Total and partial cross sections of the ¹²С(γ,3α) reaction
The total cross-section of the ¹²С(γ,3α) reaction in the energy range from the threshold to 40 MeV has been measured by the method using a diffusion chamber. It has been established that the two-stage mechanism is dominant: first, α-particles and a ⁸Ве nucleus are formed, then the latter disintegr...
Gespeichert in:
| Datum: | 2004 |
|---|---|
| Hauptverfasser: | , |
| Format: | Artikel |
| Sprache: | English |
| Veröffentlicht: |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2004
|
| Schriftenreihe: | Вопросы атомной науки и техники |
| Schlagworte: | |
| Online Zugang: | http://dspace.nbuv.gov.ua/handle/123456789/80513 |
| Tags: |
Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
|
| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Zitieren: | Total and partial cross sections of the ¹²С(γ,3α) reaction / S.N. Afanas’ev, A.F. Khodyachikh // Вопросы атомной науки и техники. — 2004. — № 5. — С. 14-18. — Бібліогр.: 17 назв. — англ. |
Institution
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
irk-123456789-80513 |
|---|---|
| record_format |
dspace |
| spelling |
irk-123456789-805132015-04-19T03:02:07Z Total and partial cross sections of the ¹²С(γ,3α) reaction Afanas’ev, S.N. Khodyachikh, A.F. Ядерная физика и элементарные частицы The total cross-section of the ¹²С(γ,3α) reaction in the energy range from the threshold to 40 MeV has been measured by the method using a diffusion chamber. It has been established that the two-stage mechanism is dominant: first, α-particles and a ⁸Ве nucleus are formed, then the latter disintegrates into two α-particles. Partial cross-sections of channels of forming excited states of ⁸Ве were measured. Методом дифузійної камери в магнітному полі обмірен повний перетин реакції ¹²С(γ,3α) в єнергетичному інтервалі від порога до 40 MеВ. Встановлено, що основним є двохступеневий механізм: спочатку утворяться α-частка і ядро ⁸Ве, яке потім розпадається на дві α-частки. Обмірено парціальні перетини каналів утворення збуджених станів ядра ⁸Ве. Методом диффузионной камеры в магнитном поле измерено полное сечение реакции ¹²С(γ,3α) в энергетическом интервале от порога до 40 МэВ. Установлено, что основным является двухступенчатый механизм: сначала образуются α-частица и ядро ⁸Ве, которое потом распадается на две α-частицы. Измерены парциальные сечения каналов образования возбужденных состояний ядра ⁸Ве. 2004 Article Total and partial cross sections of the ¹²С(γ,3α) reaction / S.N. Afanas’ev, A.F. Khodyachikh // Вопросы атомной науки и техники. — 2004. — № 5. — С. 14-18. — Бібліогр.: 17 назв. — англ. 1562-6016 PACS: 25.20-X http://dspace.nbuv.gov.ua/handle/123456789/80513 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| language |
English |
| topic |
Ядерная физика и элементарные частицы Ядерная физика и элементарные частицы |
| spellingShingle |
Ядерная физика и элементарные частицы Ядерная физика и элементарные частицы Afanas’ev, S.N. Khodyachikh, A.F. Total and partial cross sections of the ¹²С(γ,3α) reaction Вопросы атомной науки и техники |
| description |
The total cross-section of the ¹²С(γ,3α) reaction in the energy range from the threshold to 40 MeV has been measured by the method using a diffusion chamber. It has been established that the two-stage mechanism is dominant:
first, α-particles and a ⁸Ве nucleus are formed, then the latter disintegrates into two α-particles. Partial cross-sections of channels of forming excited states of ⁸Ве were measured. |
| format |
Article |
| author |
Afanas’ev, S.N. Khodyachikh, A.F. |
| author_facet |
Afanas’ev, S.N. Khodyachikh, A.F. |
| author_sort |
Afanas’ev, S.N. |
| title |
Total and partial cross sections of the ¹²С(γ,3α) reaction |
| title_short |
Total and partial cross sections of the ¹²С(γ,3α) reaction |
| title_full |
Total and partial cross sections of the ¹²С(γ,3α) reaction |
| title_fullStr |
Total and partial cross sections of the ¹²С(γ,3α) reaction |
| title_full_unstemmed |
Total and partial cross sections of the ¹²С(γ,3α) reaction |
| title_sort |
total and partial cross sections of the ¹²с(γ,3α) reaction |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2004 |
| topic_facet |
Ядерная физика и элементарные частицы |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/80513 |
| citation_txt |
Total and partial cross sections of the ¹²С(γ,3α) reaction / S.N. Afanas’ev, A.F. Khodyachikh // Вопросы атомной науки и техники. — 2004. — № 5. — С. 14-18. — Бібліогр.: 17 назв. — англ. |
| series |
Вопросы атомной науки и техники |
| work_keys_str_mv |
AT afanasevsn totalandpartialcrosssectionsofthe12sg3areaction AT khodyachikhaf totalandpartialcrosssectionsofthe12sg3areaction |
| first_indexed |
2025-07-06T04:31:30Z |
| last_indexed |
2025-07-06T04:31:30Z |
| _version_ |
1836870575895609344 |
| fulltext |
TOTAL AND PARTIAL CROSS SECTIONS OF THE 12С(γ,3α) REACTION
S.N. Afanas’ev, A.F. Khodyachikh
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
e-mail: afanaserg@kipt.kharkov.ua
The total cross-section of the 12С(γ,3α) reaction in the energy range from the threshold to 40 MeV has been mea-
sured by the method using a diffusion chamber. It has been established that the two-stage mechanism is dominant:
first, α-particles and a 8Ве nucleus are formed, then the latter disintegrates into two α-particles. Partial cross-sec-
tions of channels of forming excited states of 8Ве were measured.
PACS: 25.20-X
1. INTRODUCTION
The results of photodisintegration of a carbon nucle-
us into three alpha particles are interesting for the stud-
ies of the mechanism of interaction of the electromag-
netic radiation with nucleus and for checking of nucleus
models. Ascertained data on the 12C(γ,3α) reaction at
low energies are useful to astrophysics for construction
of evolutionism of stars.
At energies up to 40 MeV the process of 12С nucleus
photodisintegration into three α particles can proceed
via two mechanisms: immediate disintegration into
three interactive α particles and two-stage disintegration
with formation of intermediate 8Ве nucleus and subse-
quent its disintegration into two α-particles.
Up to the present the certain choice between them is
not done: in work [1] a satisfactory agreement with the
experiment in the model of immediate disintegration
was obtained, while in [2] it was necessary to involve
the second mechanism.
Previously, the experimental study of the 12C(γ,3α)
reaction was carried out more than once on monochro-
matic beams from inverse reactions and radioactive
sources, as well as, on the bremsstrahlung beams from
the electron accelerators, but only by the method of nu-
clear photoemulsions [3-10]. There is a considerable
disagreement in data on the reaction total cross-section.
Therefore it is useful to investigate the reactions by
the other method. The experiment with a diffusion
chamber offers some advantages: practically clean tar-
get, low threshold of α-particle registration due to the
low density of the target, magnetic field and ionization
losses will allow to identify more reliable the reaction
products.
Recently one accumulated and systematized the ex-
tensive information on low-lying excited states of 8Ве
nucleus [11] disintegrating into two α-particles. Be-
cause of an insufficient energy resolution and low statis-
tic substantiation, in this experiment we do not state a
problem to define more exactly the parameters of 8Ве
excited states, but and now this problem is under inves-
tigation [12]. The resonances observed in the αα-frame
are identified with the known states of 8Ве nucleus, and,
for the first time, the cross-sections of channels of for-
mation of these states are measured.
Preliminary results on the total cross-section and
photoproduction of a ground state of 8Ве nucleus were
reported earlier [13-14].
2. EXPERIMENTAL METHOD
The experiment was performed using the diffusion
chamber placed in the magnetic field having the
strength of 1.5 T. The chamber was irradiated with
bremsstrahlung γ-quanta from the electron accelerator
LUE-300 with a maximum energy of 150 MeV. To de-
crease the target density the chamber was filled with a
mixture of methane and helium in the proportion 1:7 up
to the pressure of 1.5 ata.
Thus it was possible to have lengths of tracks of
slow residual nuclei acceptable for measurements and
sufficient sharpness of their images on the photographic
film at pressures near to the atmospheric one. Owing to
the combination of a 4π-detector with a target of a low
density the experimental method made it possible to in-
vestigate the 12C(γ,3α) reaction practically from its
threshold. A soft component of the bremsstrahlung
spectrum has been removed by means of the beryllium
filter of a thickness 2.5 rad. units. The spectral distribu-
tion of photons was taken as the Schiff distribution one
corrected for a uniform spectrum attenuation by the fil-
ter.
For the treatment three-ray events were selected
whose tracks are near to the coplanarity and belong to
two-charge particles. As a result of measurements, one
can expect for them the obtaining of a transverse mo-
mentum balance.
The main background is expected from the 12С(γ
,n)3He2α reaction, since the experimental method does
not separate 3He and 4He. The yield of this reaction is
higher by a factor of 2.5 than in the reaction under
study. In the lab system the tracks of particles of the
12С(γ,n)3He2α reaction, as a rule, are far from the copla-
narity. Therefore, these events, in main, are separated in
the process of visual selection.
The events of the reaction under study also are imi-
tated by the 4Не(γ,n)3He process with subsequent scat-
tering of 3He on 4He. In this process three rays are al-
ways coplanar, but vertex of an event is not always in
the beam zone.
14 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2004, № 5.
Series: Nuclear Physics Investigations (44), p. 14-18.
The final identification of events was performed af-
ter measurements on the base of the momentum bal-
ance. We counted only the event whose unbalance did
not exceed 12 MeV/c. The estimated background from
the 12С(γ,n)3He2α reaction was equal to 2.6 %. The 4Не(
γ,n)3He reaction did not make the contribution.
The experimental procedure does not permit to de-
termine with a certain accuracy the kinematic parame-
ters of particles not stopped in the working volume of
the chamber, which went out at an angle less than 50° in
the direction of the magnetic field strength. For the
events, nontreated because of this, a geometrical correc-
tion was done. It is calculated under the assumption of
azimuthal symmetry, as the γ-quanta beam is not polar-
ized.
For identification of 8Ве state a kinematic model of
the reaction is developed. It is based on the literature
data on the maximum position and resonance width [11]
and corresponding suppositions about angular distribu-
tions of both the α-particle, the first leaving the 12С nu-
cleus in the system of reaction center, and the α-parti-
cles in the 8Ве rest system. In the model the error of mo-
mentum measurement and restrictions by the angle be-
tween the particle momentum and the magnetic field
vector are taken into account.
At energies near the threshold all particles stop in
the working volume of the chamber, but in the range of
30…40 MeV, as a rule, they do not stop. Therefore, the
measurement accuracy decreases from 5.3 MeV to
10 MeV.
3. EXPERIMENTAL RESULTS
3.1. The total cross-section
The total cross-section of the 12С(γ,3α) reaction in
the energy interval from the reaction threshold up to
40 MeV is presented in Fig. 1(a). The errors are statis-
tic. The integral cross-section equals to 5.58±
0.16 MeV mbn.
In the curve of carbon excitation two maxima are
observed. The first one is at Еγ=17.17±0.12 MeV with a
half-width 2.65±0.14 MeV, and the second one – at Еγ
=27.12±0.34 MeV with a half-width 4.56±0.14 MeV.
For comparison the results of earlier works [4,5,9]
are presented in Fig. 1(a) and Fig. 1(b). It should be not-
ed that the structure of curves is similar: two maxima
are observing, the position of one of them differs in-
significantly. At the same time, the difference in the
cross-section value is noticeable. In the near-threshold
area the transverse cross-section, obtained in the given
experiment, exceed the results of all the previously per-
formed measurements.
Because of the high target density in the emulsion
method the losses of low-energy α-particles are possi-
ble. In the event distribution by the kinetic energy of α-
particles about 30 % of events have, at least, one α-par-
ticle with a kinetic energy less than 1 MeV. In the cited
papers [3-10] the threshold of α-particle registration by
the kinetic energy is not given and the possible losses,
caused by it, are not discussed. At the same time, there
is information that the threshold value takes place with-
in the range from 0.3 to 1.0 MeV. In Fig. 1(b) the points
present the total cross-section for the case when exclud-
ed are the events which have, at least, one α-particle of
an energy less than 1.0 MeV. It is seen that an accord
with the results of [4,5] at Еγ<20 MeV is better.
10 15 20 25 30 35 40
0,00
0,25
0,50
0,00
0,25
0,50
b )
σ ,
mbn
E γ , MeV
a )
σ ,
mbn
Fig. 1. The total cross-section for the 12C(γ,3α) re-
action, histogram - [4], • – present data: a) dash dot
line - [1], dot line - explanation in the text; b) ο - [5],
∇ - [9].
Below, it will be clear that the minimum at energies
in the range of 20…22 MeV coincides with the bound-
ary of finishing the formation of the first and starting the
formation of the second excited states of 8Ве nuclei. The
second state has the excitation energy of 11.4 MeV and
the resonance half-width of 3.5 MeV. Therefore, its for-
mation can be accompanied by the low-energy third α-
particle. The loss of these events qualitatively explains
the relative deepening of the dip in Fig. 1(b) in this en-
ergy region.
At energies from 12 to 20 MeV the 12С nuclei has
three wide levels [15]. The position of the first reso-
nance maximum in the curve of 12С nucleus excitation
coincides, within limits of errors, with the level of
Е0=17.23 МeV and Г=1.15 МeV. But they cannot be
identified, as the resonance half-width exceeds, by a
factor of 2.3, the half-width of the level. The resonance
can obtain the contribution from the two wide level of
Е0=15.44 МeV, Г=1.5 МeV and Е0=19.2 МeV,
Г=1.1 МeV. The superposition of three levels in the
proportion 1:2:1 is shown the doted line in Fig. 1(a). In-
sufficient statistic accuracy does not permit to separate
the levels.
15
The dashed line in Fig. 1(a) shows the calcula-
tion [1] of the total reaction cross-section in the model
when the nucleus composed of three α-particles disinte-
grate immediately into three particles if the γ-quantum
interacts with one of them. The predicted cross-section
is close by the value to the experimental one, but the po-
sition of the resonance maximum does not coincide.
3.2. Analysis of the in-pair relative energy
distribution
The in-pair relative energy of two α-particles was
determined as:
2( - ) / 4ik i kW p p m= r r
(1)
where i,k,m are the numbers and the mass of α-particles,
respectively. It is not possible to select from three pairs
of α-particles of every event a pair that was produced as
a result of 8Ве disintegration. Therefore, for the distribu-
tion of the in-pair relative energy of two α-particles,
three values of Wik for every event are plotted in Fig. 2.
In the curve of αα-system excitation, shown in
Fig. 2(a) with a step of 20 keV in the range 0≤Wik≤
0.25 MeV the resonance is revealed. The solid line
presents the phase distribution calculated by formula
of [16]:
1 21 2( ) ( )ik ik ikf W W W Wmax= −Ч , (2)
where Wmax is the maximally possible value of the 8Ве
excitation energy, equal to the maximum energy of the
γ-quanta in the given interval minus the reaction thresh-
old. The phase distribution is calculated for the
bremsstrahlung beam with a maximum energy of
32 MeV. The fitting of experimental data of the Brait-
Weigner curve gave, as a result, Е0=0.089±0.004 МeV,
Г=0.056±0.003 МeV. It is known [17] that in the case
of the 8Ве ground state disintegration into two α-particle
there takes place a resonance with a maximum at
Е0=0.092 MeV and the half-width Г=6.8±1.7 eV. The
positions of maxima are in good agreement. Therefore,
it can be assumed that the resonance is the result 8Ве nu-
clei ground state production. The half-width observed in
the experiment is the apparatus value, and it is the mea-
surement error for the in-pair relative energy of two α-
particles Wik.
The dash-dot line in Fig. 2(a) shows the distribution
obtained by the mathematic simulation under supposi-
tion of isotropic angular distributions in the 8Ве rest sys-
tem. The angular distributions in the system of the α-
particle and 8Ве center are taken from the preliminary
experiment [14]. The agreement with the experiment ev-
idences on the model correctness. The events with pro-
duction of the ground state of the 8Ве nucleus were not
used for construction of the following distributions on
Wik.
In the distribution of all other events on Wik, distinct
resonances are not observed. The 8Ве excited states
were observed in the limited γ-quanta energy intervals.
0,0 0,1 0,2
0
25
50
0 3 6 9 12
0
100
200
0 8 16
0
30
60
0 15 30
0
50
100
a)
b)
c)
d)
N
/
M
eV
,
a.
u.
W , M e V
Fig. 2. The in-pair relaive energy of two α-parti-
cles distribution. Point - the present experiment, full
line – the phase distribution, dash-dot line – the model.
a) the ground state of 8Be, b) the first excitation state of
8Ве, c) the second excitation state of 8Ве, d) the super-
position of third and fourth excited states of 8Ве
Fig. 2(b) presents the distribution on Wik in the γ-
quantum energy range from 16 to 20 MeV, as it was
found that the first excitation of the 8Ве state is pro-
ducesd only in the region of the first maximum in the
curve of Fig. 1. The solid line is the curve of the phase
distribution. In the experiment two maximum are ob-
served. The first one has the parameters Е0=3.12±
0.04 MeV, Г=1.89±0.07 MeV, and the second one
Е0=8.13±0.12 MeV, Г=4.17±0.24 MeV. The dashed
curve shows the results of mathematical simulation with
the parameters of the first excited state of 8Ве [11]. The
simulation result is not sensitive to the form of angular
distributions of 8Ве in the reaction center system. The
better agreement with the experiment is obtained for the
case when the angular distributions of α-particles in the
8Ве rest system are taken in the form dσ/dΩ∼(1+sin2θ
cos2θ). The curves are normalized for the area under the
experimental curve. The agreement of the mathematical
model with the experiment makes it possible to identify
the first resonance with the first excited state of 8Ве.
The second resonance is the background one. It be-
comes apparent in the system of the α-particle, the first
leaving the 12С nucleus, and the 8Ве fission product. The
events, referred to the first excited state of 8Ве, were ex-
cluded from the further analysis.
Distribution of other events by the in-pair relative
energy of two α-particles reveals the maximum in the
region of 17 MeV. Distribution of events, one Wik value
of which lies in the range from 15.0 to 18.0 MeV, is
16
presented in Fig. 2(d). The solid line shows the phase
distribution for gamma-quantum energy from 25 to
40 MeV. It is known [11] that the 8Ве nuclei has two
narrow nearly-lying excited states with parameters
Е0=16.6 МeV, Г=0.1 MeV and E0=16.9 МeV,
Г=0.07 MeV. Simulation is performed for equiprobable
production of these states. The better agreement with
the experiment is obtained for the case when the angular
distributions of α-particles in the 8Ве rest system were
taken in the form dσ /dΩ∼(4-3sin2θ ). The simulation
results practically do not depend on the form of 8Ве an-
gular distributions in the reaction center system. The
measurement error of the momentum δР=5.3 МeV/c
was found from the analysis of event distribution by the
momentum unbalance in the given energy range. The
events referred to the third and fourth excited states of
8Ве were excluded from the further analysis.
Fig. 2(c) presents the event distribution in the energy
range from 20 to 25 MeV. The difference with the phase
distribution is visible. In the experiment observable are
two maximum with parameters Е0=1.23±0.36 MeV,
Г=1.51±0.37 MeV and Е0=10.86±0.21 MeV, Г=2.91±
0.23 MeV. Simulation is performed for the resonance
with parameters E0=11.4 MeV and Г=3.5 МeV [11].
The better agreement with the experiment is obtained
for the case when the angular distributions of α-parti-
cles in the 8Ве rest system were taken in the form dσ /d
Ω∼(1-2sin2θ+2sin2θ cos2θ ). The simulation results
practically do not depend on the form of 8Ве angular
distributions in the reaction center system. The agree-
ment of the mathematical model with the experiment
permits to identify the second resonance with the second
excited state of 8Ве. The maximum at Е0=1.23±
0.36 MeV is the background resonance in the system of
two α-particles leaving the nucleus at different time.
3.3. Partial cross-sections
To determine the probability of formation of 8Ве
states the event distributions by the energy of relative
motion of two α-particles in the narrow energy intervals
of γ-quanta were plotted. It has been found that the
ground state is produced at energies from 8 to 32 MeV.
The total cross-section of the ground state of 8Ве is
shown in Fig. 3(a) in comparison with the result of [7].
The integral cross-section equals to 0.501±
0.044 MeV mbn.
At energies up to 20 MeV the main contribution is
obtained from the channel of formation of the 8Ве first
excited state. In Fig. 2(b) is seen that the model de-
scribes rather well the experimental points at 9≤Wik≤
12 MeV and there is no appreciable contribution from
the second excited state. The total cross-section of the
channel of formation of the 8Ве first excited state is ob-
tained as a difference of the total cross-section of the re-
action (Fig. 1(a)) and the total cross-section of ground
state formation (Fig.3 (a)) and that is shown in Fig.3 (b)
in comparison with the results of [6,7]. A possible cause
of the significant disagreement was discussed above.
The integral cross-section of this reaction channel σ
int=2.240±0.094 MeV mbn.
0,0
0,1
0,0
0,1
0,2
0,0
0,4
0,00
0,05
10 15 20 25 30 35 40
0,0
0,1 e)
d)
E
γ , M e V
c)
b)
a)
σ
, m
b
n
Fig. 3. The partial cross-section for the 12C(γ,3α)
reaction by mode of breakup: a) via the ground state of
8Be, b) via the first excitation state of 8Ве, c) via the sec-
ond excitation state of 8Ве, d) via the superposition of
third and fourth excited states of 8Ве, e) uncertain
events. • –present data, full line - [7], ο - [6], dash
line - [2].
In the energy range from 20 to 27 MeV after deduc-
tion of events relating to the nonseparated third and
fourth excited states, the Wik distributions do not reveal
other resonances except the second excited state. The
total cross-section of second excited state formation is
shown in Fig. 3(c). The integral cross-section σint=1.273
±0.081 МeV mbn. The earlier cross-section of this reac-
tion channel was not measured.
The total cross-section of formation of nonseparated
third and fourth excited states is shown in Fig. 3(d). The
integral cross-section σint=0.629±0.068 МeV mbn.
At Еγ>27 MeV remained still 140 events which can-
not be referred to any of above-mentioned excited
states. These events are either the products of immediate
12С disintegration into 3α or the products of the subse-
quent reaction with formation of higher excited states.
The cross-section of formation of these events is shown
in Fig. 3(e). The integral cross section σint=0.937±
0.082 МeV mbn.
The normalized (for experiment) calculation [2] of
the cross-section of the partial channel of 8Ве 0+ state
formation in the model of immediate α-particle release
is shown in Fig. 3(a). The position of the maximum near
18 MeV is predicted satisfactory, while the other two
are shifted in comparison with the experiment.
The normalized calculation [2] of the cross-section
of the partial channel of the 8Ве 2+ state formation is
shown in Fig. 3(b) and Fig. 3(d). From Fig. 3(b) one can
see that the first maximum of the curve coincides with
the experiment. However, the value is less by a factor of
∼ 5 and in the experiment the second maximum is not
17
observed. The calculation [2] in Fig. 3(d) is not in ac-
cordance with the experiment.
The normalized calculation of the cross-section of
the partial channel of the 4+ state formation is shown in
Fig. 2(c). It is not in accordance with the experiment.
4. CONCLUSIONS
The total cross-section of the 12С(γ,3α) reaction is
measured in the energy interval from the reaction
threshold to 40 MeV. Appreciable difference between
the results obtained by the emulsion method, particular-
ly in the range of lower energies, was observed. The dif-
ferences can be explained by the loss of low-energy α-
particles in emulsions.
In the in-pair relative energy of two α-particles a
contribution from the ground state, of the first, second,
and non-separated third and fourth excited states of 8Ве
was observed. The partial cross-sections of channels of
production of these states were measured. The ground
sate is produced at energies ranging from the reaction
threshold to 32 MeV. The first excited state makes a
contribution in the interval of γ-quantum energy from
12 to 22 MeV, the second in the interval from 20 to
27 MeV. At higher energies the superposition of non-
separated third and fourth excited states of 8Ве is pre-
vailing. The two-stage mechanism is dominant: first, α-
particles and 8Ве nucleus are formed, then the latter dis-
integrates into two α particles. Calculations in the mod-
el of both the gradual-type disintegration and the imme-
diate disintegration, when the wave function of the nu-
cleus is constructed in the shell model or in the α-clus-
ter model, are not in agreement with the experimental
results.
REFERENCES
1. R.I. Jibuti, R.Ya. Kezerashvili N.I. Schubidze.
Photodesintegration of the α-cluster nuclei on the α-
particles // Yad. Fiz. 1992, v. 55, № 12, p. 3233-3240
(in Russian).
2. R.I. Dzhibuti, V.I. Mamasakhlisov,
T.S. Macharadze. Photonuclear reactions with α-parti-
cle emission and fourparticle correlations in light nuclei
// Yad. Fiz. 1965, v. 1, p. 976-983 (in Russian).
3. F.K. Goward, J.J. Wilkins. Cross-section for the
photodisintegration of carbon into three α-particles //
Proc. of Roy. Soc. 1953, v. 217, p. 357-375.
4. F.K. Goward, J.J. Wilkins. The 12C(γ,3α) reac-
tion and energy levels of 8Be and 12C // Proc. of Roy.
Soc. 1955, v. 228, p. 376.
5. V.N. Maikov. Some photo-reactions on light nu-
clei // ZhETF. 1958, v. 34, p. 1406-1419 (in Rus-
sian).
6. C.H. Millar, A.G.W. Cameron. Photo-alpha re-
actions in nuclear emulsions // Can. J. Phys. 1953,
v. 31, p. 723-757.
7. M.E. Toms. Properties of the 12C(γ,3α) reaction
below 21.5 MeV // Nucl. Phys. 1964, v. 50, p. 561-
584.
8. V.V. Kirichenko. Alpha-particle photodisintegra-
tion light nuclei 12С и 16О // Physics of elementary
particles and atomic nuclei. 2001, v. 32, №4, p. 803-
827 (in Russian).
9. E.A. Kotikov, E.D. Makhnovskiy. Photodesinte-
gration of nuclei 12С into three charged fragment //
Izv. АN (Ser. Fiz.). 1998, v. 62, №11, p. 2286-2294 (in
Russian).
10. E.A. Kotikov, E.D. Makhnovskiy,
A.A. Zchuganova. Mechanizm photodesintegration
nuclei 12С into three α-particles // Izv. АN (S. Fiz.).
2002, v. 66, №3, p. 445-448 (R).
11. F. Ajzenberg-Selove. Energy levels of light nu-
clei A=5-10 // Nucl. Phys. 1988, v. A490, p. 1-225.
12. O.K. Gorpinich, O.M. Povoroznyk,
B.G. Struzhko Study of excited of a 8Be nucleus in the
correlative experiment // Ukr. Fiz. Zh.. 2003, v. 48,
№5, p. 407-410 (R).
13. I.V. Dogyust, V.V. Kirichenko, A.F. Khody-
achikh. Research γ12С→3α reactions at maximum
energy γ-quantum 150 MeV. Proc. of the 27th
Conf. on Nucl. Spect. and Atomic Nuclei. М.,
1977, p. 28 (in Russian).
14. S.N. Afanas’ev, A.F. Khodyachikh. The 8Be
ground state formation in 12C(γ,3α)-reaction // Prob-
lems of Atom. Sc. and Techn. Ser.: Nucl. Phys.
Inves. 2001 p. 56-58.
15. F. Ajzenberg-Selove. Energy levels of light nu-
clei A=11-12 // Nucl. Phys. 1990, v. A506, №1, p. 1-
158.
16. A.M. Baldin, V.I. Gol’danskii et al. Kinematics
of nuclear reactions. Moskva: “Atomizdat”, 1968,
456 р. (R).
17. J. Benn, E.B. Dally. Lifetime and energy of the
ground state of 8Be // Nucl. Phys. 1968, v. A106,
p. 296-312.
ПОЛНОЕ И ПАРЦИАЛЬНЫЕ СЕЧЕНИЯ РЕАКЦИИ 12С(γ,3α)
С.Н. Афанасьев, А.Ф. Ходячих
Методом диффузионной камеры в магнитном поле измерено полное сечение реакции 12С(γ,3α) в энерге-
тическом интервале от порога до 40 МэВ. Установлено, что основным является двухступенчатый механизм:
сначала образуются α-частица и ядро 8Ве, которое потом распадается на две α-частицы. Измерены парци-
альные сечения каналов образования возбужденных состояний ядра 8Ве.
ПОВНИЙ І ПАРЦІАЛЬНІ ПЕРЕТИНИ РЕАКЦІЇ 12С(γ,3α)
18
С.М. Афанасьєв, О.Ф. Ходячих
Методом дифузійної камери в магнітному полі обмірен повний перетин реакції 12С(γ,3α) в єнергетично-
му інтервалі від порога до 40 MеВ. Встановлено, що основним є двохступеневий механізм: спочатку
утворяться α-частка і ядро 8Ве, яке потім розпадається на дві α-частки. Обмірено парціальні перетини ка-
налів утворення збуджених станів ядра 8Ве.
19
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
e-mail: afanaserg@kipt.kharkov.ua
PACS: 25.20-x
3.1. The total cross-section
3.2. Analysis of the in-pair relative energy distribution
3.3. Partial cross-sections
4. ConclusionS
REFERENCES
С.Н. Афанасьев, А.Ф. Ходячих
С.М. Афанасьєв, О.Ф. Ходячих
|