the n_tof-ph2 neutron fluence from the ptb fission chamber c. guerrero (cern)
DESCRIPTION
The n_TOF-Ph2 neutron fluence from the PTB fission chamber C. Guerrero (CERN). The neutron fluence from the PTB fission chamber. A total of 201.4(5) mg 235 U divided in 5 deposits on Platinum backings. - PowerPoint PPT PresentationTRANSCRIPT
C. Guerrero “The n_TOF-Ph2 neutron fluence from PTB”
n_TOF Analysis Meeting , CERN 23-24 November 2010
The n_TOF-Ph2 neutron fluence from the PTB fission chamber
C. Guerrero (CERN)
C. Guerrero “The n_TOF-Ph2 neutron fluence from PTB”
n_TOF Analysis Meeting , CERN 23-24 November 2010
Tantalum electrodes(0.125 mm, Ø 86 mm)
Platinum backings (0.125 mm, Ø 86 mm)
235U deposits (1.138e-5 at/b, Ø 76 mm)
Stainless steal (0.55 mm)
Tant
alum
win
dow
(0
.15
mm
)
Aluminum chamber (ONLY IN 2009)
Alum
inum
win
dow
(1 m
m)
The neutron fluence from the PTB fission chamberA total of 201.4(5) mg 235U divided in 5 deposits on Platinum backings.
The PTB chamber is calibrated, meaning that the mass of 235U and the detection efficiency are well known from previous “international intercomparisons”.
SiMon MGAS (ONLY IN 2009)
PTB
47 cm of air
DAQ: 2 flash-ADC channels (signal with 90 ns rise-time)
1) Small dynamic range for good a/FF separation
2) Large dynamic range to minimize saturation of signals from Fission Fragments.
The results from both channels are in perfect agreement.
C. Guerrero “The n_TOF-Ph2 neutron fluence from PTB”
n_TOF Analysis Meeting , CERN 23-24 November 2010
The neutron fluence from the PTB fission chamber
Set-Up 2009 (water as moderator) Set-Up 2010 (10B-water as moderator)
Experimental check of the alignment Electrical isolation from the grillage
Aluminum container used when not WSTA
C. Guerrero “The n_TOF-Ph2 neutron fluence from PTB”
n_TOF Analysis Meeting , CERN 23-24 November 2010
Pulse Height distribution of the PTB fission chamber. The red blue lines correspond to the amplitude calculated from the pulse area.
Tantalum resonances
Aluminium dips
7-9% difference at thermal
Comparison of the expected yield calculated from the thin sample approximation and from detailed simulations of the assembly with MCNP (D. Villamarin@CIEMAT)
Calculation of the fluence from the Counting Rate (CR), efficiency (edet)and expected yield (natsn,f).
Determination of the neutron fluence
Bias @ 0.45 of maximum
maximum
2009
C. Guerrero “The n_TOF-Ph2 neutron fluence from PTB”
n_TOF Analysis Meeting , CERN 23-24 November 2010
Figure 3. The n_TOF-Ph2 neutron flux (100 bins/decade) resulting from the analysis of the TB fission chamber.
x18
x13
x1.6 x1.2
The neutron fluence with normal and borated water (100 bpd)
Dstat=1%
Dstat=3%
Artifacts related to the g-flash and the lack of electrical isolation in 2009
C. Guerrero “The n_TOF-Ph2 neutron fluence from PTB”
n_TOF Analysis Meeting , CERN 23-24 November 2010
The neutron fluence: Borated vs. Water moderator
Water10B-water
C. Guerrero “The n_TOF-Ph2 neutron fluence from PTB”
n_TOF Analysis Meeting , CERN 23-24 November 2010
The neutron fluence: Borated vs. Water moderator
AVG RATIOS3-300 keV = 0.99
300-600 keV = 1.01600-1000 keV=1.04
Dstat~3%
? ? ?
Water10B-water
C. Guerrero “The n_TOF-Ph2 neutron fluence from PTB”
n_TOF Analysis Meeting , CERN 23-24 November 2010
PTB vs. Simulations: FULL ENERGY RANGE
C. Guerrero “The n_TOF-Ph2 neutron fluence from PTB”
n_TOF Analysis Meeting , CERN 23-24 November 2010
PTB vs. Simulations: LOW ENERGY RANGE
~18% difference at thermal!
Difference in shape?
C. Guerrero “The n_TOF-Ph2 neutron fluence from PTB”
n_TOF Analysis Meeting , CERN 23-24 November 2010
PTB vs. Simulations: HIGH ENERGY RANGE
C. Guerrero “The n_TOF-Ph2 neutron fluence from PTB”
n_TOF Analysis Meeting , CERN 23-24 November 2010
PTB vs. Simulations: 3 – 100 keV
Normalization point
5% diff. in magnitude
Different depths?
C. Guerrero “The n_TOF-Ph2 neutron fluence from PTB”
n_TOF Analysis Meeting , CERN 23-24 November 2010
PTB vs. Simulations: 100 – 500 keV
C. Guerrero “The n_TOF-Ph2 neutron fluence from PTB”
n_TOF Analysis Meeting , CERN 23-24 November 2010
PTB vs. Simulations: 100 – 500 keV (MCNP scaled up 5%)
C. Guerrero “The n_TOF-Ph2 neutron fluence from PTB”
n_TOF Analysis Meeting , CERN 23-24 November 2010
PTB vs. Simulations: 500 – 1000 keV (MCNP scaled up 5%)
C. Guerrero “The n_TOF-Ph2 neutron fluence from PTB”
n_TOF Analysis Meeting , CERN 23-24 November 2010
ConclusionsThe experimental data from the PTB have been fully analyzed, including all the statistics available.
The reduction in the neutron flux with 10B-water with respect to water is:x18 at thermalx1-1.6 in the eVx1 above a few hundreds eV
The two fluxes agree within 1% in the region between ~3 keV and 600 keVAbove 600 keV, the flux with 10B-water is observed to be 4% smaller than that with water (why?)
Comparison with simulations (normalized to PTB @ 7-10 keV)• Thermal peak: simulation ~20% higher than data• Thermal tail (0.2-0.5 eV): slightly different shape• 3-20 keV: good agreement• 20-1000 keV: good agreement in shape, but simulation ~5% lower than data.• 600-1000 keV: data resolution very limited, but there seems to be some
disagreement (5-12%) between the dips in the experiment and simulations.
Questions (maybe answered from the analysis of MGAS and SiMon)Are the PTB data in the high energy region? How does it compare to MGAS?What could explain large (20%) difference at thermalCould the thickness of Al explain the 5% factor above 20 keV? What about the aperture
angle in MCNP?