1. Cryostatting and modulation of neutron fluxes in low background experiments
Akhmatov Z.A1, Khokonov A.Kh1,2, Masaev M.B1, Romanenko V.S1.
1Kabardino-Balkarian State University, Nalchik, Kabardino-Balkaria , Russia
2Institute for Nuclear Research of the Russian Academy of Science
BNO-50

2. Content
Introduction
Using of the neutron monitor constructive NM-64 to form a directional flux of thermal neutron.
Cryostatting of the NM-64 constructive with the help of liquid nitrogen vapors and a copper cold line.
Cooling and slowing down of neutrons in liquid nitrogen.
On the possibility of cryostatizing neutrons in the constructiv NM-64 compound using an vacuumited graphite rod.
Conclusions

3. Neutron monitor NM-64 with 10BF3 proportional counter

4. Block diagram of including scintillation chamber
1 - photocathode photomultiplier, 2- high-voltage source, 3-amplifier-discriminator and comparator, 4-interface unit, 5- ADLINK 7233H board, 6-PCI bus data transfer,7 - pressure sensor,8- temperature sensor, 9-Counter ADLINK-8554, 10- GPS Receiver, 11- The registering computer, 12- The voltage source is ± 12V.

5. The results of measuring the count rate of the counter SNM-15 before (1) and after (2) placing the neutron monitor NM-64 in a one-sheet lead configuration.
In the lead construct, the tempo of the account increased 1.7 times.

6. Scheme of the constructive of the neutron monitor NM-64
1- Proportional thermal neutron counter SNM-15, polyethylene pipe (2 cm), 3 - lead rings (6 cm),
4 - polyethylene reflector retarder (10 cm)

7. Amplitude spectrum of the counter SN-04

8. The number of neutrons recorded per unit of time by a counter in the one-velocity approximation
τ - the outer normal to the surface
σ - the thermal neutron capture cross section
v0 - neutron velocity
n0 - neutron concentration
n1 - concentration of the nuclei of the working isotope
l - the length of a segment cut off inside the counter by a beam along the neutron velocity

9. Khokonov A. Kh. Physics of Atomic Nuclei, 2010, Vol. 73, №9, pp

10. Neutron capture cross section energy dependence neutron for interaction with 10B and 11B

11. Neutron monitor construction and MC neutron trajectory simulation
a) - the scheme of the monitor
b) the result of simulating the passage of neutrons with an initial energy of 20 MeV through the monitor.

12. Helium cryostat for obtaining cold neutrons
1- stainless steel housing, 2- a container with liquid helium, 3-nitrogen chamber, connector of temperature sensor, 5- temperature sensor, 6 - a window for sluicing, flange connector of the vacuum system, 8- the vacuum pump, 9 - manometer, reinforcement head, 11- safety valve, 12 - cork, 13- sample holder with a cold line, thin-walled tube, 15 - vacuum valve

13. Assembling a helium cryostat

14. Registration sistem

15. Shape control of PM pulse for neutron event

16. Cooling the lead constructive monitor with nitrogen vapors

17. Detecting of the neutron flux by the ZnS + Li-6 scintillation detector, May 25, 2015

18. Detecting of the neutron flux by the ZnS + Li-6 scintillation detector, May 26, 2015

19. Detecting of the neutron flux by the ZnS + Li-6 scintillation detector, May 27, 2015

20. Counting rate rise during cooling of lead rings of MN-64

21. Cooled graphite used in experiment

22. Conclusions
An experimental setup for neutrons cryostatting inside the construction of monitor NM-64 was assembled where neutrons have been generated by cosmic rays.
The possibility of modulation of the thermal neutron flux generated by cosmic rays in the construction of the neutron monitor NM-64 was investigated.
3. The neutron counting rate grows few times when cooled the graphite cube (T=80 K) placed inside the lead rings of neutron monitor
4. The cryostat for neutron cooling by liquid helium is constructed.