SHELL EFFECTS ON THE SPACING OF NUCLEAR LEVELS

1956 ◽  
Vol 34 (8) ◽  
pp. 804-829 ◽  
Author(s):  
T. D. Newton
Keyword(s):  
Cross Sections ◽  
Level Density ◽  
Magic Number ◽  
Slow Neutron ◽  
Magic Numbers ◽  
Heavy Nuclei ◽  
Total Cross Sections ◽  
Shell Effects ◽  
Complete Set ◽  
Nuclear Levels

Recent measurements of resonances in slow neutron total cross sections yield good estimates of the average level spacing, D, in medium and heavy nuclei. These spacings show large variations, by factors of 103 to 105, in the region of magic numbers of nucleons. There are also variations by smaller factors between nuclei with even and odd numbers of protons or neutrons. The even–odd effect is a co-operative phenomenon; it can be approximately treated by redefining the ground state to be used for a Fermi gas model. After this correction the gas model should predict D with reasonable accuracy since it is required only to define the density of a complete set of states. The magic number variations are shown to be fitted by an improved approximation to the single-nucleon level density. This is obtained from the observed sequence of single-particle spins and the assumption that the energy interval between spin subshells is constant. Fifty-two observed spacings are fitted by a two-parameter formula with an average uncertainty factor 3. Many of the larger remaining differences between observation and the predictions of the model are qualitatively explicable as expected departures from this uniform spacing hypothesis.

Slow Neutron Crystal Spectrometry: The Total Cross Sections of Co, Er, Hf,Ni58,Ni60, Ho, and Fission Sm

1952 ◽  
Vol 87 (3) ◽  
pp. 487-493 ◽  
Author(s):  
S. Bernstein ◽  
L. B. Borst ◽  
C. P. Stanford ◽  
T. E. Stephenson ◽  
J. B. Dial
Keyword(s):  
Cross Sections ◽  
Slow Neutron ◽  
Total Cross Sections

Total Cross Sections of Heavy Nuclei for Fast Neutrons

1952 ◽  
Vol 88 (1) ◽  
pp. 83-90 ◽  
Author(s):  
D. W. Miller ◽  
R. K. Adair ◽  
C. K. Bockelman ◽  
S. E. Darden
Keyword(s):  
Cross Sections ◽  
Fast Neutrons ◽  
Heavy Nuclei ◽  
Total Cross Sections

PARITY AND TIME REVERSAL VIOLATION IN RESONANCE NEUTRON TOTAL CROSS SECTIONS WITH POLARIZED TARGETS

1990 ◽  
Vol 05 (11) ◽  
pp. 2181-2194 ◽  
Author(s):  
C. R. GOULD ◽  
D. G. HAASE ◽  
N. R. ROBERSON ◽  
H. POSTMA ◽  
J. D. BOWMAN
Keyword(s):  
Cross Sections ◽  
Time Reversal ◽  
Analytic Form ◽  
Spin Representation ◽  
Resonance Neutron ◽  
Total Cross Sections ◽  
Polarized Target ◽  
Complete Set ◽  
Closed Analytic Form ◽  
Polarized Targets

The formalism for evaluating parity and time reversal violating terms in total cross sections of polarized targets and low energy resonance neutrons is reviewed. A complete set of symmetry violating terms (P-odd, T-even; P-odd, T-odd; and P-even, T-odd) is obtained by analyzing the dependence of the cross section on the statistical tensors describing the beam and target. Results are tabulated in numerical and closed analytic form, using the j-spin representation. P-odd, T-even experiments are classified, with emphasis on experiments with an unpolarized beam and a polarized target where the effect of induced polarization is found to be small. Different combinations of partial neutron widths are shown to enter when P-odd, T-odd effects are compared to P-odd, T-even effects. The results for P-even, T-odd experiments for single level and two level mixing are summarized.

scholarly journals The effect of deformation parameter of heavy nuclei on level density parameter

2019 ◽  
Vol 12 (25) ◽  
pp. 38-43
Author(s):  
Mahdi Hadi Jasim
Keyword(s):  
Cross Sections ◽  
Collective Motion ◽  
Level Density ◽  
Reaction Cross ◽  
Neutron Resonance ◽  
Density Parameter ◽  
Heavy Nuclei ◽  
Nuclear Level Density ◽  
S Wave ◽  
Level Density Parameter

The possible effect of the collective motion in heavy nuclei has been investigated in the framework of Nilson model. This effect has been searched realistically by calculating the level density, which plays a significant role in the description of the reaction cross sections in the statistical nuclear theory. The nuclear level density parameter for some deformed radioisotopes of (even- even) target nuclei (Dy, W and Os) is calculated, by taking into consideration the collective motion for excitation modes for the observed nuclear spectra near the neutron binding energy. The method employed in the present work assumes equidistant spacing of the collective coupled state bands of the considered isotopes. The present calculated results for first excited rotational band have been compared with the accumulated values from the literature for s-wave neutron resonance data, and were in good agreement with those data.

Lack of Evidence for Shell Effects in the (n,p) and (n,α) Reaction Cross Sections at 14 MeV Neutron Energy

1970 ◽  
Vol 25 (12) ◽  
pp. 1977
Author(s):  
S.M. Qaim
Keyword(s):  
Experimental Data ◽  
Neutron Energy ◽  
Cross Sections ◽  
Nuclear Reactions ◽  
Magic Number ◽  
Reaction Cross ◽  
Conclusive Evidence ◽  
Shell Effects ◽  
Reaction Cross Sections ◽  
Proton Shell

Abstract The systematics of cross sections for (n,p) and (n,a) re-actions induced by 14 - 15 MeV neutrons have been reinvesti-gated. No clear evidence for the existence of any proton shell effects in these two reactions was found. The existence of shell effects in nuclear reactions induced by 14 - 15 MeV neutrons has been postulated by several workers1-4 , but the evidence presented has been rather weak. With the availability of more and better experimental data in recent years, a fresh look at this postulate seemed highly desirable. In case of (n,p) and (n,2n) reactions, the claim for the occurence of shell effects has already been recently repudiated5,6 ; but for (n,α) reactions there seems to exist no evidence against the original claims1,2 that the cross section shows a minimum when the atomic number of the re-sidual nucleus is a magic number. The present article describes briefly a reinvestigation of the systematics of the (n,p) and (n,α) reaction cross sections in the light of the latest experimental data. At 14 MeV neutron energy there appears to be no conclusive evidence for any significant proton shell effects in these two re-actions.

Total cross sections for fission of heavy nuclei by intermediate-energy protons

2007 ◽  
Vol 71 (6) ◽  
pp. 809-811 ◽  
Author(s):  
A. A. Kotov ◽  
L. A. Vaishnene ◽  
V. G. Vovchenko ◽  
Yu. A. Gavrikov ◽  
V. V. Polyakov ◽  
...  
Keyword(s):  
Cross Sections ◽  
Intermediate Energy ◽  
Heavy Nuclei ◽  
Total Cross Sections

scholarly journals New studies and a short review of heavy neutron-rich transfer products

2020 ◽  
Vol 56 (9) ◽  
Author(s):  
H. M. Devaraja ◽  
S. Heinz ◽  
D. Ackermann ◽  
T. Göbel ◽  
F. P. Heßberger ◽  
...  
Keyword(s):  
Cross Sections ◽  
Production Cross ◽  
Short Review ◽  
Heavy Nuclei ◽  
Model Calculations ◽  
Nucleon Transfer ◽  
Shell Effects ◽  
Fragmentation Reactions ◽  
Nuclear Shell ◽  
Nuclear Shell Effects

Abstract We present new results on multi-nucleon transfer reactions in low-energy collisions of $$^{48}\hbox {Ca}+{}^{238}\hbox {U}$$ 48 Ca + 238 U measured at the velocity filter SHIP of GSI Helmholtz Centre, where we observed around 90 different nuclides from Tl to Am ($$Z=$$ Z = 81–95). We followed the idea to use uranium targets for the synthesis of neutron-rich MNT products, particularly in the region below lead, which was triggered by model calculations. The $$\gamma $$ γ , $$\alpha $$ α and spontaneous fission activities of the populated nuclides have been analyzed for their identification. The cross-sections of the observed isotopes for elements $$Z = $$ Z = 81–93 as a function of their mass number have been investigated. Excitation energy, total kinetic energy and the influence of nuclear shell effects on the production cross-sections of the observed transfer products have been studied. Also we present a compact review and comparative analysis of various multi-nucleon transfer and fragmentation reactions which are aimed at the synthesis of neutron-rich nuclides along the $$N=126$$ N = 126 shell closure in heavy nuclei.

ELECTROMAGNETIC STRENGTH IN HEAVY NUCLEI – EXPERIMENTS AND A GLOBAL FIT

2011 ◽  
Vol 20 (02) ◽  
pp. 431-442 ◽  
Author(s):  
R. BEYER ◽  
E. BIRGERSSON ◽  
A. R. JUNGHANS ◽  
R. MASSARCZYK ◽  
G. SCHRAMM ◽  
...  
Keyword(s):  
Cross Sections ◽  
Ground State ◽  
Level Density ◽  
Strength Function ◽  
Model Parameters ◽  
Heavy Nuclei ◽  
Dipole Strength ◽  
Dipole Resonance ◽  
Radiative Neutron ◽  
Radiative Neutron Capture

A global parameterization is presented for the electromagnetic strength in heavy nuclei which gives a rather good fit to respective data in nuclei with mass numbers A between 50 and 240. It relies on a Lorentzian description of the isovector giant dipole resonance and it needs only a very small number of parameters to describe the electric dipole strength down to low excitation energy of importance for radiative capture processes. The resonance energies are chosen to be in accordance to liquid drop model parameters adjusted to ground state masses and to rotation invariant determinations of ground state deformation and triaxiality. By a straightforward use of this information a surprisingly smooth variation of the GDR width with A and Z is found and a full agreement to the predictions of the electromagnetic sum rule is assured. Predictions for radiative neutron capture cross sections compare well to respective data, when the proposed photon strength function is combined with standard prescriptions for the level density in the product nuclei.

THERMONUCLEAR REACTIONS IN MEDIUM AND HEAVY NUCLEI

1966 ◽  
Vol 44 (1) ◽  
pp. 151-174 ◽  
Author(s):  
J. W. Truran ◽  
C. J. Hansen ◽  
A. G. W. Cameron ◽  
A. Gilbert
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Level Density ◽  
Strength Function ◽  
Mass Range ◽  
Reaction Rates ◽  
Nuclear Radiation ◽  
Heavy Nuclei ◽  
Nuclear Level Density ◽  
The Cross

A method is outlined by which thermonuclear reaction rates can be determined from the statistical properties of nuclei. Assuming that the contribution to the cross section of a given resonance is given by the Breit–Wigner single-level formula, the total rate is determined by integrating the product of the cross section, weighted by the nuclear level density, and the velocity over energy. The nuclear radiation widths were calculated on the assumption that electric-dipole transitions are dominant. The particle widths were determined by approximating the nuclear strength function by that value calculated for a black nucleus. Nuclear cross sections calculated in this manner are compared with experiment both for charged-particle reactions on lighter nuclei and for neutron-capture reactions proceeding on nuclei in the mass range A > 60. Good agreement is obtained in both cases.

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