Coincidence Matrix Research Articles

A twelve detector coincidence spectrometer for on-line and off-line measurements of nuclear g-factors

A twelve detector γ-γ directional correlation setup is described which has been designed and constructed for high precision on-line and off-line IPAC measurements. A ring of twelve BaF 2 detectors which may be replaced by Ge detectors is arranged around a superconducting magnet providing a maximum magnetic field of 4.5 T. In on-line experiments the magnetic field has the direction of the beam which passes through a central bore of the magnet. The data acquisition system stores directly the E γ1 - E γ2 coincidence matrices for all 66 two-detector combinations in two 8 Mbyte RAMs, one for each of the two field directions. This allows a very fast data evaluation with a small on-line computer. The apparatus got into operation one-and-a-halve years ago and revealed excellent properties.

FourtyTwo - a two-dimensional analysis program for γ-γ coincidence matrices

A program for two-dimensional analysis of γ-γ coincidence matrices is described. The program is tailored to the Digital Equipment VT340 colour graphic terminal and written in VAX Fortran. The program provides viewing of the matrix as well as projections in both energy coordinates, determination of centroids and volumes of peaks, full two-dimensional Gauss fits to a maximum of five peaks in an arbitrarily shaped area of the matrix, etc.

Analysis of multidimensional spectra: estimating the continuum

We have developed a two-dimensional fitting program which extracts coincidence intensities and their uncertainties from a γγ coincidence matrix. The data are fitted by peaks and ridges on a two-dimensional continuum. The continuum is described as the product of components of a presumed Compton distribution for the set of detectors contributing to each axis of the continuum. Peaks and ridges are based on simple Gaussians.

Lifetime measurements of high spin states in Yb nuclei

Transition rates for high spin discrete line states in 168Yb have been extracted using a Doppler Shift Attenuation Method and a loss of collectivity has been found at the highest spins. Similar results for other Yb nuclei are reviewed and an explanation, involving a reduction of deformation due to changes of intrinsic structure, is given. It is shown that this loss of collectivity for the yrast and near-yrast bands is in sharp contrast to the recent finding that the transitions contributing to the ridge structure in a γ-γ coincidence matrix retain full collectivity up to the highest spins. Possible reasons for this difference are discussed

On the reduction of data storage from high-dispersion experiments

Multi-dimensional coincidence experiments produce large data volumes, which need to be stored on computer disks for further retrieval and analysis. In this paper, two methods are dicussed and applied to coincidence matrices from gamma-ray spectroscopy experiments, which reduce the space needed on computer disks by a factor 3 to 10.

Statistical analysis of γ-γ coincidence matrices

A simple method based on unidimensional fits has been developed to estimate all γ-γ coincidence intensities due to a given nucleus in a bidimensional coincidence matrix. Uncertainties are evaluated in every part of the analysis. Statistical tests enable us to check the quality of the results. The method was used for establishing the 218Ra level scheme obtained through a heavy-ion induced reaction.

Unfolding the response function of high-quality germanium detectors

The form and unfolding of the response function of the germanium detectors in the γ-ray spectrometer TESSA2 or similar devices is discussed, both for singles-type spectra and γ - γ coincidence matrices. The reliable unfolding which is possible allows quantitative studies of the γ-ray continuum from (HI, xn) reactions to be made with high resolution germanium detectors.

LINGAT — Linearly fitted gating: An accurate method for background-correction in two-dimensional data sets

An accurate method for background-correction in two-dimensional data sets, i.e. energy-time or energy-energy (coincidence) matrices, is presented. It is based on linear fitting in the dependent parameter, whence its name LINGAT. Examples show that this method is far superior to the classical peak-minus-background method, albeit more tedious to use. The advantages lie in its ability to separate close-lying peaks in energy and in background. The use of the error spectra in time analyses is discussed.

Experimental moments of inertia in Pd and Cd isotopes and their interpretation within the extended Nilsson-Strutinsky model

High-spin properties of even Pd and Cd isotopes have been studied by means of a 118 MeV 12C beam impinging onto a 100Mo target. The γ-rays following the reaction were recorded using six NaI(Tl) detectors in a two-dimensional coincidence arrangement. Energy-correlation spectra were extracted from the coincidence matrix and used to obtain information on the collective moment of inertia I . The gross properties of the behaviour of this moment of inertia are discussed within an extended Nilsson-Strutinsky model. The experimentally observed variation of the moment of inertia at high rotational frequencies is tentatively explained as being due to an increase of I as the band approaches its termination.

On the moment of inertia in deformed Ba-Xe nuclei as deduced from gamma-gamma energy correlation experiments

The γ-rays following reactions induced by bombarding targets of 114, 116, 118, 120, 122Sn with 118 MeV 12C ions were investigated using six NaI(Tl) detectors in a two-dimensional coincidence arrangement. Experimental energy-correlation spectra were extracted from the original coincidence matrices. The energy-correlation spectra exhibit the features expected for rotational nuclei and were used to deduce information on the moment of inertia I (2) = ΔI/Δω . The gross properties of the behaviour of I (2) in the Ba-Xe region are discussed together with their interpretation within the cranked shell model (CSM).

Gamma-Gamma Energy Correlations and Moment of Inertia in Barium Nuclei

A two-dimensional γ-ray coincidence spectrum is recorded using several NaI (T1) detectors during the bombardment of a 124Sn target with 118 MeV 12C ions. Essentially four residual nuclei are produced, namely 128,129,139Ba and 126Xe. After subtraction of an uncorrelated background from the coincidence matrix, a correlated spectrum is obtained. This spectrum exhibits a valley along the 45° diagonal from about Eγ ≃ 0.5 MeV to Eγ ≃ 1.35 MeV, reflecting the rotational properties of the residual nuclei. The width of the valley decreases up to a transition energy Eγ ≃ 0.8 MeV. This width is directly related to the moment of inertia \U0001d4a5band(2) = dI/dω and is found to be in good agreement with the deduced values from known ground-band energies, although the nucleus probably decays through many different paths in this energy region. For the regions 800 < Eγ < 1050 keV and 1200 keV < Eγ < 1300 keV, the width of the valley remains nearly constant and the moment of inertia (2\U0001d4a5band(2)/ℏ2 = 80 and 95 MeV-1, respectively) is close to the rigid-body value. A "bridge" across the valley at Eγ = 1.12 MeV is interpreted as being due to band crossing. Cranked shell model calculations indicate that the aligned angular momentum at this rotational frequency may result from the occupation of the highest aligned h9/2 or i13/2 neutron orbitals.

Gamma-gamma energy correlations and moment of inertia in 130Ce

High-spin properties of 130Ce have been studied by using the reaction ( 12C, 6n). The γ-rays following this reaction were detected by six NaI(Tl) detectors in a two-dimensional coincidence arrangement. An experimental γ-ray energy-energy correlation spectrum was extracted from the original coincidence matrix. The matrix of the correlated spectrum shows a valley along the 45° diagonal extending up to E γ ≈ 1.2 MeV, thus indicating a collective behaviour beyond the region of known discrete lines. From the width of the valley a collective moment of inertia is deduced.

Direct decomposition of the experimental γ-γ coincidence matrix

Development here is the direct method of decomposition of the experimental matrix of γ-γ coincidences. Intensities of coincidences are calculated by an approximation of the total coincidence matrix within the framework of the chosen model of the coincidence spectra with the instrumental parameters and the a priori data on the scheme of the excited states of the nucleus under study. A two-dimensional Gaussian is used to describe an elementary coincidence peak. The volume value of the Gaussian is a measure of the γ-γ coincidence intensity in the given cascade. The method described was used for processing the experimental data in 104Rh, 108Ag, 122,124Sb and 134Cs studies via the (n, γ) reaction. The method is also valid in the analysis of any of two-parameter distributions which correspond to correlated events and which can be presented as two-dimensional matrices.

A trigger system using cathode read-out chambers and a coincidence matrix

We describe a system of cathode read-out multiwire proportional chambers which performed the trigger of the CERN NA3 experiment. These large chambers-the biggest measures 4.8 × 5.1 m 2-have been operated successfully since May, 1978. The cathodes are divided into about 1000 graphite cells painted on a mylar foil. The same cells are reproduced in silver paint on the other side of the mylar foil, which allows a capacitive transmission of the signals deposited on graphite cells. The signals are then transmitted to the amplifiers via copper strips which may be up to 2 m long. The amplifiers are currently operated with a sensitivity of 1 μA on 50 ω. A coincidence matrix, using fast ECL circuitry, uses the signals given by these chambers to select particles having large transverse momenta, in about 100 ns. This gives a very powerful trigger for the experiment studying high mass dimuon production by hadrons: about 60% of the triggers are true dimuons. An improved version of the coincidence matrix allows on-line selection of dimuons above a given invariant mass.

A fast programmable coincidence matrix

The design and performance of a fast coincidence matrix of size 25 × 36 is described. The matrix is programmable either manually or by computer control via a CAMAC output register. The input-output delay is 28 ns.

Nanosecond Coincidence Measurements

This article summarizes some of the basic information regarding the design and use of circuits --i.e., coincidence circuits--for time coincidence measurements on pulses having durations of the order of nanoseconds. The design features of contemporary circuits are discussed. Some performance parameters are listed and techniques of evaluating the performance of coincidence circuits are mentioned. The sendinig, transmission, and receiving of fast pulses is reviewed. The special cases of majority logic and coincidence matrices are briefly discussed.

Study of thermal neutron capture in potassium

The 39K(n,γ)40K reaction has been studied using a Ge(Li) and a Ge(Li)–Ge(Li) spectrometer. A total of 252 gamma-ray transitions has been observed and a gamma–gamma coincidence matrix involving 62 transitions has been established. A decay scheme based on the experimental results is deduced for 202 of the observed gamma-ray transitions. Spins and parities of some excited states have been estimated from the deduced branching ratios. The neutron separation energies of the 40K and 42K nuclei have been determined as 7800.5 ± 0.2 and 7535.2 ± 1.5 keV respectively.

A multicounter goniometer for gamma-gamma angular correlation measurements

A multicounter goniometer for gamma-gamma angular correlation measurements was newly designed and constructed. It consists of 12 photomultipliers with NaI(Tl) crystals placed radially at intervals of 30° and a 12 × 12 coincidence matrix circuit which follows 12 linear amplifiers and 2 × 12 single channel pulse height analyzers. Coincidence counts at 11 angles between 30° and 330° are taken simultaneously for each of the 12 counters, so that with this method angular correlation measurements can be made within a time reduced by a factor 12 × 11, as compared with the ordinary method.

Measurements of differential cross sections and polarization effects in pion-proton elastic scattering in the momentum range 875 to 1579 MeV/ c

In this paper we discuss some measurements that have been made at Nimrod of differential cross sections and polarization effects in πp elastic scattering. The principal aims of this work were to determine the spins and parities of the N * 1/2 (1688) and the N* 3/2 (1920) isobars and to examine the behaviour of the π+p elastic scattering cross section at momenta around 950MeV/ c where a shoulder exists in the total cross sections. Table 1 gives the values of the momenta at which the measurements were made and figure 1 illustrates their relation to other work that has been done in or near this region. A schematic diagram of the experimental arrangement for measuring the differential cross sections is shown in figure 2. An array of scintillation counters, used in conjunction with a coincidence matrix detected particles scattered from a 4 in. long liquid hydrogen target. All events were accepted in which two and only two outgoing particles were detected in coincidence by any combination of two counters on opposite sides of the beam. The number of counts for each combination was stored in the magnetic core store of a 512 channel pulse height analyser