ISIS Benchmark Experiment for Neutron Shielding

SINBAD ABSTRACT NEA-1552/38

ISIS Deep-Penetration of Neutrons through Concrete and Iron Shields

1. Name of Experiment:
------------------
ISIS Benchmark Experiment on Deep-Penetration Neutrons through Concrete and
Iron Shields (1998)

2. Purpose and Phenomena Tested:
----------------------------
The purpose of this experiment was to measure the deep-penetration neutrons
through a thick bulk shield at an intense spallation neutron source facility,
ISIS, of the Rutherford Appleton Laboratory (RAL), United Kingdom [1], [2].

3. Description of the Source and Experimental Configuration:
--------------------------------------------------------
The source is a thick tantalum target (total length of 296.5 mm) impinged
by 800 MeV - 200 �A protons, producing neutrons. This target, placed at the
center of the target station, is shielded with approximately 3-m-thick steel
and 1-m-thick ordinary concrete in the upward direction, through which the
neutrons are transmitted (Fig.1 and Fig.2). On top of the shield of the
target station (Fig.3), the neutron flux attenuations through concrete and
iron shields, which were additionally placed up to 1.2-m and 0.6-m thicknesses
respectively (Fig.4), were measured using activation detectors of graphite,
bismuth, aluminum and a multi-moderator spectrometer using indium-oxide
activation detector. The attenuation lengths for concrete and iron of
high-energy neutrons above 20 MeV at 90 degrees to the proton beam axis were
obtained from the 12C(n, 2n)11C reaction rates. The neutron energy spectra
in the energy range from thermal to 400 MeV behind concrete and iron were also
obtained by an unfolding analysis using the reaction rates of 12C(n, 2n)11C,
27Al(n, a)24Na, 209Bi(n, xn)210-xBi (x=4~10), and 115In(n, g)116mIn.

4. Measurement System and Uncertainties:
------------------------------------
Two types of graphite activation detectors were used: one was a disk type of
8-cm diameter � 3-cm thickness; the other was the Marinelli type (Fig.5),
for measuring the spatial neutron flux distribution on the shield top without
an additional shield and behind additional concrete and iron shields of
various thicknesses. This detector uses the 12C(n, 2n)11C reaction : the half
life of 11C is about 20 min., which makes a good rapidly activated
neutron flux monitor for an energy above 20 MeV.

Bismuth detectors (8-cm diameter � 1.1-cm thickness), were used to obtain the
high-energy neutron spectrum by using 209Bi(n, xn)210-xBi (x=4~12) reactions.
Their threshold energies regularly increase from 22 MeV of 209Bi(n, 4n) to 70
MeV of 209Bi(n, 10n) with an interval of 8 MeV corresponding to the binding
energy per nucleon. The half lives of 200Bi to 206Bi are between 36.4 min. and
15.31 days.

The aluminum detector was of the Marinelli type with the same size as the
graphite detector (see Fig.5). The threshold energy of the 27Al(n,a)24Na
reaction is 3.25 MeV and the half life of 24Na is 15.02 hr. The cross-section
data shown in Fig.6 are from the ENDF/B-VI high-energy library
calculated by Fukahori using the ALICE code [3].

As for the Indium-oxide loaded multi-moderator activation detector, In2O3
powder (2.875 g) was filled in a spherical cavity of 0.735-cm radius in a
cylindrical acryl, and it was placed in a spherical polyethylene moderator
(Bonner sphere) [4]. Five kinds of detectors were used, which used four kinds
of moderators and no moderator(bare). Fig.7 shows a cross-sectional view of
these detectors. Using the reaction rates of the detectors, the neutron energy
spectrum can be available through an unfolding technique.

A neutron dose meter (Rem Ion Monitor, Harwell, U.K.) and a gamma-ray dose
meter (RO2, Eberline, Inc., U.S.A) were used in a current mode for measuring
the neutron and gamma-ray dose-equivalent rates, respectively. This
REM-counter was a conventional BF3 ion-chamber covered with a polyethylene
moderator of cylindrical shape, which had low sensitivity to neutrons of
energies higher than 20 MeV.

The specifications of each detector can be found in the Table 1. The response
functions and cross sections of the activation detectors are tabulated in
Table 2. The initial guess spectra that were used for the unfolding are
tabulated in Table 3.

The errors of the results (reaction rates) of the experiment can be estimated
by the equation :

delta(R) = squareroot(delta(Qh)2 + delta(c)2 + delta(p)2)

- delta(Qh) is the error of the beam current which was estimated to be about 1%,
- delta(c) is the statistical error of the photo peak area
- delta(p) is the error of the peak efficiency of HPGe detector estimated by
the EGS4 Monte Carlo code, which is within a few %.

delta(R) is then dominated by delta(c), which varies from 2 to 50% depending on
the total peak counts

5. Description of Results and Analysis:
-----------------------------------
The neutron energy spectra were obtained on the floor without an additional
shield, behind a 60-cm-thick additional concrete shield and a 30-cm-thick
additional iron shield.

The obtained neutron spectrum on the shield top floor has two components: a
hadron cascade peak of around 100 MeV in the energy range above 10 MeV and
a broad peak including evaporation and slowing down neutrons around 500 keV
below 10 MeV. The neutron spectrum through an additional 60-cm-thick concrete
shield placed on the shield top shows an evaporation peak around 1 MeV and a
rather flattened lethargy spectrum down to thermal energy, especially in the
low-energy component below 100 keV. This reflects the slowing-down effect due
to the elastic collisions of light elements, like hydrogen in the concrete.
This spectrum has a typical 1/E slowing-down spectrum after the concrete.

The neutron spectrum through a 30-cm thick iron shield also has a typical
spectrum after the iron, where high-energy neutron components above a few MeV
are slowed down to less than 1 MeV by inelastic collisions with iron; also, a
broad peak over the region from 10 eV to 500 keV is remarkable due to the low
inelastic cross section of iron in this energy region and the increasing
neutron capture cross section below 10 keV.

The neutron attenuation length for concrete at 90 degrees to the 800-MeV proton
beam axis obtained in this study is compared with other experimental and
calculated results (Fig.8 and Table 4): the present value of 125.4 g/cm2 is
just between the values of 120 g/cm2 for 25-GeV proton by Stevenson et al. [5]
and 143 g/cm2 for 12-GeV proton by Ban et al. [6] For the attenuation length of
iron, the present value of 161.1 g/cm2 is slightly larger than that of 148 g/cm2
obtained by Jeffrey et al.using a 800-MeV proton accelerator at Los Alamos
National Laboratory [7]. Stevenson and Ban have also given values of
147(+/-)10 g/cm2 for 25-GeV protons and 188(+/-)12 g/cm2 for 12-GeV protons,
respectively : the present value is just between them.

The calculations of the benchmark using the MARS Monte Carlo code are described
in [18] and [19].

6. Special Features:
----------------
None

7. Author/Organizer
----------------
Experiment and analysis:
T. Nunomiya, N. Nakao*, P. Wright, T. Nakamura, E. Kim, T. Kurosawa,
S. Taniguchi, M. Sasaki, H. Iwase, T. Shibata, Y. Uwamino, S. Ito,
and David R. Perry
*High Energy Accelerator Research Organization (KEK),
Oho 1-1, Tsukuba, Ibaraki, 305-0801, Japan
Phone: +81-298-79-6004

Compiler of data for Sinbad:
S. Kitsos
OECD/NEA, 12 bd des Iles, 92130 Issy les Moulineaux, France

Reviewer of compiled data:
I. Kodeli
OECD/NEA, 12 bd des Iles, 92130 Issy les Moulineaux, France

8. Availability:
------------
Unrestricted

9. References:
----------
[1] T. Nunomiya, N. Nakao, P. Wright, T. Nakamura, E. Kim, T. Kurosawa,
S. Taniguchi, M. Sasaki, H. Iwase, T. Shibata, Y. Uwamino, S. Ito, and
D. R. Perry, "Experimental Data of Deep-Penetration Neutrons through a
Concrete and Iron Shield at the ISIS Spallation Neutron Source Facility
using an 800-MeV Proton Beam", KEK Report 2001-24 (Feb. 2002).

[2] T. Nunomiya, N. Nakao, P. Wright, T. Nakamura, E. Kim, T. Kurosawa, S.
Taniguchi, M. Sasaki, H. Iwase, Y. Uwamino, T. Shibata, S. Ito and D. R. Perry,
"Measurement of deep penetration of neutrons produced by 800-MeV proton beam
through concrete and iron at ISIS", Nucl. Instr. Meth. B 179 (2001) pp89-102

[3] M. Blann, Code ALICE/89, Private Communication (1989).

[4] Y. Uwamino, T. Nakamura, A. Hara, "Nucl. Instr. Meth." A239 (1985) 299.

[5] G. R. Stevenson, K. L. Liu and R. H. Thomas, "Health Phys." 43 (1982) 13.

[6] S. Ban, H. Hirayama, K. Kondo, S. Miura, K. Hozumi, M. Taino, A. Yamamoto,
H. Hirabayashi and K. Katoh, "Nucl. Instr. Meth." 174 (1980) 271.

[7] J. S. Bull, J. B. Donahue and R. L. Burman, "Proceeding of the fourth workshop
on simulating accelerator radiation environments", Knoxville, Tennessee,
(September 1998) 201.

[8] A. Carne, G. H. Eaton, F. Atchison, T. A. Broome, D. J. Clarke, B. R.
Diplock, B. H. Poulten and K. H. Roberts, "SNS Target Station Safety
Assessment (Support Document to SNS Target Station Hazard Survey
SNS/ENV/N1/83 Rev.1)". SNSPC/P6/82,(1983).

[9] M. Kinno and S. Yokosuka, Fujita, Co., Japan, Private Communication (1999).

[10] E. Kim, T. Nakamura and A. Konno, "Nucl. Sci. Eng." 129 (1998) 209.

[11] Y. Uno, Y. Uwamino, T. S. Soewarsono and T. Nakamura, "Nucl. Sci. Eng."
122 (1996) 247.

[12] "Evaluated Nuclear Data File", ENDF/B-VI, National Neutron Cross Section
Center, Brookhaven National Laboratory (1990).

[13] T. Fukahori, Proceeding of the 1990 Symposium on Nuclear Data, Tokai,
Japan, JAERI-M 91-032 (1991) 106.

[14] H. G. Hughes, et. al., "MCNPX for Neutron-Proton Transport", Proceedings
of the International Conference on Mathematics and Computation, Reactor
Physics & Environmental Analysis in Nuclear Applications, American
Nuclear Society, Madrid Spain, (September 1999).

[15] M. B. Chadwick, L. J. Cox, P. G. Young and A. S. Meigooni, "Nucl. Sci.
Eng." 123 (1996) 17.

[16] International Commission on Radiological Protection, ICRP
Publication 51, (1987).

[17] S. Ban, H. Hirayama and K. Katoh, "Nucl. Instr. Meth." 184 (1981) 409

[18] T. Nunomiya, N. Nakao, H. Iwase and T. Nakamura, "Deep-Penetration
Calculation for the ISIS Target Station Shielding Using the MARS Monte
Carlo Code", KEK Report 2002-12 (Mar. 2003).

[19] N. Nakao, T. Nunomiya, H. Iwase and T. Nakamura, "MARS14 deep-Penetration
calculation for the ISIS Target Station Shielding", Nucl. Instr. and Meth.
A 530 (2004) pp379-390.

10. Data and Format:
---------------

DETAILED FILE DESCRIPTIONS
--------------------------

Filename Size[bytes] Content
--------------- ------------- -----------------
1 isis-abs.htm 23.030 This information file
2 isis-exp.htm 62.993 Description of Experiment
3 isis-fig1.gif 20.352 Fig. 1: Cross-sectional view of the neutron spallation
target station with an 800-MeV proton beam at ISIS. (preview)
4 isis-fig1.tif 36.370 Fig. 1: high quality tif
5 isis-fig2.gif 91.461 Fig. 2: Sketches of tantalum target and target assembly
with reflectors and moderators(preview)
6 isis-fig2.tif 318.710 Fig. 2: high quality tif
7 isis-fig3.gif 39.033 Fig. 3: Cross-sectional view of the shielding plug
above the target vessel.(preview)
8 isis-fig3.tif 72.946 Fig. 3: high quality tif
9 isis-fig4.gif 46.041 Fig. 4: Horizontal and vertical cross-sectional views
of iron igloo and additional shield. The five detector
positions of "center", "up", "down", "left" and "right"
are shown as white circles in the upper figure. (preview)
10 isis-fig4.tif 59.842 Fig. 4: high quality tif
11 isis-fig5.gif 14.817 Fig. 5: Cross-sectional view of the disk and Marinelli-
type graphite activation detectors.(preview)
12 isis-fig5.tif 18.844 Fig. 5: high quality tif
13 isis-fig6.gif 4.118 Fig. 6: Cross section data of the 27Al(n,a)24Na
reaction from ENDF/B-VI calculated by Fukahori using the ALICE code. (preview)
14 isis-fig6.tif 28.756 Fig. 6: high quality tif
15 isis-fig7.gif 43.845 Fig. 7: Cross-sectional view of indium-oxide
multimoderator activation detectors.(preview)
16 isis-fig7.tif 18.178 Fig. 7: high quality tif
17 isis-fig8.gif 6.504 Fig. 8: Comparison of various data on the neutron
attenuation length for concrete as a function of
the incident proton energy.(preview)
18 isis-fig8.tif 17.210 Fig. 8: high quality tif
19 isis-fig9.gif 176.698 Fig. 9: Experimental setup with a 120-cm-thick
additional concrete shield and surrounding iron igloo
at the top center of the target station.(preview)
20 isis-fig9.tif 1.063.832 Fig. 9: high quality tif
21 isis-fig10.gif 163.214 Fig. 10: Experimental setup with a 60-cm-thick
additional concrete shield using activation detectors
and a Bonner sphere.(preview)
22 isis-fig10.tif 1.063.832 Fig. 10: high quality tif
23 isis-fig11.gif 168.146 Fig. 11: Experimental setup with a 10-cm-thick
additional concrete shield using activation detectors. (preview)
24 isis-fig11.tif 1.063.832 Fig. 11: high quality tif
25 isis-fig12.gif 3.422 Fig. 12: Measured cross section data of the 12C(n, 2n) reaction (preview)
26 isis-fig12.tif 21.582 Fig. 12: high quality tif
27 isis-fig13.gif 8.810 Fig. 13: Measured and calculated cross section data of
the 209Bi(n, xn) (x=4~10) reaction.(preview)
28 isis-fig13.tif 67.454 Fig. 13: high quality tif
29 isis-fig14.gif 9.142 Fig. 14: Response functions of indium-loaded multi-
moderator detectors and a comparison with the measured data.(preview)
30 isis-fig14.tif 61.312 Fig. 14: high quality tif
31 isis-fig15.gif 53.639 Fig. 15: Proton beam-current history measured at the
RIKEN and graph plotted at the accelerator control room (preview)
32 isis-fig15.tif 173.302 Fig. 15: high quality tif
33 isis-fig16.gif 59.941 Fig. 16: Spatial distribution of the 12C(n, 2n)11C
reaction rate with the thickness of an additional
concrete shield.(preview)
34 isis-fig16.tif 44.110 Fig. 16: high quality tif
35 isis-fig17.gif 52.220 Fig. 17: Spatial distribution of the 12C(n, 2n)11C
reaction rate with the thickness of an additional iron shield.(preview)
36 isis-fig17.tif 46.010 Fig. 17: high quality tif
37 isis-fig18.gif 49.968 Fig. 18: Attenuation profiles of the 12C(n, 2n)11C
reaction rates as a function of the distance from
the shield top at the "center", "up", "down", "left"
and "right" positions.(preview)
38 isis-fig18.tif 102.708 Fig. 18: high quality tif
39 isis-fig19.gif 36.252 Fig. 19: Attenuation profiles of the 209Bi(n, xn)210-xBi
(x=4~10) reactions at the "center" position for an
additional concrete shield and iron shield. (preview)
40 isis-fig19.tif 67.408 Fig. 19: high quality tif
41 isis-fig20.gif 29.527 Fig. 20: Attenuation profiles of the neutron and
gamma-ray dose equivalents at the "center" position
compared with the 12C(n, 2n) reaction rate for an
additional concrete shield and iron shield.(preview)
42 isis-fig20.tif 81.682 Fig. 20: high quality tif
43 isis-fig21.gif 16.950 Fig. 21: Neutron energy spectra on the shield top
floor, 60-cm-thick additional concrete shield and
30-cm-thick additional iron shield.(preview)
44 isis-fig21.tif 27.018 Fig. 21: high quality tif
45 isis_nse.pdf 1.949.212 Reference
46 KEKrep2002-12.pdf 1.513.153 Reference

File isis-exp.htm contains the following tables:

Table 1: Physical properties of the activation detectors used in this
experiment
Table 2: Bonner sphere response functions used in the SAND2 unfolding which
were calculated using MCNPX2.1.5 with LA150 library
Table 3: Initial guess spectra used in SAND2 unfolding calculated by Nakao
et al. using the ANISN code
Table 4: Comparison of the experimental attenuation lengths of high-energy
neutrons at 90 degrees to the proton beam axis
Table 5: Atomic compositions and averaged densities of the target system
and the surrounding materials
Table 6: Shielding material information
Table 7: Reaction rate of graphite activation detector - Reaction rate as a
function of the detector position
Table 8: Reaction rate of graphite activation detector - Reaction rate as a
function of the additionnal shield thickness
Table 9: Attenuation lengths of high-energy neutrons for concrete and iron at
five positions on the additional shield in g/cm2
Table 10: Reaction rate of Bi activation detector
Table 11: Reaction rate of Al activation detector
Table 12: Reaction rate of Indium-loaded multi-moderator detectors (Bonner sphere)
Table 13: Dose equivalent rate measured by using rem counter
Table 14: Neutron energy spectra on the shield top floor, on the 60-cm-thick
additional concrete and on the 30-cm-thick additional iron shield
Table 15: Physical quantities to be calculated
Table 16: ICRP Publ. 51 [16] neutron to dose conversion factor

Figures are included in GIF and TIF formats.

SINBAD Benchmark Generation Date: 6/2005
SINBAD Benchmark Last Update: 3/2006