Fourfold Coincidence Research Articles

Controlled sign gate through mode entangled states

We propose a model to perform controlled sign (CS) gate flip in two stages that is free of the use of detectors discriminating between one- and two-photon number states. The CS gate with mode entangled qubits and two-photon quantum channel is used at the first stage to produce a more perfect four-photon quantum channel. A two-photon quantum channel can be constructed using a spontaneous parametric down converter and methods of linear optics. We describe the CS gate performance with the help of a four-photon quantum channel at the second stage. The success probability of the CS gate performance with both two- and four-photon quantum channels is 1/4. The use of usual detectors at the first stage leads to the appearance of a noisy quantum channel that is shown not to have influence on the valid CS gate flip at the second stage whose outcome is characterized by fourfold coincidence registration of photons. The success probability of such a CS gate in two stages is 1/16.

Spins and parities of levels in fission fragments

Efficient methods for using triple and fourfold γ-ray coincidence data to give information on spins and parities of levels in secondary fission fragments are described. Triple-γ angular correlations and double-γ angular correlations culled from triple coincidences with one γ ray observed isotropically for selectivity have been used to give information on the multipole nature of transitions; directional linear polarization data culled from fourfold coincidences with one isotropically observed γ ray have been used to provide parity information. Results for known cascades agree with predicted correlation and polarization patterns. Examples of the techniques applied to transitions in Mo106 produced in the decay of Cm248 are given.

Novel transmission detector used for total cross section measurements

A new apparatus for total cross section measurements was developed and tested at Saturne II, Sacalay. The transmission ratios are determined using a ring-counter system coded in the Gray code, involving an exclusive four-fold coincidence between 4 counters among 8. Beam rate effects are suppressed by an electronic device which permits reaching an accuracy of better than 10 −4 in any transmission ratio. The apparatus was first used at SIN for the measurements of the total polarized proton-proton cross section difference Δσ L and of the spin correlation parameter A 00 kk in pp → pp and pp → dπ + reactions, and then at Saturne II for Δσ γ and Δσ L measurements in p-p scattering.

Simultaneous counting of true and random events in a four-fold coincidence system using two time-to-pulse-height converters

A system for measuring quadrupole coincidences is described which allows the simultaneous counting of true and random events. The system is realized by summing the output pulses of two time-to-pulse-height converters and uses only conventional electronic systems. The results of different experimental tests are reported which support the reliability of the system. The system can also be employed for triple coincidence experiments.

Adsorption and desorption of lead on low-index and stepped copper surfaces

Results from LEED, AES and isothermal desorption experiments are reported for monolayers of lead on low-index and stepped copper surfaces. Data for the (100), (711), (511), (311), (211) and (111) substrate orientations are discussed. Plots were made of the Auger peak-to-peak heights as a function of time during adsorption. These plots show breaks corresponding to the formation of dense monolayers and also earlier breaks due to changes in the sticking probability at the completion of submonolayer structures. The breaks permit a calibration of the spectrometer. For all substrate orientations LEED patterns were obtained with four-fold coincidence periodicities which are interpreted in terms of dense rows of lead atoms. For the stepped surfaces these rows are always parallel to the step directions. The desorption data (peak-to-peak heights as a function of time) show zero-order kinetics with initially a fast reaction and then a slow reaction that sets in at a coverage that depends on the orientation. The dominance of the fast reaction for (111) is related to the subsistence of islands of the compact monolayer arrangement down to low coverages.

Verbesserung der genauigkeit und laufgüte sechsglierdriger koppel-schwingrastgetriebe

In order to produce dwell-rise-dwell motions cam mechanisms can be designed much simpler than linkages. Because of the many advantages of linkages, more attention should be spent to their design and at first to the six-linked structures which fulfill the given problem by smallest expense. The six-bar coupler linkage is discussed here. It realizes the dwells by approximation of the coupler-curve to a circle which is represented by the length of an additional coupler link. Many investigations have been made to meet this problem best. So the circle point curve (Burmester-curve) represents a four-fold coincidence of coupler-curve and circle. If a dwell at the end of an oscillating motion is ordered, the curvature of coupler-curve must show an extremum value. If, in addition, two end-dwells are asked for the classic Burmester Theory never can solve this problem. Now the computer-aided design is able to give new ideas as follows: The major size of coupler-curves is well-known by tables like Hrones and Nelson's atlas and also the ranges usable for dwell-motions. Such four-bars are computer-programmed to find maximum values of curvature automatically. Deviations of the transmitting link from radius of maximum curvature enlarge the duration of dwell but increase the errors during the dwell period. In each case a four-fold coincidence is realized. The computer automatically finds all extremum curvature point and there are no difficulties in finding a second end-dwell. Using special four-bars with equal lengths of coupler, output link and coupler point distance, symmetrical coupler curves are produced in which extremum curvatures correspond to crank displacements of 180°. If non-symmetrical motions are wanted, four-bars with general dimensions have to be computer-investigated. It should be stated that by the method explained eight precision points of coupler curve have been found when the maximum of them is nine. For each problem a certain number of usable four-bars can be found. The computer cam then be ordered to find that one having smallest maximum acceleration. Further investigations in this direction should be started in order to find the limits of six-linked mechanisms and to learn exactly for which requirements linkages of higher order have to be used, i.e. how to produce longer dwells and those ones with higher accuracy, also how to produce two dwells having a larger difference in back and forth motion between dwells and finally how to design linkages for more than two dwells.

Double positron-electron pair production by 6.6-MeV gamma rays

Double positron-electron pair production by 6.6-MeV $\ensuremath{\gamma}$ rays was investigated via measurement of fourfold coincidence rates of annihilation quanta in targets of beryllium, boron, carbon, aluminum, sulphur, copper filings, and solid copper. Following an accounting for the interfering bremsstrahlung-cascade and direct-cascade effects a measure of the cross section for the process, relative to that for single-pair production, was obtained as $\frac{{\ensuremath{\sigma}}_{\ensuremath{\pi}\ensuremath{\pi}}}{{\ensuremath{\sigma}}_{\ensuremath{\pi}}}=(1.82\ifmmode\pm\else\textpm\fi{}0.58)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$.NUCLEAR REACTIONS Measured $\ensuremath{\sigma}$ for double-pair production at 6.6 MeV.

Size spectra of extensive air showers and primary cosmic-ray spectrum

Results on the size spectra of the extensive air showers, in the size range 105 <N < 107, recorded with two different triggering requirements, are presented. The differential size spectrum for showers recorded by means of a fourfold coincidence between the EAS array detectors is represented byF(N)dN= (1.01 ±0.10)-10-10(N/105)-2.8±0.05dNm-2s-1 .

An investigation of the absolute intensity of muons at sea-level

The absolute intensity of muons at sea-level has been measured using a telescope consisting of two arrays of crossed neon flash tube detectors triggered by a four-fold Geiger counter coincidence. The use of the flash tube information to delineate the particle trajectory has enabled the acceptance solid angle to be defined with an error of only 0.5%. All particles accepted by the telescope were required to penetrate a 10.3 cm thickness of lead which eliminated the soft component and ensured that only muons were detected. The total thickness of absorber penetrated by the triggering particle including all the material of the apparatus as well as that above the experimental site was 184.7 g cm −2 of lead which corresponded to a lower momentum cut-off of 0.35 GeV/ c. These intensity measurements have been made with the axial direction of the telescope in the magnetic NS azimuth for zenith angles of 0°, 45°, 60° and 80°. A comparison with the universally accepted value of the vertical absolute intensity for muons at sea-level given by Rossi from the work of Greisen is included and this shows that the present result (9.13 ± 0.12) × 10 −3 cm −2 s −1 sr −1) is higher by 9%. General agreement with this conclusion is provided by Allkofer et al. although the latter authors claim the Greisen result to be too low by some 26%. A tentative comparison between the present result and that obtained by Allkofer et al. is also given although due to the difference in the lower momentum cut-offs associated with the two instruments use has to be made of the integral spectrum measured by Allkofer and Clausen, the accuracy of which allows only qualitative agreement to be claimed. The variation of absolute intensity with zenith angle obtained in this work has been shown to be adequately represented by the expression I Θ = 9.13 × 10 −3 cos 2.16 Θ for angles less than 75°. Since no other absolute intensity measurements have been performed for zenith angles in the range 0° to 85° a comparison is made of the exponent and this indicates the existence of good agreement between the results from the various workers. The data at large zenith angles has been analysed separately and this is presented together with the work of Jakeman and Wilson.

Comment on the Experimental Investigation of Photon - Photon Collisions in Electron - Positron Storage Rings

Continuing our calculations on photon-photon collisions in electron-positron storage rings, i.e., reactions of the type ${e}^{\ensuremath{-}}{e}^{+}\ensuremath{\rightarrow}{e}^{\ensuremath{-}}{e}^{+}{A}^{\ensuremath{-}}{A}^{+}$ (where $A=e,\ensuremath{\mu},\ensuremath{\pi},K,\dots{}$), we now introduce realistic experimental conditions, in particular two cutoff parameters: a minimal emission angle (${\ensuremath{\psi}}_{min}$) with respect to the beam axis for the particles ${A}^{\ifmmode\pm\else\textpm\fi{}}$ to be produced, and a minimal relative energy loss (${\ensuremath{\chi}}_{min}$) for the outgoing electron and positron (to be detected practically in their forward directions). Taking realistic values for ${\ensuremath{\psi}}_{min}$ and ${\ensuremath{\chi}}_{min}$, their effect on the invariant mass spectrum of the pair ${A}^{\ensuremath{-}}{A}^{+}$ and on the integrated cross section is shown. In particular, the modification of the energy behavior, due to these cutoffs, is exhibited. In spite of the drastic character of the restrictions considered, it is shown that fairly high counting rates may still be expected (for $A=e,\ensuremath{\mu},\ensuremath{\pi}$) in the four-fold coincidence experiments suggested, with electron-positron storage rings of the next generation (beam energy 2-3 GeV, luminosity \ensuremath{\sim} ${10}^{32}$ ${\mathrm{cm}}^{\ensuremath{-}2}$ ${\mathrm{sec}}^{\ensuremath{-}1}$).

A fourfold coincidence system to measure positron-gamma angular correlations

A method is described to measure positron-gamma angular correlations. The positrons are detected in a plastic scintillator. The disturbance of the energy selection, caused by Compton scattering of annihilation quanta in the plastic, has been avoided by counting these quanta simultaneously in two NaI(Tl) crystals placed face to face near the plastic. The problem of subtracting random coincidences in the fourfold coincidence system is discussed and the results of test measurements on 86Rb and 22Na are compared with previous results.

Decay Asymmetry of Cosmic Ray Muons

In this paper an account is given of the investigations on the decay asymmetry of cosmic-ray muons carried out in two different energy bands with the help of a multiplate cloud chamber. Although similar investigations have been made in different laboratories with scintillation counters, employing the delayed coincidence technique for the detection of the decay electrons, the cloud chamber has been chosen for some special advantages which are discussed in the paper. The most important among these are (i) the decay electrons are detected from zero delay up to a delay of about 50 milliseconds, which is never possible in the delayed coincidence method, (ii) the change of direction of the decay electrons in the absorbing material due to scattering is avoided by dividing the whole absorber into thin plates separated by gaps in which the electrons are observed. Even if these electrons are subsequently scattered their original direction of emission is clearly observed, as shown in figure 1 (a) and (b). After careful scanning of about 36 000 photographs taken by means of a fourfold coincidence and anticoincidence system about 1500 unambiguous μ-e decay events were selected. Of these, 1021 events correspond to a muon momentum interval 0.30-0.40 GeV/c and 482 events to a momentum interval 1.3-1.4 GeV/c at the experimental station, which was situated at a height 2.2 km. The up-down ratios of electrons emitted in the two momentum intervals are 1.17 ± 0.05 and 1.18 ± 0.08 respectively, which yield partial longitudinal polarizations of 0.34 ± 0.09 and 0.36 ± 0.11 after correcting for the depolarization effect of the atmosphere and moderator. Our results, therefore, show no evidence for the increase in the degree of polarization with increase of momentum of the muons which some workers have observed. The absolute magnitude of the polarization observed is consistent with a K/π ratio of about 5% in the pion spectral region 0.2 to 5.6 GeV.

Cloud-Chamber Study of Hard Collisions of Cosmic-Ray Muons with Electrons

The energy distribution of the secondary electrons produced in targets of carbon or paraffin by the $\ensuremath{\mu}\ensuremath{-}e$ scattering process for muon momenta in the range 5-50 Bev has been measured for electron energies up to 10 Bev, or c.m. momentum transfer up to 100 Mev. A vertical array of three cloud chambers immersed in a magnetic field of 11 000 gauss was used with a fourfold coincidence system. Two flat rectangular proportional counters, suitably biased, together with two Geiger-M\uller trays, provided fair rejection of uneventful penetrating particles and a high efficiency for selection of the narrow electronic showers characteristic of the high-energy electromagnetic events. On 5900 counter triggered photographs there were 291 accepted events, having one or more (\ifmmode\pm\else\textpm\fi{}) electrons with energy \ensuremath{\ge}0.10 Bev, believed to originate in $\ensuremath{\mu}\ensuremath{-}e$ collisions in the (carbon or paraffin) target above the top chamber, from incident muons in the momentum interval 5-50 Bev. The data are compared with a calculation based on the Bhabha formula for spin \textonehalf{} muons, taking into account the momentum distribution of the incident muons, the energy loss and shower development in the target and the chamber walls, and a theoretical efficiency factor. Arguments are given to show that direct pair production and bremsstrahlung of the muons in the target and in the Pb shield above the apparatus produce negligible effects. The experiment permits a reliable measurement of only the relative distribution. When arbitrarily normalized, the calculated distribution is in fairly good agreement with the data, except for a small systematic difference suggesting an excess of observed events for the harder collisions. Although the discrepancy is interpretable as a statistical fluctuation, the data are fitted much better over the entire range when the basic cross section is modified by a factor, ${F}^{2}$ (greater than unity), with $F=1+|{q}^{2}|{{\ensuremath{\lambda}}_{\ensuremath{\mu}}}^{2}$ where $q$ is the invariant of the 4-momentum transfer in units of $\ensuremath{\hbar}$, and ${\ensuremath{\lambda}}_{\ensuremath{\mu}}$ is the Compton wavelength of the muon. This may be the first indication of a deviation from standard quantum electrodynamics for hard $\ensuremath{\mu}\ensuremath{-}e$ collisions. More strongly it shows that, if there is a deviation, it is not representable by a form factor less than unity.

Anti-Coincidence Circuit for Use in the Millimicrosecond Region

An anti-coincidence circuit for use in the millimicrosecond range was attained by modifying a crystal diode coincidence circuit. A fifth diode was added to the original fourfold coincidence circuit in series with the 1-k resistor. The circuit was tested with pulses from five scintillation counters arranged as a telescope in the 80-Mev meson ( pi /sup +/) beam at the Nevis cyclotron. (M.C.G.)

Cosmic Ray Expedition

THIS month (August 1949) a party of American men of Science, sponsored by the National Geographic Society and by the Bartol Research Foundation, will visit the Canadian settlement Churchill on Hudson Bay, to investigate the cosmic-ray intensity at a height of twenty miles. A fourfold coincidence arrangement of Geiger counters carried aloft on free balloons will be used, and the observations, together with data for the atmospheric pressure, and the temperature within the apparatus, will be transmitted by radio and recorded on moving tape on the ground. Previous height measurements of cosmic rays up to 30,000 ft. were made with specially equipped B-29 aircraft. Churchill is chosen as the venue of the expedition because of its high geomagnetic latitude (69°). It is hoped to determine whether at 100,000 ft. height the cosmic-ray intensity continues to increase with geomagnetic latitude ; if not, one interpretation would be that the cut-off is caused by the action of a solar magnetic field. Canadian meteorologists stationed at Churchill will take part in the work. It may be hoped that it has been possible to arrange to use these flights for the determination of the winds at 100,000 ft., on which our information is still very scanty.

Evidence for the Radioactivity of Slow Mesotrons

A beam of mesotrons is selected by means of a fourfold coincidence system of counters, and is allowed to pass through a block of iron 10 cm thick. The absorption of mesotrons by the iron is recorded by means of a battery of anticoincidence counters. It is found that a certain fraction of the stopped mesotrons is associated with the emission of an ionizing particle from the absorber. A special coincidence recording system, whose resolving time is of the order of one microsecond, enables one to establish that the emission of the particles is delayed with respect to the passage of the mesotron by a few microseconds. The delayed particles are interpreted as the electrons resulting from the $\ensuremath{\beta}$-decay of the mesotron. The present experiment establishes only the order of magnitude of the mean life of the mesotron at rest, but more quantitative measurements are in progress.

Mean Life of Slow Mesotrons

The author recently described1 an experiment which enabled him to detect the disintegration electrons emitted by mesotrons at the end of their range. This is a preliminary report of new results obtained with an improved arrangement which was designed to measure a decay curve of mesotrons at rest. The set-up may be briefly described as follows. A fourfold coincidence counter set defines a beam of mesotrons, which impinges upon a block of iron 10 cm thick and 2.5 cm wide. A battery of anticoincidence counters, placed below the iron, selects the events in which a mesotron is absorbed. It is found that a fraction of these absorption processes is associated with the emission of a particle from the absorber. This particle may be a disintegration electron, or possibly a scattered mesotron. A system of circuits simultaneously records the numbers n1, n2 and n3 of such particles emitted within, respectively, 36, 3.1 and 1.2 microseconds after the passage of the primary mesotron. It is found that many of the particles are delayed, which is expected to be the case for the disintegration electrons, but not, of course, for scattered mesotrons. The conditions of the experiment are such that n1, n2 and n3 are affected by a “background” due to undelayed processes (scattered mesotrons + showers) which, however, is identical (not statistically) for all three; hence the differences are significant. Since we can safely assume that all mesotrons have decayed within 36 microseconds, we may write:

Mesotron Production in the Atmosphere

With Geiger-M\uller tubes arranged for fourfold vertical coincidence, a Rossi-Hsiung type of experiment was performed in an aeroplane up to an altitude of 25,000 feet. A sheet of lead 8.1 cm thick placed between the counter tubes and another lead plate of 2.2 cm thickness was alternately changed from the position above all the tubes to a position between the second and third tubes. From the difference between the counting rates in the two cases, it was found that at an altitude of 25,000 feet an average of 2 ionizing penetrating particles (mesotrons) per minute were ejected in the forward direction from a lead plate (38 cm\ifmmode\times\else\texttimes\fi{}5.2 cm\ifmmode\times\else\texttimes\fi{}2.2 cm) by the action of non-ionizing rays (photons). This value aleads to a cross section for the production of mesotrons by photons which is in at least rough agreement with the theory.

New Evidence for the Existence of Penetrating Neutral Particles

An experiment of the Rossi-Hsiung type was performed at an altitude of 14,200 ft. with a fourfold coincidence array of Geiger-M\"uller tubes in a vertical position. Thicknesses of 12.7 to 17.3 cm of lead served as absorber between the counters. Additional varying thicknesses were placed alternately above and between the counters, i.e., in positions $A$ and $B$. For small thicknesses the ratio of the counting rates with the lead in position $A$ to that for position $B$ was very little greater than unity. This means very slight production of barytrons by photons at this altitude. For greater thicknesses (19 to 23 cm), however, the ratio $\frac{A}{B}$ becomes 1.06\ifmmode\pm\else\textpm\fi{}0.02. Working at sea level, and having the bottom tube shielded with 25 mm of lead, Hsiung obtained the same results. Maass, using no shield for the tubes, found the ratio $\frac{A}{B}$ equal to 1.2. The most reasonable interpretation of the fact that this ratio is greater than unity seems to be the production of barytrons by non-ionizing primaries. In view of the great thickness of lead required to give the maximum effect, these non-ionizing particles must be much more penetrating than photons. This high penetrating power suggests their identification with the neutrettos (neutral particles having mass and other properties similar to the barytron) postulated by Heitler.