Triple Coincidence Research Articles

Fragmentation of CH4 caused by fast-proton impact.

The cross sections of the different breakup channels of ${\mathrm{CH}}_{4}$, produced by 4-MeV proton impact, have been measured using the coincidence time-of-flight technique. The relative abundances of the different breakup channels were evaluated for collisions in which the molecule broke into two charged fragments as well as for collisions where only a single charged molecular ion or fragment was produced. These relative abundances are compared to the ones measured for photodissociation, and for electron and proton impact. Only the ${\mathrm{CH}}_{4}^{+}$ ion survives long enough to be detected as a molecular ion, while the doubly charged ${\mathrm{CH}}_{4}^{2+}$ ion dissociates rapidly. The most probable final product of the fragmentation of doubly charged methane as formed by fast-proton impact is ${\mathrm{H}}^{+}$+${\mathrm{CH}}_{2}^{+}$+H. The abundance of ${\mathrm{H}}_{\mathit{m}}^{+}$+${\mathrm{CH}}_{\mathit{n}}^{+}$ (m+n\ensuremath{\le}4) ion pairs decreases rapidly with increasing m, as suggested by Siegbahn [Chem. Phys. 66, 443 (1982)]. The momentum of neutral fragments, in channels where they are produced, is small in comparison with the momentum of the charged fragments so that two-body breakup holds approximately. The deviation from two-body breakup increases with increasing number of neutral hydrogen atoms produced. The sensitivity of the experimental method enabled us to extend the study of the fragmentation pattern of ${\mathrm{CH}}_{4}^{2+}$ to include small breakup channels such as ${\mathrm{CH}}_{4}^{2+}$\ensuremath{\rightarrow}${\mathrm{H}}_{3}^{+}$+${\mathrm{CH}}^{+}$. Furthermore, some breakup channels of the triply charged ${\mathrm{CH}}_{4}^{3+}$ have been detected as triple coincidences.

Coincidence studies of the slow dissociation reactions of benzene monocations in the 21–35 eV photon energy range

Metastable ion transitions are investigated, with benzene as an example, using reflectron mass spectrometry and synchrotron radiation. Photoelectron—photoion coincidence (PEPICO) spectra contained two types of metastable peaks, m * and m ** . These are shown to be due to dissociation in the dirft tube and the electrostatic mirror section respectively through the use of double and triple coincidence measurements between photoelectrons, photoneutrals and photoions. The combined results enabled precursor ions to be assigned in both single-step and sequential fragmentations. The results confirmed previous analyses of benzene metastable transitions induced by electron excitation. The evolution of product ion yields, and the ratio of metastable to fast dissociation reactions, as a function of photon excitation energy are rationalized in terms of the internal energy deposited in the parent cation.

High energy electron fluxmeter

An instrument for measurement of high energy electrons (1-10 MeV) in the Earth's radiation belts has been designed, calibrated and flown on-board the CRRES spacecraft. The instrument uses a triple coincidence arrangement with two solid state detectors and a BGO scintillator crystal to identify electrons and discriminate against energetic protons. A thorough description of the construction and calibration is presented along with an example of on-orbit data.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Removal of false coincidences in triple coincidence experiments employing continuous excitation

The competing processes in molecular dissociative double ionization can be studied by producing three-dimensional, triple coincidence maps. Even at modest count rates these maps exhibit structured and unstructured background due to false coincidences. A technique for removing these false coincidences is described and applied to the case of the double ionization of CF4 produced by synchrotron radiation at a wavelength of 20 nm.

A flow-through detector for nano-Curie activities encountered in HPLC analysis of PET tracer metabolites

The need for a flow-through detector with high efficiency and vanishingly low background arises in HPLC (high-pressure liquid chromatography) analysis of PET (positron emission tomography) tracer metabolites, where the free drug input function must be separated from the total circulating activity in sequential blood samples. Subnanocurie activities of positron emitters in 100 mu l plasma samples are chemically resolved, and then assayed by a triple coincidence beta - gamma - gamma -detector. Multiple coincidence logic between a BC-400 plastic scintillator flow-cell, sandwiched between two large NaI(Tl) gamma detectors, reduces the background event rate to 10/sup -3/ to 10/sup -6/ counts per second, with an overall efficiency of 25% for /sup 18/F-labeled eluates. Careful attention is paid to the construction of the beta cell, maintaining the chemical resolution of the HPLC system while optically transporting the few beta scintillation photons to multiple photomultipliers without losing the solid angle to the surrounding mantle of gamma detectors.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dynamic moment of inertia of the 192Hg superdeformed band at high rotational frequencies

The superdeformed band in 192Hg has been extended to higher transition energies from a new analysis of a large set of double and triple coincidence data. Contrary to the results of cranked shell model calculations including monopole pairing, the dynamic moment of inertia I (2) is found to continue to increase with rotational frequency.

Energy damping and intermediate-velocity fragment emission in peripheral Kr+Au collisions at 43 MeV/u

Triple and four-fold coincidences among fragments have been measured in the reaction 84Kr+Au at 43 MeV/u. All events showing the projectile-like nucleus and fission fragments of the target-like nucleus, and all events with one additional intermediate-velocity fragment, were analysed in the frame of a dissipative collision and a participant-spectator model. The mechanism is basically that of a dissipative collision but the emission of the intermediate velocity fragment by the target differs from an equilibrated evaporation.

Observation of Coulomb excitation of unstable nuclei utilization of a secondary beam

An experimental technique to detect γ-rays from secondary-beam Coulomb excitation was developed. A secondary beam of 76Kr produced by the inverse reaction 9Be( 70Ge, 3n) was Coulomb excited by a 208Pb target. Weak γ-rays from the secondary-beam Coulomb excitation were discriminated from those of a primary beam by measuring triple coincidences of primary γ-rays, scattered particles and emitted γ-rays from the second target. Coulomb excitation of the unstable nucleus was observed for the first time in the medium heavy mass region. The observed yield of the 2 + → 0 + transition in 76Kr is consistent with that which is estimated from the known B(E2: 0 + → 2 +) for this nucleus.

Analysis of the Copulsatility of Anterior Pituitary Hormones*

We have used combinatorial algebra and computer simulations to calculate expected means, variances, and probabilities of hormone-peak coincidences in 2 or more endocrine pulse series. We illustrate application of this conditional probability analysis to pulsatile LH, FSH, and/or PRL data. We observed that 1) serum LH and FSH pulses in 14 young men were randomly associated on different days (P greater than 0.10), but highly synchronized on any given day (P less than 0.0001); 2) serum LH and FSH (P less than 0.0001), LH and PRL (P = 0.023), and FSH and PRL (P = 0.0003) peaks were significantly coupled in healthy postmenopausal women; and 3) the number of triple coincidences among LH, FSH, and PRL release episodes in postmenopausal women significantly exceeded chance expectations (P less than 0.0001). We conclude that suitable statistical coincidence analysis can offer an informative tool with which to evaluate nonrandom event concordance in endocrine investigations, such as clinical studies of the temporally coordinated release of anterior pituitary hormones.

The deformation of the neutron-rich isotopes102Mo and104Mo

The half-lives of low-lying levels of the neutron-rich isotopes102Mo and104Mo have been measured at the fission product separator Josef with the s-γ-γ triple coincidence technique. Values of t1/2= 126(4)ps and 0.72(4)ns have been obtained for the 21+ levels at 296 keV and 192 keV in102Mo and104Mo, respectively. Deformation parameters of sq=0.28(1) and 0.31(1), respectively, are deduced, which are smaller than those of the isotones of Sr and Zr. The interacting boson model accounts well for the trend of 2+ energies in the Mo isotopes but slightly overpredicts the B(E2) values at saturation. A smooth dependence of τ 21+ vs. E 21+ is found for the A ∼ 100 region in agreement with the hydrodynamical model.

Capture of quasifree electrons into highly charged, heavy projectiles

In collisions between highly charged, heavy ions and light target atoms at adiabaticity parameters of 0.5 ≤ v 2 u 2 ≤ 0.75 , resonant transfer and excitation (RTE) is an important charge-exchange process. Experiments for medium Z-ions are reviewed. Special emphasis is given to the competing radiative electron capture (REC) process. The general dependences of REC are discussed. In particular, we elucidate results obtained by the triple X-ray/X-ray/charge-changed particle coincidence technique for hydrogenic projectiles up to 36Kr 35+ ions. With this method we could isolate a single RTE resonance, the 2s2p 1P 1 state, which stabilizes radiatively to the metastable 1s2s 1S 0 state. This state can only decay via two photon emission (2E1). Applying the triple coincidence technique we observed additional strong photon coincidences induced by cascades following REC into high projectile states.

About some experimental aspects of double and triple coincidence techniques to study electron impact double ionizing processes

A critical discussion is given of some of the experimental parameters involved in measurement of the three-, four- and five-fold differential cross sections obtained in (e,2e), (e,(3-1)e) and (e,3e) experiments, respectively. Features observed in the triple coincidence time-delay spectrum are attributed to fully accidental, semi-accidental or true triple coincidence events. Formulas are given that allow computation of the true coincidence rate, the percentage statistical error and the signal-to-background ratio, and to optimize the gas density-electron beam current product for any given experiment. The effective coincidence energy resolutions and transmission functions are defined, and their importance clearly demonstrated.

Sources of light particles in peripheral collisions.

By studying light charged particles emitted in coincidence with projectile-like fragments, we probe heavy ion reaction mechanisms that result in the production of light particles in peripheral collisions. Triple coincidence {alpha}-{alpha}-{sup 12}C correlations in the reactions of 35 MeV/nucleon {sup 16}O with Ni conclusively identify previously known sources of light particles. The fast, beam velocity component of {alpha} particles in coincidence with projectile-like fragments is associated with the breakup of the projectile. The correlations suggest that the origin of the intermediate velocity component of {alpha} particles is the target nucleus. Both of these components are characterized by {alpha} particles emitted during the early stages of the collision.

The 20Ne+ 159Tb reaction studied with the KX-ray method at 15 [formula omitted

Employing the KX-ray method, in which coincidences are measured between projectile-like fragments (PLF) and the characteristic KX rays from the target-like fragments (TLF), partial cross sections dσ-(Z PLF , Z TLF )/ dΩ PLF were obtained for the 20Ne+ 159Tb reaction at E lab = 294 MeV for both the quasi-elastic (QE) and the deep-inelastic (DI) components. By in addition measuring triple coincidences with charged particles at back angles the results could be corrected for charged particle evaporation from the TLF. Primary PLF cross sections were reconstructed for both components and the corresponding probabilities for sequential charged particle decay of the fragments were deduced. The very different behaviour of the QE and DI components will be discussed. As in a previous study of the 14N+ 159Tb reaction large cross sections are observed for channels in which only nucleons and α-particles are emitted. Statistical model calculations were performed to deduce the excitation energy distribution of the primary PLF's. Comparison with other methods to reconstruct primary cross sections are made. The predictions of several models are evaluated.

Double K-shell vacancy production in the electron capture decay of 139Ce.

The probability of double K-shell vacancy production in the electron capture decay of $^{139}\mathrm{Ce}$ to the 166-keV level of $^{139}\mathrm{La}$ has been investigated. Triple coincidences between the 166-keV gamma ray, the La satellite K\ensuremath{\alpha} x ray, and the La hypersatellite K\ensuremath{\alpha} x ray were measured using two intrinsic Ge detectors. We looked for the sum of two of the three radiations in one detector in coincidence with the third radiation in the other detector. The probability of double K-shell vacancy production per K-shell electron capture (${\mathit{P}}_{\mathit{K}\mathit{K}}$) was found to be (2.0\ifmmode\pm\else\textpm\fi{}1.6)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}6}$. From this and the known ${\mathit{P}}_{\mathit{K}\mathit{K}}$ for $^{131}\mathrm{Cs}$ we estimate a probability for zero K-shell vacancy production (shakedown) per K-shell electron capture of \ensuremath{\lesssim}2.4\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$ for $^{139}\mathrm{Ce}$.

Pion absorption in flight on 4He

We have measured double and triple coincidences following π + and π − absorption on 4He at various pion energies. Differential and integrated cross sections are determined for all possible absorption channels. We study and compare the two-nucleon absorption on nucleon pairs with isospin I = 0 and I = 1. In the dNN final-state two absorption mechanisms are identified, one with only one spectator nucleon and one with phase-space behavior. The existence of a three-nucleon absorption component with a spectator nucleon is established and a four nucleon phase-space-like contribution is also identified and found to be small. The total absorption cross section is directly determined by adding the integrated cross sections of all measured reaction channels.

Pathophysiology of Pulsatile and Copulsatile Release of Thyroid-Stimulating Hormone, Luteinizing Hormone, Follicle-Stimulating Hormone, andα-Subunit*

Under physiological conditions, TSH, LH, FSH, and alpha-subunit are released in discrete pulses. To further characterize their neuroregulation and to investigate possible copulsatile secretion of these glycoprotein hormones, we studied the 24-h pulse profiles of all four hormones in each of four subject groups: young men, young women, postmenopausal women, and subjects with untreated primary hypothyroidism. Gonadotropin pulse properties in euthyroid men and women were similar to those previously reported, and hypothyroid subjects had normal gonadotropin pulse patterns. TSH release was pulsatile in all groups; hypothyroid subjects had increased pulse amplitude, but loss of the usual nocturnal increases in pulse amplitude. alpha-Subunit concentrations were pulsatile in all groups, with minimal circadian variation; postmenopausal and hypothyroid subjects had increased alpha-subunit pulse amplitude. We then tested pulse concordance among the four simultaneous hormone series. alpha-Subunit and the gonadotropins were significantly coreleased (triple coincidence), suggesting that all three hormones are closely linked to processes that regulate GnRH secretion. alpha-Subunit bursts were also significantly coincident with those of TSH in men, postmenopausal women, and hypothyroid subjects. Interestingly, TSH pulses were significantly concordant with those of LH and FSH, and all four hormones were significantly concordant in men, postmenopausal women, and hypothyroid subjects. In conclusion, the present findings imply that an underlying unified signal coordinates pulsatile hormone secretion from both gonadotrophs and thyrotrophs.

An improvement to the space resolution of charged tracks

A simple tracking method is to look for the U , X and V triple coincidences in a wire chamber, but the space resolution is in general not satisfactory. In this paper, we consider the use of space correction for the inclined planes in a chamber. The resolution can be much improved for both the proportional chamber and the drift chamber. For proportional chambers, the combination of this method and the 1 4 wire-spacing “drift distance” technique, further improved the resolution.

Charge separation mass spectrometry: Part 2. Methyl compounds

Charge separation following double ionization of organic methyl compounds has been studied using the photoelectron—photoion—photoion triple coincidence technique. Two- and three-body dissociation pathways are observed with intensities related to the thermochemical stability of the products and to their odd/even electron numbers. The decay mechanisms show some evidence for rearrangement process via ylide dications prior to charge separation. The kinetic energy releases in the charge separation reactions can be rationalized in terms of a maximum charge separation within the molecular structure of the dications. The possibility and implications of dissociative double ionization of methyl compounds in the interstellar medium are discussed.

Strong harmonic E3 vibrations in 96Zr

A half-life of 46±15 ps has been determined for the 1897 keV first 3 − state of the doubly closed subshell nucleus 96Zr using a plastic-BaF 2Ge triple coincidence fast timing method. The deduced large B(E3)↑ value of 69 −17 +34 single particle units is consistent with the harmonic trend for strong octupole vibrators, and it is reproduced by an RPA calculation suggesting the 2p 3 2 →1g 9 2 proton and 2d 5 2 →1h 11 2 neutron particle-hole excitations as main ingredients.