Multiparticle photonuclear reactions on p-shell nuclei in the intermediate energy interval
Photonuclear reactions on ¹²C and ¹⁶O with one or two nucleons in the final state have been investigated by the method of diffusion chamber in a magnetic field. The experimental results are discussed in the framework of the model of photon absorption by a nucleon pair.
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| Published in: | Вопросы атомной науки и техники |
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| Date: | 2001 |
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| Format: | Article |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2001
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| Cite this: | Multiparticle photonuclear reactions on p-shell nuclei in the intermediate energy interval / A.F. Khodyachikh // Вопросы атомной науки и техники. — 2001. — № 1. — С. 13-14. — Бібліогр.: 7 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860193911747641344 |
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| author | Khodyachikh, A.F. |
| author_facet | Khodyachikh, A.F. |
| citation_txt | Multiparticle photonuclear reactions on p-shell nuclei in the intermediate energy interval / A.F. Khodyachikh // Вопросы атомной науки и техники. — 2001. — № 1. — С. 13-14. — Бібліогр.: 7 назв. — англ. |
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| container_title | Вопросы атомной науки и техники |
| description | Photonuclear reactions on ¹²C and ¹⁶O with one or two nucleons in the final state have been investigated by the method of diffusion chamber in a magnetic field. The experimental results are discussed in the framework of the model of photon absorption by a nucleon pair.
|
| first_indexed | 2025-12-07T18:07:50Z |
| format | Article |
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MULTIPARTICLE PHOTONUCLEAR REACTIONS ON P-SHELL NU-
CLEI IN THE INTERMEDIATE ENERGY INTERVAL
A.F. Khodyachikh
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
Photonuclear reactions on 12C and 16O with one or two nucleons in the final state have been investigated by the
method of diffusion chamber in a magnetic field. The experimental results are discussed in the framework of the
model of photon absorption by a nucleon pair.
PACS: 13.75 Gx.
The mechanism of (γ,np)- and (γ,N)-reactions has
been a subject of research interest for many years. At
energy above the giant resonance the photonuclear reac-
tions represent an effective instrument for the intranu-
clear correlation investigations. A study of the photon
absorption mechanism by the correlated np pair offers a
possibility to look into the problem of nucleonic interac-
tions at small and medium distances. The phenomeno-
logical quasideuteron model has successfully explained
(γ,np)- and (γ,N)-reactions at intermediate energies. By
this model single-nucleon emission arises when either
the proton or the neutron escapes, the other participating
nucleon being reabsorbed into the nucleus through final-
state interactions. One important result that confirms
this point of view is the observation of the ratio R=σ(γ
,no)/σ(γ,po) equal to 1 for light self-conjugate nuclei. Re-
cently, the model has got a further development in new
microscopic approaches. An agreement with experimen-
tal results was achieved taking into account meson ex-
change currents and collective nucleus characteristics in
the framework of shell model. Experimental results
about of a highly excited final nuclear state formation in
(γ,np)-and (γ,N)-reactions are needed to verify the pre-
diction of the model.
The experiment was performed by the method of
diffusion chamber in the magnetic field of strength
1.5 T. The chamber, filled with a mixture of methane
(13%) and helium, was exposed to a beam of
bremsstrahlung photons with an endpoint energy of
150 MeV. Owing to the gas filling, the tracks of slow
residual nuclei had measurable lengths, and their images
on a photographic film were sufficiently clear at pres-
sures close to atmospheric one. Low density of the
chamber medium and the magnetic field made it possi-
ble to measure the kinematics parameters of all charged
particles and derive information about highly excited fi-
nal nuclear states that decay through hadrons. A large
angular acceptance permits one to measure angular dis-
tributions of multiparticle photonuclear reaction prod-
ucts in a broad energy range. The energy dependence of
the angular distribution asymmetry for multiparticle re-
action products was chosen for investigating the interac-
tion mechanism at energies above the giant resonance.
The (γ,np)- reaction cross sections on 12C, 16O and
14N nuclei were measured at energies from threshold up
to 150 MeV [1,2]. The asymmetry of angular distribu-
ions with respect to a right angle was defined in a mod-
el-independent way:
β=[∫0
π/2(dσ/dΩ)dθ - ∫π/2
π(dσ/dΩ)dθ]/∫0
π(dσ/dΩ)dθ. (1)
Fig. 1 displays the asymmetries of the angular distribu-
tions of protons and neutrons [2] as functions of energy
in the intervals 30-40, 40-55, 55-75, 75-100, and 100-
150 MeV. With energy increasing, the asymmetry be-
comes more pronounced. Within errors, it takes the
same value both for particles from the different reac-
tions and for nucleons from the same reaction. This re-
sult can be expected within the model of photon absorp-
tion by the np pair. The full curve represents the asymme-
try calculated for A(γ,np)(A-2) kinematics within the
quasideutron model. This result satisfactorily reproduces ex-
perimental data at energies above 40 MeV.
40 80 120
-0.1
0.0
0.1
0.2
0.3
-neutrons from 12С,
-protons from 12С
-neutrons from 16О,
-protons from 16О
β N
Eγ, MeV
Fig. 1. Nucleon angular distribution asymmetry βN
as a function of photon energy
In the model of photon absorption by a nucleon pair,
the residual nucleus is a spectator. Therefore, it is natu-
ral to expect that its angular distribution will be isotrop-
ic in the laboratory frame. The asymmetry of the angu-
lar distributions of residual nuclei in the laboratory
frame is shown in Fig.2 as a function of energy [2]. This
asymmetry is nonzero over the entire energy interval
and, within errors, takes the same value for the two re-
actions. At the energies excess of 40 MeV the asymme-
try changes weakly with increasing energy. In region of
intermediate energies, there are FSI-induced distortions
in the A(γ,np)(A-2) reaction. In the quasideutron model,
the asymmetry of the angular distribution of residual nu-
cleus can be due to FSI: nucleons traveling predomi-
nantly in the forward direction transfer a part of their
momentum to a residual nucleus. The calculation within
the quasideuteron model that takes into account FSI in
the simplest form (see the curve in Fig. 2) satisfactorily
describes the experimental data.
Five multiparticle reactions were investigated in the
energy interval from their threshold up to 150 MeV:
1. a) γ+12C→p+11B0, b) γ+12C→p+11B*
→
11B0+γ′,
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2001, № 1.
Series: Nuclear Physics Investigations (37), p. 13-14.
13
2. a) γ+16O→p+15N0, b) γ+16O→p+15N*
→
15N0+γ′,
3. γ+12C→p+11B*
→α+7Li,
4. γ+12C→n+11C*
→α+7Be,
5. γ+12C→p+11B*
→t+α+α.
50 100 150
0.00
0.25
0.50
β r
Eγ , MeV
Fig. 2. Asymmetry βr ( l.s.) vs energy. Experimental
data are represented b y the histogram and
points for the reactions 12C(γ,pn)10B and 16O(γ,pn)14N,
respectively. The curve is explained in the text
It has been found that multiparticle reactions go
through a two-particle stage. Energy characteristics of
intermediate excited nuclear states were specified. The
excited states formed in reactions (3)-(5) have broad
maxima. The first two reactions were analyzed without
separation into channels.
Fig. 3 shows the asymmetry coefficient of the nucle-
on angular distribution as a function of energy. With en-
ergy increasing, the asymmetry coefficient also quickly
grows. Within errors, it takes the same value both for
protons and neutrons.
40 80 120
-0.2
0.0
0.2
0.4
0.6
0.8
3
2 1
notations of reactions
1-(1), -(2), -(3), -(4)
β N
Eγ , MeV
Fig. 3. Asymmetry βN vs energy in the laboratory
frame, curves are explained in the text
This result can be expected within the model of pho-
ton absorption by an np pair. Curve 2 represents the
asymmetry calculated within the quasideuteron model.
Curve 3 shows the asymmetry obtained for free-
deuteron photodisintegration.
Fig. 4 displays the asymmetry of the nucleon angu-
lar distributions as a function of intermediate nuclear
excitation energy when the γ-quanta energy equals
80 MeV [4]. The asymmetry of angular distributions of
nucleon photoproduction when the intermediate nucleus
remained in the ground or low excited state were de-
rived from literary data by substituting the experimental
data [5-6] into (1). All the data manifest the dependence
of the asymmetry coefficients on the excitation energy
of the intermediate nucleus. The curve shows the asym-
metry calculated within the quasideuteron model.
0 10 20
0.0
0.5
1.0
reactions: -- (1)[5], -- (2)[6],
-- (3), --(4), --(1),
--(2), --(5), --[7]β N
Ex, MeV
Fig. 4. Asymmetry βN as a function of intermediate
nuclear excitation energy
Recently, a considerable progress in description of
the data has been achieved by incorporating the effects
of meson-exchange currents and the coupling of the
initial and final states in to the giant resonance [7]. The
diamonds and the doted curve represent the asymmetry
obtained by substituting the calculated angular
distribution in the 12C(γ,p)11B reaction from [7] for Ex =
0.0, 7.0 and 13 MeV into (1). The (γ,p) process is
dominated by pion exchange currents if Ex=13 MeV.
The ground-state data are better described by the
random phase approximation (RPA) model that includes
multistep processes and meson exchange currents [7].
There is an agreement with the experimental data.
The experimental results are in agreement with the
model of the γ-quantum absorption by the nucleon pair.
REFERENCES
1. A.F. Khodyachikh, I.V. Dogyust. The A(γ,pn)(A−2) re-
action on p-shell nuclei. // Ukraine Jour. Phys. 1995,
v. 40, p. 775-787 (in Russian).
2. I.V. Dogyust, A.F. Khodyachikh, V.P. Yarkov. 14N(γ
,pn)12C reaction up to meson production threshold //
Yadern. Fiz. 1995, v. 58, p. 773-778 (in Russian).
3. A.F. Khodyachikh. Asymmetry of the angular dis-
tributions of photoproducts of the A(γ,pn)(A-2) reac-
tions on 12C and 16O nuclei at energies up to 150
MeV // Yadern. Fiz. 1999, v. 62, p. 1355-1358 (in
Russian).
4. A.F.Khodyachikh. The angular distribution asym-
metry in A(γ,N)(A-1) reaction on p-shell nuclei //
VANT. 1999, v. 1, p. 14-15 (in Russian).
5. D.I.S. Findlay, R.O. Owens. The 16O(γ,p0) reaction
at intermediate photon energies // Nucl. Phys. 1977,
v. A229, p. 385-393.
6. J.L. Matthews et al. High energy photoprotons from
light nuclei // Nucl. Phys. 1976, v. 267, p. 51-76.
7. P.D. Harty, J.c. NcGeorge et al. 12C(γ,p)11B cross
section from 80 to 157 MeV // Phys. Rev. 1995,
v. C51, p. 1982-1990.
14
MULTIPARTICLE PHOTONUCLEAR REACTIONS ON P-SHELL NUCLEI IN THE INTERMEDIATE ENERGY INTERVAL
A.F. Khodyachikh
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
|
| id | nasplib_isofts_kiev_ua-123456789-78437 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T18:07:50Z |
| publishDate | 2001 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Khodyachikh, A.F. 2015-03-17T11:10:12Z 2015-03-17T11:10:12Z 2001 Multiparticle photonuclear reactions on p-shell nuclei in the intermediate energy interval / A.F. Khodyachikh // Вопросы атомной науки и техники. — 2001. — № 1. — С. 13-14. — Бібліогр.: 7 назв. — англ. 1562-6016 PACS: 13.75 Gx. https://nasplib.isofts.kiev.ua/handle/123456789/78437 Photonuclear reactions on ¹²C and ¹⁶O with one or two nucleons in the final state have been investigated by the method of diffusion chamber in a magnetic field. The experimental results are discussed in the framework of the model of photon absorption by a nucleon pair. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники IHEPNF NSC KIPT in the last decade Multiparticle photonuclear reactions on p-shell nuclei in the intermediate energy interval Mногочастичные фотоядерные реакции на ядрах р-оболочки в области промежуточных энергий Article published earlier |
| spellingShingle | Multiparticle photonuclear reactions on p-shell nuclei in the intermediate energy interval Khodyachikh, A.F. IHEPNF NSC KIPT in the last decade |
| title | Multiparticle photonuclear reactions on p-shell nuclei in the intermediate energy interval |
| title_alt | Mногочастичные фотоядерные реакции на ядрах р-оболочки в области промежуточных энергий |
| title_full | Multiparticle photonuclear reactions on p-shell nuclei in the intermediate energy interval |
| title_fullStr | Multiparticle photonuclear reactions on p-shell nuclei in the intermediate energy interval |
| title_full_unstemmed | Multiparticle photonuclear reactions on p-shell nuclei in the intermediate energy interval |
| title_short | Multiparticle photonuclear reactions on p-shell nuclei in the intermediate energy interval |
| title_sort | multiparticle photonuclear reactions on p-shell nuclei in the intermediate energy interval |
| topic | IHEPNF NSC KIPT in the last decade |
| topic_facet | IHEPNF NSC KIPT in the last decade |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/78437 |
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