25th European Cosmic Ray Symposium
4-9 September 2016 Torino
Characteristics of EAS
neutron component obtained
with PRISMA-32 array
D.M. GROMUSHKIN, F.A. BOGDANOV, A.A. PETRUKHIN,
O.B. SHCHEGOLEV, YU.V. STENKIN, V.I. STEPANOV AND I.I. YASHIN
National Nuclear Research University MEPhI
(Moscow Engineering Physics Institute)
Institute for Nuclear Research of the Russian Academy of Sciences
PRISMA-32 experimental setup
32 en-detectors
array (composed of
two 16-detector
clusters) is located
inside the
experimental hall
situated on the 4th
floor of the NEVOD
building around the
water pool in
MEPhI. This
explains
inhomogeneous
structure of the
array.
-
Effective area of the detector : 0.36 m2;
Detector spacing: 2.5  5 m2;
Array area : ~ 500 m2.
Array works since 2012.
Measuring range:
- In charged particles : 5 - 75000/det.;
- By neutrons : 1 - 1000/det.;
- Primary energy: (0.3 – 30 PeV).
In the talk, the analysis of data collected during 2012-2016 is presented.
The design of the electron-neutron detector (en-detector)
1 – PE water tank;
2 – PE lid;
3 – FEU-200 PMT ;
4 - ZnS(Ag)+6LiF
scintillator;
5 - light reflecting cone.
The effective area of the detector – 0.36 m2
In detectors we use specialized inorganic scintillator based on zinc sulphide ZnS (Ag),
activated by silver, and fluoric lithium LiF enriched to 90 % by the isotope 6Li.
6Li
+ n = 3H +  + 4.8 MeV
The thickness of the recording layer ~ 30 mg/cm2
Thermal neutron recording efficiency of such
scintillator was found to be equal to about 20%.
ZnS(Ag) also allows to register multiple passage
of charged particles.
The cluster structure of the PRISMA-32 detector
 Readout from two PMT’s
dynodes : 12 th and 7 th
with 1 ms integration.
…..
…..
…..
7d
12d
 For the pulse shape
digitizing the FADC
(ADLINK 10 bit PCI slot
PCI-9810) is used (20000
samples with 1 µs step).
…..
…..
…..
Trigger
block
М1
≥2
…..
…..
…..
shaper
…..
…..
…..
FADC
7d
12d
preamplifier
…..
…..
…..
7d
 2-fold coincidence trigger
condition is applied for
each cluster of 16 endetectors to store the
data.
FADC
7d
FADC
…..
…..
…..
preamplifier
FADC
HV
±12V
The neutrons are recorded as delayed pulses inside a time gate of 20 ms. Online program pre-analyzes the data and stores the energy deposit (above the
threshold of 5 m.i.p.) and the number of recorded neutrons in each detector.
Industrial
PC 2
Local PC1
shaper
Industrial
PC 1
Local PC2
12d
12d
Example
of EAS oscillogramme and delayed neutrons
30
Амплитуда,
code ADC
Amplitude,
код А
40
20
нейтроны
neutrons
10
0
0
5000
10000
15000
Время, мкс
300
Амплитуда,
АЦП
ADC
code
Amplitude, код
15
Амплитуда,
кодADC
АЦП
code
Amplitude,
20000
Time, µs
Электромагнитная
компонента
EAS
charged particles
200
100
0
neutrons
нейтроны
10
5
0
0
2
4
6
8
10
12
Время, мкс
Time,
µs
14
16
18
20
500
600
700
800
Time,
µs
Время, мкс
900
1000
Soft triggers: two or more detectors were hit in each cluster, sum of energy
deposits in all detectors exceeded 70 rel. particles, and number of detectors with
recorded neutrons exceeded four in both clusters.
Delay times of thermal neutron distributions measured by PRISMA-32.
P1
P2
all
M3
-1
10
F=0.3*(0.8*EXP(-X/0.6)+0.11*EXP(-X/4.6))+3.5E-3
F(T)
F1=0.12*(0.8*EXP(-X/0.53)+0.18*EXP(-X/4.4))+1.9E-3
-2
10
F2=0.2*(0.8*EXP(-X/0.5)+0.1*EXP(-X/3.4))+1.6E-3
-3
10
0
5
10
15
20
T, ms
T=0 corresponds to the time of the trigger (EAS passage)
As one can see, the measured time distributions can be fitted by the
two-exponential function.
 first exponent - neutrons thermalized in concrete under the detector
 second exponent - neutrons thermalized in roof and walls.
EAS size integral spectrum
in thermal neutrons
multiplied by n1.95
Experimental integral spectra in the
number of thermal neutrons with
selection in EAS age s.
6
I(>n)*n
1.95
10
5
10
PRISMA-32
s < 0.8
0.8< s < 1.7
all
M3
4
-1
10
10
10
Nn
100
F=0.3*(0.8*EXP(-X/6)+0.11*EXP(-X/46))+3.5E-3
F(T)
F1=0.12*(0.8*EXP(-X/5.3)+0.18*EXP(-X/44))+1.9E-3
-2
10
In the picture, spectrum with  = 1.95 is
presented for all neutrons, and it is close
to our expectations. It demonstrates that
the EAS size spectrum 10in thermal
0
5
neutrons can be well fitted with a pure
power law function in a range 10 – 100 n.
The spectrum with s < 0.8 has the index
larger than for spectrum of all detected
neutrons.
are produced
10
15 High multiplicities
20
T, ms
by young showers.
F2=0.2*(0.8*EXP(-X/5)+0.1*EXP(-X/34))+1.6E-3
-3
Lateral distribution function of EAS thermal neutrons
10
n, m
-2
Selection:
A>=2
8-fold
1
F(R)=8*EXP(-R/1)+4.3*EXP(-R/10.5)
0.1
0
5
10
15
20
25
R, m
LDF is well fitted by a two-exponential function. This plot can be used for
estimation of the EAS core location accuracy.
Mean number of recorded neutrons as a function of total energy deposit
in all detectors
PRISMA-32
4
10


3
10
<n> 102
1
10
exp
0
10
2
3
4
5
6
7
Lg(/MIP)
It is seen that the function follows a power law in a wide range of EAS size. It is
seen that the mean number of recorded neutrons reaches 100 neutrons per 32
detectors and correspond to ~ 105 particles of EAS.
Summary
1. Parameters of EAS thermal neutron component for more
than four years of PRISMA array operation are
measured.
2. Results could be useful for new projects aimed to study
EAS hadronic component.
3. To convert obtained spectra of thermal neutrons to
spectrum of PCR it is necessary to provide a careful
simulation.
4. The new array of en-detectors is being installed now on
the roofs of buildings around the Experimental complex
NEVOD.
Thank you for your attention
en-detectors
By measuring barometric coefficient
we can estimate portion of neutrons
originated from radon
Главной особенностью
нового метода является
возможность
регистрации адронной
компоненты ШАЛ,
через измерение
тепловых нейтронов,
производимых этими
адронами.
Главной особенностью данного детектора является чувствительность к
двум основным компонентам ШАЛ: адронной (н) и электронной (э).