, the individual mass excess of each given
>> isotope (that is the difference wrt A x amu) must be considered,
>> this is important because generally speaking nuclear reactions tend
>> to produce residuals which are less stable than the original target
>> nucleus therefore implying an apparent energy loss (that is energy
>> going into residual nucleus mass)
>>
>> Fluka has detailed tables with the experimental excess masses for some
>> 4000 isotopes and those are the basis for the energy balance.
>>
>> Considering your example, the Fluka "nuclear" mass of 40-Ar is 37.21554
>> GeV and its "nuclear" excess mass (that is the difference wrt 1/12 of
>> the 12-C "nuclear" mass) is -0.03401 GeV, the "nuclear" mass of
>> 38-Ar is 35.35288 GeV and it excess mass is -0.03419 GeV, and the (lab)
>> threshold for pi+ + 40-Ar -> pi+ + n + n + 38-Ar is
>> 0.01653 GeV (the reaction Q is -0.01647) as you can calculate from the
>> numbers above (and the pion and neutron masses), which is somewhat larger
>> than 2 x neutron excess mass which is 0.01614, exactly by those
>> ~ 400 keV that you (correctly) found apparently missing.
>>
>> Hope this helps!
>> Alfredo
>>
>> +----------------------------------------------------------------------+
>> | Alfredo Ferrari || Tel.: +41.22.76.76119 |
>> | CERN-EN/STI || Fax.: +41.22.76.69474 |
>> | 1211 Geneva 23 || e-mail: Alfredo.Ferrari_at_cern.ch |
>> | Switzerland || |
>> +----------------------------------------------------------------------+
>>
>> On Thu, 26 Apr 2018, Shirley Li wrote:
>>
>>> Dear FLUKA users,
>>>
>>> I'm looking at pion inelastic interaction in argon and trying to
>>> understand
>>> the energy balance. I'm wondering how are nucleus masses calculated or
>>> what
>>> database are they taken from? In mgdraw, I record all secondary
>>> particles
>>> out of an inelastic interaction, including the residual nuclei, to look
>>> at
>>> the energy balance.
>>>
>>> For example, in the attached output file, the first reaction is pi +40Ar
>>> ->
>>> pi + 2n + 2 gamma + 38Ar. If I include nucleus mass, i.e, m_40ar =
>>> 39.96u &
>>> u = 0.9315 GeV, the total energy before reaction is 38.0575 GeV. The
>>> total
>>> energy after reaction is 38.0571 GeV, not an exact match. And the
>>> difference becomes larger when the residual nucleus has a smaller A.
>>> I'm
>>> not sure if the difference is because I used wrong nucleus masses.
>>>
>>> Thank you very much!
>>>
>>> Shirley
>>>
>>>
>
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Received on Fri Apr 27 2018 - 11:14:05 CEST