radioattivita' naturale · 2014. 6. 13. · 4 preamble early 1900: the discharge of electroscopes...

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Radioattivita' naturale

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Raggi Cosmici

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PreambleEarly 1900: the discharge of electroscopes due to ionization induced by natural radioactivity (Rutherford)

DiscoveryIn 1909 Theodor Wulf used an enhanced electroscope at the top of the Eiffel Tower. Ionisation rate lower than at its base, but... less than expected.

In 1911 Domenico Pacini measuring of the rate of ionization over a lake, over the sea, and at a depth of 3 meters from the surface, concluded that a part of the ionization must be due to sources other than the radioactivity of the Earth.[11]

In 1912, Victor Hess carried three enhanced-accuracy Wulf electrometers[12] to an altitude of 5300 meters in a free balloon flight. He found the ionization rate increased approximately fourfold over the rate at ground level.[12]. Hess still measured rising radiation at rising altitudes.[12] He concluded "The results of my observation are best explained by the assumption that a radiation of very great penetrating power enters our atmosphere from above."

In 1913–1914, Werner Kolhörster confirmed Victor Hess' earlier results by measuring the increased ionization rate at an altitude of 9 km.

Hess received the Nobel Prize in Physics in 1936 for his discovery.[13][14]

http://en.wikipedia.org/wiki/Theodor_Wulfhttp://en.wikipedia.org/wiki/Domenico_Pacinihttp://en.wikipedia.org/wiki/Cosmic_ray#cite_note-11http://en.wikipedia.org/wiki/Victor_Francis_Hesshttp://en.wikipedia.org/wiki/Cosmic_ray#cite_note-HessNobelPresSp-12http://en.wikipedia.org/wiki/Hot_air_balloonhttp://en.wikipedia.org/wiki/Cosmic_ray#cite_note-HessNobelPresSp-12http://en.wikipedia.org/wiki/Cosmic_ray#cite_note-HessNobelPresSp-12http://en.wikipedia.org/wiki/Werner_Kolh%C3%B6rsterhttp://en.wikipedia.org/wiki/Nobel_Prize_in_Physicshttp://en.wikipedia.org/wiki/Cosmic_ray#cite_note-13http://en.wikipedia.org/wiki/Cosmic_ray#cite_note-14

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Early Cosmic Rays

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The Cosmic Ray energy spectrum

⇒ power law(s) flux

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C.R. flux isotropic and time independent … but low energy (< 1 GeV/c)

● The “solar wind” consists ofhot particles with enoughkinetic energy to escape thesun’s gravity:

• Cosmic Rays diffuse towards the Earth through this plasma● Particles having energies less than ~ 1 GeV/nucleon interact with it

⇒ Solar modulationimportant for atmospheric neutrinos!

vesc=√ 2GMR ≈620 kms

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Anticorrelation with Sunspots

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Composition

• Primary composition:– 90% protons– 9% helium nuclei– 1% electrons(depends on energy)• Charged particles deflected bymagnetic fields– Near the Earth’s magnetic field– In the galaxy’s magnetic field– In the magnetic fields betweengalaxies• When cosmic rays arrive, theygenerally do not point back to their source.

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Composition

• Primary composition:– 90% protons– 9% helium nuclei– 1% electrons(depends on energy)• Charged particles deflected bymagnetic fields– Near the Earth’s magnetic field– In the galaxy’s magnetic field– In the magnetic fields betweengalaxies• When cosmic rays arrive, theygenerally do not point back to their source.

Propagation effects

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Propagation of Galactic C.R.'s

● (Li,Be,B) and (Sc→Mn) ~absent in stellar nucleosynthesis

● Produced by collisions of C.R.nuclei with interstellar medium (ISM)

σSpallation ⊗ ρISM (~1 p/cm3) → X ≈ 5-10 g/cm2

L = X/(mpρISM) ≈ 3 x 1024 cm ≈ 1 Mpc

>> Galaxy disk thickness (dG~ 300 pc)

τGCR = L/c ≈ 3 Myr

● GCR are confined by the Galactic magnetic field [O(μG)]

● Max. confinement energy for RL ≈ dG:

RL ≈ 1.1 103 E(eV)/Z cm @ 3 μG ⇒ Emax ≈ Z 10

18 eV

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UHECRCR's above 1018 are extragalactic

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Acceleratori di particelle

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Rivelatori di particelle

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Review of Particle Properties/Detectors-at-accelerators

Review of Particle Properties/Detectors-non-accelerators

http://pdg.lbl.gov/2013/reviews/rpp2013-rev-particle-detectors-accel.pdfhttp://pdg.lbl.gov/2013/reviews/rpp2013-rev-particle-detectors-non-accel.pdf

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Neutrone e positrone

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J. Chadwick, “Possible Existence of a Neutron.” Nature , 129 , 312 (1932)

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C. D. Anderson, “The Positive Electron.” Phys. Rev. , 43 , 491 (1933)

6 mm lead

B = 1.5 T

p [GeV/c] = 0.3 B[T] R[m]

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Pione e muone

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Pione e muone

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−dEdx

∝E

−dEdx

≈const

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S. H. Neddermeyer and C. D. Anderson , J. C. Street and E. C. Stevenson, “Note on the Nature of Cosmic Ray Particles.” “New Evidence for the Existence of a Particle of Mass Intermediate between the Proton and Electron.” Phys. Rev. , 51 , 884 (1937). Phys. Rev. , 52 , 1003 (1937).

1x2x3x4

L = lead

C = Cloud chamber

R vs Ionisation

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M. Conversi, E. Pancini, and O. Piccioni, “ On the Disintegration of Negative Mesons.” Phys. Rev. , 71 , 209 (1947).

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M. Conversi, E. Pancini, and O. Piccioni, “ On the Disintegration of Negative Mesons.” Phys. Rev. , 71 , 209 (1947).

"As a personal opinion, I would suggest that modern particle physics started in the last days of World War II, when a group of young Italians, Conversi, Pancini, and Piccioni, who were hiding from the German occupying forces, initiated a remarkable experiment. In 1946, they showed that the « mesotron » which had been discovered in 1937 by Neddermeyer and Anderson and by Street and Stevenson, was not the particle predicted by Yukawa as the mediator of nuclear forces, but was instead almost completely unreactive in a nuclear sense. Most nuclear physicists had spent the war years in military-related activities, secure in the belief that the Yukawa meson was available for study as soon as hostilities ceased. But they were wrong.", L. Alvarez, Nobel lecture 1968

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π-

D. H. Perkins, “Nuclear Disintegration by Meson Capture.” Nature , 159 , 126 (1947).

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C. M. G. Lattes, G. P. S. Occhialini, and C. F. Powell, “Observations on the Tracksof Slow Mesons in Photographic Emulsions.” Nature , 160 , 453 (1947).

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A. G. Carlson, J. E. Hooper, and D. T. King, “Nuclear Transmutations Produced byCosmic-Ray Particles of Great Energy – Part V. The Neutral Meson.” Phil. Mag. , 41 ,701 (1950).

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water/heavy water

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π→μν π→eν →eνν

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Antiprotone

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E. Amaldi et al., Nuovo Cimento, 1, 492 (1955)

Emulsioni esposte a RC ad alta quota (pallone)

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O. Chamberlain, E. Segre', C. Wiegand, and T. Ypsilantis, “Observation of Antiprotons.”Phys. Rev. , 100 , 947 (1955).

● Deflessione di 21° per il campo magnetico di Bevatron● Deflessione di 32° dal magnete M1● Focalizzazione in Q1 (3 quadrupoli magnetici

consecutivi): focalizza le particelle verso il contatore S1● S1 primo contatore a scintillazione● Q2 focalizza di nuovo le particelle verso M2● Deflessione di 34° dal magnete M2● S2 secondo scintillatore● C1 contatore Cerenkov β > 0.79● C2 contatore Cerenkov 0.75 < β < 0.78● S3 terzo scintillatore

Misura di velocita':

1) Contatori Cerenkov2) S1-S2 TOF

p = 1.19 GeV/c ⇒ β = 0.78 → 0. 765 (dopo S1, S2, C2)

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Particelle strane

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G. D. Rochester and C. C. Butler, “Evidence for the Existence of New UnstableElementary Particles.” Nature , 160 , 855 (1947).

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Produzione associata di particelle strane

471 GeV/c π- interaction in Berkeley 10” bubble chamber

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Tecniche

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● Fundamental textbook by W. H. Barkas (1963)● Nuclear Emulsion, used to record the tracks of charged

particles, is a photographic plate.● A photographic emulsion consists of a large number of

small crystals of silver halide, mostly bromide.● The sensitivity to light has allowed silver halides to

become the basis of modern photographic materials.● Silver halide crystals dispersed in a gelatin● The method of recording tracks of charged particles in

photographic plates is based upon two achievements of modern technology, the photographic emulsion and the optical microscopes.

● Three main phases:

● Latent image formation● Chemical development● Image viewing / data analysis

Nuclear Disintegration

Nuclear Emulsion

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Latent image formation

The absorption of energy in a sensitized crystal of silver bromide leads to a concentration of a few silver atoms of the sensitizing layer, initially dispersed over the surface, into an aggregate which can act as a development centre, i.e. a Latent Image

By Fuji Film Electron micrograph of Silver Halide Crystals

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Chemical development

Emulsion Films drying after development

● Photographic developer is a chemical amplifier acting on the latent image.

● Rather complex physics-chemical process is able to transform those grains with a suitable development centre into metallic silver

● After development emulsion placed in a second bath (fixer) which dissolves the unaffected grains of silver halide but leaves the small black granules of silver

● Finally, the emulsion plates are washed and dried

52Pion Interaction

Data analysis

Nuclear Emulsion particle detectors feature the highest position and angular resolution in the measurement of tracks of ionizing particles... but

very slow analysis (scanners at microscopes)

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Bubble chambers

A vessel filled with a superheated transparent liquid (most often liquid hydrogen) used to detect electrically charged particles moving through it. Invented in 1952 by Donald A. Glaser (1960 Nobel Prize in Physics).

Same principle of cloud (Wilson) chamber but inverse phase transition(supersaturated vapor).

BC data scan and measurement

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The bubble chamber is similar to a cloud chamber in application and basic principle. It is normally made by filling a large cylinder with a liquid heated to just below its boiling point. As particles enter the chamber, a piston suddenly decreases its pressure, and the liquid enters into a superheated, metastable phase. Charged particles create an ionisation track, around which the liquid vaporises, forming microscopic bubbles. Bubble density around a track is proportional to a particle's energy loss.

Bubbles grow in size as the chamber expands, until they are large enough to be seen or photographed. Several cameras are mounted around it, allowing a three-dimensional image of an event to be captured. Bubble chambers with resolutions down to a few μm have been operated.

The entire chamber is subject to a constant magnetic field, which causes charged particles to travel in helical paths whose radius is determined by their charge-to-mass ratios and their velocities. Since the magnitude of the charge of all known charged, long-lived subatomic particles is the same as that of an electron, their radius of curvature must be proportional to their momentum. Thus, by measuring their radius of curvature, their momentum can be determined.

Why did bubble chambers supersede cloud chambers?

1. density factor: suitable (and used for) as target and detector

2. possible use of Liquid Hydrogen

http://en.wikipedia.org/wiki/Cloud_chamberhttp://en.wikipedia.org/wiki/Boiling_pointhttp://en.wikipedia.org/wiki/Pistonhttp://en.wikipedia.org/wiki/Metastablehttp://en.wikipedia.org/wiki/Liquid_bubblehttp://en.wikipedia.org/wiki/Micrometershttp://en.wikipedia.org/wiki/Helixhttp://en.wikipedia.org/wiki/Charge-to-mass_ratiohttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Momentum

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Gargamelle @ CERN

BEBC @ CERN

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First Ω - event (BNL)

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Nuclear emulsion vs. bubble chamberCommon features:● Imaging techniques (only these before 1980's): static support of

images● not triggerable (BC: could only trigger photo snapshot)● No time resolution (NE: always | BC: ~ 1 ms/cycle)● Slow data analysis (slower for NE)

Differences:● Duty cycle (NE: 1 | BC: ~O(%), but possible to syncr. with

accelerator cycle)● Spatial resolution (NE: ~1 μm | BC: ~0.1-1 mm)

● Magnetic spectrometry (NE: No because of mult. scatt. | BC: Yes)

Early 70's: emulsion technique decliningBC widely used in hadron spectroscopy and neutrino physics

Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48What is Nuclear Emulsion in Particle and Nuclear Physics?Latent Image FormationThe DevelopmentWhat is Nuclear Emulsion?(2)Slide 53Slide 54Slide 55Slide 56Slide 57

radioattivita' naturale · 2014. 6. 13. · 4 preamble early 1900: the discharge of electroscopes...

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