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MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS -1963
917 2 2 1966
(to be submitted to the International Conference on Nuclear Physics,
Gatlinburg, Tennessee, September 12-17, 1966)
ORNL-P-2412
Conf=660906-21
MASTER
A Search for the Trineutron
S. T. Thornton, C. M. Jones, J. K. Bair, and H. B. Willard
Oak Ridge National Laboratory
Oak Ridge, Tennessee
CF'STI PRICES
Hc s/. • °, MN SẼ
ABSTRACT
Experimental and theoretical evidence has recently been proposed
for the existence of the trineutron, a stable particle composed of three
neutrcns bound by 1.0 MeV. A search for the trineutron in the reaction
T(n,p)n with 20.8 MeV neutrons has been made and no evidence for the
existence of the trineutron was found.

LEGAL NOTICE
RELEASED FOR ANNOUNCEMENT
.
IN NUCLEAR SCIENCE ABSTRACTS
This report was prepared as an account of Government sponsored work. Neither the United .
States, nor the Commission, or any person acting on behalf of the Commission:
A. Makes any warranty or representation, expressed or implied, with respect to the accu-
racy, completeness, or usefulness of the information contained in this report, or that the use
of any information, apparatus, method, or process disclosed in this report may not infringe
privately owned rights; or
B. Assumes any liabilities with respect to the use of, or for damages resulung from the
use of any information, apparatur, meubod, or procesu disclosed in this report.
As 18ed in the above, "person acting on beball of the Commission" Includes any em-
ployee or contractor of the Commission, or employee of such contractor, to the extent that
auch employee or contractor of ine Commission, or employee of such contractor prepares,
d18seminates, or provides access to, any irformation pursuant to his employment or contract
with the Commission, or his employment with such contractor.
Research sponsored by the U.S. Atomic Energy Commission under contract
with the Union Carbide Corporation.
TOak Ridge Graduate Fellow from the University of Tennessee under appointment
from the Oak Ridge Associated Universities.
- 2 -
We wish to report an experimental search for the trineutron, nº, a
bound state of three neutrons. Experimental evidence for such a stable
particle has been proposed by Ajdačić' et al.- who detected a peak at 6.4
MeV in the proton spectrum resulting from the bombardment of tritium with
14.4 MeV neutrons. This peak could only be explained by the reaction
T(n,p)n" with a Q value of -7.5 MeV and a corresponding trineutron binding
energy of 1.0 MeV.
Theoretically, it had always been assumed that the trineutron could
not exist. In particular, Zel'dovich' stated that from the pair interaction
of neutrons it is "obvious" that n3 does not exist. Since the work of
Ajdačic' et al.- the question of trineutron stability has been reexamined. :
Baz, Gol'danskii and Zel.'dovich conclude that the existence of the trineutron
is extremely improbable singe an excited state of T = 3/2 would have to
exist for tritium (~ 8.2 MeV) and possibly for Hes (~7.7 MeV). They also ..
point out that the binding energy of the third neutron which is already
negative for He’ decreases systematically for decreasing 2. From the pairing
interaction of neutrons one can conclude+ that if the trineutron exists
then the quadneutron must exist also, Experimental evidence for the dineutron?
and the quadneutronº has not been found. In addition, Tang and Bayman' have
made a variational calculation of the binding energy of nt by considering
two dineutron clusters. They conclude that there cannot be a bound nor a
resonant state of nt. Using the result of Brueckner, Gammel, and Kubiso
and of Levinger and Simmons that the neutron gas is not bound, Tang and
Bayman then make the general conclusion that systems containing only neutrons
- 3 -
Our interest in the trineutron was increased by the recent work of
Mitra and Bhasinº who suggest that the trineutron could possibly exist even
though the dineutron and quadneutron do not. They point out that a moderately
attractive 'p force could bind three neutrons together since the 's
force,
which predominates in the dineutron and quadneutron, is negligible for
the trineutron. Since the existence of the trineutron would be of great
importance in the understanding of the few nucleon problem, we have repeated
the experiment of Ajdačić et al. using neutrons of higher energy.
In our experiment neutrons of 20.8 MeV were produced by the f(a,n)He
reaction utilizing the ORNL 5.5 MV Van de Graaff accelerator and a double-
foil tritium gas cell. The neutrons entered a second tritium gas cell at oº
with respect to the deuteron beam and the charged particle products were
observed, again at Oº, with a AE-E surface barrier detector telescope. With
two parameter analysis of AE versus AE + E we could easily distinguish
protons, deuterons, and tritons with an overall energy resolution of better
than 300 keV. Tritium was replaced by He" in the second gas cell to measure
the background.
The possible charged particle products in the n + T interaction are
n + Inn + T
elastic scattering
- D + 3n Q = -8.49 MeV
+ d + 2n Q = -6.26 MeV
P + n (Q = -7.5 MeV)
The triton elastic scattering cross section was estimated from known
cross sections 1,12 to be about 50 mb/sr at oº, and our measurement of this
cross section was used to normalize the proton and deuteron spectra.
Two peaks in the deuteron spectrum are seen in Fig. 1. The peak
at 13.6 MeV is due to the T(n,a)2n reaction and indicates strong final
state interactions between the two neutrons. The 16.3 MeV peak can be
attributed to a Hey impurity resulting in the He(n,a)d reaction.
The proton spectrum is shown in Fig. 2. The maximum possible proton
energy from the T(n,p)3n reaction is 12.2 MeV, whereas the proton peak from
the trineutron reaction should appear at about 13 MeV. No net counts are
observed above 12.2 MeV. The integrated number of counts between 6.5 and
14.4 MeV is 163 +94 which corresponds to a cross section of 3.5 2.0
If the trineutron reaction cross section at 20.8 MeV neutron energy
· were equal to the 3.8 mb/sr value that Ajdačic et al. measured with 14.4
MeV neutrons, we should have counted 180 protons at about 13.0 Mev.
Within the limit of our error, no evidence for the existence of the
trineutron was found.
- 5-
REFERENCES
1. V. Ajdačic, M. Cerineo, B. Lalović, G. Paić, I. Šlaus, and P. Tomaš,
Phys. Rev. Letters 14, 444 (1955).
2. Ya. B. Zel'dovich, JETP (U.S.S.R.) 38, 1123 (1960).
[Translation: Soviet Phys. JETP 11, 812 (1969)].
3. A. I. Baz', v. I. Gol'danskii, and Ya. B. Zel'dovich, Usp. Fiz. Nauk
85, 445 (1955).
[Translation: Soviet Phys, -Usp. 8, 177 (1965)).
4. A. I. Baz, v. I. Gol'danskiſ, and Ya. B. Zel'dovich, Usp. Fiz. Nauk
72, 211 (1960).
[Translation: Soviet Phys.-Usp. 3, 729 (1961)].
5. H. B. Willard, J. K. Bair, and C. M. Jones, Phys. Letters 9, 339 (1954).
6. J. P. Schiffer and R. Vandenbosch, Phys. Letters 5, 292 (1953).
7. Y. C. Tang and B. F. Baymar., Phys. Rev. Letters 15, 165 (1965).
8. K. A. Brueckner, J. I. Gammel, and J. Ț. Kubis, Phys. Rev. 118, 1095 .
(1960).
9. J. S. Levinger and L. M. Simmons, Phys. Rev. 124, 916 (1961).
10. A. N. Mitra and V. S. Bhasin, Phys. Rev. Letters 16, 523 (1966).
Angular Distributions in Neutron Induced Reactions (Brookhaven National
Laboratory Report No. BNL-400, 1.952), 2nd Ed., Vol. 1.
Neutron Cross Sectins (Brookhaven National Laboratory Report No.
12.
BNL-325, 1958), and Ed.
-6-
FIGURE CAPTIONS
Fig. 1. Deuteron spectrum (lab system) at oº from the reaction of 20.8
MeV neutrons with tritium. A smooth curve has been drawn as
.
an aid in following the data.
Fig. 2. Proton spectrum (lab system) at oº from the reaction of 20.8
MeV neutrons with tritium. The arrows indicate the maximum
possible proton energy from the reaction T(n,p)3n and the position
of the expected proton peak from the T(n,p)n reaction under the
assumption that the trineutron is bound by 1.0 MeV.
*:.
*
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a
???*$,fiki
ORNL-DWG 66-6385

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COUNTS
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-20 -
9
10
11
12 13 14 15 16
DEUTERON ENERGY (MeV)
7
18
19
Fig. 1

ORNL-DWG 66-6386
:
T(nipin3
Tln, Pmax)31
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COUNTS
?
8
13
14
15
9 10 11 12
PROTON ENERGY (MeV)
Fig. 2
END
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DATE FILMED
10/21 / 66







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