Measurement and simulation Measurement and simulation of the - - PowerPoint PPT Presentation

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 1

Measurement and simulation Measurement and simulation

• f the neutron response and detection efficiency
• f the neutron response and detection efficiency
• f a
• f a Pb

Pb – – scintillating scintillating fiber fiber calorimeter calorimeter

• A. Ferrari
• A. Ferrari

Fondazione Fondazione CNAO ( CNAO (Milano Milano) )

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 2

The KLOE The KLOE Pb Pb-

• scintillating

scintillating fiber fiber calorimeter calorimeter

1.2 mm 1.35 mm 1.0 mm

Active material:

• 1.0 mm diameter scintillating fiber (Kuraray SCSF-81,

Pol.Hi.Tech 0046), emitting in the blue-green region: λPeak ~ 460 nm.

• Core: polystyrene, ρ=1.050 g/cm3, n=1.6

High sampling structure:

• 200 layers of 0.5 mm grooved lead foils (95% Pb and 5% Bi).
• Glue: Bicron BC-600ML, 72% epoxy resin, 28% hardener.
• Lead:Fiber:Glue volume ratio = 42:48:10

Designed and put in operation as e.m. calorimeter Good performance in time and energy response: σ(E)/E = 5.7 %/√E(GeV) σ(t)= 54 ps/√E(GeV) and high photon efficiency see NIMA 482 (2002) 364-386

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 3

Why Why looking looking for for neutron neutron detection detection efficiency efficiency ? ?

Detection of neutrons of few to few hundreds of MeV is traditionally performed with organic scintillators (principle of operation: elastic neutron scattering on H atoms, with production of protons detected by the scintillator itself) ⇒ efficiency scales with thickness ⇒ ~1%/cm

see C. Birattari, A.Ferrari, M.Pelliccioni et al., NIMA 297 (1990) 250-257, NIM A 338 (1994) 534-543

On the other hand, the extended range extended range rem rem counters counters used in radiation protection are based on a structure scintillator/medium-high Z material, which enhances the neutron efficiency an intense Monte Carlo study has been performed with the FLUKA code, which is well validated for the hadronic physics, till the low energy region an experimental test has been carried out with the neutron beam

• f the The Svedberg Laboratory of Uppsala (October 2006)

[with TARI program support]

an intense Monte Carlo study has been performed with the FLUKA

FLUKA code, which is

well validated for the hadronic physics, till the low energy region an experimental test has been carried out with the neutron beam

• f the The Svedberg Laboratory of Uppsala (October 2006)

[with TARI program support]

An estimate with KLOE data ( n are produced by K- interactions in the apparatus walls) gave: ε ∼ 40% for low energy neutrons (Ekin ≤ 20 MeV) , confirmed by KLOE MC (expected: ∼ 10% )

• Measurement of the neutron e.m. form factors in the time-like region (DANTE)
• Search for deeply bounded kaonic nuclei (AMADEUS)

n are important

for the DAΦNE-2 program @ LNF

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 4

The The neutron neutron beam beam line at TSL line at TSL

A quasi-monoenergetic neutron beam is produced in the reaction 7Li(p,n)7Be. 42% of neutrons at the max energy The absolute neutron flux in the peak is measured after the collimator by 2 monitors of the beam intensity. Accuracy: ~ 10%

5.31 m KLOE calorimeter module KLOE KLOE calorimeter calorimeter module module EKIN (MeV)

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 5

(1) (3) (2)

3 large data sets collected with different

beam intensities: 1.5 kHz/cm2, 3.0 kHz/cm2 and 6.0 kHz/cm2

The The experimental experimental setup setup and the data set and the data set

( 2 ) Beam position monitor: array of 7 scintillating counters, 1 cm thick. ( 1 ) Old prototype of the KLOE calorimeter: 60 cm long, 3 x 5 cells (4.2 x 4.2 cm2), read out at both ends by Hamamatsu/Burle PMTs ( 3 ) Reference counter: NE110, 10×20 cm2, 5 cm thick

A rotating frame allows for:

• vertical positions (data taking with n beam)
• horizontal positions (calibration with cosmic rays)

n

Y X Z

For each configuration, several scans with different trigger thresholds Typical run: 0.5-1.5 Mevents, 1.7 kHz DAQ rate Cosmic rays run (beam off) for calibrations with MIPs. last plane not integrated in the acquisition system

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 6

The The measurement measurement of the

• f the global

global efficiency efficiency

RNEUTRON: from beam monitor via neutron flux intensity measured by TSL. RTRIGGER: use coincidence between sides.

• Scintillator: T1 trig = Side 1×Side 2
• Calorimeter: use the analog sum of 12

PMs/side (first four planes) T1 trig = ΣA×ΣB

Global efficiency measurement Global efficiency measurement

integrated on the full spectrum

I.

• I. The

The method method

fLIVE: live time fraction α: for preliminary measurement, assume full acceptance and no background ε = RTRIGGER RNEUTRON × fLIVE × α

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 7

• II. The
• II. The scintillator

scintillator efficiency efficiency

The measurement of the scintillator efficiency gives a cross calibration of the measurement method and of the beam monitor accuracy, with small corrections due to the live time fraction The energy scale was calibrated with a 90Sr β source. 10% accuracy for horizontal scale (threshold) and the vertical one (ε) Threshold (MeV e− equiv. energy)

ε (%)

Results agree with “thumb rule” (1%/cm): 5% for 5 cm thick scintillator (with a threshold of ∼2.5 MeV electron equivalent energy) Agreement within errors with previous published measurements in the same energy range, after a rescaling of them to

• ur thickness

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 8

• III. The
• III. The calorimeter

calorimeter efficiency efficiency

Energy scale setting done by MIP

calibration of all channels, and using the MIP/MeV scale factor used in KLOE 10% uncertainty on both horizontal and vertical scales

Stability wrt very different run conditions:

a factor 4 variations of both live time fraction (e.g. fLIVE=0.2 → 0.8) and beam intensity (1.5 → 6.0 kHz/cm2).

Very high efficiency, about 4 times

larger than the expected if only the amount of scintillator is taken into account: ~ 8% for 8 cm

• f scintillating fibers.

Very high efficiency Very high efficiency, about 4 times

larger than the expected if only the amount of scintillator is taken into account: ~ 8% for 8 cm

• f scintillating fibers.

ε ε (%)

Compare with our scintillator efficiency measurement, scaled by the scintillator ratio factor 8/5 Thr (MeV e− equiv. energy)

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 9

The The neutron neutron spectrum spectrum from from ToF ToF

n

Correct raw spectra for T0

and convert into ns Since the trigger is phase locked with the RF ( time structure: 45 ns), rephasing is needed for neutrons with Ekin < 50 MeV (5.3 m far from the target) ToF (ns)

From ToF spectrum obtain β of the neutron

Assuming neutron mass, obtain Ekin

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 10

Energy Energy vs vs ToF ToF

Energy released Energy released vs vs ToF ToF

ToF (ns) Energy (MeV eq. el.) Energy (MeV eq. el.)

threshold: 15 mV

Charge response Charge response The collected charge is here expressed as the energy of an electron that gives the

same charge response

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 11

LEAD GLUE FIBERS

base module replicas

200 layers Using the FLUKA tool LATTICE the fiber structure of the whole calorimeter module has been designed. In the base module the calorimeter is simulated in detail, both under the geometrical point of view and with respect to the used materials

The The calorimeter calorimeter simulation simulation with with FLUKA FLUKA

All the compounds have been carefully simulated.

• for the fibers, an average density between

cladding and core has been used : ρ = 1.044 g/cm3

• glue: 72% epoxy resin C2H4O, ρ=1.14 g/cm3,

+ 28% hardener, ρ=0.95 g/cm3

1.5% C4H10N2 Diethylenediamine 1.5% C6H20N3 Aminoethylpiperazine 7% C6H15NO3 Triethanolamine 90% C7H20NO3 Polyoxypropylediamine hardener composition

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 12

The readout simulation The readout simulation The simulation of the Birks effect The simulation of the Birks effect

Fluka gives energy deposits in the fiber. The light is propagated by hand at the end of the fiber taking into account the attenuation. The energy read-out has been simulated by including:

• the generation of photoelectrons

the generation of photoelectrons

• the constant fraction distribution

the constant fraction distribution

• the discriminator threshold.

the discriminator threshold.

• No trigger simulation is included at the moment.

dL/dx = k dE/dx / [ 1 + c1 dE/dx + c2 (dE/dx)2]

c1 = 0.013 c2 = 9.6×10-6 The energy deposits are computed in Fluka taking into account the Birks effect, that is the saturation of the light output of a scintillating material when the energy release is high, due to the quenching interactions between the excited molecules along the path of incident particles: In literature and in GEANT:

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 13

Proton beam

Li target n 5.5°

The The simulation simulation of the

• f the beam

beam line line

Z(cm) Y(cm) Shielding (concrete and steel) Calorimeter

7Li Target

Gaussian angular distribution (Journal of Nuclear Science and Technology, supplement 2(2002), 112-115) At the Li-target At the calorimeter Ekin(MeV)

The beam line has been simulated starting from the neutrons out of the Litium target

A t t h e e n t r a n c e

• f

t h e b e a m m

• n

i t

• r

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 14

Neutron Neutron interactions interactions in the in the calorimeter calorimeter

Each primary neutron has a high probability to have elastic/inelastic scattering in Pb 2.2 2.3 glue 7.0 10.4 fibers 31.4 32.6 Pb Pinel(%) Pel(%) target In average, secondaries generated in inelastic interactions are 5.4 per primary neutron, counting only neutrons above 19.6 MeV. 3.2% He-4 0.2% He-3 0.2% triton 0.4% deuteron 6.8% protons 26.9% photons 62.2% neutrons

above 19.MeV

Typical reactions on lead:

n Pb

→

x n + y γ + Pb n Pb

→

x n + y γ + p + residual nucleus n Pb

→

x n + y γ + p + residual nucleus

In addition, secondaries created in interactions of low energy neutrons (below 19.6 MeV) are - in average - 97.7 particles per primary neutron. 1.1% photons 4.7% protons 94.2% neutrons Simulated neutron beam: Ekin = 180 MeV

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 15

A A typical typical inelastic inelastic process process

n Z(cm) p n1 n2 n3 n4 X ( c m )

primary vertex

En = 175.7 MeV En (p) = 126 MeV

The enhancement of the efficiency appears to be due to the huge inelastic production of neutrons on the lead planes. These secondary neutrons:

• are produced isotropically;
• are produced with a non negligible fraction of e.m. energy and
• f protons, which can be detected in the nearby fibers;
• have a lower energy and then a larger probability to do

new interactions in the calorimeter with neutron/proton/γ production. The enhancement of the efficiency appears to be due to the huge inelastic production of neutrons on the lead planes. These secondary neutrons:

• are produced isotropically;
• are produced with a non negligible fraction of e.m. energy and
• f protons, which can be detected in the nearby fibers;
• have a lower energy and then a larger probability to do

new interactions in the calorimeter with neutron/proton/γ production.

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 16

Neutron Neutron yield yield inside the inside the calorimeter calorimeter

X(cm ) Z(cm) beam Neutron fluence

Ekin (MeV) Φ (E)

cos(θ) dN/dΩ (n sr-1 per prim)

1° plane

4° plane

I s

• t

r

• p

i c a n g u l a r d i s t r i b u t i

• n

s f r

• m

i n e l a s t i c s c a t t e r i n g

Energy distribution Energy distribution

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 17

The The proton proton yield yield inside the inside the calorimeter calorimeter

X(cm) Z(cm) beam Proton fluence

Φ (E) Ekin (MeV)

cos(θ) dN/dΩ (prot sr-1 per prim) Protons are mainly concentrated along the direction of the primary beam

Energy distribution Energy distribution Angular distribution Angular distribution

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 18

A A key key point point: the high : the high sampling sampling frequency frequency

The energy deposits of the ionizing particles (protons and excited nuclei) are distributed mainly in the nearby fibers: the high sampling frequency is crucial in optimizing the calorimeter

Zdeposit –Zprim.vert (cm) Xdeposit -Xprim.vert (cm)

neutron lateral profile neutron lateral profile proton lateral profile proton lateral profile Interaction vertex in lead (protons and res nuclei) Interaction vertex Interaction vertex in lead in lead (protons and res nuclei) (protons and res nuclei)

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 19

Ekin (GeV) Protons Neutrons E.m. energy Others E(ril)/E(tot)

(ril)

Particle contribution to the energy response Particle contribution to the energy response

E E(tot

(tot) ) ( (ril ril) ) =

= Σ Σ E Ep

p( (ril ril) ) +

+ Σ Σ E En

n( (ril ril) ) +

+ Σ Σ E Eem

em( (ril ril) ) +

+ Σ ΣE Eresnuc

resnuc( (ril ril) )

Particle Particle contribution contribution to to the the energy energy released released in the in the fibers fibers: :

Evaluating the particle contribution to the energy response, we have to take into account:

• the contribution of the highly ionizing particles:

protons and excited nuclei;

• the contribution of the e.m. energy

The neutron contribution is not to take into account in general, because the neutrons transfer energy to the nuclei of the fibers basically as invisible energy. We don’t know if at least a part of this energy can produce somehow scintillating photons. For this reasons, we evaluate first the efficiency without taking into account the neutron energy deposits, then we do the exercise to re-calculate the efficiency also including the neutron contribution, as a superior limit to the true value.

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 20

Integrated efficiency: 50% Integrated efficiency: 50%

The The simulated simulated efficiency efficiency vs vs energy energy

ε (%)

Ekin (MeV)

Preliminary Preliminary Preliminary

No cut in released energy!

No trigger simulation Simulation of the discriminator

threshold applied only at the cell level not at the cluster level By taking into account neutron

energy deposits: ε ≈ 56% To be read as a superior limit !!

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 21

Data Data vs vs Monte Carlo Monte Carlo

The whole cluster algorithm procedure is under study A first comparison at the cell level has

been made (in this example: threshold = 15 mV) The agreement Data/MC is good, except for the lower energy region

n

To be included in the simulation:

local shielding, metallic supports, …

to simulate the background due to the neutrons scattered on the materials in the experimental hall

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 22

Tcell(ns) MC

• Exp

Ekin(MeV) ε(%)

A A study study on the detection

• n the detection efficiency

efficiency vs vs energy energy

A fast Monte Carlo procedure has been used to test the sensitivity of the time distribution to the shape of the efficiency curve

n

• two efficiency functions (Fermi-Dirac) are used in Monte carlo generation

time distributions for the central cell in the first plane are calculated and

compared with the experimental data (threshold = 15 mV) In this example: Tcell(ns) MC

• Exp

Ekin(MeV) ε(%)

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 23

Conclusions Conclusions

We think that this work is the starting point for the study and the development of a new, compact, cheap, fast and efficient neutron detector We think that this work is the starting point for the study and the development of a new, compact, cheap, fast and efficient neutron detector

A first comparison Data/Monte Carlo has been done and is satisfactory.

Work is in progress to tune the Monte Carlo.

The first measurement of the detection efficiency of a high sampling

lead-scintillating fiber calorimeter to neutrons, in the kinetic energy range [20, 178] MeV has been performed at The Svedberg Laboratory, Uppsala . The efficiency integrated over the whole neutron energy spectrum ranges between 40% and 50%, at the lowest trigger threshold used.

A detailed Monte Carlo study, carried out with FLUKA, showed that that the origin of

a such enhancement is related both to an effect shower-like, due to the inelastic processes in the Pb-scintillating fiber structure of the calorimeter, AND to the high sampling fraction used of this detector.

New tests on neutron beam in different energy regions are in program

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 24

Some additional information…

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 25

Details on DAQ Details on DAQ

• Scintillator trigger: Side 1 – Side 2 coincidence (T1=S1×S2)
• Calorimeter trigger: based on analog sum of the signals of the first

4 plan out of 5 (T1=ΣA×ΣB).

• Trigger signal is phase locked with RF signal (T1 free).
• Vetoed from retriggering by a 5-35 ms busy signal and by the DAQ

busy.

• The final trigger signal is: T2 = T1free.AND.NOT(BUSY).
• T1free, T2, and the n monitor

signals are acquired by a scaler asynchronous from DAQ.

• Fraction of live time: T2/T1free;

essential for the efficiency evaluation. T2/T1FREE

Thr (mV)

• Neutron rate proportional to neutron monitor via neutron flux intensity (I0)

and peak fraction (fP)

• An absolute rate calibration should be provided by scintillator counter.
• Calorimeter scintillator efficiency rate is almost independent from beam

monitor.

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 26

Time structure Time structure

4.2 ms 2.4 ms

40 ns

41 ns

∼ 5 ns FWHM RF Macro structure Calorimeter Trigger signal

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 27

Test of phase locking Test of phase locking

Beam RF T1(Free) Test done with a random trigger at 60KHz

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 28

S1(ADC counts) Thr (mV)

1.15 count/mV

Trigger threshold calibration: mV to ADC counts

Scintillator Scintillator calibration calibration

β source to set the energy scale in MeV:

90Sr β− endpoint 0.564 MeV; 90Y β− endpoint 2.238 MeV.

Fit of the b spectrum, with ADC counts to MeV factor as a free parameter.

0.021 MeV/count

S1

ADC counts

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 29

Calorimeter calibration Calorimeter calibration

ΣA ⇒ 1.6 count/mV ΣB ⇒ 2.0 count/mV

ADC counts mV

• Cell response equalized: MIP

peak at ∼600 ADC counts.

• Trigger threshold calibration:
• HP attenuators used for ΣA

and ΣB not to exceed the dynamic range of the ADC; different attenuation factors: fA=2.0, fB=1.7.

• Threshold in counts studied

with different methods.

• Energy scale set with MIPs

using the conversion factor from KLOE: a MIP in a calorimeter cell corresponds to an electron of 35 MeV.

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 30

100 mV 40 mV 15 mV

TOF distributions with different trigger thresholds

Anna Ferrari VCI 2007, Wien, February 22nd, 2007 31

Simulation of the energy read-out

fiber (active material) energy deposit given by FLUKA

The light is propagated by hand at the end of the fiber using the parametrization:

Kuraray Politech

The number of photoelectrons generated by the light collected by each fiber is evaluated: Attenuation

na , b

pe− fib generated according to

a Poisson distribution the constant fraction distribution is simulated (15% fr., 10 ns t.w.) to obtain the time

Ea,b

(fib) = E(dep) ·[0.35 e-x(a,b)/50 + (1- 0.35) e–x(a,b)/430 ]

Ea,b

(fib) = E(dep) ·[0.35 e-x(a,b)/50 + (1- 0.35) e–x(a,b)/330 ]

ta,b

(fib) = t(dep) + X(a,b) /17.09

na,b

(pe-fib) =E(fib)(MeV)(a,b) · 25

t(a,b)

(p.e.) = t(a,b) (fib) + tscin+ 1ns (smearing)

na,b

(pe-cell) = ∑ t(pe)<300ns na , b

pe− fib