CH Weekly Reports

09/19/22

• Investigated non-linearity of peak sensing ADC due to issues arising in energy calibrations and efficiency measurements.

• Modified existing calibration code to use non-linear regression to account for ADC.

• Sourced material needed for CaGaS Phase II setup.

• Calculated ADC dead time for live-time correction to efficiency measurement count rates and calculated dead time per experiment.

• Designed holder for Gd foils needed for CaGaS Phase II experiment. To be 3D printed and tested for tolerances.

09/26/22

• Printed both parts of the Gd foil holder for CaGaS Phase II.
  • Parts fit together adequately considering they're 3D printed and not machined.
  • M3 bolts threaded through first part of the holder.
  • M3 nuts pressed into the second part of the holder.
  • Parts printed out of PETG plastic with low density infill (10%).

• Edited rebinning code for energy calibrations for data sets collected with ADC to account for changes in calibration code.
  • Energy calibration script now uses 2nd order polynomial regression to account for nonlinearity of ADC
  • The coefficients from the regression are passed to another script to rebin ADC data from channel to energy, preserving bin count, but bin width will increase as a function of energy.
    • End goal is to pass coefficients into rebinning function and draw energy calibrated plot in the same script.

• Designed Gd₂O₃ powder holder for CaGaS Phase II.
  • Have spray on clear coat to seal plastic after printing is complete in hopes that powder will not stick between printed layers when used.

• Documented Gd holders in wiki with rendered images and a description of intended use.

• Continued to research live time correction for HPGe count rates and think I have applied the correction correctly at the initial measurement level, which will be propagated through to efficiency calculations.

• Researched and tested different integration methods for more accurate measurement of counts in energy peak to compare to Gaussian fit.

• Created tentative list of committee members with major advisor for PhD proposal defense and future dissertation defense.

10/03/22

• Sat in on 30 minute proposal defense presentation by another Ph.D. candidate.

• Began the 3D print of Gd₂O₃ holder for CaGaS Phase II.
  • Both parts printed and fit together tightly. Need to be sealed for use with powder.
  • Updated wiki documentation with images of the holders.

• Working with ISU Environmental Health & Safety to set up time to treat and coat lead bricks to build CaGaS Phase II setup.
  • Air monitoring and respirators are required per ISU EH&S safety protocols.

• Designed and printed a holder for Cs137 calibration source for storage in lab (signed off with RSO) for easy point calibrations using HPGe.

• Researched dead time adjustment in Practical Gamma-ray Spectrometry by Gordon Gilmore
  • Collected 50 data points for ADC gate width, read out controller trigger width, and the delay between end of gate and beginning of read trigger.
  • Found dead time per pulse which includes memory storage time, thanks to reading the aforementioned book.

• Worked to re-plot and integrate Eu152 peaks, but source data file seems to be corrupted. Will collect new set of data on Monday (10/10/22) when I can access calibration sources.
  • Re-plotting is necessary for new integration with 2nd order polynomial binning and new live time correction.
  • Collecting a new Eu152 spectrum is needed before CaGaS Phase II for new energy calibration as NIM bin has been power cycled and spec-amp gain has shifted.

10/10/22

• Moved extra lead for CaGaS Phase II from lead storage at ISU to lab for coating prior to use.

• Coated 30 lead bricks for CaGaS Phase II setup.

• Fixed energy calibration code thanks to input from a colleague.
  • Machine precision and how ROOT interprets bins was cause of the issue.

• Designed tools to use to level and compact powder into the powder holder for use during CaGaS Phase II.
  • Designed new covers for powder holder to better accommodate for different thicknesses of powder.

• Experimentally confirmed minimum dead and maximum bounds on dead time of data acquisition system per event after questions from colleague and plotted voltage traces for documentation.

• Refit ¹⁵²Eu energy peaks with gaussians + linear background and recalculated efficiencies using live time correction.
  • Finished replotting and calculating uncertainty in HPGe efficiency measurements to present next week, all calibration sources (¹⁵²Eu, ¹³⁷Cs, & ⁶⁰Co).

• Met with collaborators and discussed FY23 work scope.
  • Setup recurring meetings biweekly starting 10/19/22.

• Contributed to Paul's SOW for FY23.

10/17/22

• Uploaded new versions of efficiency measurement plots to wiki.

• Wrote up efficiency measurement results, explained in detail how the calculations work.
  • Wrote up and defined equations for uncertainty calculations, found lack of count statistics is highly influencing uncertainty in efficiency measurements. Working to rectify by collecting new data sets with ¹⁵²Eu with increased run time.
  • Collected new on & off axis ¹⁵²Eu spectra and overnight background for background subtraction. -> Power stability issues to clean room crashed DAQ2 for background run.
    • Had data acquisition failure due to high count rate halfway through one run, estimated run time based on ratio of rates from previous measurements and decay of ¹⁵²Eu source between past and present runs.

• Created slides and presented HPGe Efficiency write up to collaborators.
  • Met with advisor and verified methods for calculations were reasonable.

• Adjusted design of powder flattening tool to make it easier to use and 3D print.

• Continued work on write up of experimental design and results for CaGaS Phase I.

• Started drafting run plan for CaGaS Phase II.
  • Currently includes runs using He3 tube to measure thermal neutron rate in detector tunnel as a function Gd thickness.
  • HPGe using varying thicknesses of Gd foils and powder.
  • Plan is to vary the distance between detector & gadolinium to be able to account for coincidence peaks problem.

10/24/22

• Finished 3D printing all Gd₂O₃ powder flattening/compacting tools designed previously.

• Stayed up to date with INL required training modules.

• Used feedback from Ph.D. committee members to improve efficiency measurements.

• Debugged and replaced part of signal propagation chain for HPGe electronics chain.

• Finished full automation of energy calibration code. Now takes ADC spectrum, energy calibrates, rebins, replots, and scales by runtime.
  • Commented code and uploaded to ISU wiki & DAQ2 for preservation with brief explanations of functionality and methods.

• Wiped down the freshly coated lead bricks from last week and moved them into the clean room to use in CaGaS Phase II construction.

• Discussed efficiency measurements with Paul and received his feedback on how to improve the analysis, mostly pertaining to the fitting function used in integrating energy peaks.
  • Also covered altering construction plans of CaGaS Phase II to increase shielding, will depend on material available, and plans for collaboration through FY23.

• Dismantled efficiency measurement setup and began construction of CaGaS Phase II setup.
  • Assembled 2" of borated poly on 4ftx4ft steel table
  • Flattened sheets of BorAl and laid out base for CaGaS apparatus.

• Met with Chuting, Paul, major advisor, and OSU faculty to discuss experiment details for next spring/summer.

10/31/22

• Continued to construct CaGaS Phase II and document construction process in order to simulate after.
  • Milled polyethylene for Gd holders to sit flush with BorAl window.
  • Finished construction wednesday morning and began tuning data acquisition system for optimal dead time (Jefferson Lab CODA).

• Began CaGaS Phase II experiments.
  • Analyzed first run found that energy resolution is very poor, ~5 KeV FWHM.
  • Tested Cs137 source in setup instead of Cf252 to determine if smearing due to higher count rate with large energy range.
  • One problem seems to be pre-amp in HPGe is adding heat and increasing detector temp, which reduces resolution. Could be disconnected ground cable, not sure yet.
    • Paul has reached out to Craig Maddigan at Ametek (who has helped us previously) to help debug detector. Began working through checklist Craig Maddigan had provided us previously when having detector issues.
  • Count rate is not in the range of causing issues for daq system, allowing for minimum dead time.

• Mirrored Phase II setup after determining it is necessary to thermal cycle detector over weekend.
  • Detector tunnel and source tunnel have been exchanged and detector is cooling again.
    • This orientation seems to shield detector better than before due to lack of concrete wall/BPoly scattering neutrons into rear of detector.

• Presented first design to collaborators on Wednesday afternoon.

11/07/22

• HPGe is nonfunctional currently (Monday)
  • Had conference call with John Barncord from Ortec and Paul. John is 2 day air shipping a new sieve pill, o-ring, and high vacuum grease to ISU to use in X-Cooler here.
  • Arranged for poptop pumpdown at IAC as detector must be warm to swap sieve pill and o-ring.

• Swapped HPGe out for He3 tube in CaGaS Phase II setup and began taking measurements.
  • Set event limit to 10,000,000 events so run will automatically end. Count rate without converter is ~130Hz, with 0.1mm Gd is ~17Hz.

• Sheared 0.13mm Gd foil to 10cm x 10cm for use in Phase II setup and began collecting data using the foil.

• Analyzed spectrum collected from He3 tube and overlaid the data for no converter and 0.1mm Gd converter.
  • Did not continue with more thicknesses due to mean free path of neutrons in Gd is so small.

• Removed He3 detector and swapped in NaI detector, energy resolution is poor and signal is too fast currently.
  • Finding a way to delay the NaI signal after triggering ADC gate.

• Removed poptop and delivered to IAC for pumpdown.

• HPGe poptop has been pumped down to 1·10^-6 torr and I have delivered it back to ISU.
  • Will be reattached to cooler as soon as o-ring, sieve pill, and high vacuum grease arrive.

• Worked with colleague at LLNL who has experience with this specific detector, conclusion is issue is most likely electronics.
  • Borrowed tail pulse generator to test HPGe pre-amp, which may show distortion in signal if that is the problem.

• Cleaned HPGe thermal contacts and received new parts from ortec.
  • Reassembled poptop and X-Cooler assembly, put HPGe detector back in position in CaGaS setup, and began the cooling process.

• Verified that inhibit system works as intended and bias voltage will ramp down if positive voltage is measured across shutdown cable.

• Swapped NIMbin for one with a blackmax power supply, should be more stable.

• Added magnetic switch to X-Cooler and HPGe pre-amp power such that if UPS battery is drained, X-Cooler will turn off and warm detector up. Bias voltage will be killed by power outage, and if X-Cooler loses power for >10mins, full thermal cycle is needed.

11/14/22

• HPGe is functional.
  • Maintaining ~110K with new sieve pill, o-ring, high vacuum grease, and fresh poptop pumpdown.
  • Used tail pulse generator to pass signal through pre-amp, signal looks somewhat noisy, however could be due to length of cables and noise intrinsic to lab setup. Bias voltage was not active at the time of test, but detector was at operating temperature.
    • Noise is not an issue and system was designed to work around this.

• Acquired Gd foil data with thickness beginning at 0.1mm & ending at 0.62mm.
  • Had one failure of CODA during a Gd foil run. CODA was restarted, run restarted, original failed run marked as failure to be excluded from data set.
    • CODA restarted at the end of each day now. No failures since.

• Measured Gd powder mass and associated thicknesses while setting up for Gd powder measurements.
  • Started with ~0.7mm thick layer of compacted powder in 10cm x 10cm basin.

• Performed quick analysis after each CaGaS Phase II run to verify functionality maintained for HPGe detector.

• Held regular check-ins with Paul and discussed optimal way to perform Gd powder mass measurements and deposit/removal of powder when varying thickness.
  • Discussed what the "background" measurement would be for this setup. Options are either no ²⁵²Cf source or no form of Gd converter. MCNP simulation run by Paul says no converter gives fast neutron flux of 1.3, compared to 1 with converter (volume averaged).

• Collected all Gd thickness measurements, overnight backgrounds, and no converter. CaGaS Phase II data collection complete.

11/21/22

• Compiled CaGaS Phase II data by run type and copied to a second data acquisition machine at ISU, then copied to local machine for analysis.
  • Multiple copies now exist in across 3 computers as backups.

• Developed game plan for next step of work with Paul, including MCNP simulations, CaGaS Phase II analysis, Lithium dead layer of HPGe, etc.

• Uploaded remaining images & organized all of CaGaS Phase II setup images.

• Started CaGaS Phase II analysis.
  • Overnight background runs show no noticeable change detector resolution or effects due to neutron damage. Slight shift in gain from beginning to end but can easily be compensated for.
    • Note: Change in gain most likely due to power to room causing rapid power cycle in NIMbin containing spec-amp. Shift is very minor, ~3 ADC channels which is ~1.2 KeV.

• Revised first draft of proposal document.
  • Brought previous parts in line with CaGaS Phase II and began drafting CaGaS Phase II write up.

11/28/22

• Worked on mcnp with Paul.
  • Successfully implemented tally plotting after having prior issues with Xming & XQuartz on laptop and desktop.
  • Began optimizing number of cores used for mcnp sims. Variance reduction being enabled changes this dramatically.
  • Got MCNPVised working on windows 10, next is trying to import complicated geometries from our simulations and not examples from manual.

• Discussed OSURR design in-depth with Paul. Proposed shielding/converter design changes that may reduce noise and while preserving signal.

• Met with Chuting, Paul, & Mirion regarding detector type and purchase.
  • Included design overview and proposed changes.

• Continued to revise and expand proposal document/dissertation draft.

12/05/22

• Continued MCNP work.
  • Discovered issue with tagging photons produced via pair annihilation, worked to debug.
  • Started to recreate simulations such that MCNPVised can parse the input card correctly.
  • Adjusted low energy cut off for electrons in sample state of PAS simulation to search for trend in annihilated photons seen in detector.
    • Simulation time decreases as energy cut off increases.
    • Decided on 1KeV electron energy cut off as photon flux due to annihilation does not seem to have a strong dependence on cut off energy, and 1KeV is MCNP default.

• Discovered 4 inch Bismuth plug in fast neutron beam line at OSURR that we had not accounted for in MCNP.
  • Successfully added Bismuth as material.
  • Added planes to define extent of Bi plug in beam port.
  • Rendered simulation setup with Bi plug and can run simulation without errors.

• Began optimization of Gd in In Situ PAS experiment simulations. Currently looking for annihilation photon rate from sample to drop off as function of Gd thickness.

• Researched the fast neutron beam line at OSURR and found multiple documents informing the simulation design. The neutron spectrum exiting the beam port may not be as expected and will need to be simulated. Began work on designing new MCNP simulation using code found in a document written by an OSU graduate student and creating a new source spectrum to estimate the exit spectrum from the collimator at OSURR.

12/12/22

• Paul simulated the reactor spectrum into Bismuth over weekend and passed new spectrum to me.
  • Currently signal is too low for design to be feasible. Gd thickness is being optimized with new spectrum, design changes will be necessary.
    • Next step is to shrink radius of sample to less than 1 mean free path of 511KeV photons.
    • Also enlarged radius of sample as annihilation photons decreased as sample radius decreased. Increased as sample radius increased.
  • Varied experimental design and materials in attempt to maximize annihilation events in sample material.

• Began building efficiency measurement simulation to estimate dead layer thickness of HPGe used in CaGaS Phase II for publication.

• Researched other possible TRIGA reactors to use in case OSURR cannot provide necessary flux for viable experiment.

12/19/22

• Finished design of all new MCNP simulation for efficiency measurements. 
  • Crystal curvature radius solution used was provided by Paul.
  • Simulation accurately maps space in which measurements took place, including steel table used to support experimental setup and proximity to concrete wall and floor.
    • A lot of this geometry can be reused in CaGaS Phase II simulations.
  • Found Co60/Eu152/Cs137 button source diagrams and added into source.
    • Attempted to use MCNP heavy ion functionality for spontaneous photon emission, found it was more straightforward to use a discrete distribution with energies and intensities provided by NNDC.
    • Used gammas emitted per second as weight of source.
  • Imported 3D models for detector stands and source holder. 
• Found vendor for 30% borated poly (current expectation is to use 5%).

12/26/22

• Curtailment.

01/02/23

• Monday - Last day of curtailment.

• Fixed fatal errors in efficiency measurement simulations and began testing the simulation.
  • Calculated the gaussian energy broadening parameters to match simulated Co60 energy peaks to that measured with HPGe in ISU lab.

• Calculated atom percentages for 30% w/w Boron from B4C present in borated polyethylene to use in materials card in MCNP.
  • Reran an OSURR simulation with 30% borated poly to investigate change in fast neutron flux on HPGe detectors.

• Discussed possible paths forward with Paul regarding lack of signal in simulations for In Situ PAS.

• Began writing code to strip tally data from MCNP outfiles and plot simulated data.

• Read through reviewer comments and collaborator's edits for Accurate Activity Determination of a Californium Neutron Source paper.

01/09/23

• Swapped all poly in OSURR sims to 30% w/w boron from B₄C.
  • Resulted in net loss of annihilation photons with relatively unchanged fast neutron flux on HPGe detector.

• Delivered feasible design of OSURR InSitu PAS experiment to collaborators.
  • Began optimizing design parameters.

01/16/23

• Continued to optimize OSURR experimental setup.
  • Sample height and diameter, detector distance, shielding arrangement, and materials.

• Investigated possible detector crystal sizes.
  • Including fast neutron flux, total count rate, dead time effects, etc.

• Met with Mirion to discuss detector purchase and found lack of needed information on our side.
  • Calculated energy deposited per second in detector.

01/23/23

• Modeled OSURR experimental setup in fusion 360.
  • Finding location and orientation for CP5 units.

• Proposed detector configuration and orientation to Mirion for review.

• Finalized MCNP model of secondary collimator for minimal fast neutron flux and maximum signal.
  • Added secondary collimator design to 3D model, need to create engineering drawings and have a vendor produce the collimator pieces.

• Reviewed experimental setup with OSURR and began making necessary modifications.
  • Have to move away from beam port by ~15cm due to beam shutter control.
    • Modeled in MCNP for expected signal loss and change in noise/fast neutron flux in HPGe.

01/30/23

• Found mass of shielding arrangement and detectors that will need to be supported.
  • Calculated the thickness of aluminum (or steel) plate needed for <1mm deflection as base of In-Situ setup.
  • Began drafting support structure for experimental setup.

• Met with OSURR team to discuss to experimental setup and details of setup period.
  • Calculated expected dose rates from neutrons & photons exterior to detector shielding (closest to entry to experimental cell) for OSURR team.

• Continued to adjust and refine 3D model of experimental setup to determine amount of material needed to be cast/machined vs purchased.
  • Adjusted secondary collimator model to be easier to cast/machine.
  • Created engineering drawings of the collimators.
  • Contacted vendors regarding custom lead collimator machining/casting.

02/06/23

• Created preliminary design for lead brick arrangement in detector shielding to mate with collimator exit.
  • Made using standard sized bricks, only need piece for cyrostat arm entry machined, may be a way around that too.

• Added cryostat arm and entry point into detector shielding in MCNP, no change in fast neutron flux, annihilation rate, noise level, etc.

• Collaborated with Paul on preliminary support structure designs allowing for continuous vertical adjustment.
  • Preferential to add shielding below detector arrangement to match vertical dimensions to poly chamber.

• Continued refining dissertation outline with advice from Paul and ISU Physics department faculty members.

• Met with Ibrahim to discuss his interpretation of dose tally results from MCNP sims.
  • Further work needed, follow up meeting with Ibrahim next week.

02/13/23

• Began working with vendors regarding lead collimator construction.
  • Reworked engineering drawing to include information needed for quote.
  • Sent requests for a quote to more lead specialty companies.
  • Designed mold for lead collimator as one vendor required us to send a mold to them for casting.
    • Worked with Paul to simplify poly/lead design to use materials on hand at OSURR and make casting of production of collimator simpler.

• Added lead above, below, and upstream of Hercules shielding in MCNP to help with seams and making support structure easier.
  • Altered cryostat arm entry point to 4"x4" square hole which could be produced without extra lead being cast/machined.

• Reworked dose tallies in MCNP and verified results across multiple areas and thicknesses of water boxes.
  • Met with colleague at LLNL to discuss interpretation of tally results.
  • Met with Ibrahim from OSURR and discussed expected dose rates. Will be comparing another simulation to measurements he will be taking for us.

• Enabled photonuclear physics in MCNP and debugged problem nuclides.
  • Compared all important rates (511's, fast neutron flux, dose, etc), no concerning changes.

02/20/23

• Simulated dose rates at OSURR without experimental setup present using MCNP.

• Changed collimator material to tungsten in MCNP on advice of vendor.
  • Tungsten would be easier to manufacture.
  • Found that tungsten is expected to decrease fast neutron flux by 20%, total gamma rate on detector, while preserving signal rate.

• Continued CaGaS write up (for dissertation & publication).

• Verified engineering drawings for polyethylene manufacturing and fixed small issues.

• Investigated possible activation of target/converter/shielding that could prevent changing of sample.
  • Work around in place.

• Discussed OSURR scope of work with Chuting & Paul and brought everyone up to date with current status.

• Collaborated on task list with Paul and we divided tasks to be completed.

• Worked to optimize gadolinium thickness in MCNP interior components have been finalized.

• Designed interior aluminum framing to protect detector/support lead roof.

2/27/23

• Updated vendors for collimator with design for half collimator and tungsten material request (if service offered).

• Adjusted design of interior lead support for Hercules Shielding arrangement due to missing bracket.
  • Created preliminary pricing quote for materials excluding aluminum plates.

• Continued work on Lithium dead layer simulations for On-Axis HPGe detector used in CaGaS Phase II experiments.
  • Added mesh tallies to code.
  • Finished varying dead layer thickness and simulating Co60 source.
  • Added in Eu152 source and ran all planned simulations.
  • Continued work on tally processing script.

• Received experimental results from OSURR for dose rates which do not match simulation.
  • Worked to verify flux for neutron beam at OSURR and inquired about discrepancies in data vs quoted flux.
  • Adjusted beam parameters that were incorrect including a small adjustment to source weighting and divergence (not from flux inquiry above).
  • Updated OSURR on dose rate simulations.
  • Verified flux from raw data provided by OSURR.

3/6/23

• Updated MCNP simulation with new flux distribution from data provided by OSURR.
  • The change increased total rate on detector, increased signal rate, and decreased fast neutron flux on HPGe crystal.
  • Tallied dose for OSURR, simulation still low compared to measurement.
  • Read literature to verify methods of dose rate calculation using tally results from MCNP.
  • Met with OSURR regarding dose rates and continued with their suggestions in MCNP.
    • Tested different size poly spheres all at the location I proposed to OSURR.

• Continued to work with vendors on collimators.
  • Have vendor with more reasonable quote. Passed quote to Chuting for procurement.
  • Modified the tungsten material card to be tungsten alloy (97W, 2Ni, 1Fe) expected in experiment.

• Created update slides for collaborator meeting.

• Built off axis geometry for dead layer simulations and corrected a density error in on axis simulations.
  • Began rerunning on-axis simulations with correct density materials.

3/13/23

• Compiled dose tally simulation results and provided to OSURR.

• Met with Paul, Chuting, & OSURR to discuss SOW and schedule beam time.

• Continued work on dissertation.
  • Mostly figure compilation and order according to outline.

• Finished detector lead shielding design after reducing number of lead bricks to buy.

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PAS Experiment