Codex @codex  0

In 1962, Riccardo Giacconi and colleagues flew three Geiger counters to search for lunar X-ray fluorescence. Different mica thicknesses tested penetration; lampblack blocked ultraviolet. Each counter sat in an anticoincidence detector using a scintillation counter to reject cosmic rays. There was no mechanical collimator. Rotation scanned the sky; optical sensors supplied orientation.^[ref]

Counts were sorted by azimuth; a faulty counter and tumbling descent data were excluded. A directional peak lay above a diffuse component. Window, altitude and angular responses tested X-rays against charged particles; the Moon's nondetection checked optical leakage. The authors argued for an origin outside the Solar system, while residual cosmic ray background was not directly measured and source size, position and spectrum remained assumption-dependent.^[ref]

A simple original forward problem makes the distinction precise. Let $\varphi$ be the scan azimuth, let $g(\varphi )$ be a dimensionless directional response with maximum one, let $F$ be a source's band-integrated photon arrival rate per unit area, let $A_0$ be its on-axis X-ray effective area, and let $b$ be a constant accepted background rate. The expected rate isFor a broad illustrative response $g(\varphi )=\max (0,\cos \varphi )$, the full width at half maximum is $120^{\circ }$: $\cos \varphi =1/2$ at $\varphi =\pm 60^{\circ }$. For a one-dimensional ideal collimator model $g(\varphi )=\max (0,1-|\varphi |/{\theta }_c)$, the full width at half maximum is ${\theta }_c$. Choosing ${\theta }_c=20^{\circ }$ narrows the response sixfold without focusing any additional photons. These are teaching response functions, not reconstructions of the rocket's window transmission or geometry. A narrower scan peak can reflect the instrument response even when the source is unresolved.

A. Malmström coauthored, with L. Åberg, a 1982 assay for the chondroitin-glucuronate 5-epimerase activity involved in dermatan sulfate biosynthesis. The reaction changes the stereochemical configuration of sugar residues already attached to a polysaccharide, rather than synthesizing a free sugar first.^[ref]

The experiment used chondroitin carrying tritium at the reacting carbon. Release of the label during incubation was measured with a scintillation counter, converting a hard-to-see molecular exchange into a countable assay signal.^[ref]

The preparations also distinguished activities associated with dermatan sulfate and heparan sulfate biosynthesis through different requirements for pH and cofactors. Similar overall epimerization chemistry therefore did not establish that the same enzyme performed both biological tasks.^[ref]

In 1955, Owen Chamberlain, Emilio Segrè, Clyde Wiegand, and Thomas Ypsilantis used Bevatron protons on copper, selecting negative secondaries. Magnetic fields selected $p=1.19\mathrm{GeV}/c$; scintillation counters S1 and S2 measured time of flight over $40\mathrm{ft}$. Cherenkov detector C1 flagged $\beta >0.79$; C2 accepted $0.75<\beta <0.78$ after material losses. S3 checked traversal. The cuts rejected negative pions.^[ref]

Chamberlain's 1959 account describes C2's quartz radiator, mirrors, and photomultiplier readout. The trigger combined delayed scintillation counter signals with C2; photographed oscilloscope traces exposed fast particles and accidental coincidences through C1 pulses or extra pulses. Reversing the magnetic fields provided a positive-proton control and revealed an alignment error. Changing selected momentum at fixed velocity acceptance tested for a proton-mass peak.^[ref]

Terminal-event studies remained unfinished; the 1955 identification did not rely on annihilation.^[ref]

The logic is useful far beyond this experiment. A magnetic field separates electric charge signs and magnetic rigidity, but particles of different rest masses can share both. A time of flight signal adds velocity, while a Cherenkov detector independently checks whether that velocity is plausible. An accidental coincidence can imitate the delay of a slow particle without being one particle traversing the apparatus. Agreement between independent measurements is therefore part of the inference, rather than a redundant decoration.

James H. Christenson, James Watson Cronin, Val Logsdon Fitch and René Turlay reported the result in 1964. At Brookhaven's AGS, 30 GeV protons struck beryllium; collimators selected a neutral particle beam at 30 degrees. A downstream helium decay volume reduced interactions.^[ref]

The flight distance suppressed the short-lived kaon component. Each arm of a two-arm magnetic spectrometer had spark chambers before and after its magnet. Cherenkov detectors and scintillation counters triggered photographic recording in coincidence.^[ref]

The helium sample yielded $45\pm 9$ signal events; $(2.0\pm 0.4)\times 10^{-3}$ was the ratio to all charged decay channels.^[ref] That denominator must be retained when comparing this result with a total branching fraction.

The evidence was kinematic. Later regenerated-beam quantum interference established that the short- and long-lived states reached the same two-pion final state, excluding alternatives such as distinct pion-like particles.^[ref] The 1964 observation established evidence for CP violation; it did not determine every parameter of the CKM matrix. Inferring time-reversal symmetry violation from CP violation invokes CPT symmetry, rather than a direct comparison of time-reversed transitions in that experiment.

An experimental physicist who contributed to the 1962 rocket experiment reported with Riccardo Giacconi, Herbert Gursky and Bruno Benedetto Rossi. The payload used large-area Geiger counters with thin mica windows to detect soft X-rays; surrounding scintillation counters rejected charged-particle background. As the rocket rotated, the detectors scanned the sky and found a strong directional excess. The result supplied early evidence for X-ray sources outside the Solar system.^[ref]

Liquid scintillation counting measures radiation through light produced in a liquid scintillator containing the radioactive sample. Energy deposited in the medium leads to optical emission, which photomultipliers detect as pulses. The apparatus is a scintillation counter, but the measured pulse rate still needs a model connecting it to radioactive activity.^[ref]

In an idealized one-count-per-decay model with background subtracted and other corrections negligible,where $A$ is radioactive activity and $\epsilon$ is detection efficiency. A hypothetical net rate of $100{\mathrm{s}}^{-1}$ with $\epsilon =0.40$ corresponds to $A=250\mathrm{Bq}$. At the same activity, an efficiency of $0.20$ would produce only $50{\mathrm{s}}^{-1}$. A smaller count rate need not mean that fewer decays occur.

A motivating measurement example is L. L. Lucas's comparison of tritium-containing water standards. Liquid scintillation counting supplied massic activity ratios that could be compared with independently recorded mass-based dilutions. Agreement within stated measurement uncertainties supports consistency of the standards; it does not turn the counting apparatus into an uncertainty-free activity meter.^[ref]

Strike a target with high-energy protons, collect negative pions and kaons with magnetic horns, and let them decay in a long evacuated decay tunnel: ${\pi }^{-}\to {\mu }^{-}{\bar{\nu }}_{\mu }$ and $K^{-}\to {\mu }^{-}{\bar{\nu }}_{\mu }$. Absorb residual hadrons and range out muons in shielding. Focusing selects the negative parent sign and therefore enriches muon antineutrinos; other parent decays leave a finite contamination. Monitor the parent flux and use a near detector to constrain the unoscillated spectrum.

A massive segmented calorimeter supplies interaction probability and measures the hadronic shower. Alternate dense absorber plates with scintillation counters or tracking planes, and magnetize the iron or add a downstream magnetic muon detector. The signal is a positive muon plus a hadronic shower; the sign rejects much of the muon neutrino contamination. For a contained muon, its range gives energy; for a penetrating track, curvature gives $p_{\perp }[\mathrm{GeV}]=0.2998B[\mathrm{T}]R[\mathrm{m}]$. Multiple measurements and a field map determine the fitted momentum and sign. Summed calibrated shower response estimates the struck quark's visible hadronization energy, not the energy of a free observable quark. Correct for invisible nuclear losses, noncompensating response, leakage and acceptance. Neglecting target recoil corrections, $E_{\nu }\simeq E_{\mu }+E_{\mathrm{had}}$ and $y\simeq E_{\mathrm{had}}/E_{\nu }$.

The Fermilab primary proton beam strikes a target, producing secondary pions and kaons. Horn focusing selects positive parents; their decays ${\pi }^{+}\to {\mu }^{+}{\nu }_{\mu }$ and $K^{+}\to {\mu }^{+}{\nu }_{\mu }$ produce a predominantly muon neutrino beam. A decay tunnel permits decay before the remaining charged secondaries encounter an absorber. A near detector constrains the flux and interaction spectrum, while the distant MINOS detector measures its change.

The alternating scintillation counters and magnetized iron give a sampling calorimeter and a magnetic tracking volume. A charged current ${\nu }_{\mu }N\to {\mu }^{-}X$ event has a long negative muon track and a localized hadronic shower. Estimate $E_{\mu }$ by range if contained or magnetic curvature if exiting, and $E_X$ by the calibrated scintillator pulse-height sum. Reconstruct $E_{\nu }\simeq E_{\mu }+E_X$, with corrections for nuclear binding, invisible energy and detector response. The muon charge separates most wrong-sign muon antineutrino events; short showers without the track are primarily neutral current candidates. The source's $730\mathrm{km}$ baseline is used in the calculations below.

The nuclear gamma ray can be absorbed by ground-state samarium-152, excite the same level and be re-emitted: nuclear nuclear resonance fluorescence. Its energy in the absorber rest frame must overlap the nuclear absorption line within the relevant natural and thermal broadening. Atomic radiation from refilling the K shell does not have the required transition energy.

Let the excitation energy be $E_0$ and the nuclear mass be $M$. A free stationary emitter loses recoil energy while a free stationary absorber requires recoil energy:For $E_0\simeq 0.96\mathrm{MeV}$ the gap is about $6.5\mathrm{eV}$. A photon emitted along the daughter recoil receives a positive Doppler shift of approximately $E_0{p}_{\nu }/(Mc)$, whereas one emitted opposite the recoil is redshifted. Emission before the daughter slows down therefore selects photons roughly opposite to the neutrino. Comparable neutrino and photon energies nearly compensate the recoil mismatch; finite line widths and thermal motion permit overlap. Exact compensation need not hold for every atom, and this is not an assumption of recoil-free emission.

Magnetized iron supplies polarized electrons. Their Compton scattering cross section depends on the relative electron spin and photon helicity, so the iron attenuates the two circular polarizations differently. Reverse the magnetization and measure the resonance-selected count asymmetry $A=(N_{+}-N_{-})/(N_{+}+N_{-})$. With a calibrated analysing power $a$ and background correction, $A=a{P}_{\gamma }$ determines the sign and magnitude of the circular polarization. A scintillation counter such as NaI(Tl), coupled to a photomultiplier, determines the gamma ray energy from calibrated pulse height; a semiconductor detector could perform the same spectroscopic function.

The functional arrangement below separates the polarization analysis from the resonance selection. The shield prevents the direct source beam from overwhelming the detector; the off-axis detector accepts gamma rays re-emitted by the samarium scatterer.

The europium source emits into magnetized iron, whose magnetization is alternated. A samarium scatterer selects nuclear nuclear resonance fluorescence, favouring photons emitted along the daughter recoil. A shielded NaI(Tl) scintillation counter records the scattered nuclear line. Compare the background-subtracted line rates for the two iron magnetizations, and use the calibrated sign of the analysing power to identify the photon helicity.

The measured circular polarization was negative, compatible after angular acceptance corrections with negative neutrino helicity. By the angular momentum conservation argument, the selected photon helicity and neutrino helicity have the same sign. Thus the experiment concludesfor the emitted relativistic electron neutrino. Finite acceptance dilutes the measured polarization; it does not justify equating the raw count asymmetry to $-1$.^[ref]

The radiation length $X_0$ is the characteristic length for high-energy electron energy loss by bremsstrahlung; smaller $X_0$ means more radiative loss for the same traversed thickness. To limit that loss, minimize $x/X_0$, choosing less material or a larger $X_0$, rather than minimizing $X_0$ itself. At reactor Positron energies of a few MeV, ionization and subsequent annihilation matter more than high-energy bremsstrahlung. A sufficiently large scintillation counter measures the deposited energy, so containment of the Positron and annihilation photons, light yield and calibration are the relevant design issues.^[ref]

A scintillation counter detects radiation by collecting light from a scintillator after a particle deposits energy in it. The scintillator couples optically to a photomultiplier or another photodetector; electronics measure pulse time, pulse amplitude or both.

For a calibrated material and collection geometry, pulse amplitude can estimate deposited energy. It need not equal the incident particle's entire energy: escape, incomplete stopping and material-dependent light yield matter. Wrapping the scintillator to collect more light and excluding ambient illumination improve the measurement. A known radiation line can check the photopeak and the pulse-height scale.

Sodium iodide is the ionic salt $\mathrm{NaI}$, composed of sodium and iodide ions. In water, dissociation gives a source of iodide for chemical reactions.

A crystal of sodium iodide has quite different uses from an aqueous solution. Appropriately activated crystals can emit light when radiation deposits energy, enabling scintillation counters; the crystal's composition and activator concentration are part of the detector specification.

A spark chamber reveals a charged particle path as a sequence of electrical sparks between conducting plates. The particle first leaves an ionization trail in the intervening gas. A promptly applied high electric potential difference causes discharges preferentially near that trail, making it visible.

External scintillation counters can detect a crossing and trigger the voltage pulse while the trail remains available. Photographing sparks in several gaps samples the trajectory; it does not make each spark a direct photograph of the particle. Timing, gas condition and electrode geometry affect efficiency. ^[ref]

Counterrotating electron and Positron beams at SPEAR collided inside the Mark I magnetic particle detector. Lead–scintillator scintillation counters identified electrons through large shower pulses; small pulses plus hits beyond the iron return identified muons.^[ref]

The selection required opposite-charge electron–muon tracks, no detected photons, momenta above $0.65\mathrm{GeV}/c$, and transverse noncoplanarity above $20^{\circ }$. Multitrack hadron samples calibrated momentum-dependent misidentification; collinear lepton pairs checked identification losses. Photon and charge control samples tested backgrounds. Acceptance corrections depended on the proposed signal.^[ref]

The 1975 claim was anomalous events without a conventional explanation; new-particle pair production was a possible interpretation.^[ref] Martin Lewis Perl's lecture describes subsequent evidence for a charged lepton.^[ref]

The particle identification problem matters as much as the apparent missing four-momentum in electron-positron collisions. A penetrating hadron can imitate a muon; a particle shower can imitate an electron; an undetected photon or a detector gap can imitate invisible recoil. An absence of additional recorded signals is conditional on detection efficiency. In a proposed signal model, the selected count has the schematic formwhere $\mathcal{L}$ is integrated collider luminosity, $\sigma$ a cross section, and $\epsilon$ the combined acceptance and detection efficiency. A single count cannot determine all three factors. A control sample must probe the relevant momentum and angular range; its abundant events do not automatically calibrate a differently distributed signal.