1. Characteristics of EAS neutron component obtained with PRISMA-32 array
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

2. 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.
Measuring range:
- In charged particles : /det.;
- By neutrons : /det.;
- Primary energy: (0.3 – 30 PeV).
- Effective area of the detector : 0.36 m2;
- Detector spacing: 2.5  5 m2;
Array area : ~ 500 m2.
Array works since 2012.
In the talk, the analysis of data collected during is presented.

3. 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 +  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.

4. The cluster structure of the PRISMA-32 detector
Readout from two PMT’s dynodes : 12 th and 7 th with 1 ms integration.
Local PC2
For the pulse shape digitizing the FADC (ADLINK 10 bit PCI slot PCI-9810) is used (20000 samples with 1 µs step).
Local PC1
2-fold coincidence trigger condition is applied for each cluster of 16 en-detectors to store the data.
The neutrons are recorded as delayed pulses inside a time gate of 20 ms. On-line 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.

5. Example of EAS oscillogramme and delayed neutrons
Amplitude, code ADC
Time, µs
neutrons
EAS charged particles
Amplitude, code ADC
Amplitude, code ADC
Time, µs
Time, µs
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.
- измерение энерговыделения от электромагнитной компоненты;
- определение числа нейтронов в течение 20 мс с шагом 100 мкс;
метка события;
- запись основных мониторных параметров работы установки.

6. Delay times of thermal neutron distributions measured by PRISMA-32.
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.

7. 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.
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 in thermal 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. High multiplicities are produced
by young showers.

8. Lateral distribution function of EAS thermal neutrons
LDF is well fitted by a two-exponential function. This plot can be used for estimation of the EAS core location accuracy.

9. Mean number of recorded neutrons as a function of total energy deposit in all detectors
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.

10. Summary
Parameters of EAS thermal neutron component for more than four years of PRISMA array operation are measured.
Results could be useful for new projects aimed to study EAS hadronic component.
To convert obtained spectra of thermal neutrons to spectrum of PCR it is necessary to provide a careful simulation.
The new array of en-detectors is being installed now on the roofs of buildings around the Experimental complex NEVOD.

11. Thank you for your attention
en-detectors

13. By measuring barometric coefficient
we can estimate portion of neutrons
originated from radon

14. 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).