Problem 2387

Summary:	Missing 140 keV gamma line from Mo-99
Product:	Geant4	Reporter:	Raymond Hei Man Tsang <rhmtsang>
Component:	processes/hadronic/models/radioactive_decay	Assignee:	Laurent Desorgher <laurent.desorgher>
Status:	ASSIGNED ---
Severity:	normal	CC:	Alberto.Ribon, dennis.herbert.wright
Priority:	P4
Version:	10.4
Hardware:	All
OS:	All
Attachments:	Plots showing the discrepancy Mo99 simulation result Bug fixed

Description Raymond Hei Man Tsang 2021-06-15 21:42:52 CEST

Created attachment 701 [details]
Plots showing the discrepancy

An actual sample with about 2.8 kBq of Mo-99 (and other isotopes) was counted in a HPGe detector. The counting setup was simulated in GEANT4 10.4. The data and simulation were compared (See data-sim-comparison.pdf in the attached tarball, red is data, blue is simulation.) On page 2, a peak at 140 keV is found in the data but is missing in the simulation. 

From the actual HPGe data, I checked that the halflife of the isotope associated with the gamma line is about 66.4 hours, very close to the halflife of Mo-99 (65.9 h). (See decay.pdf in the attached tarball.) 

This line should exist according to this database:
http://nucleardata.nuclear.lu.se/toi/nuclide.asp?iZA=420099

It seems like the 140 keV gamma line from Mo-99 is missing in the GEANT4 data files.

Comment 1 Raymond Hei Man Tsang 2021-06-16 22:34:46 CEST

Created attachment 702 [details]
Mo99 simulation result

Comment 2 Raymond Hei Man Tsang 2021-06-16 22:37:39 CEST

I have some additional information.

First, a clarification. The 140 keV line isn't missing. It is just that its intensity is lower than expected. 

Second, I looked through my code to see if there is anything wrong. I noticed that I have set "/grdm/nucleusLimits 99 99 42 42" in the macro, but the 140 keV line actually comes from Tc99[142.683] the decay product of Mo99. So, I suspected that the decay might have been suppressed by my own command. So, I reran the simulation again without the nucleus limits command. However, this time I'm still getting a similar result. (See attached Mo99.pdf, the X-axis is deposited energy in keV.) From my actual counting data, the 140 keV peak is more than 10 times higher than the peak at 181 keV, consistent with the LBL/Lund DB: http://nucleardata.nuclear.lu.se/toi/nuclide.asp?iZA=420099 .

Comment 3 Raymond Hei Man Tsang 2021-07-06 20:45:41 CEST

Created attachment 704 [details]
Bug fixed

Comment 4 Raymond Hei Man Tsang 2021-07-06 20:47:16 CEST

I think I have identified the culprit. 

In PhotonEvaporation5.2/z43.a99, if I change the value in the 3rd column on the 5th line from 7.299e-9 to 100, then the simulated and actual Mo-99 spectra match much better. (Please see page 2 of the attached data-comparison-v2.pdf, labelled "Bug fixed".)

Of course, I would like an official confirmation that this is what fixes it.