1. Plans for Neutron Irradiations at RINSC
Bjorn Burkle, Soumya Ghosh, Ulrich Heintz, Nick Hinton, Meenakshi Narain, Sinan Sagir, Eric Spencer
Brown University
7/31/2017
Ulrich Heintz - USCMS irradiation meeting

2. Rhode Island Nuclear Science Center
Brown University
 30 miles
RINSC
2 MW light water cooled pool-type reactor
Sample delivery methods
Pneumatic rabbit system
Sample sizes up to 35 mm  90 mm
1-MeV equivalent flux  7  1011 n/cm2/s
Beam ports
Accommodate larger samples up to 8” wafers
1-MeV equivalent flux  2 x 1011 n/cm2/s
7/31/2017
Ulrich Heintz - USCMS irradiation meeting

3. Ulrich Heintz - USCMS irradiation meeting
Irradiation plan
Range of fluences (from talk by Timo Peltola/Nural Akchurin – TTU)
Best procedure would be to use the pneumatic rabbit system.
This delivers samples into the reactor core for a precise time while the reactor is running.
The rabbits can accommodate samples of up to 1" by 3.6". The TTU samples should just fit.
Send through 6 rabbits, one for each fluence.
Sandwich the sample between two sheets of Cadmium to absorb thermal neutrons and include a Co Al wire and an Fe foil in each rabbit to normalize the flux.
7/31/2017
Ulrich Heintz - USCMS irradiation meeting

4. Neutron flux spectrum (beam port)
Based on irradiated high purity foils we determined the neutron flux at the RINSC reactor as a function of neutron energy in a 6” beam port
We measure the 1-MeV eq flux for Silicon to be about (3.8±0.6)× n/c m 2 /s
The nominal flux quoted by RINSC is 2× n/c m 2 /s
The discrepancy is not too surprising as the flux spectrum has never been measured and the reactor staff used a guess for the spectrum to convert their counting rate to a 1-MeV eq. fluence.
Our measurements also indicate that there may be a +/-25% variation across the size of the 6" beam port.
CAVEAT: the annealing analysis of samples irradiated in the beam port implies a much smaller fluence.
7/31/2017
Ulrich Heintz - USCMS irradiation meeting

5. Neutron flux spectrum (beam port)
Our measured flux spectrum
Neutron flux (/cm2/s)
Neutron energy (MeV)
7/31/2017
Ulrich Heintz - USCMS irradiation meeting

6. Neutron flux spectrum (rabbit)
The flux in the rabbit system is about 71011 neq/cm2/s
Based on counting an irradiated Co-Al wire (standard flux measurement technique employed by the reactor)
This implies irradiation times between 3.6 minutes (for 1.5E14) and 4 hours (for 1E16).
To normalize flux
First send through a Co-Al wire and a Fe foil to measure flux. We can directly compare the iron foil to the counts from our flux measurement in the beam port.
Then determine the times needed for the desired fluences.
We have not carried out any neutron flux spectrum measurements in the rabbit system. For now we will assume that the spectrum is the same as in the beam port as the sample ends up close to where the beam port is in the core to determine the 1 MeV eq flux.
At a later time irradiate a set of different foils and verify the flux spectrum in the rabbit. This may then lead to a (hopefully small) correction of the fluence values estimated based on the spectrum measured in the beam port.
7/31/2017
Ulrich Heintz - USCMS irradiation meeting

7. Temperature management
The reactor staff measured the maximum temperature that the samples get to in the rabbit for us and they determined that the max temperature reached in a 1 hour irradiation time is 90°F (or 32°C).
We are investigating sending a temperature logger with the samples in the rabbit but this requires some paper work because we have never irradiated anything like it before. It will therefore take a bit of time to find the right logger, order them, and get it approved. We will not wait for this to start irradiations
After irradiation the samples will be put in a freezer right away until they have cooled down enough for shipment. We will use insulated boxes provided by TTU and dry ice for shipment.
7/31/2017
Ulrich Heintz - USCMS irradiation meeting

8. Ulrich Heintz - USCMS irradiation meeting
Next Steps
Calibration of flux
Send through a Co-Al wire and a Fe foil to normalize the flux.
This will be delivered to the reactor tomorrow.
Then determine the times needed for the desired fluences.
Irradiation procedure
Expect to receive the samples from TTU this week.
Send through 6 rabbits with samples and irradiate them for the predetermined times asap.
7/31/2017
Ulrich Heintz - USCMS irradiation meeting