On ¹²C(γ, n)¹¹B reaction mechanism in the intermediate energy range
The experimental research results for two reactions of photodisintegration of a carbon nucleus which proceed with the knocking out the nucleons from different shells are considered. The total cross-section dependence with respect to energy and dependence of expansion coefficients of the nucleon angl...
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| Опубліковано в: : | Вопросы атомной науки и техники |
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| Дата: | 2011 |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2011
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| Цитувати: | On ¹²C(γ, n)¹¹B reaction mechanism in the intermediate energy range / E.S. Gorbenko, R.T. Murtazin, A.F. Khodyachikh // Вопросы атомной науки и техники. — 2011. — № 3. — С. 31-34. — Бібліогр.: 9 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860249840442671104 |
|---|---|
| author | Gorbenko, E.S. Murtazin, R.T. Khodyachikh, A.F. |
| author_facet | Gorbenko, E.S. Murtazin, R.T. Khodyachikh, A.F. |
| citation_txt | On ¹²C(γ, n)¹¹B reaction mechanism in the intermediate energy range / E.S. Gorbenko, R.T. Murtazin, A.F. Khodyachikh // Вопросы атомной науки и техники. — 2011. — № 3. — С. 31-34. — Бібліогр.: 9 назв. — англ. |
| collection | DSpace DC |
| container_title | Вопросы атомной науки и техники |
| description | The experimental research results for two reactions of photodisintegration of a carbon nucleus which proceed with the knocking out the nucleons from different shells are considered. The total cross-section dependence with respect to energy and dependence of expansion coefficients of the nucleon angle distributions by trigonometric functions on energy are compared. Both reactions have dependence non-regularities within the 34...44 MeV energy interval, it can be explained as a change of mechanism the nucleus absorbs a photon. It is shown that a joining of the quasideuteron mechanism has a identical energy threshold if nucleons are detached from the different shells of a carbon nucleus.
Обговорюються результати експериментального дослідження двох реакцій фоторозщеплення ядра вуглецю, що йдуть з відокремленням нуклонів з різних оболонок. Порівнюються залежності повних перерізів та коефіцієнтів розкладання кутових розподілів нуклонів за тригонометричними функціями від енергії. В обох реакціях виявлено нерегулярності в залежностях при енергіях в інтервалі від 34 до 44 МеВ, які пояснено зміною механізму поглинання фотона ядром. Знайдено, що включення квазидейтронного механізму має однаковий енергетичний поріг при відділенні нуклонів з різних оболонок ядра вуглецю.
Обсуждаются результаты экспериментального исследования двух реакций фоторасщепления ядра углерода, идущих с отделением нуклонов из разных оболочек. Сравниваются зависимости полных сечений и коэффициентов разложения угловых распределений нуклонов по тригонометрическим функциям от энергии. В обеих реакциях обнаружены нерегулярности в зависимостях при энергиях в интервале от 34 до 44 МэВ, которые объяснены изменением механизма поглощения фотона ядром. Найдено, что включение квазидейтронного механизма имеет одинаковый энергетический порог при отделении нуклонов из разных оболочек ядра углерода.
|
| first_indexed | 2025-12-07T18:42:08Z |
| format | Article |
| fulltext |
ON 12C(γ, N)11B REACTION MECHANISM IN THE
INTERMEDIATE ENERGY RANGE
E.S. Gorbenko, R.T. Murtazin∗, A.F. Khodyachikh
National Science Center ”Kharkov Institute of Physics and Technology”, 61108, Kharkov, Ukraine
(Received April 11, 2011)
The experimental research results for two reactions of photodisintegration of a carbon nucleus which proceed with
the knocking out the nucleons from different shells are considered. The total cross-section dependence with respect
to energy and dependence of expansion coefficients of the nucleon angle distributions by trigonometric functions on
energy are compared. Both reactions have dependence non-regularities within the 34...44 MeV energy interval, it can
be explained as a change of mechanism the nucleus absorbs a photon. It is shown that a joining of the quasideuteron
mechanism has a identical energy threshold if nucleons are detached from the different shells of a carbon nucleus.
PACS: 25.20.Dc; 25.20-x
1. INTRODUCTION
The mechanism of a knocking out the single nucleon
from the nucleus within an area of giant resonance
and out of it is an object for numerous experimen-
tal and theoretical studies [1-3]. At the same time
virtual and actual photons can be used as the test
particles. At the energies above the giant resonance
one can mainly discuss the role of a two mechanisms:
direct nucleon knockout and photon absorption by
nucleon pair. The model of the direct neutron and
proton knockout expects different response of the dif-
ferential cross-sections. It is expected that asymme-
try coefficient of the neutron angle distributions will
be small and negative since this particle has no elec-
tric charge. Conversely a proton asymmetry coeffi-
cient is positive and noticeably differs from a zero.
The pair absorption model predicts equal value of
the asymmetry coefficients for both nucleons. We
researched γ +12 C → n + 3He + 2α reaction earlier
in the giant resonance region and very close to reso-
nance area [4], hereinafter this reaction will be desig-
nated as (γ, n). It was shown reaction runs through
two-particle phase and the conclusion is a neutron
is separated from the s-shell of 12C nucleus. The
irregularities in total cross-section and in angle dis-
tributions parameters were found out in the range of
40 MeV , it is clarified as opening the channel when
nucleon pair absorbs the photon. It is interesting
to research the reaction for comparison in case nu-
cleon is detached from the p-shell. For this purpose
the γ +12 C → p + 11B reaction was chosen, in what
follows it will be indicated as (γ, p). In our experi-
ment this reaction was studied without a separation
by the excited states of a final nucleus. The fact fi-
nal nucleus does not split into hadrons is an evidence
it sits in the low excited state, so one can consider
nucleon detachment comes from p-shell. We inves-
tigated this reaction sooner [5]. In present experi-
ment the measurements were carried out because of
processing system gets modernized and this improves
energy resolution.
2. EXPERIMENTAL RESULTS
a. (γ,n)- reaction
There is a dependence of the reaction total cross-
section on the photon energy [4] is shown on a Fig.1,a.
Fig.1. The total-cross section dependence on energy
∗Corresponding author E-mail address: mahayogin@i.ua
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY, 2011, N3.
Series: Nuclear Physics Investigations (55), p.31-34.
31
The cross-section shows the wide resonance which has
a peak in the area of 37 MeV . Beyond the maximum
the cross-section has a rapidly decreasing. There
is non-regularity near the 43 MeV . The speed of a
cross-section decreasing is diminished after this irreg-
ularity. The event distribution of the effective mass
of 3He + 2α particles was obtained and it has the
narrow resonance shape. Making a comparison with
a phase distribution we can see that the particles
are decay products of the 11C∗ excited state. There-
fore the reaction goes through two-particle stage.
Neutron gets knocked out first and then intermedi-
ate nucleus of 11C∗ having excitation energy with a
maximum at Ex = 14.7± 0.3 MeV , disintegrates in
three particles. Wide detector’s solid angle allowed
measuring the angle distribution of the neutrons in
range from 0 up to π. The angle distributions asym-
metry coefficient of β is defined as a ratio difference
of the outputs to the front and rear half-spheres
correspondingly to integrate output:
β =
π
2∫
0
(dσ/dΩ)dθ −
π∫
π
2
(dσ/dΩ)dθ
π∫
0
(dσ/dΩ)dθ
(1)
the dσ/dΩ - differential cross-sections which depend
on polar angle of θ. There is a asymmetry coefficient
dependence on energy [4] is shown on the Fig.2,b.
The value of coefficient is small at the energies below
40 MeV and direct knock-out model explains it: one
can expects a symmetric angle distribution [7] rela-
tive 90◦ since neutron does not have negative effective
quadrupole charge. At the 38.0±1.5 MeV we can see
the discontinuity. The rapid change of asymmetry
coefficient and total cross-section irregularity were il-
lustrated as a change of the reaction mechanism. The
mechanism of the direct knockout is prevailed below
the 40 MeV . In the range above 40 MeV photon gets
absorbed by the np-pair. The neutron leaves a nu-
cleus and the proton stays in it. A solid line shows a
result of calculation bye the phenomenological quasi-
deuteron model [4] and this calculation is conformed
to an experiment. High excitation energy of a 11C
and the shape of the neutron angle distributions in
the c. m. system indicate that a 11C∗ has Iπ = 1
2
+
state. Therefore one can conclude neutron gets de-
tached from the s-shell of the 12C nucleus.
b. (γ,p)- reaction
The experiment was carried out with an aid of the
diffusion chamber which was placed in the magnetic
field, a chamber was irradiated bye the bremsstralung
γ-quanta with a peak energy of 150 MeV . The 11B
tracks are short and wide, this fact is an inconve-
nience to determine the pulse direction. On the con-
trary proton’s pulse direction are determined with a
good precision but to determine pulse module with
necessary precision the track projection on the me-
dian plane not always has enough length. Thus,
energy of the γ - quantum was evaluated using pro-
ton direction cosines and 11B kinetic energy which
was obtained using the value of range. The 11B
track length was calculated bye its projection on
the plane laying via γ-quantum and proton pulses.
There is a dependence of the (γ, p)-reaction total
cross-section on the photon energy is shown on a
Fig.1,b. The cross-section has a giant resonance with
a maximum at 23 MeV . Beyond the maximum the
cross-section is quickly diminished. At the energy of
30 MeV and above this speed is slumped. One can
see that cross-section is non-monotonically dimin-
ished at the 36 ± 1.5 MeV . For comparison empty
circles represent the experimental data [2], it was
obtained using labeled photons beam with a high
energy resolution and big statistical supply in the
reaction of formation of the 11B ground state dur-
ing the proton registration angularly 60◦. The results
were normalized in the point placed at Eγ = 25 MeV .
There is total cross-sections accordance during the
energy change. The curve of 1 shows a calculation
in the context of a phenomenological quasideuteron
model [4]. The curve 2 is a calculation using the
shell model. The photon interacts with a two cor-
related nucleons. The meson exchange currents are
taken into account [6]. The curves are normalized
at the 35 MeV . The quasideuteron mechanism de-
scribes energy dependence of the total cross-section
satisfactorily. The differential cross-sections are plot-
ted in the center-of-mass system for the energy
intervals of different width. For the 32...36 MeV
and 42...46 MeV they are shown on the Fig.2.
Fig.2. Differential cross-section of the 12C(γ,p)11B
reaction
32
The differential cross-sections of the all intervals were
fitted with the least square method by function (2):
dσ/dΩ = a + bsin2θ + csin2θcosθ . (2)
The solid line is a fitting result. The asymmetry
coefficient β of the angle distributions, which is cal-
culated by (1), with respect to energy is shown on
a Fig.3,a. From the reaction threshold its value
is increased and at the 35 MeV considerably ex-
ceeds the asymmetry coefficient of the (γ, n) reac-
tion which is shown on a Fig.3,c. In the area of a
giant resonance an asymmetry arises because of in-
terference of the dipole and quadrupole transitions.
Fig.3. Dependence of the angle distribution coeffi-
cients on energy
One can see a difference in the response of the asym-
metry coefficients for reactions with a proton and
neutron output as the direct knockout model does
predict it. At the energy above 40 MeV asymme-
try coefficients of the both reactions are almost the
equal and have the same energy dependence. The
asymmetry rise can be qualitatively explained us-
ing kinematic approach: γ-quantum interacts with
a pair of the nucleons. The passage to the center
of inertia of the reaction causes angle distributions
asymmetry of the nucleons leaving nucleus. The
Fig.3,b shows the a/b ratio with respect to photon’s
energy. Coefficients of a and b were obtained un-
der fitting of the angle distributions by a function
(2). The dots are placed in the middle of a energy
intervals the differential cross-sections plotted for.
In the giant resonance region this ratio are uniform
within the errors. The dotted line - ratio the electric
dipole approach expects, it is 2
3 for the transition
to ground state of the final nuclei [8]. An eleva-
tion of this value can be explained as contribution
of the excited states forming. At the energy above
than 34 MeV the ratio is decreased in discrete steps.
The change limit is 36 ± 2 MeV . 2 MeV error is
equal to the half of a width of the interval within
cross-sections are plotted. The solid line is result
in the context of a phenomenological quasideuteron
model [4]. There is agreement with an experiment.
The energy dependence of the asymmetry coefficient
which is shown on the Fig.3,c for (γ, n) reaction has
a discontinuous changing as well. Changing energy
which was determined analogously to (γ, p) reac-
tion, is 36.3± 22 MeV . Hence the energy coefficients
drastically changing at are the same for both reac-
tions within the errors. Previously the quasideuteron
mechanism was theoretically investigated more than
once in the context of a shell model taking into ac-
count nucleon-nucleon correlation [9]. The different
contribution was predicted to the total cross-section
of the interaction processes with nucleon pairs whose
partners are in same or different shell. The not equal
contribution dependence on γ-quantum energy was
also expected. The Fig.4 compares dependence of the
total cross-sections of the (γ, n) and (γ, p) on energy
and and the dependence of the photoproduction to-
tal cross-section of the 11B ground state on energy.
Fig.4. Energy dependence comparison of the total
cross-sections for both reactions
The photoproduction total cross-section of 11B
ground state [2] was registered angularly 60◦ and
it is designated as the empty circles. The data was
normalized at γ-quantum energy of 40 MeV . The to-
tal cross-sections have practically equal dependence
on energy.
3. SUMMARY
The measurement of the total cross-section and an-
33
gle distributions of the γ +12 C → p +11 B reaction
which proceeds with a nucleon detachment from
p-shell are performed. The total cross-section de-
pendence on energy at 34.0 ± 1.5 MeV has a non-
monotonous subsiding. The a/c ratio has discon-
tinuous changing at energy of 36 ± 2 MeV . The
comparison with the same dependences concerning
γ +12 C → n +3 He + 2α reaction which runs with
a detachment of a nucleon from s-shell is carried
out. For this reaction one can see the total cross-
section monotony at 43.0 ± 2.0 MeV and discontin-
uous changing of the angle distributions asymmetry
at 36 ± 2 MeV . These irregularities were explained
as the two-particle absorption channel was opened.
Above giant resonance the relative changing of the
total cross-sections with respect to energy change is
same. The results are in concordance with calcula-
tions of the model which depicts nucleon pair absorbs
a photon considering meson exchange currents.
References
1. J.I. Johansson, H.S. Sherif. Importance of the di-
rect knockout mechanism in relativistic calcula-
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2. P.A. Doyle, P.S. Turner, H. Ruijter, J-O. Adler,
B-E. Andersson et al. Angular distributions for
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v.54, p.3076-3087.
3. A. Kozin, R.P. Rassool, M.N. Thompson, et al.
High-resolution measurement of the 12C(γ,p)11B
reaction to excited states for Eγ=50-70 MeV
//Phys. Rev. C. 1998, v.58, p.2167-2173.
4. S.N. Afanas’ev, E.S. Gorbenko, A.F. Khody-
achikh. Study of the mechanism of carbon nu-
cleus four-particle photodisintegration reactions
// Yad. Fiz. 2007, v.70, p.873-881 (in Russian).
5. V.V. Kirichenko, Yu.M. Arkatov, P.I. Vat-
set, I.V. Dogyust, A.F. Khodyachikh. Reaction
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1978, v.27, p.588-597 (in Russian).
6. K. Mori, P.D. Harty, Y. Fujii, et al.
12C(γ,p0+1)11B cross section from 44 to 98
MeV // Phys. Rev. C. 1995, v.51, p.2611-2615.
7. M. Cavinato, M. Marangoni, P.I. Ottaviani,
A.M. Saruis. Photoreactions of 12C, 12O and
40Ca in self-consistent RPA theory //Nucl. Phys.
1982, v. A373, p.445- 482.
8. R.W. Carr, J.E.E. Baglin. Table of angular dis-
tribution coefficients for (gamma, particle) and
(particle, gamma) reactions , NDT, 1971, v.10,
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9. W. Weise, M.G. Huber, M. Danos. A microscopic
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О МЕХАНИЗМЕ РЕАКЦИЙ 12C(γ, N)11B В ПРОМЕЖУТОЧНОЙ ОБЛАСТИ
ЭНЕРГИЙ
Е.С. Горбенко, Р.Т. Муртазин, А.Ф. Ходячих
Обсуждаются результаты экспериментального исследования двух реакций фоторасщепления ядра уг-
лерода, идущих с отделением нуклонов из разных оболочек. Сравниваются зависимости полных сече-
ний и коэффициентов разложения угловых распределений нуклонов по тригонометрическим функциям
от энергии. В обеих реакциях обнаружены нерегулярности в зависимостях при энергиях в интервале
от 34 до 44 МэВ, которые объяснены изменением механизма поглощения фотона ядром. Найдено, что
включение квазидейтронного механизма имеет одинаковый энергетический порог при отделении нук-
лонов из разных оболочек ядра углерода.
ПРО МЕХАНIЗМ РЕАКЦIЙ 12C(γ, N)11B У ПРОМIЖНIЙ ОБЛАСТI ЕНЕРГIЙ
Є.С. Горбенко, Р.Т. Муртазiн, О.Ф. Ходячих
Обговорюються результати експериментального дослiдження двох реакцiй фоторозщеплення ядра ву-
глецю, що йдуть з вiдокремленням нуклонiв з рiзних оболонок. Порiвнюються залежностi повних
перерiзiв та коефiцiєнтiв розкладання кутових розподiлiв нуклонiв за тригонометричними функцiями
вiд енергiї. В обох реакцiях виявлено нерегулярностi в залежностях при енергiях в iнтервалi вiд 34 до
44 МеВ, якi пояснено змiною механiзму поглинання фотона ядром. Знайдено, що включення квазидей-
тронного механiзму має однаковий енергетичний порiг при вiддiленнi нуклонiв з рiзних оболонок ядра
вуглецю.
34
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| id | nasplib_isofts_kiev_ua-123456789-111130 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T18:42:08Z |
| publishDate | 2011 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Gorbenko, E.S. Murtazin, R.T. Khodyachikh, A.F. 2017-01-08T14:37:00Z 2017-01-08T14:37:00Z 2011 On ¹²C(γ, n)¹¹B reaction mechanism in the intermediate energy range / E.S. Gorbenko, R.T. Murtazin, A.F. Khodyachikh // Вопросы атомной науки и техники. — 2011. — № 3. — С. 31-34. — Бібліогр.: 9 назв. — англ. 1562-6016 PACS: 25.20.Dc; 25.20-x https://nasplib.isofts.kiev.ua/handle/123456789/111130 The experimental research results for two reactions of photodisintegration of a carbon nucleus which proceed with the knocking out the nucleons from different shells are considered. The total cross-section dependence with respect to energy and dependence of expansion coefficients of the nucleon angle distributions by trigonometric functions on energy are compared. Both reactions have dependence non-regularities within the 34...44 MeV energy interval, it can be explained as a change of mechanism the nucleus absorbs a photon. It is shown that a joining of the quasideuteron mechanism has a identical energy threshold if nucleons are detached from the different shells of a carbon nucleus. Обговорюються результати експериментального дослідження двох реакцій фоторозщеплення ядра вуглецю, що йдуть з відокремленням нуклонів з різних оболонок. Порівнюються залежності повних перерізів та коефіцієнтів розкладання кутових розподілів нуклонів за тригонометричними функціями від енергії. В обох реакціях виявлено нерегулярності в залежностях при енергіях в інтервалі від 34 до 44 МеВ, які пояснено зміною механізму поглинання фотона ядром. Знайдено, що включення квазидейтронного механізму має однаковий енергетичний поріг при відділенні нуклонів з різних оболонок ядра вуглецю. Обсуждаются результаты экспериментального исследования двух реакций фоторасщепления ядра углерода, идущих с отделением нуклонов из разных оболочек. Сравниваются зависимости полных сечений и коэффициентов разложения угловых распределений нуклонов по тригонометрическим функциям от энергии. В обеих реакциях обнаружены нерегулярности в зависимостях при энергиях в интервале от 34 до 44 МэВ, которые объяснены изменением механизма поглощения фотона ядром. Найдено, что включение квазидейтронного механизма имеет одинаковый энергетический порог при отделении нуклонов из разных оболочек ядра углерода. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Ядерная физика и элементарные частицы On ¹²C(γ, n)¹¹B reaction mechanism in the intermediate energy range Про механiзм реакцiй ¹²C(γ, n)¹¹B у промiжнiй областi енергiй О механизме реакций ¹²C(γ, n)¹¹B в промежуточной области энергий Article published earlier |
| spellingShingle | On ¹²C(γ, n)¹¹B reaction mechanism in the intermediate energy range Gorbenko, E.S. Murtazin, R.T. Khodyachikh, A.F. Ядерная физика и элементарные частицы |
| title | On ¹²C(γ, n)¹¹B reaction mechanism in the intermediate energy range |
| title_alt | Про механiзм реакцiй ¹²C(γ, n)¹¹B у промiжнiй областi енергiй О механизме реакций ¹²C(γ, n)¹¹B в промежуточной области энергий |
| title_full | On ¹²C(γ, n)¹¹B reaction mechanism in the intermediate energy range |
| title_fullStr | On ¹²C(γ, n)¹¹B reaction mechanism in the intermediate energy range |
| title_full_unstemmed | On ¹²C(γ, n)¹¹B reaction mechanism in the intermediate energy range |
| title_short | On ¹²C(γ, n)¹¹B reaction mechanism in the intermediate energy range |
| title_sort | on ¹²c(γ, n)¹¹b reaction mechanism in the intermediate energy range |
| topic | Ядерная физика и элементарные частицы |
| topic_facet | Ядерная физика и элементарные частицы |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/111130 |
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