COMPOSIZIONE dei RAGGI COSMICI - Welcome to the INFN …lipari/lez2.pdf · Composizione dei Raggi...
Transcript of COMPOSIZIONE dei RAGGI COSMICI - Welcome to the INFN …lipari/lez2.pdf · Composizione dei Raggi...
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