New Measurements Of Independent Fission Fragment Yields And Energies, And Prompt And Delayed Gammas For

Stockpile Stewardship Data Needs

Adam HechtUniversity of New Mexico

2020 Stewardship Science Academic Programs SymposiumFebruary 26, 4:10 pm

Project Goals

• Leverage our fission spectrometer UNM-SPIDER to measure yields and energies for 235U and 239Pu

• Add gamma detectors for fission product correlated prompt and delayed gammas

• Develop stand alone parallel plate ionization chamber (PPIC) for higher energy neutrons beams, measure fission tagged prompt and delayed gammas

Project RoadmapNNSA grant DE-NA0003901Funding began July 2019. 7 month status.

Milestones and Deliverables:Year 1:• Improvement and testing of existing fission fragment spectrometer.

This will include improved mass resolution. • Development of PPIC for high efficiency fission tagging.• For both instruments:

- coupling to gamma ray detectors for fission tagged prompt and quasi-prompt gammas.• This includes tests with 252Cf.

Year 2:• Fielding of both detectors on the neutron beamline at the LANSCE.• Collection of preliminary improved fragment yield data on 235U or 239Pu, coupled with gamma data.• Collection of preliminary PPIC data on 235U or 239Pu, coupled with gamma ray data.• Preliminary data analysis of correlated data for distribution.Year 3:• Continued data collection on 235U and 239Pu, focus on the one not examined in Year 2, also coupled with gamma ray data.• Continued data analysis of correlated data for distribution.• Submit high resolution 235U(n,f) and 239Pu(n,f) data set with correlated E, v, A, Z, and gammas to data evaluators.• Submit prompt and quasi-prompt fission gammas for 235U(n,f) and 239Pu(n,f) over a range of neutron energies to data evaluators.Beyond Year 3:• Continued fission fragment spectrometer correlated measurements of other fission targets.• Data collection on fission tagged gammas (and cross sections) for other actinides using PPIC.

From July 2019:

Supporting• PhD student Phoenix Baldez• PhD student Mark Wetzel• Undergraduate Lauren Crabtree

Publications• Measurements of 252Cf fission product energy loss through thin silicon nitride and carbon foils, and

comparison with SRIM-2013 and MCNP6.2 simulations, P. Baldez, S. Fellows, R.E. Blakeley, M. Tanguay, M.L. Wetzel, A.A. Hecht, D. Mayorov, F. Tovesson, J. Winkelbauer, Nuclear Instruments and Methods B 456, 142-147 (2019); https://doi.org/10.1016/j.nimb.2019.06.027

Talks/Conference Proceedings• Developments in New Measurements of Fission Cross-Sections, Fragment Yields, and Prompt and

Quasi-Prompt Gammas for Nuclear Data Needs, Adam Hecht, Phoenix Baldez, Mark Wetzel, International Workshop on Fission Product Yields 2019, Santa Fe, NM, Sept. 30-Oct. 4, 2019.

• The UNM Fission Spectrometer for individual fission fragment identification from 239Pu and 235U with correlated A, Z, E, and fission tagged gamma-ray data, Phoenix Baldez, Mark Wetzel, Adam Hecht. ANS Winter Meeting, Washington DC, 2019.

Phoenix Baldez

MarkWetzel

linear scale235U + thermal n

log scale235U + thermal n

Find A, Z, gammas

UNM E-V fission spectrometer

Extract A:

Correlated E,A,Z,NMeasure TOF – TOF detection region v = L/TOFMeasure E directly – ionization chamber

Extract Z: Ionization chamber as TPC, active cathode and anode

Extract N: A and Z N

UNM E-V fission spectrometer

Extract A:

Correlated E,A,Z,NMeasure TOF – TOF detection region v = L/TOFMeasure E directly – ionization chamber

SPIDER Collaboration

• SPectrometer for Ion DEtermination in fission Research (SPIDER)

• LANL led collaboration

• LANL SPIDER Spectrometer – Paired arms: 2v – 2E measurement to

correlate both fragments– many arm pairs systems to increase

efficiency– Not currently equipped to measure Z

• In this presentation: Experiments performed on UNM spectrometer– 235U with LANSCE FP12 “cold” n beam– 252Cf at UNM

Transmission TOF Components

Microchannel plateDetector (MCP)

40 ug/cm2 C

Ionization Chamber

Fission Product

cathode

Frisch gridanode

200 nm SiN windows

4000 6000 8000 10000 12000 14000 16000

IC Channel

4000

6000

8000

10000

12000

14000

16000

ToF

Chan

nel

IC (ch) vs. ToF (ch)

Raw Data: 235U

4000 6000 8000 10000 12000 14000 16000

IC Channel

4000

6000

8000

10000

12000

14000

16000

ToF

Chan

nel

IC (ch) vs. ToF (ch)

Raw Data with cuts on scatter: 235U

Now find mass byM = 2E/v2

… with corrections

Light fragments

Heavyfragments

Energy loss corrections

200 nm (58 ug) SiN window to IC180 nm (40 ug) electron conversion carbon foil

(thin foils very hard to handle)

Thin windows/foilsreduce

E loss correction(and broadening)

ELSource

ELCover ELFoil #1 ELFoil #2 ELSiN

TOF region

Combine v in TOF and E in IC to find A, but E different in TOF and ICAddback fits also deal with pulse height defects

What are the energy loss corrections?

How to calculate energy loss corrections for fission products?

P. Baldez, S. Fellows, R.E. Blakeley, M. Tanguay, M.L. Wetzel, A.A. Hecht, D. Mayorov, F. Tovesson, J. Winkelbauer, Measurements of 252Cf fission product energy loss through thin silicon nitride and carbon foils, and comparison with SRIM-2013 and MCNP6.2 simulations, NIM B 456, 2019.

ELSource

ELCover ELFoil #1 ELFoil #2 ELSiN

TOF region

0

1

2

3

4

5

6

7

8

9

60 80 100 120 140 160 180

Yield (%)

Mass Number (A)

U-235 + nth Fission Product Yield (%)(3 Runs, 50K Counts)

England & Rider University Spectrometer Results

Plus: Highly correlated particle-by-particle for E, v, A, Z, N, gammas soon

Mass resolution?

• fwhm/M• Need to calibrate with ion beam

since 252Cf (etc) has broad mass distribution

• Simulations…

Eic vs ETOF

TOFEic

Eic vs TOF

TOF

96

95

94

Eic vs TOF

TOF

96

95

94

4000 6000 8000 10000 12000 14000 16000

IC Channel

4000

6000

8000

10000

12000

14000

16000

ToF

Chan

nel

IC (ch) vs. ToF (ch)

But don’t see single mass stripes yet…

Light fragments

Heavyfragments

Mass resolution?

• TOF 63.9 ns, fwhm 0.372 ns, 2δt/t = 0.0058 = 1.16%– This plot is distribution of times for many particles, not precision for single particle

• Better MCPs, CFD, TDC? CAEN VME

psps

1m TOF measurementα from 239Pu

= 1.1% for 1 amu light A

distribution of times for many particles

Mass resolution?

• Foil thickness vs. TOF distribution fwhm

Alpha TOF

Mass resolution?

• IC Trinuc alpha measurement• 1.18% fwhm/E• 0.26 - 0.31% light - heavy fragments ?

Ionization Chamber and Z determination- axial time projection chamber

4

Fission Product

Cathode not grounded

electron drift

Frisch Grid

Anode

“active cathode” isolated by Teflon standoffTiming from cathode, anodeExamine electrons’ drift time to FG to extract range

cathode

Stopping is charge dependent

Range & Z- Active cathode design enables timing measurements- Determination of penetration depth/range

80 90 100 110 120 130 140 150 160

Mass (amu)

7

7.2

7.4

7.6

7.8

8

8.2

8.4

8.6

8.8

9

Mea

n R(

A) (c

m)

Mean R(A)

Measured Range

TRIM Light

TRIM Heavy

235U

Dealing with charge state distributions,Q, of Fission Fragments, not directly with Z

Example variations through foil of just a single atom species

Fig: N.K. Skobelev, Instruments and Experimental Techniques, 51, pp 351-357, 2008.Qav: R.D. Evans, The Atomic Nucleus, 1955.

y = 0.0267x - 0.0057

-0.2

-0.1

0

0.1

0.2

-10 -5 0 5 10

dA Heavy

y = -0.142x + 0.3064

-0.6-0.4-0.2

00.20.40.60.8

11.2

-4 -2 0 2 4 6

dZ light

y = -0.0438x - 0.0072

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

-6 -4 -2 0 2 4 6

dZ heavy

y = 0.0591x - 0.0029

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

-10 -5 0 5 10

dE Light

y = 0.058x - 0.0043

-0.4

-0.2

0

0.2

0.4

-10 -5 0 5 10

dE heavy

y = 0.0335x - 0.0043

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

-10 -5 0 5 10

dA Light

Zi(R,A,E)Light = -7.04225*(Ri-8.52)+0.23592*(Ai-96)+0.416197*(Ei-90.563)+0.16507

Zi(R,A,E)Heavy = -22.8311*(Ri-7.41)+.609589*(Ai-139)+ 1.324201*(Ei-57.036)-.39269

dR

dA

dR dR dR

dR

dZ

dA dZ

dR

dE

dE

SRIM SIMULATIONS

Functional dependence of R(Z,A,E) to get Z(R,A,E)

Zi(R,A,E)Light = -7.04225*(Ri-8.52)+0.23592*(Ai-96)+0.416197*(Ei-90.563)+0.16507

Zi(R,A,E)Heavy = -22.8311*(Ri-7.41)+.609589*(Ai-139)+ 1.324201*(Ei-57.036)-.39269

For Light:

For Heavy:

Not bad

Needs better simulation/calibration

Gammas in coincidence with well characterized individual particles

quasi-prompt to delayed gamma detectionFF arrive ~ 50 ns post fissionPrompt gamma detection

Already have 3 Ortec GMX 25% HPGe (good around neutrons) and other gamma detectors

Detectors look good

Already have 3 Ortec GMX 25% HPGe (good around neutrons) and other gamma detectors

Parallel Plate Ionization Chamber (PPIC) for fission tagged gamma rays

Build IC based on Parallel Plate Ionization Chamber (PPIC) for fission tagging, good FF/α discrimination

F. Tovesson, T. S. Hill, Phys. Rev. C 75, 034610 (2007).

Fission spectrometer efficiency currently ~10 -4PPIC ~ 1

• Fission tagged gammas, but not v,Z,N coincidence• Discriminate alpha vs FF

• Mockup at UNM• The LANL PPIC may be available

Current Workmeasurements

• Testing IC at UNM with 252Cf• Examining 100 nm (replace 200 nm) windows

for improved resolution• Wrote beamtime proposal for 239Pu data at

LANSCE• Will calibrate FFS IC at LBL 88” cyclotron

– Test full FF Spectrometer?

Current Workequipment

• Ordered new MCPs for TOF• Acquired new SiN windows for IC

– designing new window layout with Norcada• Creating gas interlock – to run with thinner windows

– Ordered pressure gauge reader with logic output• Ordering CAEN power supply with

– overcurrent shutoff– logic input for shutoff– latch off at shutoff

• Will look at getting LANL PPIC running vs. building a new device

Plans• Improve mass resolution of full spectrometer• Get PPIC up and running• Test both with 252Cf and Ge detectors• Run 239Pu, 235U with fission tagging in PPIC and

with correlated data in full spectrometer• Look at target availability and measure others

Thank You!

Phoenix Baldez

Adam Hecht

MarkWetzel

Schmitt data from: H.W. Schmitt, J.H. Neiler, F.J. Walter, Phys. Rev. 141, 1966

Heavy fragment Z reconstruction too sensitive to small changes in E?

Zi(R,A,E)Light = -7.04225*(Ri-8.52)+0.23592*(Ai-96)+ 0.416197*(Ei-90.563)+0.16507

Zi(R,A,E)Heavy = -22.8311*(Ri-7.41)+.609589*(Ai-139)+ 1.324201*(Ei-57.036)-.39269

For Light:

For Heavy:

Not much Bragg peak for fission products

Do see range difference

140Xe, 70 MeV

90Sr, 115 MeV

80Ge, 121 MeV

Cathode not grounded

electron drift

FG Anode

Z determination - Active Cathode (> 0.5 MeV/amu)

Cathode not grounded

electron drift

Range Z dependent

Measure range from Cathode vs. anode time= IC ∆t

using e drift velocity

FG Anode

T. Sanami, M. Hagiwara, T. Oishi, M. Baba, M. Takada, NIM A 589, 2008.