Counter Controlled Cloud Chamber Research Articles

Walther Bothe and Bruno Rossi: The birth and development of coincidence methods in cosmic-ray physics

In 1924, Walther Bothe and Hans Geiger applied a coincidence method to the study of Compton scattering with Geiger needle counters. Their experiment confirmed the existence of radiation quanta and established the validity of conservation principles in elementary processes. At the end of the 1920s, Bothe and Werner Kolhörster coupled the coincidence technique with the new Geiger–Müller counter to study cosmic rays, marking the start of cosmic-ray research as a branch of physics. The coincidence method was further refined by Bruno Rossi, who developed a vacuum-tube device capable of registering the simultaneous occurrence of electrical pulses from any number of counters with a tenfold improvement in time resolution. The electronic coincidence circuit bearing Rossi’s name was instrumental in his research on the corpuscular nature and the properties of cosmic radiation during the early 1930s, a period characterized by a lively debate between Millikan and followers of the corpuscular interpretation. The Rossi coincidence circuit was also at the core of the counter-controlled cloud chamber developed by Patrick Blackett and Giuseppe Occhialini, and became one of the important ingredients of particle and nuclear physics. During the late 1930s and 1940s, coincidences, anti-coincidences and delayed coincidences played a crucial role in a series of experiments on the decay of the muon, which inaugurated the current era of particle physics.

Interaction mean free path of the particles emitted in cosmic ray nuclear explosions

The measurements of the interaction mean free path of the near minimum ionizing particles emitted in cosmic ray nuclear explosions are discussed. A new determination of this mean free path has been made at mountain altitude, using a counter controlled cloud chamber containing thin lead foils. The result is 200±25% g cm−2 Pb.

P M S Blackett, G Occhialini and the invention of the counter-controlled cloud chamber (1931–32)

Among the most important detecting devices in the 1930s, cosmic-ray experimental physics figures the so-called ‘counter controlled cloud chamber’. This apparatus was jointly developed in 1932 by P M S Blackett, the cloud chamber expert at the Cavendish Laboratory in Cambridge and by G Occhialini, who mastered the counting coincidence technique following his work under the guidance of B Rossi in Florence. In this paper we address the original technical description of the apparatus and place its development within the historical and scientific framework of 1930s physics.

13.—A Search for the Quark in Extensive Air Showers, using a Counter-controlled Cloud Chamber

SynopsisA search is reported for the relativistic e/3 quark among the cores of Extensive Air Showers initiated by primaries with energies greater than 1014 eV. The detector is a high-pressure cloud chamber filled with helium at 28 atmospheres, and is counter controlled. The experimental conditions avoid the criticisms levelled at the McCusker experiment and are such that the tracks of e/3 quarks cannot be simulated by singly charged shower particles either through statistical variations in primary ionisation or otherwise. The primary ionisation density, measured using a gap-counting technique on post-expansion electron and muon tracks, is compared with predictions from the theory of Budini et al. (1960). The agreement achieved shows that the theory is a reliable foundation for methods of identifying quark candidates, and measuring charges. The experiment has been running for 5000 hours. No quark candidates have been found. With an acceptance angle of 0·3 sr and an area of 140 cm2, this sets the upper limit of flux of e/3 quarks at 4 × 10−9 cm−2 sec−1 sr−1 with 95 per cent, confidence. The experiment is being continued.

On knock-on electrons of cosmic-ray muons in condensed matter (at 12° N)

The dependence of knock-on electron probability on the momenta of muons producing the knock-on electrons in condensed matter has been investigated by using a counter controlled cloud chamber. A search has also been made on the nature of the energy spectrum of the knock-on electrons from muons in the momentum region (0.80±0.05) to (1.70±0.05) Bev/c. It appears from the results of the measurements that there is a very weak dependence of knock-on electron probability on the primary muon momentum in the investigated muon spectral region (i.e. (0.80±0.05) to (1.70±0.05) Bev/c). The angular distributions and hence the energy spectra of the emergent electrons are found to be independent of muon momentum.

Energy spectrum of muons from their knock-on electrons

The energy spectrum of muons producing knock-on electrons in medium- and low-Z elements has been determined. The energy of a muon can be determined from the energy it transfers to a knock-on electron and the angle which the knock-on electron makes with the direction of incidence of the primary muon. The energies of 289 and 271 incident muons producing knock-on electrons of energies greater than 25 MeV in carbon and aluminium and of 273 muons producing electrons of energy greater than 60 MeV in copper plates placed inside a counter-controlled multiplate cloud chamber, have been determined. The spectrum of muons at this place is then obtained after taking into account the variation of knock-on cross-section with muon energy and integrating this cross-section over electron energy intervals (ɛmin to ∞) considered in this experiment. The spectra of muons thus obtained compare favourably with the corresponding sea-level spectra as obtained by the Durham magnetic spectrograph.

Recoil Proton Polarization from 225-Mevπ−−pScattering

${\ensuremath{\pi}}^{\ensuremath{-}}$ mesons of energy 225 Mev were scattered from liquid hydrogen. The polarization of the recoil proton has been measured at two angles. For analyzing the polarization, a counter controlled cloud chamber was used. Recoil protons, which experienced scatterings in a carbon plate of the cloud chamber, were photographed stereoscopically. The pictures were later projected, and the necessary measurements of the scattering were made directly in three dimensions. The computed polarizations are -0.13\ifmmode\pm\else\textpm\fi{}0.16 at a laboratory recoil angle of 15\ifmmode^\circ\else\textdegree\fi{}, and +0.36\ifmmode\pm\else\textpm\fi{}0.29 at 31\ifmmode^\circ\else\textdegree\fi{}. The positive sign is for polarization in the direction of the vector cross product of the incident pion momentum and the recoil proton momentum. A comparison of the data is made with various sets of scattering phase shifts which represent the differential cross-section data equally well. The results favor the Orear type of Fermi set in which the $S$-wave ${\ensuremath{\alpha}}_{1}$ phase shift is positive.

Cloud chamber study of cosmic ray electronic showers under dense materials (II)

Pictures have been taken by means of a counter controlled cloud chamber on electronic showers produced in lead plates 1, 3 and 4 cm thick. The angular distribution of tracks has been compared with the calculations ofRoberg andNordheim and ofFranchetti andGiovaknozzi. The distribution of showers as a function of the number of electrons has been used to check the results given byJanossy andMessel and byArley.

An Improvement in High Speed Expansion of Counter-Controlled Cloud Chamber

An Improvement in High Speed Expansion of Counter-Controlled Cloud Chamber

Search for Highly Absorbable Negative Cosmic-Ray Particles at Sea Level

A search has been made at sea level for negative cosmic-ray particles (other than electrons) which are absorbed in 147 g/${\mathrm{cm}}^{2}$ of lead and which have momenta greater than that of mu mesons of this range. The momentum and sign of the charge of those particles stopping in the absorber were determined by means of a counter controlled cloud chamber operated in a magnetic field. During 1400 hours of operation no negatively charged particle in the momentum interval 0.4-1.7 Bev/c was recorded as stopping in the absorber. This result has been used to show that the intensity of negative particles with strong nuclear interaction cannot amount to as much as 0.05 percent of the total intensity of negative particles in this momentum interval. It has been shown that the local production of negative mu mesons in the momentum interval 0.5-1.0 Bev/c is less than 8.8\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}5}$ particle/(${\mathrm{cm}}^{2}$ steradian hr meter). A lower limit of 6.9\ifmmode\times\else\texttimes\fi{}${10}^{5}$ g/${\mathrm{cm}}^{2}$ of lead has been set on the removal path length of mu mesons in the momentum interval 0.4-1.6 Bev/c.

Cloud chamber study of cosmic ray electronic showers under dense materials (I)

Pictures of electronic showers have been taken by means of a counter controlled cloud chamber. This 1st paper deals essentially with the methods employed in analysing the collected data. As an example, the results obtained with a lead plate 2 cm thick inside the chamber are described. They include angular distributions, distributions according to the number of electrons, ratio of photon initiated to electron initiated showers.

A Search for Penetrating Showers from Hydrogen at Sea Level Using a Cloud Chamber

The extent to which multiple production of $\ensuremath{\pi}$-mesons takes place in local sea-level penetrating showers was studied with a counter controlled cloud chamber in a magnetic field. The rates at which penetrating showers occur under carbon, aluminum, and lead were determined and a search was made for them under liquid hydrogen. In a total operating time of 626 hours with an average thickness of 2.28 g/${\mathrm{cm}}^{2}$ of liquid hydrogen above the chamber, no penetrating showers were found which could have originated in the hydrogen. On the basis of the rates at which such showers occur in heavier materials and the number of them formed in the material of the Dewar while operating with hydrogen, one would have expected to detect a minimum of 6 showers from the hydrogen if the cross section for the production of penetrating showers were the geometric area of the nucleus (taken as 6\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}26}$ ${\mathrm{cm}}^{2}$ for hydrogen). It can then be concluded that the majority of sea-level local penetrating showers detected below heavy materials by an apparatus of this kind can be attributed mainly to plural production. From momentum measurements in the magnetic field, the minimum value which can be assigned to the momentum of the incident nucleons which causes the average penetrating shower detected with this apparatus was estimated at 6 B ev/c. It follows that the multiple production of charged mesons in a single nucleon-proton collision at about 6 Bev probably does not occur in more than 15 percent of the cases.The ratios of the rates at which penetrating showers were detected under C, Al, and Pb were proportional to the geometric area of the nuclei within statistical limits.An event found in the hydrogen which is very similar in appearance to the $\ensuremath{\mu}$-meson interaction first observed by Braddick and Hensby is discussed. A photograph of a nuclear collision in lead is described in which very little energy is transferred to the lead nucleus although the incident particle has a momentum estimated to be 40 Bev/c.

On the Nuclear Interactions of Cosmic Ray Shower Particles in Lead

Using counter controlled cloud chamber in conjunction with hodoscope, nuclear interactions which were caused by secondary shower particles were investigated, and these events classified as high and low energy showers by the inspection of hodoscope pictures. The results show that the multiplicities of the low and the high energy secondary showers are 2.8±0.4 and 3.1±0.4 respectively and from angular distributions of tertiary particles, it is concluded that the mesons are presumably produced multiplily and isotropically in C-system.

The Differential Range Spectrum of Cosmic-Ray Mesons at Sea Level

The low energy region of the differential range spectrum of cosmic-ray mesons at sea level has been investigated by means of a counter controlled cloud chamber. The results obtained in the region from 18 g/${\mathrm{cm}}^{2}$ to 76 g/${\mathrm{cm}}^{2}$ of air equivalent absorber have proved to be about 20 percent higher than predictions based upon similar measurements at greater absorber thicknesses. A possible explanation of this discrepancy lies in the consideration of the effect of multiple scattering of mesons in previous experiments. The present experiment employs a geometrical arrangement of the apparatus which minimizes the corrections to be applied to the data to allow for loss of mesons from the apparatus due to scattering. The earlier work in the field has not been corrected for scattering effects and can, as a result, be expected to give too low a value of the spectrum. The average differential intensity of mesons measured in the range interval mentioned above is 6.86\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ (particles/sec/sterad/g). The differential range spectrum of protons was also measured and is in good agreement with other work which measured the spectral values at somewhat higher energies than those encountered here. The proton intensity is 2.12\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ (particles/sec/sterad/g) in the region 16.5 to 42.3 g/${\mathrm{cm}}^{2}$ of air equivalent and 0.67\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ (particles/sec/sterad/g) in the region 42.5 to 63.3 g/${\mathrm{cm}}^{2}$ of air equivalent.

Nuclear Interactions in Gold of Secondary Particles Emitted in Penetrating Showers

A large counter controlled cloud chamber containing 16 gold plates totaling 308 g/${\mathrm{cm}}^{2}$ in thickness was operated at an altitude of 11,500 ft. Forty of the pictures of penetrating showers obtained were selected for the determination of the mean free path for nuclear collisions of ionizing secondary particles. The result was found to be 230\ifmmode\pm\else\textpm\fi{}60 g/${\mathrm{cm}}^{2}$, corresponding to 0.7\ifmmode\pm\else\textpm\fi{}0.2 times the cross section equal to the geometric area of the gold nucleus. The 14 percent of the nuclear events used in making this determination were large angle scatterings of a penetrating secondary particle with no observable disintegration products emerging from the gold plate in which the scattering occurred. The number of secondary nuclear events occurring, which are not observed because of the absorption of all tertiary particles, was estimated to be 18 percent of the total. The momenta of the secondary particles used in this determination ranged between ${10}^{9}$ and ${10}^{10}$ ev/c. The lowest energy penetrating shower which has a high probability of tripping the counter coincidence circuit used was estimated to be 1.5\ifmmode\times\else\texttimes\fi{}/${10}^{10}$ ev.The number of high energy protons among the secondary particles used in the determination of the collision mean free path was less than 11 percent, and the total fraction of protons is less than 30 percent. The 88\ifmmode\pm\else\textpm\fi{}3 percent of the penetrating showers observed in the experiment showed the presence of an observable electron cascade. The average number of penetrating secondaries of minimum ionization emitted in penetrating showers of an average energy of 3\ifmmode\times\else\texttimes\fi{}${10}^{10}$ ev, and either not showing any electronic cascade or showing the presence of an electronic cascade having an energy less than or equal to 7\ifmmode\times\else\texttimes\fi{}${10}^{9}$ ev, is 7\ifmmode\pm\else\textpm\fi{}1 per shower. The corresponding average multiplicity of secondary particles of minimum ionization in penetrating showers of 6\ifmmode\times\else\texttimes\fi{}${10}^{10}$ ev average energy, which show the presence of an electron cascade of an energy greater than 7\ifmmode\times\else\texttimes\fi{}${10}^{9}$ ev, is 11\ifmmode\pm\else\textpm\fi{}2 per shower. Evidence is given that the angular distribution of the mesons in the center-of-mass system of a nucleon-nucleon collision at energies above 1.5\ifmmode\times\else\texttimes\fi{}${10}^{10}$ ev is not isotropic and is probably collimated in two cones of about 50\ifmmode^\circ\else\textdegree\fi{} half-angle around the directions of the velocities of the nucleons in the center-of-mass system.

The Differential Range Spectrum of Cosmic-Ray Mesons

A counter-controlled cloud chamber has been used to investigate the differential range spectrum of mesons at sea level. The chamber contains eight lead plates each 7\textonehalf{} in. wide and one-half in. thick. A lead absorber of variable thickness, up to 27 in., may be placed above the chamber. The number of mesons observed the stop in the chamber per unit time has been found for various thicknesses of absorber above the chamber. A plot of the counting rate of particles which stop versus the thickness of absorber above the chamber reveals a broad low peak which has its maximum at a 6-in. thickness of absorber. The counting rate at the peak is 2.20\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ count/sec./sterad/g, about 10 percent higher than the counting rate with no absorber. Correction has been made for particles lost through scattering in the absorber. The corrected results show a more marked peak whose maximum occurs with a 9-in. thickness of absorber. The counting rate at the maximum of the corrected curve is 3.73\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ count/sec./sterad/g.

Cloud chamber observations on the electromagnetic component from nuclear explosions and the development of the nuclear cascade

The results of a research on nuclear explosions, made at the Laboratorio della Testa Grigia (3500 m a.s.l.) with a counter controlled cloud chamber are reported. Principal aim of the research is to study the electromagnetic component arising from nuclear explosions and the development of the nuclear cascade.

A Doubly Charged Cosmic Ray Particle

AMONG more than a thousand stereoscopic counter-controlled cloud chamber photographs of mesons which we have obtained during the past six months while studying the scattering of mesons of different energies in lead plates, we have obtained the photograph reproduced herewith. Each one of the stereoscopic cameras made an angle of 22½° with the normal to the chamber. The chamber was triggered by a triple coincidence Geiger – Muller counter system with 25 cm. of lead below the chamber and above the lowest counter, so at least one of the particles must penetrate 25 cm. of lead. There was no lead on the top of the chamber. The usual argon–alcohol mixture was used in the chamber.

Neutron and Negative Proton

ABOUT a year ago, I proposed a method of detecting the decay of the neutron1. Recently, it has been reported that Kapitza has, in the course of the analysis of cosmic ray spectra, discovered the negative proton. Whether this news is true or not, it is quite reasonable to suppose that a free neutron has also the probability of being I+radioactive*, thus producing a negative proton. This process would, of course, occur only if the mass of the negative proton is smaller than that of the neutron. To detect the existence of this negative proton, one may apply the method similar to that proposed in my previous note1 and then search for the I+ rays. If the negative proton is the anti-particle of the ordinary proton, the annihilation process might be expected to occur with the emission of one or two photons of energy about 109 eV. These photons will, on encountering the wall of the containing vessel, produce electron showers of a considerable number of particles which may easily be detected by using a counter-controlled cloud chamber arranged in usual ways. These showers can very easily be distinguished from the showers of cosmic rays since we know that the latter are mostly in downward directions.

Cloud-Chamber and Counter Studies of Cosmic Rays Underground

A counter controlled cloud chamber and two counter coincidence sets were used to study the nature of the cosmic rays observable underground. The experiments were performed in a copper mine at depths of 71, 141, 582, and 657 meters water equivalent. The data are easily interpreted, if one assumes that underground the primary rays are mesotrons and that the soft rays and showers are electronic secondaries produced by the penetrating mesotrons.