The Karlsruhe 4π barium fluoride detector

doi:10.1016/0168-9002(90)90179-A

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

Volume 292, Issue 3, 15 July 1990, Pages 595-618

https://doi.org/10.1016/0168-9002(90)90179-A Get rights and content

Abstract

A new experimental approach has been implemented for accurate measurements of neutron capture cross sections in the energy range from 5 to 200 keV. The Karlsruhe 4π barium fluoride detector consists of 42 crystals shaped as hexagonal and pentagonal truncated pyramids forming a spherical shell with 10 cm inner radius and 15 cm thickness. All crystals are supplied with reflector and photomultiplier, thus representing independent gamma-ray detectors. The energy resolution of the 4π detector is 14% at 662 keV and 7% at 2.5 MeV gamma-ray energy, the overall time resolution is 500 ps and the peak efficiency 90% at 1 MeV. The detector allows to register capture cascades with 95% probability above a threshold energy of 2.5 MeV.

Neutrons are produced via the ⁷Li(p, n)⁷Be reaction using the pulsed proton beam of a Van de Graaff accelerator. A collimated neutron beam is passing through the detector and hits the sample in the centre. The energy of captured neutrons is determined via time of flight, the primary flight path being 77 cm. The combination of short primary flight path, a 10 cm inner radius of the spherical BaF₂ shell, and the low capture cross section of barium allows to discriminate background due to capture of sample-scattered neutrons in the scintillator by time of flight, leaving part of the neutron energy range completely undisturbed. This feature, together with the high efficiency and good energy resolution for capture gamma-rays, allows to separate the various background components reliably enough, that the capture cross section ratio of two isotopes can be determined with an accuracy of ≤ 1.0%. The detector will be used for nuclear astrophysics to investigate the origin of the heavy elements in the slow neutron capture process.

References (40)

M. Laval et al.
Nucl. Instr. and Meth.
(1983)
P.E. Koehler et al.
K. Wisshak et al.
Nucl. Instr. and Meth.
(1984)
K. Wisshak et al.
Nucl. Instr. and Meth.
(1987)
K. Wisshak et al.
The Karlsruhe 4π Barium Fluoride Detector
G. Reffo et al.
Nucl. Sci. Eng.
(1982)
F. Corvi et al.
Nucl. Sci. Eng.
(1986)
R.L. Macklin et al.
Phys. Rev.
(1967)
R.L. Macklin
Nucl. Sci. Eng.
(1987)
D.J. Wagenaar et al.
Nucl. Instr. and Meth.
(1985)

P.E. Koehler et al.

Nucl. Instr. and Meth.

(1986)

D.J. Morrissey et al.

Nucl. Instr. and Meth.

(1984)

G. Schatz et al.

Ein Programm zur Berechnung der Ansprechwahrscheinlichkeit eines $4π- Szintillationsz a ̈ hlers$

K. Wisshak et al.

Nucl. Sci. Eng.

(1982)

E. Malwitz

Crystalball-Trägerkugel Konstruktion und Fertigung

submitted to Phys. Rev....

C.E. Rolfs et al.

Cauldrons in the Cosmos

(1988)

F. Käppeler et al.

Rep. Prog. Phys.

(1989)

Cited by (123)

Neutron capture measurements with high efficiency detectors and the Pulse Height Weighting Technique
2023, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Citation Excerpt :
Later, high efficiency segmented detectors were built using inorganic materials such as NaI, BaF2 or BGO. Some examples are the detectors at the Kurchatov Atomic Energy Institute [56] (NaI), at the Rensselaer Polytechnic Institute (RPI) [57] (NaI), at the FZK Karlsruhe [58] (BaF2), and at the Research Reactor Institute of the Kyoto University [59] (BGO). From the results we have presented in the previous section, this should not be a problem when measuring cross sections of actinides, since the efficiency is not expected to change from one resonance to another.
Neutron capture cross section measurements in time-of-flight facilities are usually performed by detecting the prompt $γ$ -rays emitted in the capture reactions. One of the difficulties to be addressed in these measurements is that the emitted $γ$ -rays may change with the neutron energy, and therefore also the detection efficiency. To deal with this situation, many measurements use the so called Total Energy Detection (TED) technique, usually in combination with the Pulse Height Weighting Technique (PHWT). With it, it is sought that the detection efficiency depends only on the total energy of the $γ$ -ray cascade, which does not vary much with the neutron energy. This technique was developed in the 1960s and has been used in many neutron capture experiments to date. One of the requirements of the technique is that $γ$ -ray detectors have a low efficiency. This has meant that the PHWT has been used with experimental setups with low detection efficiencies. However, this condition does not have to be fulfilled by the experimental system as a whole. The main goal of this work is to show that it is possible to measure with a high efficiency detection system that uses the PHWT, and how to analyze the measured data.
Neutron physics with accelerators
2018, Progress in Particle and Nuclear Physics
Neutron-induced nuclear reactions are of key importance for a variety of applications in basic and applied science. Apart from nuclear reactors, accelerator-based neutron sources play a major role in experimental studies, especially for the determination of reaction cross sections over a wide energy span from sub-thermal to GeV energies. After an overview of present and upcoming facilities, this article deals with state-of-the-art detectors and equipment, including the often difficult sample problem. These issues are illustrated at selected examples of measurements for nuclear astrophysics and reactor technology with emphasis on their intertwined relations.
DALI2: A NaI(Tl) detector array for measurements of γ rays from fast nuclei
2014, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Citation Excerpt :
An alternative direction is toward higher efficiency measurements. The BaF2-crystal array was developed for astrophysical (n,γ) studies at Karlsruhe [10]. Another example, CAESAR, an array of CsI(Na) scintillators, is optimized for high γ-ray detection efficiency in in-beam γ-ray spectroscopy experiments at the National Superconducting Cyclotron Laboratory at Michigan State University [11].
A NaI(Tl) detector array called DALI2 (Detector Array for Low Intensity radiation 2) has been constructed for in-beam γ-ray spectroscopy experiments with fast radioactive isotope (RI) beams. It consists typically of 186 NaI(Tl) scintillators covering polar angles from ~15° to ~160° with an average angular resolution of 6° in full width at half maximum. Its high granularity (good angular resolution) enables Doppler-shift corrections that result in, for example, 10% energy resolution and 20% full-energy photopeak efficiency for 1-MeV γ rays emitted from fast-moving nuclei (velocities of $v / c ≃ 0.6$ ). DALI2 has been employed successfully in numerous experiments using fast RI beams with velocities of v/c=0.3–0.6 provided by the RIKEN RI Beam Factory.
Recent results on studying photon strength functions in rare-earth nuclei
2014, Nuclear Data Sheets
Determination of Resonance Parameters and their Covariances from Neutron Induced Reaction Cross Section Data
2012, Nuclear Data Sheets
Cross section data in the resolved and unresolved resonance region are represented by nuclear reaction formalisms using parameters which are determined by fitting them to experimental data. Therefore, the quality of evaluated cross sections in the resonance region strongly depends on the experimental data used in the adjustment process and an assessment of the experimental covariance data is of primary importance in determining the accuracy of evaluated cross section data. In this contribution, uncertainty components of experimental observables resulting from total and reaction cross section experiments are quantified by identifying the metrological parameters involved in the measurement, data reduction and analysis process. In addition, different methods that can be applied to propagate the covariance of the experimental observables (i.e. transmission and reaction yields) to the covariance of the resonance parameters are discussed and compared. The methods being discussed are: conventional uncertainty propagation, Monte Carlo sampling and marginalization. It is demonstrated that the final covariance matrix of the resonance parameters not only strongly depends on the type of experimental observables used in the adjustment process, the experimental conditions and the characteristics of the resonance structure, but also on the method that is used to propagate the covariances. Finally, a special data reduction concept and format is presented, which offers the possibility to store the full covariance information of experimental data in the EXFOR library and provides the information required to perform a full covariance evaluation.
Reaction cross sections for the s, r, and p process
2011, Progress in Particle and Nuclear Physics
The origin of the heavy elements beyond Fe can be ascribed to the slow ( $s$ ) and rapid ( $r$ ) neutron capture processes, except for minor contributions from the $p$ process. The mechanisms and recent model approaches for the related scenarios are briefly sketched with emphasis on the role of reaction cross sections for quantitative descriptions. Recent achievements in experimental techniques and advanced facilities are illustrated by selected experimental results.

View all citing articles on Scopus

View full text