Wilson cloud chamber measurements of the separated spectra of positrons and electrons produced by gamma quanta of 6.14 MeV differ considerably from the theoretically predicted spectra by BETHE and HEITLER, but are in good agreement with those of a modified theory of pair creation

Bagge, E. R.

El-Ela, A. A.

Hassan, S.

English

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175
HE4,4-8
MISSING ENERGIES AT PAIR CREATION
Ahmed Abu El- Ela
Department of Physics,Faculty of Science
Mansoura University , Mansoura , Egypt
Soad Hassan and Erich R.Bagge
Institut fuer Reine und Angewandte Kernphysik
der Universitaet Kiel , Olshausenstrasse 40-60
2300 Kiel , W.-Germany
ABSTRACT
Wilson cloud chamber measurements of the separated spectra
of positrons and electrons produced by gamma quanta of
6.14 MeV are differing drastically from the theoretically
predicted (identical) spectra by BETHE and HEITLER , but are in good
conformity to those of a modified theory of pair creation by of one
of the authors (B).
I. The experimental arrangement
A Wilson cloud chamber of the Blackett type (30 cm in diameter, 6 cm
illuminated depth), filled with Helium at 1.2 bar gas pressure and a
water alcohol mixture was operated to investigate pair creation by gammas
of 6.14 ; 6.90 ; 7.11 and 8.87 MeV. These quanta will be emitted after
irradiation of UREA (produced with highly enriched N15-nuclei) by the
neutrons in the tangential hole of the 18 MW swimming pool reactor of the
GKSS-Research-Centre Geesthacht near Hamburg. The cylindrical glass ring
of the cloud chamber had a hole of I cm diameter, covered by a thin
plexiglass foil to allow the gammas entering of the expansion room
without passing the glass. Two Helmholtz coils produced inside the
chamber a nearly homogeneous magnetic field of 703 Gauss (deviations from
the homogeneity less than I% wthin the illuminated volume). Helium was
used to reduce the stopping power of the gas and also its motions due to
its small expansion ratio (1.07 for _=1.67). By this way positrons of
d energies above 30 KeV became measurable. But also below this limit pairs
were still recognizable and could be distinguished from Compton electrons
although the energies could not be determined precisely enough to present
credible values.
The cioud chamber was installed at a distance of about 6 m from the
reactor behind its 3.5 m concrete radiation shield. After an irradiation
for at least one minute in the middle of the tangential hole a cartridge
filled with 0.7 g UREA was transported within 3.2 sec to a lead bloc at
• the cloud chamber by a pressurised pipe line. A hole in the lead bloc
"focussed" the gammas to a 25 um gold foil inside the chamber.(Fig.1)
https://ntrs.nasa.gov/search.jsp?R=19850027703 2020-03-20T17:05:38+00:00Z
_76
HE4,4-8
2. The evaluation method and the energy sum spectrum of thepairs
The particle pathes were photographed stereoskopally by two
Hasselblad cameras at 12 cm distance of the optical axes and at a
distance of one meter from the cloud chamber. About 4000 pictures were
taken and 243 pairs on them have been evaluated on a Pulfrich
stereokomparator by two persons (A,E.E. 121 pairs (see [I]) and S.H.
122 pairs) Independly and under slightly modified calibrating conditions.
The two separate measurements gave practically the same results for the
positron- and electron-spectra.
In figure 2 we show here the energy sums of 122 pairs which
demonstrate the energy deficits for the 3 lines at 6.14 ; 6.91 and 8.87
MeV by their asymmetries (soft rise of frequencies on the low energy side
of the maxima and rapid fall down at higher energies). It should be
noted that the 7.11 MeV-line has too low intensity and cannot be
separated well from the 6.91-1ine.
3. The separated energy spectra of the positrons and the electrons
Figures 3 and 4 present the separated spectra of the positrons and
electrons for 114 pairs (57 pairs by A.E.E. and the others by S.H.) of
the 6.14 MeV-quanta. The corresponding spectra for the two types of
particles, 69 pairs of the couple 6.90 and 7.11MeV and 29 pairs for the
8.87 MeV-line, not shown here, are practically of the same behaviours.
There is no question that the separated particle spectra are differing in
a drastic way from the predictions of the well known theory of BETHE and
HEITLER (dotted curves) [2] (1934), but are in a relatively good
conformity to a modified theory of pair creation by BAGGE [3] (1977)
(solid curves), b
References
[I] Ahmed Abu E!-Ela, Dr.rer.nat-thesls, university of Kiel 1984
Ahmed Abu Ei-Ela and Erich R.Bagge, Atomkernenergie/Kerntechnik, °
45,208 (1984)
[2] H.A. Bethe and W.Heitler, Proc.Roy.Soc.,140,83 (1934)
[3] Erich R.Bagge Atomkernenergle/Kerntechnlk,25,251-256 (1975)
26,73-75 (1975) °
33,116-125 (1979)
177
fiE 4,4-8
2 HetmhoLtz-
colts
pipe Line
to the re_tor
urea wRh
30 cm
Figure ]. The Wilson cloud chamber arrangement with the Helmholtz
coils, the pipe line for the cartrigde transport and the
25 _m gold foil as target for the pair production.
6,14
14
N
12 Enlrgilspektrum der Paar¢
( 122 Paar¢ )
_)1
10 - _ ET = E_*E,
= Eki*E_n+2 moC2
w 8
6
= 4
2
3 4 5 6 7 8 9 10 11 12 13
• Figure 2. The energy sum spectrum of the positron-electron pazrs pro-
duced by gamma quanta of 6.]4_6.90; 7.]] andS.87 MeV.
These quanta are emitted by ]_O-nuclel, generated by irra-
diation of ]5N-nuclei with the thermal neutrons of a
swimming pool reactor and a subsequent B-decay of 7.13 sec
lifetime.
t'78
HE 4,4-8
50 50
6,1&.McV I
6.14MeV 45 11_ Paare/_5 11&Paarei
N ELEKTRONEN
N POSITRONEN
40 4O
3S E+= E_i+ mc2 35 E. = E_i n + r_ 2
E_= E_. rnc_ E = E_'_+m¢2
E T = E+* E_ ET = E, + E_
30 30
25 25
20 20 I--_"-_ B-H Theorie '15 B-H Theorie 15
IIII / _ / \X
lO \ 1o
5 5_,,j
0 0.2 0,4 0.6 0.8 1.0 0 0.2 0.4 0.6 08 1.0
E_
E, --_-
Figure 3. Figure 4
The positron spectrum of 114 pairs Here the corresponding elec-
created by 6.]4 MeV quanta alone, tron spectrum of the same
Noteworthy is the high frequency pairs as in figure 3 shows
of low kinetic energy positrons that these particles received
in full contradiction to BETHE mainly the highest possible "
and HEITLER's theoretically energies at pair creation by
predicted (dotted) curve _2_ . the 6,]4 MeV-quanta. There is
no chance to say that posi- b
trons have identical spectra
as BETHE and HEITLER's theory
did it. The solid curves in
the two figures 3 and 4 are
derived in a modified theory
of pair creation by BAGGE C3_.


Missing energies at pair creation

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