LASL INTENSE 14-MeV NEUTRON SOURCE. Page: 5 of 12
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neutrons, hot high pressure hydrogen, fluid mechan-
ics computation, accelerators, tritium, radiochemis-
try, and metallurgy. Finally, it suggests a short
program which would establish the feasibility of the
project, establish a reasonably firm design from
among the possible variations, establish a good cost
estimate including the location of suitable equip-
meit available as government surplus, and work out
a subsequent program which could be followed to the
completion of the then proposed facility.
The generation of 14 MeV neutrons from the DT
reactions using a Cockcroft-Walton machine is a
standard technique. In general a beam of deuterons
is stopped in tritium-in-metal target such as devel-
oped at Los Alamos.' The specific yield from such
targets is about 3 x 108 neutrons/joule and their
intensity is limited by target heating. If one as-
sumes that he might cool the target sufficiently
well to retain the tritium loading at 3 kW/cm2 (1.1
kW/cm2 has been achieved),5 the maximum source in-
tensity is (3 x 108) x (3 x 103) 102 neut/cm2-sec.
The present idea is to use a windowless gas target
in order to gain a factor of 10 in specific yield
(neutrons/joule) and a factor of 100 in allowable
beam power density. This is an old idea, mentioned
as hb;ing been attempted without success in refer-
ence 5. Recently, however, a windowless gas target
has been made to work at Los Alamos,e for a differ-
When a current iB of ions of one of the heavy
hydrogen isotopes traverse gas at density ng of
the other, most are simply slowed down, losing ener-
gy E as dE = -n e(E) dX, where a is the stopping
power of the gas for the ion in units of (say) keV-
barn:. A small fraction will, however, produce neu-
trons N as
dN = IB n o(E) dX
= -1B [(E)/e(E)] dE,
where a is the cross section in barns. Standard
data7" for e and a are displayed for both the D+
beam case: T(d,n)a and the T beam case: D(t,n)z
in Figs. 1 and 2. The differential yield, a/c in
neutrons/joule, displayed in Fig. 3, is integrated
to find the yield
Y = f
- [a(E)/e(E)! dE, neurons
The range or required target thickness is
R = f
- [1/e(E)] dE, atoms
The yield Y and range Ro for the case of a thick
target (Eout = 0) are displayed in Figs. 4 and S.
[Note that we may equate the ion range and the tar-
get thickness or projected range since the differ-
ence is only (me/3.5 mi) = 0.005%.]
As has already been alluded to, the experimen-
tal difficulties are most straw igly dependent upon
the beam and target power. Therefore the specific
yield, Yo/Ein, which is ploted in Fig. 6 is of
special interest. Notice that there is no efficien-
cy advantage to accelerating either species ovtr the
other: a maximum of 3 x 109 neutrons/joule is avail-
able either way. One chooses therefore to accelerate
the tritium in order to minimize the tritium inven-
tory and the associated costs and hazards. One fur-
ther notes that the maximum is very broad; the range
E. = 250 keV to 370 keV has a specific yield within
O 10o 200 300
ION ENERGY. E, keV
Fig. 1. Stopping power for D+ in T2 and for T+
- T' BEAM_
_ 0+ BEAM-
i i i
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Henderson, D.B. LASL INTENSE 14-MeV NEUTRON SOURCE., report, January 1, 1972; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1026021/m1/5/: accessed April 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.