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Status of 54 Fe and 57 Fe(n, g ) analysis Giuseppe Giubrone Instituto de Fisica Corpuscular

Status of 54 Fe and 57 Fe(n, g ) analysis Giuseppe Giubrone Instituto de Fisica Corpuscular Valencia n_ToF meeting, CERN, April 2012. OUTLINE. Overview of the measurements 54 Fe Analysis 54 Fe Capture Kernels 57 Fe Preliminary overview. Experimental Details.

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Status of 54 Fe and 57 Fe(n, g ) analysis Giuseppe Giubrone Instituto de Fisica Corpuscular

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  1. Status of 54Fe and 57Fe(n,g) analysis Giuseppe Giubrone Instituto de Fisica Corpuscular Valencia n_ToF meeting, CERN, April 2012

  2. OUTLINE • Overview of the measurements • 54Fe Analysis • 54Fe Capture Kernels • 57Fe Preliminary overview

  3. Experimental Details Isotopic composition Samples Experimental setup for 54Fe (2010 ) and 57Fe(2011) Borated water moderator

  4. Fe-54 anlysis: Overview ENDF n_TOF • When compared versus ENDF, most of the s-wave and p-wave resonances are clearly visible in the n_TOF data with good statistics up to high neutron energies of about 100 keV. • In the n_TOF data, additional resonances are visible, some are from sample impurities but also new resonances of Fe-54 not evaluated thus far.

  5. Fe-54 analysis n_TOF neutron flux: the main preliminary aspect in the present analysis August 2011 December 2011 Gold Normalization factor = 0.58 Gold Normalization factor = 0.66 • The present anlysis uses the previous flux evaluation from August 2011 Regarding the capture kernels reported here, the new evaluation seems to have an effect of only 1-2% up to En<10keV and of up to 10-20% from 10keV <En<1MeV. This effect will be taken into account afterwards, when the flux evaluation is definitive.

  6. Fe-54 analysis Threshold Correction During a capture measurement, the detectors registers counts only above a certain electronic threshold. Given a threshold corresponding to t channel in the i binned response distribution Ric for N simulated prompt cascade, the weighted count rate is given by: iR While for an ideal zero threshold detection system, this quantity would be higher, iR The deviation beetwen these two values for a 250keV threshold isgiven by: Ft=iR/iR This deviation give s an estimate of how much the calculated experimental yield is affected by the counts lost below this threshold .

  7. Fe-54 analysis As the cross section are measured with respect to a reference sample(Gold in our case), is convenient to simulate a large number of cascade for the 4.9eV resonance for 197Au, and for all spin groups and parity for the 54Fe resonance. Considering a 250keV threshold , the correction to apply at the experimental yield is: Ftot=Ft(54Fe)/Ft(198Au) For both detectors Ftot is 0.94(±0.05%). Therefore , a correction of 6% is applied to the fitted 54Fe Kernels. Next slides show a comparison between the simulated and measured (Bicron) detector response, for the 4.9eV Au resonance and for all the spin-groups in 54Fe.

  8. Fe-54 analysis Comparison between simulated and measured deposited energy 198Au

  9. Fe-54 analysis Simulated response for different spin groups for 54Fe

  10. Fe-54 capture kernels Some examples of R-Matrix analysis with the code Sammy • In general very good statistics at low neutron energies (<100keV), whereas at higher energy the main source of uncertainty are the statistical fluctuations. • The s-wave resonance at 7.7 keV with a Gn/Gg ratio > 500 represents a very good case for studying the possible effect of neutron sensitivity in our data. • R-matrix analysis with SAMMY has been completed. • Capture kernels have been corrected for the aforementioned threshold correction.

  11. Fe-54 capture kernels Fe-54: Summary of Capture Kernels Coomparison n_TOF vs. Corvi et al. vs Allen et al. vs ENDF • Below 100keV the statistical uncertainty remains of the same order as the systematic one (few percent), thus representing the most accurate data-interval of the present measurement. • Above 100keV, larger (statistical) errors arise, but still in many cases comparable to previous available data (Corvi et al, and Allen et al.). • In average, the agreement with previous reported data and with the evaluations is reasonable, although in several cases there are remarkable discrepancies. This is illustrated in more detail in the next slide which shows the ratio of the kernels.

  12. Fe-54 capture kernels Average deviation of capture kernels n_TOF vsCorvi et al.(Geel) • In average, n_TOF kernelsare in reasonable agreement with Corvi’s data measured at Geel. • Below 60keV the average deviation is of 1% • Beyond 60keV the average deviation in of 4% • The latter may be partially ascribed to the neutron flux used in this analysis (Aug. 2011), which above 10keV differs substantially from the latest flux evaluation (Dec. 2011).

  13. Fe-54 capture kernels Average deviation of capture kernels n_TOF vs Allen et al.(ORNL) Comparing n_ToF versus Allen et al. data from ORNL, the deviation is of 7% below 60keV , and of 14% beyond 60keV.

  14. Fe-54 capture kernels Fe-54 analysis: neutron sensitivity • No clear trend is observed in the plot of the kernel versus Gn/Gg, which is typically used to detect possible effects of neutron sensitivity problems in the data.

  15. Summary & Outlook of 54Fe analysis • All resonances observed at n_TOF have been analyzed with SAMMY • Threshold correction has been calculated for the Au-reference sample and for all spin-parity groups of the 54Fe-data • Capture kernels have been corrected for the threshold effect. • Kernels have been compared versus two main evaluations (ENDF and Suchoruchkin) and also versus the two previous measurements at Geel and at ORNL. • Reasonable average agreement has been found with respect to the Geel data. The average deviation is of 1% below 60keV and 4% above 60 keV. • Last step for obtaining final results implies to account for the differences in the n-flux curve, mainly for resonances above 10 keV.

  16. 57 Fe (only a preliminary overview)

  17. Fe-57 analysis Fe-57 anlysis: Overview ENDF N_TOF • It seems that resonaces up to about 200 keV can be analized in 57Fe • 57Fe will be analized following the same approach as 54Fe, once the analysis of 54 Fe • has been finished. • The new evaluated n-flux will be used in this case from the beginning.

  18. Fe-57 analysis Fe-57 anlysis: Overview 1.63keV(57Fe) 358keV(58Fe) 230keV(58Fe) 1.49keV (56Fe) 588keV(Cu63?)

  19. Summary • Weighting function was calculated for both detectors. • Energy calibration completed. • Weighting function uncertainty calculated for Gold samlple. • Weighting function uncertainty for 57Fe is ongoing. • Threshold correction for 57Fe is ongoing. • Final version of the flux it will use for 57Fe analysis.

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