V. S. Narasimham

Cosmic-ray intensity measurements deep undergound at depths of (800÷8400) m w.e.

SummaryAn experiment has been carried out to investigate the variation of vertical cosmic-ray intensity with depth in the range (800÷8400) m w.e. Counter telescopes with plastic scintillator layers and Geiger counter trays, kept in the horizontal plane and in coincidence, were employed. The experiment was carried out in the Kolar Gold Fields (Mysore State, India). The results obtained at depths of 816, 1812, 3410, 4280, 6380 and 8400 m w.e. are given.RiassuntoSi è effettuato un esperimento per studiare la variazione dell’intensità verticale dei raggi cosmici nell’intervallo (800÷8400) m a.e. Si sono adoperati telescopi di contatori con strati di scintillatori plastici e vassoi di contatori di Geiger posti orizzontalmente e in coincidenza. L’esperimento fu eseguito nei Kolar Gold Fields (Stato di Mysore). Si riportano i risultati ottenuti alle profondità di 816, 1812, 3410, 4280, 6380 e 8400 m a.e.

The Kolar Gold Fields neutrino experiment II. Atmospheric muons at a depth of 7000 hg cm-2 (Kolar)

An experiment has been performed in the Kolar Gold Fields in Southern India to search for the interaction products of cosmic ray neutrinos. In the course of four years operation of the detectors at a depth of 2316 m of rock, some 165 particles were recorded which were attributed to muons of atmospheric (as distinct from neutrino-) origin and the present paper describes the results of measurements on these particles. The measured vertical intensity at the depth in question (2316 m of Kolar rock corresponding to 7.6 x 105 g cm-2 of standard rock) is (1.1 ± 0.2) 10-6 m-2 s-1 sr-1. Including measurements at shallower depths by other workers, from sites elsewhere in the same Gold Fields, a best fit to the data gives the relation I(h) = 7.73 x 10-3 exp (–h/790) m-2 sr-1 s-1 for depth range 4000 < h < 9500 hg cm-2 Kolar rock (1 hg cm-2 = 102 g cm-2). An approximate estimate has been made of the mean energy of the atmospheric muons at the depth of operation; its value, ca. 330 GeV, is not inconsistent with the expected value.

The intensity and angular distribution of cosmic rays far underground

An apparatus incorporating scintillators, Geiger counters and neon flash-tubes has been operated at three locations underground in the Kolar Gold Fields, India, to measure the vertical intensity and angular distributions of penetrating cosmic-ray muons. The intensities at the three depths (816, 1812 and 4100 metres water equivalent of rock) are, respectively; (2.39 ± 0.15) × 10-6, (2.00 ± 0.12) × 10-7 and (4.63 ± 0.57) × 10-9 cm-2 sec-1 sterad-1. The angular distributions are well represented by expressions of the form I(θ) = I(0)cosnθ, where θ is the zenith angle, and the values of n at the successive depths are 1.93 ± 0.22, 3.03 ± 0.16 and 5.12 ± 0.82.

The Kolar Gold Fields neutrino experiment I. The interactions of cosmic ray neutrinos

Final results are presented of an experiment to study the interactions of cosmic ray neutrinos deep underground, at a depth of 7.6 x 105 g cm-2 (standard rock). Clear examples have been recorded of neutrino-induced muons, including cases of upward moving particles and neutrino interactions within the detector assembly itself. The observed rate of events is compared with expectation and conclusions are made about the variation of the inelastic cross-section with energy and the lower limit to the mass of the intermediate boson. An examination has also been made of the celestial coordinates of the detected neutrinos and details are presented.

Energy spectrum of cosmic-ray muons at sea level

SummaryThe integral energy spectrum of cosmic-ray muons at sea level in the energy range (200÷7500) GeV is deduced from the results obtained by us (as reported in an earlier paper) on the variation of vertical cosmic-ray intensity with depth in the range (800÷8400) m w.e. In doing this, the effect of fluctuations in the energy losses of muons is taken into account. The deduced muon energy spectrum is compared with direct magnet spectrograph observations and with the muon energy spectrum deduced by the Bristol group from their observations on γ-ray cascades at high altitudes. The exponents of the integral production spectra of parents of muons are given and an upper limit to the energy losses of muons in nuclear collisions is set.RiassuntoDai risultati da noi ottenuti (e riferiti in un precedente articolo) sulla variazione della intensità verticale dei raggi cosmici con la profondita nell’intervallo (800÷8400) m a.e. si deduce lo spettro integrale dell’energia dei muoni dei raggi cosmici al livello del mare nell’intervallo di energia (200÷7500) GeV. Nel far ciò si tiene conto dell’effetto della fluttuazione nella perdita di energia dei muoni. Si confronta lo spettro d’energia dei muoni, cosi dedotto, con le osservazioni dirette allo spettrografo magnetico e con lo spettro d’energia dedotto dal gruppo di Bristol dalle loro osservazioni sulle cascate di raggi γ a grandi altezze. Si danno gli esponenti degli spettri integrali di produzione dei muoni generatori e si pone un limite superiore alle perdite di energia dei muoni nelle collisioni nucleari.

Muon intensities and angular distributions deep underground

Recent measurements of the intensity of muons below 3000 m.w.e. (metres water equivalent) underground have been combined to give an estimate of the depth-intensity relation and the angular distribution for atmospheric muons down to a maximum depth of approximately 9000 m.w.e. It is found that the vertical intensity can be represented by the expression I(0, h) = 9.8 × 10-7 exp(-h/λ)cm-2sec-1sterad-1 where h is the depth in m.w.e. and λ = 810 ± 50 m.w.e. The corresponding angular distribution at vertical depth h is given by I(θ, h) = I(0, h) secθ exp{-(h/λ)(secθ - 1)} where θ is the zenith angle. The implication of the above angular distribution for the estimate of neutrino fluxes in deep underground cosmic-ray experiments is discussed.

V. Studies of cosmic ray neutrino interactions in the Kolar Gold Field experiment

Results are presented of an experiment to study the penetrating particles in the cosmic radiation deep underground, at a depth of 7500 m. w. e. (standard rock). The events recorded are attributable, in the main, to muons produced either in the atmosphere or by the interactions of neutrinos in the surrounding rock. The muons have been studied in some detail and it appears that the mean energy of the neutrino induced muons (probably less than about 30 GeV) is low compared with that of the muons of atmospheric origin. The significance of the celestial coordinates of the muons and the measured rate of neutrino- induced muons is discussed and the future experimental programme is indicated.