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SBE 1.016

SB2 CSEWG Benchmark

1. Name of Experiment:

SB2 Experiment on Secondary Gamma-Ray Production Cross Sections Arising from Thermal-
Neutron Capture in Each of 14 Different Elements Plus Stainless Steel (1969)

2. Purpose and Phenomena Tested:

To improve existing knowledge of gamma-ray spectra arising from thermal-neutron 
capture in materials important to reactor shielding, especially above 7 MeV.

3. Description of the Source and Experimental Configuration:

The Tower Shielding Reactor at ORNL was used as the primary source of neutrons.  A 
spherical lead-water beam shield surrounded the reactor to collimate the neutrons and
to reduce background neutrons.  Cadmium lined the face of the reactor shield and the 
collimator to eliminate thermal neutrons.  A 2-in.-thick lead disk was inserted in 
the collimator adjacent to the reactor vessel to reduce the gamma-ray intensity 
produced by the reactor.  A lead collar, 8-in. thick surrounded the collimator exit
to reduce capture gamma rays in the cadmium.

The profile of the source of thermal neutrons was determined by subtracting a
cadmium-covered BF3 detector results from the bare results.  The detector
was traversed across the vertical and horizontal midplane of the beam at 6 ft from 
the collimator (without a sample present).  Another horizontal traverse across the 
midplane of the sample space was performed to more accurately map the thermal 
neutron flux incident on the face of the sample materials.

The samples of materials were made of slabs of 4-5 ft square placed into the beam 
centerline at 45 degrees and 6 ft from the edge of the collimator.  The detector 
was placed at 90 degrees to the reactor beam centerline, 45 degrees with respect
to the slab sample normal to reduce to 0.51 MeV or less the reactor-born gamma-rays
scattered from the sample.

4. Measurement System and Uncertainties:

The 5-inch-diameter x 5-inch long NaI (Tl) crystal was located inside a spherical
lead-water shield with 4 lead irises to collimate the gamma-rays.  This reduced the
background of the gamma rays not born in the sample.  A 2-inch.thick borated 
polyethylene slab covered the outermost iris to reduce thermal-neutron effects in 
the crystal detector.  The detector is placed at 20 ft from and at the midpoint of 
the sample.  The detector viewed the entire slab face and was limited by the 
addition of two aluminum-walled tanks filled with borated water, lined with borated 
polyethylene, placed midway between the detector and the sample.

5. Description of Results and Analysis:

The experimental results for all 14 elements plus the stainless steel are presented
as cross sections versus energy.  The minimum energy is 1 MeV to approximately 10 
MeV.  The standard deviation is +/- 15% and contributions from discrete and cont-
inuum gamma rays are included in the results.  No transport calculations are 
necessary for this benchmark, hence no model description, atom densities, etc. are
needed.  Calculations could simply consist of summing the thermal-neutron absolute
capture spectra over appropriate energy intervals, however, it is recommended that
a 'standard' ENDF/B photon production group averaging code be used to accomplish 
this task.

The resulting reduced spectral intensities in photons per 100 captures were summed
over 0.5-MeV intervals and converted to units of millibarns per capture by using 
handbook values of the radiative-capture cross section at 0.0253 eV.

6. Special Features:


7. Author/Organizer:

    Experiment and analysis:
     R. E. Maerker and F. J. Muckenthaler, ORNL  

    Compiler of data for SINBAD:
     H. T. Hunter, ORNL, P.O. Box 2008, Oak Ridge, TN 37831-6362, USA

    Reviewer of compiled data:
     J. L. Parsons, ORNL, P.O. Box 2008, Oak Ridge, TN 37831-6362, USA

8. Availability:


9. References:

[1]  R. E. Maerker and F. J. Muckenthaler "Gamma-Ray Spectra Arising from Thermal
     Neutron Capture in Elements Found in Soils, Concretes, and Structural 
     Materials," ORNL-4382, UC-34-Physics, August 1969.

[2]  R. E. Maerker "SB2. Experiment on Secondary Gamma-ray Production Cross Sections
     Arising from Thermal-Neutron Capture in Each of 14 Different Elements Plus a
     Stainless Steel," ORNL-TM-5203 ENDF-227 January, 1976.
[3]  [3]  J. D. Court and J. S. Hendricks "Benchmark Analysis of MCNP ENDF/B-VI Iron,"
     LA-12884, UC-700, Dec. 1994

10. Data and Format:

           - TSR-II, Sample, Collimator, and Detector Geometry

           - 1  Percentage of Beam Intercept
           2 - 15 Measured cross section results for materials Fe, SS, N, Na, Al, 
           Cu, Ti, Ca, K, Cl,Si, Ni, Zn, Ba, and S 

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SINBAD Abstract Generation Date: 07/98

SINBAD Abstract Last Update: 07/98