Target structure permits all deuterons, except the one-in-a-million that interacts with tritium atom to produce a neutron, to pass completely through target structure and be returned to vacuum system. Since tritium atoms are not displaced as in conventional targets, tritium population will remain unchanged while under deuteron bombardment

Alger, D. L.

English

NASA Technical Reports Server

July 1974	 B74-10063 
NASA TECH BRIEF 
Lewis Research Center	 G 
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 
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be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Long Life Neutron Generator Target

Using Deuterium Pass-Through Structure 
.
The Problem: 
To develop a titanium tritide neutron generator target 
with a long useful life by near total conservation of the 
tritium. In conventional neutron generator targets, a thin 
film of titanium tritide on a water cooled copper substrate 
is generally used for production of 14 MeV neutrons by 
the T (d,n) reaction. An accelerated beam of deuterons, 
having energies from 100 to 500 KeV or higher, impinge 
on the target to produce neutrons. The deuterons do not 
pass through the target; they are implanted in the 
titanium and remain there. Since both tritium and 
deuterium are hydrogen isotopes and therefore chemically 
identical, the deuterons impinging into the tritide target 
continuously displace tritium atoms of the tritide. These 
tritium atoms diffuse to the surface and are lost to the 
vacuum system. The result is an expensive target with a 
useful life of only a few hours. 
The Solution: 
A target structure which permits all deuterons, except 
the one-in-a-million that interacts with a tritium atom to 
produce a neutron, to pass completely through the target 
structure and be returned to the vacuum system. Since the 
tritium atoms are not displaced as in conventional targets, 
the tritium population will remain unchanged while under 
deuteron bombardment. In this way, a long target life 
with constant neutron output is possible. 
How It's Done: 
The target structure consists of six layers of material as 
shown in the figure. 
The first layer is a base copper substrate disc 0.203 cm 
(0.08 in) thick with parallel grooves. 
The second layer is palladium deposited on the copper 
substrate by RF sputtering. The sputtering is done in such 
a way that the palladium coats the walls of the grooves 
and sufficient additional palladium is deposited to bridge 
the grooves. 
The third layer is a film of titanium, vacuum deposited 
on the palladium. The thickness of this layer depends on 
the range of the deuterons of the accelerator beam for 
which the target is designed.
6th layer
(TIN or Ti02( 
5th layer
(Titanium tritide) 
4th layer
(TIN or TIO2) 
3rd layer 
(Titanium) 
2nd layer - 
(Palladium) 
1st layer 
Copper
Void 
The fourth layer of titanium nitride or titanium oxide 
is a barrier layer against deuteron diffusion. It is applied 
by RF sputtering to a thickness of about 1000 angstroms. 
The fifth layer is the titanium tritide target. The 
thickness of this layer is less than the deuteron range and 
depends on the energy of the deuterons of the accelerator 
beam; i.e., for a 300 KeV beam, the titanium tritide target 
thickness was about 2.5 p meters. 
The sixth layer of titanium nitride or titanium oxide is 
another barrier layer. It is deposited by sputtering to a 
thickness of approximately 500 angstroms. 
(continued overleaf) 
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The target works in the following way. Beam deuterons 
pass through the sixth, fifth, and fourth layers and come 
to rest in the titanium third layer. The cross section for 
the T (d,n) reaction is such that only one deuteron out of 
a million interacts with a tritium atom in the fifth layer to 
produce a neutron. As the concentration of deuterons in 
the titanium layer increases, the activation energy in-
creases. The fourth layer acts as a barrier to deuteron 
diffusion in that direction but deuterons will readily pass 
through the titanium-palladium interface since the activa-
tion energy for diffusion for the two materials is 
approximately the same. Deuterons can readily leave the 
palladium surface and return to the vacuum system 
through the grooves, thus passing completely through the 
target. (If a titanium-vacuum interface were used instead 
of palladium-vacuum, the deuteron could not leave the 
surface without the addition of energy.) The sixth layer is 
a barrier layer which reduces the probability of tritium 
escaping to the vacuum and reduces loss of tritium by 
sputtering of the surface by the incident beam. 
The various layers for the target structure have been 
formed and their functions successfully tested. A com-
plete integral test of the target has not, however, been 
made as of the date of this Tech Brief. 
Note: 
No additional documentation is available. Specific 
technical questions, however, may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B74-10063 
Patent Status: 
Inquiries concerning rights for the commercial use of 
this invention should be directed to: 
NASA Patent Counsel 
Mail Stop 500-113 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135
Source: Donald L. Alger
Lewis Research Center
(LEW-1 1866)
S 
B74-10063	 Category 03


Long life neutron generator target using deuterium pass-through structure

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