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COMPOSIZIONEdei RAGGI COSMICI

Composizione dei Raggi Cosmici

Struttura della Composizione e' similealla composizione media del sistema solarecon alcune IMPORTANTI ANOMALIE:

Elementi leggeri (Li, Be, B) [Z=3,4,5] molto piu' abbondanti che nella media del sistema solare.

Anche elementi “sub-iron” (sotto il ferro)come Titanio, Vanadio molti piu' abbondanti.

Effetto Pari/Dispari meno marcato

Abbondanze dei differenti Nucleinella Materia Ordinaria:

NucleoSintesi nelle Stelle

ZH 1He 2

Li 3Be 4B 5

C 6N 7O 8

Elementi “saltati” dal processo principale dellanucleosintesi [3α → Carbonio + γ ]

Effetto dei Processi di “SPALLAZIONE” (“SPALLATION”) Frammentazione di un nucleo relativistico in un urto con protone (od un altro Nucleo)

A + p → A1 + A

2

Etot

(A) = A E0

Etot

(A1) = A

1 E

0

Etot

(A2) = A

2 E

0

In spallation processesthe energy per nucleon is roughly conserved

The existence (and the relative importance)of the secondary nucleons is an indicationthat the cosmic rays have crossed a certainamount of column density of order(of 1 interaction length)

X ∼ 10 g cm-2

Propagation of Cosmic Rays in the Galaxy

For a thereotically well motivated study of the propagation one should considerthe DIFFUSION of Cosmic Rays in the Galactic Magnetic Field.

Propagation in a Random Field

Described as

Diffusion

1-Dimension

3-Dimension

DiffusionCoefficient D

Partial DifferentialEquation describingDiffusion

N(E,x,t) = Density of Cosmic Rays of energy E at position x and time t

Source Diffusion Interactions

Volume containingMagnetic Field

Particles exiting the Volume are “lost”

[Neglecting Energy Losses]

LEAKY BOX MODEL

Source Escape

HomogeneousModel Drop the x dependence

Neglectinteractions

Hypothesis of STATIONARITY

Note: The observed spectrum has a different form from the injected spectrum

Escapeor Interaction ?

Hypothesisof stationarity:

Hypothesis is goodif τ

escape << T

Galaxy

Propagation of a “Secondary Nucleus”that is a particle that is so rare (Like Li, Be, B)that the direct acceleration is negligible.

For simplicity we can assume a generic

secondary nucleus S that is

produced a single primary nucleus P

Direct Source Escape Spallation

of primarySource

Ratio Primary/Secondary measures the product

Mean FreePath ofCR in the Galaxy

ism

ism

Boron/Carbon Ratio

Escape Length   (g cm­2)

Source Spectrum of Galactic Cosmic Rays

The spectrum of Cosmic Rayat the accelerator has the form E−α With α = 2 - 2.2

Determination of the Escape Time

Use of COSMIC CLOCKS

Isotope Be-10 Half-time : 1.6 * 106 years Comparison with Be-7 Be-9 (stable isotopes)

Beryllium-10 Measurements

NEED for an EXTENDED COSMIC RAY HALO

Emission of Synchrotron emission rom our Galaxy

Energia in RAGGI COSMICI

Condizione di Stazionarieta'

T(Galaxy) ≅ 1010 years

T(cr) ≅ 107 years

Potenza Necessaria per rinnovare la Popolazionedi Raggi Cosmici

Potenza-In = Potenza-Out

Potenza-Out = Energia -Raggi Cosmici

Tempo di Confinamento

= Energy density *Volume

Tempo di Confinamento

Energy Density of Cosmic Rays

Energy Balance  SuperNova possible Contribution