• Non ci sono risultati.

are NOT the same giving the electronic signals !!!


Academic year: 2021

Condividi "are NOT the same giving the electronic signals !!!"

Mostra di più ( pagine)

Testo completo


Scintillator Detectors


Electrons formed in ionization process

are NOT the same giving the electronic signals !!!


= phosphorescence

Phosphorescence is a property of many crystals and organic materials

Light is produced by deexcitations of



In 1903 W. Crookes demonstrated in England his

“ spinthariscope ” for the visual observation of individual scintillations caused by alpha particles impinging upon a ZnS screen. In contrast to the analogue methods of radiation measurements in that time the spinthariscope was a single- particle counter, being the precursor of scintillation counters since. In the same period F. Giesel, J. Elster and H. Geitel in Germany also found that scintillations from ZnS represent single particle events. This paper summarises the historical events relevant to the advent of scintillation counting.

ZnS: the precursor of modern scintillator counters

“2003: a centennial of spinthariscope and scintillation counting”

Z. Kolar et al., App. Rad. And Isot. 61 (2004)261




Organic scintillator

[Solid or liquid: haromatic hydrocarbons (benzene, …) ]

0.1 eV 1 ps

1 eVt ~ 10 ns Rise time Dt ~ 0.1 nsec

Low Z

Low efficiency

# g/keV ~ 8-10

p electrons energy levels

absorption fluorescence phosphorescence

Singlet Spin=0 Excited electrons are the ones NOT strongly

involved in the bonding of the material ( p electrons )

GS = S00

Fluorecence: 10


s (FAST)

Phosphorescence: 10



Emission after intra-band transition (SLOW)




Þ in Organic scintillators Absorption and Emission

occur at different wave-length

at room temperature

all electrons are in S



Inorganic scintillator

[Solid crystals: NaI, CsI, BGO, BaF


, LaBr

3, …


High Z

High efficiency

# g/keV ~ 40

[Þ 4 times better than plastic]

Excited electrons beween atomic states (from valence band to conducting band)


4 eVt ~ 230 ns Rise time Dt ~ 10 nsec

1 part/10


NaI(Tl), CsI(Na), …

Doping material is used to minimize re-absorbtion from the crystal,

since emitted light has lower

energy than energy-gap.


Similar effec in Organic Sintillator


Charged Particles identifications

Organic scintillators

the slow component (t ~ ms) due to delayed phosporescence

(from triplet state)

is larger for particles with large dE/dx energy levels

absorption fluorescence phosphorescence

singlet triplet

prompt fluorescence

(from singlet state):

~ few ns

light yield

S = scintillator efficiency kB = fitting constant







Inorganic Scintillators: CsI(Tl), BaF


, …

a particle E


=95 MeV

tf = 800 ns ts = 4000 ns

÷÷ ø çç ö

è æ -

÷ +

÷ ø ö ç ç

è æ -


s s

s f



t h t

t h

L ( ) t exp t t exp t

Light output:

Sum of two exponential functions:

fast & slow components

1. ts independent of particle nature

2. R = hs/(hf+hs) increases with decreasing ionisation density

3. tf increases with decreasing ionisation density è

it is possible to identify different particles






N.B. CsI have been used at first for particle studies:

- less fragile than NaI

- good particle discrimination


Organic vs. Inorganic


Big Disadvantage: Hygroscopic


Organic scintillators


independent of temperature between -60° and 20°

Inorganic scintillators


Strong dependence on temperature

Temperature effect

Relative Light output



Use of light Pipe:

- coupling with photodetector - need to locate photodetector

away from scintillator (magnetic field ..)


(e ~ 30%)


Output Signals

From Anode

From Dynodes



(e ~ 30%)

# photoelectrons generated

# incident photons on cathode

e =


G ~ d


d ~ 3-5

emission probability of secondary electrons

n ~ 10

Different types of PMT


Material: semiconductors

2-3 eV needed to release an electron

Linearity and Stability is required

[if electrons are released in random directions Only few will reach the surface Þ reduced gain]


Emission coefficient


Another Dynode configuration: Micro Channel Plate

Advantages: 1. fast timing 20ps (short distance, high field) 2. tollerate high magnetic fields

3. position sensitive


# g/keV ~ 40 à


Energy resolution

Never achieved in practice, due to various sources of electronic noise


Cited by Knoll Book



Documenti correlati

careers have been monetized by parents and managers across the whole history of cinema. Countries such as Canada, the United States and the United Kingdom have

If persons with disabilities who have completed at least primary education had the same probability of completing upper secondary and tertiary education as non-disabled people,

As I suggested above, the ultimate consequence of reading the proem as commonplace (or metaphorical) has been to cloud our view as to what we should see as actual

In the present work, we build on the literature about SLAM and visual odometry to implement a smoothing-based approach for UAV navigation using dense image information from a

The transformer is designed and fabricated as a symmetrical octagonal spiral structure using two-metal layer process on GaAs substrate for input balun applications of 2 GHz and 5

Fig. 3 - A) Line drawing of a cranium and mandible of Eschrichtius in right lateral view (the gray-shaded area represents the bone portions preserved in the Pliocene Belgian

Anello luxury bijoux che racchiude con grande originalità l’anima del marchio, i colori differenti delle pietre, i volumi dati dalla zirconia e cristallo di

The main contribution of this paper is to provide a complete analysis of the trade-off between performance and information flow in the simple case of the stabilization of a scalar

The differences may reside mainly in the apodosis, which is the selector of the conditional: the first two types (the second being that we have analysed in the section before)

Then we have studied the abundance gradients along the Galactic disk produced by our best cosmological model and their dependence upon several parameters: a threshold in the surface

Le scelte degli autori dei testi analizzati sono diverse: alcuni (per esempio Eyal Sivan in Uno specialista) usano materiale d’archivio co- me fotografie e filmati, altri invece

Here, to make up for the relative sparseness of weather and hydrological data, or malfunctioning at the highest altitudes, we complemented ground data using series of remote sensing

University of Michigan, Ann Arbor, MI USA GARASSINO MARINA CHIARA Fondazione IRCCS Istituto Nazionale dei Tumori, Milano IT.

Other forms of enforcement, on the other hand, lend themselves to almost complete automation, such as in the case of enforcement over (at least certain types of)

We will relate the transmission matrix introduced earlier for conductance and shot noise to a new concept: the Green’s function of the system.. The Green’s functions represent the

The linear model used to identied the components of the inertial tensor it is considered a good model, since ,if it is consider the central part of the plots, the error between

The pentraxins C-reactive protein (CRP), long pentraxin 3 (PTX3), and serum amyloid P component (SAP) are serum proteins associated with increased risk of cardiovascular events

Peculiarity of such integrable systems is that the generating functions for the corresponding hierarchies, which obey Euler-Poisson-Darboux equation, contain information about

To confirm the data obtained on primary neurons, we used a different experimental model: PC12 cells expressing the dox‐in‐ ducible G2019S LRRK2 mutant.. 12 The cells were treated

n Diathermy means “to heat up”, a term first used in the early 1900s after the observation of tissue heating without muscle contraction can occur with high frequency

Hendolin HI, Pååkænen ME, Alhava EM, Tarvainen R, Kemppinen T, Lahtinen P (2000) Laparoscopic or open cholecystectomy: a prospective randomised trial to compare post- operative

This result strongly suggests that we are observing discrete shifts from part-time to full-time work, as conjectured by Zabalza et al 1980 and Baker and Benjamin 1999, rather