Main results on nuclear physics obtained at IHEPNF NSC KIPT during the last decade
The main experimental results on nuclear physics obtained at INEPT KIPT during the last decade have been observed.
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| Date: | 2001 |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2001
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| Cite this: | Main results on nuclear physics obtained at IHEPNF NSC KIPT during the last decade / A.Yu. Buki, A.N. Vodin, A.S. Kachan. V.V. Kirichenko, B.A. Nemashkalo, E.A. Skakun, R.P. Slabospitsky, V.M. Khvastunov, I.V. Dogyust // Вопросы атомной науки и техники. — 2001. — № 1. — С. 15-25. — Бібліогр.: 84 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1859989841055318016 |
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| author | Buki, A.Yu. Vodin, A.N. Kachan, A.S. Kirichenko, V.V. Nemashkalo, B.A. Skakun, E.A. Slabospitsky, R.P. Khvastunov, V.M. Dogyust, I.V. |
| author_facet | Buki, A.Yu. Vodin, A.N. Kachan, A.S. Kirichenko, V.V. Nemashkalo, B.A. Skakun, E.A. Slabospitsky, R.P. Khvastunov, V.M. Dogyust, I.V. |
| citation_txt | Main results on nuclear physics obtained at IHEPNF NSC KIPT during the last decade / A.Yu. Buki, A.N. Vodin, A.S. Kachan. V.V. Kirichenko, B.A. Nemashkalo, E.A. Skakun, R.P. Slabospitsky, V.M. Khvastunov, I.V. Dogyust // Вопросы атомной науки и техники. — 2001. — № 1. — С. 15-25. — Бібліогр.: 84 назв. — англ. |
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| container_title | Вопросы атомной науки и техники |
| description | The main experimental results on nuclear physics obtained at INEPT KIPT during the last decade have been observed.
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| first_indexed | 2025-12-07T16:31:22Z |
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MAIN RESULTS ON NUCLEAR PHYSICS OBTAINED AT IHEPNF
NSC KIPT DURING THE LAST DECADE
A.Yu. Buki, A.N. Vodin, A.S. Kachan, V.V. Kirichenko, B.A. Nemashkalo, E.A. Skakun,
R.P. Slabospitsky, V.M. Khvastunov, I.V. Dogyust
National Science Center “Kharkov Institute of Physics and Technology, Kharkov, Ukraine
The main experimental results on nuclear physics obtained at INEPT KIPT during the last decade have been ob-
served.
PACS: 25.85.Ig; 27.90.+b, 25.30.Fj, 27.10.+h.
INTRODUCTION
One of the primary sources of information on properties
of atomic nuclei are nuclear reactions with different
bombarding particles. These reactions allow one to
study spectroscopic characteristics of some nuclear lev-
els (spins, parity, matrix element of radiative transitions
etc.) and statistical properties of levels at higher excita-
tion energies as well as other regularities of nuclear
structure. It is obvious, that when using different bom-
barding particles, from all the diversity of nuclear prop-
erties the most distinguishing are only certain of them.
Therefore, using in the study of nuclei a wide set of par-
ticles (from gamma-quanta to heavy ions) one can ob-
tain a more complete image of atomic nuclear structure.
Proceeding from this at NSC KIPT the research on nu-
clear physics was conducted traditionally on beams of
electrons, gamma-quantum, protons and more heavy
ions. So, it was possible to study the structures of nuclei
from hydrogen to uranium. The results of investigations
of earlier years were published in different journals,
monographies, reviews, e.g. [1-3] and reported at many
conferences.
The investigations performed during last 8-10 years are,
in main, a continuation of earlier developed basic lines.
They are directed to obtaining a more detailed and accu-
rate information and to more thorough analysis of this
information. For example, the studies on interactions
between polarized gamma-quanta and nuclei 12С have
shown that from all the possible mechanisms the main
one is the mechanism of quasi-linear interaction be-
tween gamma-qunta and an alpha-cluster of the nucleus
12С when the residual nucleus 8Ве is formed in excited
states. The studies on photofission of 232Тh nuclei on
beams of polarized gamma-quanta have shown that at
low photon energies the fission process is determined by
the dipole excitation. When investigating the resonance-
like structures observed in reactions of radioactive cap-
ture of protons by nuclei it is shown that due to triplet
pairing existing between an odd neutron and a proton
being on one and the same orbit, there is an appreciable
displacement of the centre of gravity in the magnetic
dipole resonance for even-even and odd-odd nuclei.
When studying the gamma-decay of isobaric-analogue
states in light nuclei it was shown that M1-transitions
from the analogue to antianalogue states are significant-
ly slowed as compared to the one-particle estimation.
Application of the method of averaged resonances in re-
actions of radiation proton capture has made it possible
to establich that the radiation force function in nuclei of
the pf-shell is determined by the spread width of E1-res-
onance with taking into account the temperature of a nu-
cleus in a final state. The study of heavy ion-atomic nu-
clear interactions allowed one to obtain new information
on mechanisms of complete and uncomplete nuclear fu-
sion of an incident particle with a target nucleus.
Below the main results obtained at IPHENP during last
8-10 years of activity are given in the text in the follow-
ing sections.
Σ-ASSYMETRY IN THE REACTION 12С(γ,α8Вe)
Now one accumulated a great volume of experimen-
tal studies on mechanisms of reactions of nuclei 12С and
16О photofission with α-particle yield [4-7]
γ+12С→3α, (1)
γ+16О→4α. (2)
The interest shown for these reactions was condi-
tioned by some causes related with examination of the
alpha-cluster nuclear structure and suppositions on the
quasi-alpha-particle interaction mechanism. In many ex-
perimental works it is shown that the mechanism of
these reactions, as a rule, is determined by two-particle
channels of photofission of nuclei 12С and 16О:
γ+12С→α+8Ве*, (3)
γ+16О→α+12С*, (4)
In this case the residual nucleus 8Ве in reaction (3) is
formed in exited state with a complete moment and a
parity Jπ=2+. However, the experimental results do not
exclude a probability of forming the residual nucleus
8Ве in a ground state with Jπ=0+. Besides, as is shown in
[8], realization of the residual nucleus 8Ве in an exited
state with Jπ=4+ is possible if one takes into account the
classical cluster structure of nucleus 12С, i.e. the distinc-
tion in the oscillator function parameters describing the
state of nucleon associations. The experimental data, we
have obtained earlier on 8Ве excitation energy in reac-
tion (3) do not exclude a possibility of forming this nu-
cleus in a state with Jπ=4+[9]. Our preliminary data on
the Σ-asymmetry show that this value is significantly
less than unity [10].
This paper is aimed to the experimental study on dis-
tributions over all possible kinematic variables for α-
particles in final state of reactions (1) and (2), as well as
on the energy dependence of the Σ-asymmetry of the
yield in reaction (2) on the beams of bremsstrahlung and
linearly polarized γ-quanta from the linear electron ac-
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2001, № 1.
Series: Nuclear Physics Investigations (37), p. 15-25.
15
celerator LUE-2000. The experiment on the study of re-
actions (1) and (2) has been carried out in two stages. In
the 1st stage we used photoemulsions of BYa-2 type irra-
diated with a beam of γ-quanta of a 300 MeV maximum
energy from LUE-2000. In the 2nd stage we used a beam
of linearly polarized γ-quanta obtained from LUE-2000.
The overall estimation of a maximally possible total
contribution from background reactions has shown that
it does not exceed 15 %. The results of the experiment
are shown in Fig. 1.
Fig. 1. Σ-assymetry in the reaction12С(γ,α8Ве)
As is seen from the figure at low-energy γ-quanta
the Σ-assymetry value is considerably less than unity
that indicates on the formation of a residual nucleus 8Ве
in excited states. So, the results obtained evidence that
the main mechanism of the reaction under study is the
mechanism of quasi-linear interaction of γ-quanta with a
alpha-cluster of 12С when the residual nucleus 8Ве is
formed in excited states. This conclusion confirms the
result we have obtained earlier for the model-indepen-
dent analysis of angular α-particle distributions in this
reaction. The results have shown also that the residual
nucleus 8Ве is formed in excited states with a complete
moment and parity Jπ = 2+.4+ [11].
NUCLEAR RESPONSE FUNCTION MOMENTS
Response functions (RF) are the extending of the
form-factor notion for all the energies ω transferred to a
nucleus. These functions express the response of a nu-
cleus to the effect of a polarized virtual photon on it.
Transversal RT(q,ω) and longitudinal RL(q,ω) RF corre-
spond to transversally and longitudinally polarized vir-
tual photon.
Response function moments (RFM) are particular
important for comparison of the theory with the experi-
mental data. Because the calculations using the least
model approach, which are the sum rules (SR), describe
RF only in the moments representation. The relation of
RF with a twice differential cross-section d2σ and kth
moment of RF ST/L
(k)(q) is described as:
d2σ ≅ σM (G(q2))2 {RL(q,ω)+[0.5+tg(θ/2)]RT(q,ω)}, (5)
where σM is the Mott cross-section, G(q) is the proton
electric form-factor, θ is the electron scattering angle, q
is the 3−momentum transferred to the nucleus;
∫
∞
=
0
k dωωω),()( T/L
(k)
T/L qRqS . (6)
The experiments on measuring RF are very com-
plex. Therefore, there are only a small number of nuclei
(about 11) for which modern R-data are obtained.
With undoubted usefulness of these data they pos-
sess also some shortcomings:
a number of problems can be solved experimentally
only for q<1.5 fm-1 while all the rest measurements, ex-
cluding 3H, 3He and 12С cases, were conducted for q≥
1.5 fm-1. With this q, the electroproduction contribution
into the RT-function excludes possibility to determine
ST-moments;
an accuracy of measurements with high ω restricts
the number of determined SL-moments by the value k=0.
To extend the investigations into the range of q∼
1 fm-1 we have carried out the measurements on 2H, 4He,
6Li and 7Li nuclei 1/ at the accelerator LUE-300. By now
the measurement data processing has given the values
ST
(0)(4He) [13] and ratio ST
(0)(7Li) / ST
(0)(6Li) [14], and
ST
(k)(2H), SL
(k)(2H) for k = −1, 0, 1 [15]. Analysis of these
data leads to the following conclusions.
Comparison of SR for 4He [16] with obtained
ST
(0)(4He) at q = 0.75-1.5 fm-1 has shown that the contri-
bution of meson exchange currents into ST
(0) is (4±7)%
(i.e. does not exceed 11%), whereas the similar investi-
gation [17] at q=1.5 − 2.5 fm-1 estimated this contribu-
tion as 15...20%.
The measurement of the ratio ST
(0)(7Li) / ST
(0)(6Li)
within accuracy of 2% allow to reveal for the first time
a difference in correlation functions of isotopes. The
question on a maximum number for finitely valued
RFM concerns to the main problems of SR [18]. Our in-
vestigation of the asymptotic for ω of experimental RF
of nucleus 2H [19] resulted in a maximum k=1. The ob-
tained parameters of RF extrapolation function decrease
the known uncertainty in experimental RFM that has a
special importance for the moments with k=1. Accord-
ing to [18], all these results of 2H RF research are relat-
ed to RF of other nuclei too. The moment with k=1 de-
pends on nucleon-nucleon forces inside the nucleus and
therefore it is interesting to compare the calculations of
this moment with experimental data. Our SL
(1)-data on
2H [15], [20] permitted to extract [21] and [22] from
some theoretical works as not being in contradiction
with the experimental ones. Here let us note, that the
calculation of the SL
(0) -moment of 2H [22] deviates by
three standard errors from the experimental value of
[15].
In our investigations of the Coulomb nuclear energy
[23,24] we used the equality
SL
(0)(q) = Z (G(q2))2, at q>2 Фm-1 . (7)
Such notion about the SL
(0)-moment was corre-
sponding to the accuracy of measurements before 80th
years. The further experiments (see [25]) have shown
the lower values of SL
(0)(q) and thus the disturbance of
1/ For measurements on 2H and 4He we have con-
structed gas targets GM-1 and GM-2 exceeding the for-
eign analogs [12] by some basic characteristics.
16
equality (7) (MIT-effect). Though these new SL
(0)-data
have changed very slightly the numerical results of
[23,24], nevertheless they required to reconsider our no-
tions about the structure of a nucleus and, in particular,
about its Coulomb energy. The most convincing expla-
nation of the MIT-effect is an idea about modification
on nuclear nucleons (see, for example, [18]) as a result
of which their radius increases, and the square of a nu-
clear proton form-factor satisfies equality (7). Note, that
according to this approach the radius and respectively,
the form-factor of a modified proton should be depen-
dent on the properties of a nucleus in which it is located.
A search for the relation between experimental values of
SL
(0)-moments and charge-and- matter density distribu-
tions in nuclei has led us to the hypothesis about a step-
wise modifications of a part of nuclear nucleons [26].
According to this hypothesis the nucleon modification
occurs when the density of the matter surrounding ex-
ceeds 0.142±0.005 Fm-3 and the properties of the modi-
fied nucleon are similar in all the nuclei. Thus, the mod-
ified nucleons take place only in the central region of
nuclei and their relative number depends on the atomic
number of this nucleus. The hypothesis under considera-
tion puts in correspondence all the known SL
(0)-data and
leads to some conclusions, among them: affirmation
about the significant increasing of the proton radius by
modification (~40%); about possibility to investigate the
charge distribution in the modified proton by measure-
ments the dependence of the moment SL
(0) on q on heavy
nuclei.
Basing on calculations of the hypothesis proposed
we have found the expression for the contribution of
proton modification into the Coulomb nuclear energy
according to which this contribution is from 0.04 MeV
for 4He to 9 MeV for 208Pb [27].
Σ-ASYMMETRY AND CROSS_SECTION
IN (1-,0)-, (1-,1) - CHANNELS OF 232Th
PHOTOFISSION
Investigations of angular distributions of fission
fragments give important information on the properties
of barriers of heavy nuclear fission and on quantum
numbers of low-lying excited states.
At low photon energies the fission is determined
mainly by the electric dipole (E1) and significantly
weaker quadrupole (E2) excitation. The fragment angu-
lar distributions are described by the formula
W(θ) = a + b sin2θ + c sin2 2θ. (8)
The coefficients a,b,c are determined by the contribu-
tions of 5 fission channels with quantum numbers (Jπ
,K)=(1−, 0), (1−,1), (2+,0), (2+,1), (2+,2), where J,π are the
spin and the parity of excited state, К is the projection J
into the nuclear symmetry axis. Since from the fitting of
equation (8) one obtains three values of a,b,c, then for
the analysis one uses three fission channels (1−,0), (1−
,1), (2+,0), neglecting the contributions of (2+,1), (2+,2)
channels. At present for nuclear photo fission the linear-
ly polarized photons are coming into use [29,30]. In
these experiments for 232Th nucleus one obtained a new
independent value i.e. the Σ−asymmetry characterizing
the analyzing power of a photonuclear reaction. The Σ−
asymmetry can not be expressed in terms of the coeffi-
cients a,b,c and via the cross-sections of three fission
channels [29,31]. At the angle θ=π/2 the expression of
the Σ- asymmetry has a simple form:
Σ(π/2) = b/( a + b ), (9)
Σ(π/2)=[2σ(1−,0)-σ(1−,1)]/[2σ(1−,0)+σ(1−,1)]. (10)
In this case the coefficient с and the cross-section σ
(2+,0) do not influence on the Σ-asymmetry [29,32]. Us-
ing expression (9) we have obtained the values of Σ-
asymmetry for 232Th nucleus from the experimental val-
ues of the coefficients a, b and their ratio b/a in the ener-
gy range up to 20 MeV. For the photon energy up to Еγ
=10 MeV we processed the data of [33], and for Еγ>
10 MeV-the results of all the photonuclear experiments.
All these experiments were carried out with the
bremsstrahlung photon spectra. The Σ−asymmetry val-
ues obtained are shown in Fig. 2. It is seen that the value
of Σ−asymmetry is close to unity at 5.65 MeV and de-
creases smoothly with energy increasing up to 20 MeV.
Despite of the fact that the data obtained with different
spectrum forms of photons (bremsstrahlung photons,
virtual photons on the electron and positron beams, co-
herent part of photon spectrum when channeling the
electrons in the silicon crystal) they are in good agree-
ment between themselves. Such a agreement indicates
that in the 232Th nucleus for the Σ−asymmetry the dipole
approximation is good fulfilled and the contributions of
(2+,1)-and (2+,2) channels of quadrupole fission do not
reveal within accuracy of experimental errors.
4 6 8 10 12 14 16 18 20 22
Eγ , МэВ
-1,0
-0,8
-0,6
-0,4
-0,2
0,0
0,2
0,4
0,6
0,8
1,0
(Jπ =1-, k=1)
(Jπ =1-, k=0)
Σ(
Θ
=9
0o )
Fig. 2. Σ−asymmetry of 232Th fission is obtained in
the present paper from the data of different works:-
[33], black triangle − [34], Ο − [35], − [36], −
[37]-bremsstrahlung photons, ◊-electrons, virtual pho-
tons [38], •-positrons, virtual photons [38], ð -
bremsstrahlung polarized photons [29], ×-polarized
photons in the process of electron channeling in the sili-
con crystal [30]
Equation (10) shows that for (1-,0)-channel the Σ-
asymmetry equals to (+1), and for the (1-,1)-channel it
equals to (-1). The lines in Fig. 2 are indicating these
values. The obtained values of the Σ-asymmetry are
positive, i.e. generally they are determined by the (1-,0)
fission channel. Up to the energy 6.5 MeV only the (1-
,0) channel reveals (Σ-asymmetry equals to +1), and
above 6.5 MeV the contribution of the (1-,1) channel de-
creasing the significance of Σ-asymmetry becomes ap-
parent. From this it follows that the energy of 6.5 MeV
is a threshold of 232Th photofission reaction through the
(1-,1) channel.
17
a)
6 8 10 12 14 16 18 20
0
5
10
15
20
25
30
35
40
45
50
σ1-
,0γ,f
мb
Eγ, МeV
b)
6 8 10 12 14 16 18 20
0
5
10
15
20
25
30
35
40
45
50
σ1-
,1γ,fмб
Eγ, МeV
Fig. 3. Fission cross-sections σ γ ,
,
f
1 0−
(a) and σ γ ,
,
f
1 1−
(b) of 232Th nuclei by bremsstrahlung photons are ob-
tained in the present paper from the data of some
works: ·−[33], black triangle−[34], ο−[35], ∇−[36], ∆
−[370]
The energetic behavior of fission cross-sections for
three main channels can be obtained by analyzing the
angular distributions of fission fragments. The coeffi-
cients a,b,c are related with the cross-sections σ(Jπ,К)
by the following way [29]:
a=3σ(1-,1)/2,
b=3σ(1-,0)/4-3σ(1-,1)/4, (11)
c=15σ(2+,0)/16.
Using these equations and experimental data for the
coefficients a,b,c [33-37], we have obtained the cross
sections σ(Jπ,К) for three fission channels. The cross
section σ(2+,0) was obtained for the energies up to
10 MeV and it was much less then dipole cross sections.
There is not data for the coefficient с above 10 MeV.
The cross sections in the dipole fission channels σ(1-,0),
σ(1-,1) are given in Fig. 3. The figure shows that the
both dipole cross sections give the peaks at 14 MeV.
Such peak position is in agreement with the data on
electron scattering [39]. An essential distinction is ob-
served near the fission threshold where the cross section
σ(1-,0) has a sharply standing out peak at the energy of
6.5 MeV. The information on the cross section σ(Jπ,К)
is available only for 238U and it has been obtained in the
experiment with target photons [40] from the fission
threshold up to 8.9 MeV. Our data for the nuclei 232Th
are qualitatively coincident with the data of [40] and can
be used for checking different theoretical models.
M1- RESONANCE IN ODD NUCLEI OF
THE SD-SHELL
When studying [41,42] the γ-decay in resonance-like
structures observed in the reaction of radiation proton
capture by the nuclei 21Ne, 25Mg, 29Si, 34S, we revealed a
new phenomenon related to the existence of triplet pair-
ing between an odd neutron and a proton being located
on one and the same orbit. It manifests in that the posi-
tion of the center of gravity (CG) of the magnetic dipole
resonance (MDR) for odd-odd 4N+np nuclei is situated
3 MeV below by the excitation energy than in even-
even 4N-nuclei. In the above mentioned papers one pro-
posed a model to explain this phenomenon. According
to this model the odd nuclei of the sd-shell could be di-
vided into two groups, depending on the state in which
the odd particle stays in the d5/2– or d3/2 subshell. To date
the numerous experimental spectroscopic information is
accumulated about the resonance states of the nuclei
27Al, 31P, 35Cl, 37Сl with the help of the reaction of radia-
tion proton capture by the nuclei 26Mg, 30Si, 34S, 36S, re-
spectively [43,47]. However, in the energy range where
one observes resonance-like structures (RLS) in this re-
action [48,49], the experimental information is insuffi-
cient to identify with assurance MDR. Therefore, we
conducted a series of measurements concerning the
identification and determination of the center of mass
position, the fine structure and the total MDR force in
the nuclei 27Al, 31P, 35Cl, 37Cl. The functions of excitation
of the reactions of 26Mg, 30Si, 34S, 36S(p,γ), 27Al, 31P, 35Cl,
37Cl, being necessary for determining the forces of reso-
nances (S=(2J+1)ГpГγ/Г), were measured in the range of
accelerated proton energies Еp=1.8-3 MeV for 27Al and
37Cl, Еp=1-2,7 MeV for 31Р, Еp=1,2-3 MeV for 35Cl [8,9].
The measurements were performed at the NSC KIPT
accelerator ESU-4. To measure the yield of γ-quanta
with Еγ>2,6 MeV we applied the ∅150x100 mm
NaJ(Tl) detector placed at a distance of 5 cm from the
target at an angle of 55o relatively to the proton beam di-
rection for excluding the dependence of γ-quanta on the
angle. The resonance forces were determined from the
comparison between the area under the resonance curve
and that one under the calibrating resonance. For 27Al
this is the resonance at Еp=1966 keV, for 31P-the reso-
nance at Еp=1880 keV, for 35Cl-the resonance at
Еp=1212 keV, for 37Сl-resonance at Еp=1887 keV, the
forces of which are well known [43]. As a result of mea-
surements in odd nuclei we revealed RLS similar to
those, which were observed for even nuclei we have in-
vestigated earlier [41,42]. In all the previous cases RLS
have had a complicated structure, i.e. they were com-
posed of the states belonging both to the М1-resonance
of the ground state and to the М1-resonance “construct-
ed” on the excited states. And only in a single case
(34Cl) CG of RLS was determined by the states of the
М1-resonance on the excited state. The final conclusion
18
on the nature of RLS observed can be made after deter-
mining all the quantum characteristics of resonance
states composing these RLS and after studying their γ-
decay. For this purpose we measured the spectra and an-
gular distributions of γ-quanta being formed during the
decay of the most intense resonances composing these
RLS. To measure the γ-spectra we used a Ge(Li)-detec-
tor with 60 cm3 volume and 4 keV resolution for Eγ
=1332 keV. The detector was placed at a distance of
7 cm from the target. The target was situated in the rota-
tion center at an angle 49О to the proton beam direction.
The measurements were conducted at angles 0°, 60°, 30
°, 90°, 45°. The correction taking into account the final
detector dimensions were selected from the literature
data. As a monitor we used a scintillation detector with
∅150х100 mm NaI(Tl) crystal. This detector was ap-
plied also for measurement of the excitation function.
The measurement results, as coefficients of expansion
by Legendre polynomials (аk), and results of angular
distributions of γ-quanta formed during the decay of res-
onances composing RLS under consideration are given
in [48,49]. The parity value is assigned to resonance
states basing on comparison of a probability for electro-
magnetic transitions having different multipolarity with
recommended upper limits (RUL) of the given quanti-
ties [50]. The probability of the γ0 transition B(M1) be-
ing considered was calculated from the expression
B(M1)↑=86,6b0S(eV)/((2J0+1)E3
γ0 (MeV)),
where b0 is the branching coefficient for the ground
state, J0 is the spin of the ground state, Eγ0 is the energy
of γ-transition to the ground state.
The distributions of probabilities for magnetic dipole
γ-transitions obtained allow one to conclude that reso-
nances composing RLS belong to states of the M1-reso-
nance on ground as well as on excited states of nuclei
27Al, 31P, 37Сl. MDRCG(Ecg = ΣkEkBk(M1)/ ΣkBk(M1))
on ground states of nuclei 31P, 35Cl, 37Сl (Fig. 4) is equal
to 8.5±0.3 MeV, 9.1±0.1 MeV, 10.5±0.2 MeV, respec-
tively, and is situated in the region expected for odd nu-
clei with an occupated d5/2-subshell. This experimental
fact evidences in favour of that in MDR formation in
nuclei 31P, 35Cl, 37Сl the nn( рр)-pair from the d5/2-sub-
shell takes part, therefore the position of MDR CG in
these nuclei is influenced by the value of nn (pp)-pair-
ing in this subshell.
MDR CG in nuclei 25Mg [43], 27Al equals to 5.8±
0.2 MeV and 6.1±0.2 MeV, respectively, and is situated
in the excitation energy range expected for the nuclei
with a unoccupied d5/2-subshell. The total force of MDR
(SМ1
EW= ΣkEkBk(M1)) in nuclei 31P, 35Cl, 37Сl equals to
10.2 MeV µN
2, 2.5 MeV µN
2, 12.8 MeV µN
2, respective-
ly, and is compared to that in 4N+2n and 4N+np nuclei
[42] that obviously also confirms the conclusion about
the fact that in formation of the M1-resonance in odd
nuclei with an occupied d5/2- subshell the valence nn(pp)-
pair takes part.
20 24 28 32 36 40
4
6
8
10
37 Cl
35 Cl 31 P
27 Al 25 Mg
Е c
m
,
М
eV
А
Fig. 4. Position of the center of mass of the M1-reso-
nance for odd nuclei of the sd-shell. ° − literature data
[45], − our data.
L-FORBIDDEN M1-TRANSITION WITH ∆
T=1 IN ODD NUCLEI d2s- SHELL
Over a long period of time it was supposed that the
main mode of the γ-decay of isobaric-analogous states
(AS) in light nuclei is the M1-transition onto the anti-
analogous state (AAS). However, later in a number of
precision experiment it was established that in some nu-
clei the M-1 transitions AS→ААS are much slowed
down as compared to the single-particle evaluation [51].
To explain these facts it was necessary to introduce into
the model representation a new degree of nuclear free-
dom, i.e. the states such as a core polarization. The de-
tailed calculations performed in the framework of a
shell model with surface δ-forces [52] have shown that
the absolute probability of AS γ-decay in odd nuclei
with 21≤А≤41 is divided among M1-transitions into
AAS and the states such as a core polarization. This
conclusion was sufficient to interprete the radiation
widths of AS decay well-known at that time in this
range of nuclei [53]. Meanwhile, in experiments of lat-
ter years one found the isovector γ-transitions which
have not been represented in the theoretical approach
proposed in [52]. First of all, they are l-forbidden transi-
tions like Т>=Т0+1/2→T<=Т0-1/2. There was not system-
atic calculations explaining the mechanism of l- forbid-
ding removing even in a simple model and, probably,
namely in virtue of the imaginary theoretical unfound-
edness, one did not give a proper consideration to them.
Proceeding from the foregoing, in this paper one
made an attempt to establish, by the way of experimen-
tal data analysis, the empirical regularities for the l-for-
bideen M1-transitions observed during the AS decay in
odd nuclei of the 1d2s-shell. It is reasonable to expect
that there are should exist certain regularities and that
their reveal would help, at least, to systematize the
knowledge on these M-1-transitions and by this to deter-
mine the further outlooks for the study of this problem
in light nuclei. The evident interest in these γ-transitions
is caused by the fundamentality of the problem i.e. clari-
19
fying the role of charge dependence of nuclear forces in
the mechanism of isospin level mixing in nuclei.
A peculiarity of the range of nuclei under considera-
tion is the presence in it both spherical and deformed
nuclei. This fact complicates significantly the problem
of identification of pure single-particle l-forbidden M1-
transitions with ∆Т=1. In this connection it is necessary
to identify the configurations using the data on the in-
tensities of state occupations measured in reactions with
transfer of one nucleon and data from the experiences
on nucleon scattering on nuclei. As an indirect way one
can use the values of mixing by multipolarities δ
(Е2/М1). However, the experimental data about these
parameters are extremely fragmentar and this does not
allow evaluating the contribution of collective compo-
nents into the structure of isobaric-analogous resonance
states. Basing on available data it can be note that, as
one would expect, the additions of a Е2-component in l-
forbidden M1-transitions are insignificant.
Information about the total radiation decay widths of
Гγ- analogous resonances is obtained from the data on
the cross-sections of the corresponding (рγ)-, (nγ) and (γ
,γ)-reactions ([54,43] and its references). For qualitative
determining the degree of delay of l-forbidden M1-tran-
sitions as compared to single-particle estimations, we
used the factors of forbidding the standard formulation
of which has the form FM=B(M1)theor/B(M1)ýêñï. Estima-
tion of the В(М1)teor value was performed by the
Moshkovsky formulas [55]. Analysis of the accumulat-
ed experimental material makes it possible to formulate
some general conclusions.
1. It is established that l-forbidden M1-transitions
with isospin change by unity are observed over all the
range of odd nuclei 21≤А≤41. Their intensity in a num-
ber of cases is comparable by the order of magnitude
with the intensity of permitted single-particle M1-transi-
tions AS →ААS.
2. It is found that the forbidding factors FM are mini-
mum (~10) for γ-transitions being observed mainly dur-
ing decay of the analogous resonances in nuclei close to
the equilibre deformation region А∼25. The maximum
of values FM >500 is related with γ-transitions s1/2⇔d3/2
in the nuclei 35Cl, which is almost spherical. While in
the upper part of the 1d2s-shell the s1/2⇔d3/2 transitions
are characterized by a significant decrease of forbidding
factors (up to ~10), one observes the tendency of FM
growth with increasing the energy of γ-transition in one
and the same AS.
3. The l-forbidden M1-transitions in nuclei having
the neutron number close to the magic number N =20
are not identified. At the same time in nuclei with Z=20
the FM values are changing in a wide interval: FM ≈10÷
100. However, it should be noted that this conclusion is
preliminary because of the lack of data and requires fur-
ther experimental evidence.
4. A marked correlation between values of FM and
values of C2S АS spectroscopic factors was not
observed. It allows one to assume that l-forbidden М1-
transitions T>→T< occurs due to the adding of other
configurations to the initial and final states of a
radiating particle. The fact that these transitions are
observed in the immediate vicinity of occupied shells
allows us to conclude that collective effects should not
play a significant role in l-forbidding removing.
However, l-forbidding weakening in the range of nuclei
А∼25 is evidently related to the increasing role of
collective effects.
APPLICATION OF THE METHOD OF
AVERAGED RESONANCES (MAR) IN
REACTIONS OF LOW ENERGY PROTON
CAPTURE BY NUCLEI
46Ti, 60,61,62,64Ni, 56,58Fe, 68Zn, 71Ga and 72Ge
Appearance of the ARM in NSC KIPT as a research
direction in the nuclear spectroscopy is related to works
[56, 57] in which, for the first time, one proposed to use
a statistical model (SM) for analysis of the experimental
data from the proton capture reaction measured under
conditions of statistical averaging for nuclei with A>40
and Ер<5 MeV. The success of applying ARM was pro-
vided with large γ-yields of the reaction in the case of
using half-thick targets. Analyses were conducted in the
framework of SM which solved its inherent problems
using optical model (OM), fermi-gas and evaporation
models. Difficulties of using the statistical model were
connected, in main, with the choice of optical potential
parameters (being well-known for higher energies) and
lack of the data on the radiative strength functions.
The work has been carried out in four stages: devel-
oping of the analysis method for γγ-correlations, differ-
ential cross sections and angular distributions of γ-rays
arising during the decay of the final states, occupied
with non-observed cascade γ-transitions; studying the
mechanisms of capture reactions; studying the value and
energy dependence of RSF in the resonance region of
nuclear excitation energy.
The present paper was aimed to the study of the RSF
in nuclei of the pf-shell in the excitation energy range of
5-13 MeV. Now, the information on RSF for these ener-
gies (corresponding to transitions from the resonance
excitation energies region) is insufficient. The method
of RSF obtaining that we have proposed earlier is based
on data of partial cross sections (PS) of the proton cap-
ture reaction. It is a model-dependent one, but it permits
to obtain the necessary information, as we use the well-
substantiated SM and ARM, in which the realization of
conditions for nuclei of the pf-shell is easy to imple-
ment.
Creation of the coincidence spectrometer and the pair
γ-spectrometer on the base of high-effective sodium and
Ge-Li detectors makes it possible to single out the
primary γ-transitions from high-excited nuclear states and
thereby to solve the tasks to be achieved.
In this latest stage of the work we measured PS of
(p,γ) -reactions on nuclei 46Ti, 60,62,64,66 Ni, 56,58 Fe, 68Zn,
71Ga and 72Ge at proton energies of 1.0-3.2 MeV. The
cross-sections are described within the framework of
SM with a standard set of OM parameters and level den-
sity. Here RSF was considered as unknown “varying”
functions.
20
6 7 8 9 10 11
10 -9
10 -8
10 -7
3
2
1
E γ ,MeV
E γ , MeV
5 6 7 8 9 10 11
10 -9
10 -8
65 Cu
3
2
1
63 Cu
S,MeV - -3
S,MeV
МэВ
-- -3
Fig. 5. Experimental and calculation values of RSF
of primary γ-transitions in 63,65Cu:•-RSF the energy
Ер=2.84 MeV for 63Cu, о-RSF at Ер=2.30 MeV for 65Cu;
Lorenz dependence of RSF (Brink-Axel model- curve 1;
statistical approach with taking into account the
temperature (Fermi-liquid model)- curve 2; the same
with taking into account the shell nuclear structure -
curve 3
As a result of PS analysis we determined the
strength functions in nuclei 45Sc, 61,62,63,65Cu, 57,59Co, 67,69-
Ga, 71Ge, 73As [58-64], Fig. 5. It was shown that defined
RSF couldn’t be described by the Lorenz curves being
parametrized via the photoabsorption reaction cross-sec-
tions. RSF analysis was performed in the framework of
a phenomenologic approach developed in the articles by
Yu. Kadmensky, V. Sirotkin, V. Plujko [65-68]. At
present the approach is adopted as a basic method for
evaluation of data on strength functions at IAEA. Upon
this the mass dependence of RSF can be revealed only
by studying a great number of nuclei.
Analysis has shown that RSF can not be considered
as Sγ dependent only on the γ-quantum energy, and take
the form S(Eγ,Tf ), where Tf is the temperature of a nu-
cleus in the final state. The RSF relation with properties
of nuclei in the final states contradicts to the Brink hy-
pothesis. It leads to its new formulation i.e. the E1-reso-
nance can be constructed on any excited nuclear state
with taking into account its excitation energy, and RSF
in the region of binding energy will be determined by
the spread E1-resonance width with taking into account
the temperature of a nucleus in the final state. As a con-
sequence, when γ-quantum energy goes to zero, RSF
should go to the nonzero limit unlike the Lorentz depen-
dence.
Conclusions on such behaviour of RSF below the
E1-resonance are confirmed in the articles by R. Chrien
(USA), Yu.P. Popov (Dubna), V.V. Plyujko (Kiev) for
144Nd, 157Gd and others.
Being guided by the theory preconditions we can say
that the primary γ-transitions into final states of nuclei
are determined by the collective movement mode, i.e.
the E1-transitions from the resonance energy region can
be considered as giant dipole excitations. And RSF’s re-
lated with them determine the emission of heated nuclei
and depend on the temperature of nuclei in the final
states. The factor taking into account the difference be-
tween RSF in a cold nucleus and RSF in a heated nucle-
us is interpreted as a mean number of the 1p-1h excited
states in the heated system placed in the external mag-
netic field.
NUCLEAR RECTIONS WITH HEAVY IONS
The mechanisms of heavy ion-nucleus interactions
have been studied by measuring and analysis of excita-
tion functions of the reactions induced by 14N and 20Ne
in 93Nb, charge and mass distributions of products and
mean recoil ranges. Experiments were performed at the
heavy ion linear accelerator of NSC KIPT. Thin metal-
lic niobium foils with thicknesses of (0.5…4.0) mg∗cm2
were irradiated by 8.5 MeV/A heavy ion beams. The
aluminum foils-absorbers were put before the targets for
decreasing incident ion energies. Al foil-catcher was
placed behind the investigated target in close geometry
to collect the recoil nuclei. The foil stack was installed
in an insulated Faraday cup into which the ion beam
was falling. The induced activities of the irradiated tar-
gets were measured by Ge(Li)-detector of 50 cm3 vol-
ume and 3.5 keV resolution for 1332.5 keV γ-line and
with the analyzer AM-02Ф1 connected with the com-
puter PC/AT-386. The accumulated γ-spectra was treat-
ed by ACTIV-code [69]. Nuclei-products were identi-
fied by the energies, relative intensities of followed γ-
transitions and half-lives [70]. The activities of Nb-foils
and Al-catchers were measured separately for determi-
nation of escape fraction of the radioactive nuclei and
calculation of the experimental recoil ranges.
a)
b)
21
Fig. 6. Ratio of theoretical cross sections to experi-
mental ones vs residual nuclei mass number in interac-
tions 14N+ 93Nb (a) and 20Ne+93Nb (b) for different ener-
gies of incident ions
The excitation functions of 14N induced reactions re-
sulting in formation of more than 20 final nuclei in the
mass number range from the nucleus-target to the com-
pound nucleus (107Cd) were measured at the incident en-
ergies (5.0...8.5) Mev/A. Approximately the same quan-
tity of nuclei was observed in the interaction 20Ne+93Nb
(compound nucleus113Sb). The experimental cross-sec-
tions of studied reactions are in reasonable agreement
with scarce data published at some incident energies by
other authors [71,72]. To analyze the experimental exci-
tation functions of heavy ion reactions the theoretical
calculations of the cross-sections have been carried out
within the framework of statistical model of nuclear re-
actions using ALICE code [73]. The agreement between
the experimental excitation functions of the reactions
producing compound-like nuclei (close to 107Cd for the
interaction 14N+93Nb and 113Sb for the interaction
20Ne+93Nb) and theoretical ones may be considered as
satisfactory. However, as the mass number of a nucleus-
product decreases the disagreement increases and reach-
es a maximum value for the target-like residual nuclei
such as 96Tc, 95Tc, 94Tc, 93mMo, 92mNb, 90Nb (Fig. 6). It can
be caused by a significant contribution of reaction
mechanisms differing from the process of formation and
subsequent decay of the compound nucleus: quasi-elas-
tic scattering, few-nucleon transfer reactions, reactions
of incomplete fusion of the incident ion with the nucle-
us-target.
Short experimental recoil ranges of 96Tc, 95Tc and
94Tc nuclei (in comparison with the heavier nuclei such
as 100Pd, 101Pd, 100Rh, 101Rh et al.) are in agreement with
the theoretical values calculated for the process of fu-
sion of α-fragment of incident 14N ion with the target
nucleus and formation of the intermediate 97∗Tc nucleus
which evaporates 1,2 and 3 neutrons respectively.
The residual 93mMo, excitation cross-section of which
exceeds the complete fusion model prediction on 2 or-
ders of magnitude, can be formed in a similar process
after emission of a nucleon combination p3n by inter-
mediate 97*Tc. The values of 90Nb and 92mNb residual re-
coil ranges more correspond to the process of quasi-
elastic scattering. The calculations of incomplete fusion
reaction cross sections in the sum rule model [74], we
have performed, do not exhaust the high yields of iso-
topes of technetium, niobium and 93mMo. Probably more
direct processes also give a significant contribution to
the production cross-sections of the mentioned above
isotopes.
NUCLEON CORRELATIONS
IN REACTIONS OF THE A(γ,pn)(A-2)
TYPE ON NUCLEI OF THE P-SHELL
Photonuclear reactions serve as one of instruments
for investigations of nucleon correlations in nuclei,
since the energy and pulse introduced into the nucleus
with a photon at the giant resonance can be absorbed
only by the correlated nucleon pair.
In the presented paper given are the results of inves-
tigations of photo processes on the γ-quantum
bremsstrahlung beam before the meson production
threshold by the method of a diffusion chamber in the
magnetic field.
Due to the high informativity the track method is
preferable for study of the multiparticle reactions because
it permits to investigate the correlations effects without
risk of distortions caused by the choice of the experiment
geometry. At present only with this method one can mea-
sure by model-independent manner a total cross-section
of multiparticle photodisintegration.
The following reactions were studied:
γ + 12C→p + n+ 10B, (12)
γ + 12C→ p + n + α + 6Li, (13)
γ + 14N→→ p + n + 12С, (14)
γ + 16О→ p + n + 14N. (15)
Reactions (12), (14), (15) were chosen to clear up
the A-dependence of nuclear reactions. Reaction (13)
was considered as a probabilistic process with the
escape of one nucleon from the s-shell. The energy of γ-
quantum was determined basing on the conservation
law and in the supposition that the final nuclei are
formed in a ground state. The details of the method of
reaction distinguishing and obtaining the kinematic
particle parameters were described earlier [75-78].
TOTAL CROSS-SECTION
The dependence of total reaction cross-sections on
the γ-quanta energy was measured. The integral cross-
section of the reaction 12С(γ,pn)10B is equal to 25±0.8
MeV mb that does not contradict to data by other
authors [79].
The maximum of the cross-section of the reaction
12С(γ,pn)α6Li seems to be less distinctive and at higher
energies too than the cross section of reaction (12). The
integral cross-section equals to 11,8±0.8 MeV mb. The
agreement between the cross-section of 14N(γ,pn)12C
reaction and the measurement results by Komar [80] is
observed. The integral cross-section of the reaction 16О(
γ,pn)14N equals to 152.1±2.7 MeV⋅mb. The results of
calculations on cross-section of reaction (15), in the
supposition that the main contribution into the matrix
element is obtained from exchange meson currents [81],
describes satisfactorily the energy dependence of the
total cross-section. The calculation [82] performed with
taking into account the nucleon exchange by one or
several mesons displays satisfactorily the energy
22
dependence of a total cross-sections with a correlation
parameter β=0.8 fm-1. Beginning from 40 MeV the
cross-sections of reactions (12-15) have a similar energy
behavior that confirms the model of γ-absorption by the
correlated nucleon pair.
THE REGION OF THE QUASI-DEUTRON
MODEL APPLICATION
The track method is effective for investigation of the
following angular and energy correlation effects being
characteristic for the quasi-deuteron model. Nucleons
escape from the nucleus almost in opposite sides that
follows from the differential cross-sections depending
on the angle of nucleon flying away. Nucleon pairs take
away the most part of energy. The part of kinetic energy
being taken away by the pn-pair appreciably differs
from the statistical one. The residual nucleus is a
spectator, therefore the angular distributions of residual
nuclei at energies higher than 50 MeV for different
nuclei are equal and practically isotropic.
In a wide energy range the reaction cross-sections
are proportional to the cross-section of deuteron
photodisintegration. The proportionality has taking
place at energies higher than 40 MeV. So, the traditional
Levinger model describes behavior of the cross-section
at energies above the region of the giant resonance.
At energies behind the giant resonance the angular
distributions of protons and neutrons in the system of
inertion center are symmetrical relatively to 90O. The
maxima of both distributions are displaced into the front
half-sphere. The forms of angular distributions of
protons and neutrons are coinciding that was observed
in other reactions too.
PULSE DISTRIBUTION OF NUCLEON PAIRS
The pulse of pn-pair in the quasi-deuteron model
and in the absence of interaction in the final state (IFS)
should not be dependent on the photon energy since it is
the intranuclear characteristic [83]. In Fig. 7 shown are
the results of the presented experiment. The
experimental data obtained for reaction (15) are in
agreement with the results of [84].
100 200 300 400 500
0
1
2
lg
F
(P
)
P, MeV/c
Fig. 7. Pulse distribution of np-pairs of reaction (12)
The experiment has demonstrated that the position of
the maximum of pulse pn-pairs distribution and
distribution width are in a strong dependence on the γ-
quantum energy. This effect evidences on a significant
IFS influence on the form of pulse distribution curve in
the range of energies close to the giant resonance.
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25
Below the main results obtained at IPHENP during last 8-10 years of activity are given in the text in the following sections.
NUCLEAR RESPONSE FUNCTION MOMENTS
NUCLEON CORRELATIONS
PULSE DISTRIBUTION OF NUCLEON PAIRS
REFERENCES
|
| id | nasplib_isofts_kiev_ua-123456789-78438 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T16:31:22Z |
| publishDate | 2001 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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| spelling | Buki, A.Yu. Vodin, A.N. Kachan, A.S. Kirichenko, V.V. Nemashkalo, B.A. Skakun, E.A. Slabospitsky, R.P. Khvastunov, V.M. Dogyust, I.V. 2015-03-17T11:11:36Z 2015-03-17T11:11:36Z 2001 Main results on nuclear physics obtained at IHEPNF NSC KIPT during the last decade / A.Yu. Buki, A.N. Vodin, A.S. Kachan. V.V. Kirichenko, B.A. Nemashkalo, E.A. Skakun, R.P. Slabospitsky, V.M. Khvastunov, I.V. Dogyust // Вопросы атомной науки и техники. — 2001. — № 1. — С. 15-25. — Бібліогр.: 84 назв. — англ. 1562-6016 PACS: 25.85.Ig; 27.90.+b, 25.30.Fj, 27.10.+h. https://nasplib.isofts.kiev.ua/handle/123456789/78438 The main experimental results on nuclear physics obtained at INEPT KIPT during the last decade have been observed. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники IHEPNF NSC KIPT in the last decade Main results on nuclear physics obtained at IHEPNF NSC KIPT during the last decade Основные результаты по ядерной физике, полученные в ИФВЭЯФ ННЦ ХФТИ в течение последнего десятилетия Article published earlier |
| spellingShingle | Main results on nuclear physics obtained at IHEPNF NSC KIPT during the last decade Buki, A.Yu. Vodin, A.N. Kachan, A.S. Kirichenko, V.V. Nemashkalo, B.A. Skakun, E.A. Slabospitsky, R.P. Khvastunov, V.M. Dogyust, I.V. IHEPNF NSC KIPT in the last decade |
| title | Main results on nuclear physics obtained at IHEPNF NSC KIPT during the last decade |
| title_alt | Основные результаты по ядерной физике, полученные в ИФВЭЯФ ННЦ ХФТИ в течение последнего десятилетия |
| title_full | Main results on nuclear physics obtained at IHEPNF NSC KIPT during the last decade |
| title_fullStr | Main results on nuclear physics obtained at IHEPNF NSC KIPT during the last decade |
| title_full_unstemmed | Main results on nuclear physics obtained at IHEPNF NSC KIPT during the last decade |
| title_short | Main results on nuclear physics obtained at IHEPNF NSC KIPT during the last decade |
| title_sort | main results on nuclear physics obtained at ihepnf nsc kipt during the last decade |
| topic | IHEPNF NSC KIPT in the last decade |
| topic_facet | IHEPNF NSC KIPT in the last decade |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/78438 |
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