[Alert_collaboration] ALERT scintillator and SiPM radiation hardness

[Whitney R. Armstrong]

Dear Jay,

I wanted to address some of your questions about radiation hardness.

> a. what is the radiation hardness of the scintillator?

> Two decades ago Stan Majewski and the detector group recommended 
> scintillating fiber and PMTs to monitor field emission.

Thank you for pointing this out. It has led some very useful references 
regarding the scintillator radiation hardness. I attached the CEBAF 
paper of Stan Majewski and Carl Zorn.

The scintillators generally don't get noticeably damaged until about 1 
Mrad absorbed dose. Using the CLAS12 FT-hodoscope study as a reference 
(https://clasweb.jlab.org/wiki/index.php/Radiation_dose_estimates) and 
assuming the 0.3 rad/h on each scintillator. It would take about 4.5 
months to reach one krad absorbed dose. Of course 0.3 rad/h is an 
extreme overestimate; the FT-hodoscope is very forward while the ALERT 
detector is at 90 degrees (with the most forward part at ~40 degrees).

So any radiation damage to the scintillator can be safely assumed 
negligible.

> b. rad hardness of SiPM?

There was a very nice study of radiation hardness of SiPMs done for 
Hall-D (http://inspirehep.net/record/1122685?ln=en).
The main conclusion: the dark current increases with absorbed dose.
The detected pulse and time resolution remain pretty much the same.

They measured the damage during the PRex experiment in Hall-A and also 
with an Am-Be source. They also found that the damage can be reversed by 
annealing at high temperatures. The highest temperatures recovering the 
fastest. 

Because the signal and timing remain the same, the main concern for 
ALERT is the dark count rate. We expect the neutron fluence to be 
dramatically less than PRex! However, we are currently working on 
simulations that will tell us precisely what to expect for ALERT. 

In conclusion, the radiation damage to the scintillators and SiPMs is 
expected to be minimal. The expected small increase in the dark current 
is currently being studied.

Please let me know if you have any questions.

Cheers,
Whitney Armstrong


-- 
Whitney R. Armstrong
-------------- next part --------------
A non-text attachment was scrubbed...
Name: fast_scint_for_high_rad.pdf
Type: application/pdf
Size: 4191457 bytes
Desc: not available
URL: <https://mailman.jlab.org/pipermail/alert_collaboration/attachments/20160630/d1b66889/attachment-0001.pdf>