L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

Fission cross section measurements with a coincidence method

235235

U

NpUNp N

N

• Measured isotopes : 233U, 234U, 232Th, 237Np, and 209Bi, natPb

• References : 235U and 238U

• Focus on isotopes with several targets :

234U (2 targets), 232Th (5 targets), 237Np (4 targets)

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

Detection layout

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

Solid angle acceptance

237Np : 10 MeV < En < 15 MeV (2 targets)

Target 1

Target 2

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

f for 234U

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

238U/235U ratio

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

f for 237Np

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

Corrected counting rate of 237Np targets

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

Raw counting rate of 237Np targets

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

Raw counting rate of 232Th targets

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

f for 237Np (raw)

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

f for 232Th (raw)

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

238U/235U ratio (raw)

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

Conclusion

• The efficiency at 0° is lower than 1 when all localisation signals are requested (unexpected)

• The cross section based on anode signals is more reliable, and a good reproducibility is obtained for different targets

• Not protected against variations of angular distribution (between 0.5 MeV and 50 MeV), and need of a normalisation factor.

• A cross section accuracy better than 10% can probably be achieved

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

Selection of fission

Singles

Coincidence

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

Use of FADCs : pile up resolution

Original signals - anode (black) - cathode right (red) - cathode left (green)

Signals after filtered derivative(convolution)

50 channels 500Ms/s

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

Use of FADCs : noise reduction

Original signals

Signals after filtered derivative(convolution)

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

Energy resolution

235U around 10eV( scaled and compared to ENDF)

234U around 570eV

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

Targets

237Np, 233U, 234U, 232Th,

209Bi, natPb

• Thin layer (0.3mg/cm2) of 8cm in diameter

• Electrodeposition on Al backing (2m thick)

234UMeasured isotopes

Reference isotopes : 235U, 238U

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

fission

α activity

234U

209Bi natPb

Targets with Ø=8cm

Extended targets

Emitting point distribution on the target

L. Tassan-Got

Fission cross section measurements with coincidences

CB n-TOF 5/12/2006

Flux from 235U and 238U (JENDL above 20 MeV)