Shielding material containing Boron 10 and gadoliunium for neutron absorption has been developed to reduce interference from low energy neutrons in measurement of fission neutron spectrum using Li-6 fast neutron spectrometer

Baker, S. I.

Ryskiewicz, R. S.

English

NASA Technical Reports Server

December 1972	 B72-10740 
• 
NASA TECH BRIEF 
Marshall Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Boron- 10 Loaded Inorganic Shielding Material 
10
A new shielding material containing boron-10 and 
gadolinium for neutron absorption has been developed 
to reduce the interference from low energy neutrons in 
the measurement of a fission neutron spectrum using 
a Li 6 fast neutron spectrometer. The material is inorganic 
which reduces the distortion of the fast neutron spectrum 
caused by interactions with hydrogen in the boron-
loaded epoxies and other organic materials commercially 
available. The material contains high concentrations of 
good neutron absorbers, approximately 80% boron-10 
and 8% gadolinium oxide by weight. Epithermal as well 
as thermal neutrons are absorbed. The highest con-
centration of boron commercially available is 45%. The 
material also has good structural integrity and does not 
sublime in a vacuum as does cadmium, another good 
thermal neutron absorber. It also has a high melting 
point. 
A 130 gram quantity of boron enriched to 92% in 
the isotope B'° was used along with 13 grams of 
Gd 2 03 to shield a spectrometer head with less than a 
1 cm thickness of shielding material surrounding it. 
A bare gold foil and a cadmium-covered gold foil were 
placed inside the shield to determine its effectiveness. 
Then the shield was placed in a high flux inside the 
empty beam port of an advanced TRIGA reactor at a 
distance of approximately 2 feet (0.6 meter) from the 
core. The neutron activation of the bare gold foil was 
reduced 6000 times and that of the cadmium covered 
foil reduced 50 times compared to the activation with-
out the shield. Thus, the shield was highly effective 
against both thermal and epithermal neutrons. Amor-
phous natural boron powder actually produced a struc-
turally stronger end product than the crystalline B'°. 
However, it is probable that the same result could have 
been obtained using a finer mesh B'° sample.
Monoaluminum phosphate, (Al(H 2 PO 4 ) 3 , a 50% 
solution in water) is used as the inorganic binder, and 
the procedure for manufacturing the shield is as follows. 
The boron, gadolinium oxide, monoalurninum phos-
phate, and water are mixed in the ratio 5:0.5:3:2 
by weight, respectively, placed in the desired container, 
and heated to 930 C until two-thirds of the volume of a 
monitor solution containing only monoaluminum phos-
phate and water has evaporated. Then a plunger is used 
to force out the excess liquid by pressing the sample at 
55 x 106
 N/rn 2 (8000 lbs/in 2 ). During the pressing, a 
quantity of monoaluminurn phosphate sufficient to 
raise the boron concentration to between 75 and 80% is 
extracted. Depending on the application, the sample is 
either left in the container or extruded. In either case, 
a clamp is applied to prevent distortion upon heating. 
In order to activate the binder, the sample is placed in 
a 215° Coven for one hour, the temperature is raised 
to 260 C for 1/2 hr, and then the oven is turned off. 
The clamp is removed after the sample has cooled to 
room temperature. 
Although the preparation of containers and plungers 
for pressing is inconvenient and expensive, the density 
of the finished product is increased. Typically, densities 
greater than 60% of the theoretical density are obtained 
using 55 x 106 N/rn 2 , and even greater densities should 
result from pressing at higher temperature and pressure. 
Note: 
No further information is available. Specific questions, 
however, may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Code A&PS-TU 
Marshall Space Flight Center, Alabama 35812 
Reference: B72-10740 
.
(continued overleaf) 
Thisdocumentwas prepared underthe sponsorship of the National	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
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https://ntrs.nasa.gov/search.jsp?R=19720000739 2020-03-17T03:44:05+00:00Z
Patent status: 
NASA has decided not to apply for a patent. 
Source: S. I. Baker, R. S. Ryskiewicz of

lIT Research Institute

under contract to

Marshall Space Flight Center

(MFS-22280)
0 
0 
B72-10740	 Category 03, 04
	
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Boron-10 loaded inorganic shielding material

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