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 360004, Russia 2Institute for Nuclear Research of the Russian Academy of Science BNO-50

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

Neutron monitor NM-64 with 10BF3 proportional counter

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.

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.

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

Amplitude spectrum of the counter SN-04

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

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

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

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.

Helium cryostat for obtaining cold neutrons 1- stainless steel housing, 2- a container with liquid helium, 3-nitrogen chamber, 4- connector of temperature sensor, 5- temperature sensor, 6 - a window for sluicing, 7- flange connector of the vacuum system, 8- the vacuum pump, 9 - manometer, 10- reinforcement head, 11- safety valve, 12 - cork, 13- sample holder with a cold line, 14-thin-walled tube, 15 - vacuum valve

Assembling a helium cryostat

Registration sistem

Shape control of PM pulse for neutron event

Cooling the lead constructive monitor with nitrogen vapors

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

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

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

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

Cooled graphite used in experiment

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.