scholarly journals Installation of NEOPTOLEMOS, the new sum spectrometer for cross section measurements of capture reactions at the ΤANDEM Accelerator Laboratory of NCSR “Demokritos”

2019 ◽  
Vol 24 ◽  
pp. 134
Author(s):  
V. Lagaki ◽  
V. Michalopoulou-Petropoulou ◽  
M. Axiotis ◽  
V. Foteinou ◽  
A. Lagoyannis ◽  
...  
Keyword(s):  
Cross Section ◽  
Large Volume ◽  
Solid Angle ◽  
Nuclear Astrophysics ◽  
Nuclear Level ◽  
Level Densities ◽  
Γ Rays ◽  
Integrated Cross Section ◽  
The University

Cross-section measurements of capture reactions are of key importance in understanding the contribution of the uncertainties of nuclear properties, such as the nucleon-nucleus potential and the nuclear level densities, entering in astrophysics abundance calculations. During the recent years, the Nuclear Astrophysics group of NCSR “Demokritos” has been conducting angle-integrated cross-section measurements using a large-volume NaI(Tl) detector installed at the Dynamitron Tandem Laboratory of the University of Bochum in Germany. Thanks to LIBRA funds a brand new cylindrically shaped NaI(Tl) detector, coined NEOPTOLEMOS, was acquired that is axially segmented in two, covering a solid angle of almost 4π for γ rays emitted at its center.

PHOTONEUTRON CROSS SECTIONS IN SILICON AND CALCIUM

1953 ◽  
Vol 31 (1) ◽  
pp. 70-77 ◽  
Author(s):  
R. G. Summers-Gill ◽  
R. N. H. Haslam ◽  
L. Katz
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Neutron Yield ◽  
Threshold Energy ◽  
Threshold Effect ◽  
Monitoring Method ◽  
Dose Monitoring ◽  
Γ Rays ◽  
Integrated Cross Section ◽  
Peak Value

Using the dropping apparatus and dose monitoring method previously reported, the cross sections for the reactions Si28(γ, n)Si27 and Ca40(γ, n)Ca39 have been measured by detecting positron activities in the residual nuclei. The Si28(γ, n)Si27 cross section has a peak value of 21 mbarns at 20.9 Mev. and an integrated cross section to 24 Mev. of 0.070 Mev-barns. The threshold energy is 16.9 ± 0.1 Mev. The Ca40(γ, n)Ca39 cross section has a peak value of 15 mbarns at 19.3 Mev. and an integrated cross section to 24 Mev. of 0.065 Mev-barns. The threshold is 15.8 ± 0.1 Mev.A comparison of our results with the neutron yield measurement of Price and Kerst at 18 and 22 Mev. gives good agreement. A further comparison with the neutron yield work of Baldwin and Elder is made.The sharp discontinuity in (γ, n) yields using lithium γ rays observed by Wäffler and Hirzel is explained as a threshold effect. Integrated cross sections increase more or less smoothly with Z.In addition, improved values for the half-lives of the residual nuclei Si27 and Ca39 have been measured. These are 4.45 ± 0.05 and 1.00 ± 0.03 sec. respectively.

The coherent scattering of γ -rays by K electrons in heavy atoms - II. The scattering of 0·32 mc 2 γ -rays in mercury

1954 ◽  
Vol 227 (1168) ◽  
pp. 59-72 ◽  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Absorptive Part ◽  
Coherent Scattering ◽  
Heavy Atoms ◽  
University Of Cambridge ◽  
Γ Rays ◽  
The Cross ◽  
The University ◽  
Scattering Cross Sections

The results of calculations for the coherent scattering of γ -rays of energy 0·32 mc 2 by K electrons in mercury are given in a form which enables one to determine scattering cross-sections at any angle, for any initial and final polarizations and for any spin orientation of the electrons. The method used in doing the computation is that described in part І, the main part of the work having been performed on the EDSAC computer at the University of Cambridge. The dispersive contribution to the cross-section agrees with previous approximate calculations. The absorptive part is calculated as well and has the effect of adding to the cross-section a contribution approximately equal to one-sixth of the dispersive contribution at all angles of scattering.

MEASUREMENT OF NUCLEAR GAMMA-RAY ABSORPTION IN CARBON

1953 ◽  
Vol 31 (4) ◽  
pp. 636-656 ◽  
Author(s):  
R. N. H. Haslam ◽  
R. J. Horsley ◽  
H. E. Johns ◽  
L. B. Robinson
Keyword(s):  
Cross Section ◽  
Gamma Ray ◽  
Nuclear Scattering ◽  
Absorption Mechanism ◽  
Nuclear Absorption ◽  
Resonance Behavior ◽  
Continuous Absorption ◽  
Γ Rays ◽  
Integrated Cross Section ◽  
Nuclear Detectors

The cross section for the absorption of γ rays by carbon has been determined as a function of photon energy by means of "nuclear detectors". The electronic absorption coefficients in the energy range 12 to 20 Mev. are found to be about 1% lower than the theoretical values. The nuclear absorption is shown to exhibit a resonance behavior. The integrated cross section in carbon is considerably lower than predicted. The contribution of nuclear scattering is found to be negligible. Differences in results as determined by three different detecting reactions, C12(γ, n)C11, O16(γ, d)P15, and S32(γ, d)P30, are discussed on the basis of detector sensitivity. It is suggested that the absorption mechanism can be represented by a continuous absorption on which is superimposed absorption peaks.

Nuclear-level densities from cross-section fluctuations

1967 ◽  
Vol 51 (1) ◽  
pp. 100-113 ◽  
Author(s):  
E. Gadioli ◽  
I. Iori
Keyword(s):  
Cross Section ◽  
Nuclear Level ◽  
Level Densities

scholarly journals Nuclear Level Densities in Intermediate and Heavy Nuclei

1967 ◽  
Vol 20 (5) ◽  
pp. 477 ◽  
Author(s):  
JL Cook ◽  
H Ferguson ◽  
AR de L Musgrove
Keyword(s):  
Cross Section ◽  
Anomalous Behaviour ◽  
Incident Neutron ◽  
Heavy Nuclei ◽  
Nuclear Level ◽  
Free Gas ◽  
Level Densities

The level densities of intermediate and heavy nuclei have been fitted to the free gas model formula with some improvement over previous fits. The predictions of tho model regarding cross section behaviour have been tested and found to lead to anomalous behaviour of the partial widths for incident neutron energies above 1�5 MeV.

A coincidence method of measuring a flux of fast neutrons

1948 ◽  
Vol 44 (1) ◽  
pp. 96-113 ◽  
Author(s):  
B. B. Kinsey ◽  
S. G. Cohen ◽  
J. Dainty
Keyword(s):  
Cross Section ◽  
Ionization Chamber ◽  
Unit Area ◽  
Solid Angle ◽  
Fast Neutrons ◽  
Proton Scattering ◽  
Coincidence Method ◽  
Γ Rays ◽  
Thick Layers

A method is described in which the rate at which fast neutrons cross unit area is measured by counting protons projected into a small solid angle in the forwards direction from thin and thick layers of polythene. The protons are detected by triple coincidences between three proportional counters mounted coaxially behind the hydrogenous layers. The method is applicable to neutrons of energies from 1 MeV. upwards, and can be used in the presence of intense γ-rays. The flux of these neutrons is calculated in terms of the rate of detection of the protons, the solid angle for proton collection, the mass per unit area of the polythene layer, and the neutron-proton-scattering cross-section. A study of the behaviour of proportional co-axial counters, used in this manner, has been made. A determination of the angular distribution of fast neutrons produced by a deuteron-deuterium source has been made by our coincidence method, and the results compared with those obtained by the ionization chamber method by Bretscher and French. Absolute values agree to within 10%.

Strenæ Natalitiæ

2018 ◽  
Author(s):  
William Gibson
Keyword(s):  
Cross Section ◽  
University Of Oxford ◽  
Vice Chancellor ◽  
The University

This chapter looks at Strenæ Natalitiæ, a volume of poems produced by the University of Oxford to celebrate the events of the birth of the Prince of Wales in 1688. The University of Oxford's Strenæ Natalitiæ was a volume of over a hundred poems, with an obligatory introductory poem contributed by vice-chancellor Gilbert Ironside. The contibutors to Strenæ Natalitiæ were not simply a cross-section of the university's membership and poetic talent, but also of its politics. In some respects, youthful naivety might have been a cause of some of the authors' willingness to embrace the birth of James Edward, despite the anxiety felt by some of their fellow authors. Some of the verse was simple, and naïve in tone. Other verses were marked by a more mystical and prophetic tone. Ultimately, the verses in Strenæ Natalitiæ were predictable in their expressions of congratulation and celebration, though some also contained carefully muted expressions of equivocation.

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