From: me@marychin.org
Date: Tue Dec 12 2006 - 01:52:32 CET
You are absolutely right. Thanks a million Alberto!
Alberto Fasso' wrote:
> The reason is probably in your test
> ETRACK.EQ.PBEAM
> both ETRACK and PBEAM are real (actually double precision) quantities, and
> it is well known that comparisons of such quantities should be done only
> by .LE. .LT. .GE. or .GT. Equality can be spoiled by rounding errors.
> Suppose for instance that PBEAM has been input as 21.5, but ETRACK
> for some reason is 24.99999999999999D0. For computing purposes it is the same
> thing, but the test of equality would fail. I suggest that you change your test
> into:
> IF (ICODE.EQ.101 .AND. ETRACK.GE.PBEAM*ONEMNS) THEN
> (ONEMNS is predefined in FLUKA as 0.999999999999999D+00)
>
> Alberto
>
>
> On Mon, 11 Dec 2006, me@marychin.org wrote:
>
>
>>Dear FLUKA friends,
>>
>>I started monoenergetic photons in homogeneous lead. Simulations were
>>repeated for different incident energy, ranging from 7.5 to 29.5 MeV. My
>>USDRAW in mgdraw.f has:
>> IF (ICODE.EQ.101 .AND. ETRACK.EQ.PBEAM) THEN
>> J = 0
>> DO I = 1, Np
>> IF (Kpart(I)==8) THEN
>> J = J + 1
>> END IF
>> END DO
>> WRITE (IODRAW) J
>> END IF
>>so that only photons at incident energy undergoing inelastic
>>interactions scores. Slowing down photons were not allowed to score. I
>>basically mean to count the number of (g,n), (g,2n) and (g,3n) events.
>>When the count is plotted against the incident energy, I expect
>>the plot to resemble the photoneutron cross section. Generally results
>>appear as expected except that at incident energies 21.5, 25.5 and 29.5
>>MeV, I miraculously get zero counts. Zero counts were obtained at
>>exactly the same three energies when the simulation was repeated with
>>carbon and calcium. I can't understand the abrupt zero and the
>>discontinuity. Could someone please help. Have I missed something?
>>
>>My results for lead is as follows. Please note the region of interest I
>>have zoomed into between 21 and 22 MeV. 21.4, 21.49 and 21.6 all
>>produced non-zero counts while 21.499 and 21.5 produced zero.
>>MeV (g,0n) (g,n) (g,2n) (g,3n)
>>7.5 709 1747 0 0
>>8.5 0 11923 0 0
>>9.5 0 37225 0 0
>>10.5 0 85953 0 0
>>11.5 0 181338 0 0
>>12.5 0 266842 0 0
>>13.5 1 328983 0 0
>>14.5 0 242696 17314 0
>>15.5 1 90913 76994 0
>>16.5 0 20916 80017 0
>>17.5 2 5257 65996 0
>>18.5 4 1634 52304 0
>>19.5 8 572 35742 0
>>20.5 9 235 21941 0
>>21 13 188 18131 0
>>21.1 10 190 17868 0
>>21.2 16 148 17409 0
>>21.3 10 169 17280 0
>>21.4 10 155 17156 0
>>21.49 12 157 17694 0
>>21.499 0 0 0 0
>>21.5 0 0 0 0
>>21.6 12 175 17529 0
>>21.7 11 158 17700 0
>>21.8 18 162 18257 1
>>21.9 13 154 18703 9
>>22 18 152 19278 18
>>22.5 20 161 22008 210
>>23.5 40 168 22886 2608
>>24.5 32 118 12426 5929
>>25.5 0 0 0 0
>>26.5 20 75 2865 9170
>>27.5 19 94 1715 10760
>>28.5 32 85 951 9397
>>29.5 0 0 0 0
>>
>>Attached inp file, as well as photoneutron cross sections for lead. The
>>cross section doesn't seem to explain the trend. Calcium, carbon and
>>lead are unlikely to have absolute-zero valleys at exactly the same 3
>>energies anyway?
>>
>>Thanks very much.
>>
>>mary
>>
>>
>>
>
>
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