measurement of delayed-neutron yield from 237 np fission induced by thermal neutrons frank...

Measurement of Delayed-Neutron Yieldfrom 237Np Fission Induced by Thermal Neutrons

Frank Laboratory of Neutron Physics - Dubna 24.06.2007-7.07.2007

G. Parzych (UwB), A.N. Lihachev (JINR), V.R. Andrianov (JINR), P. Sibczynski (US),

J. Žemlička (CTU), Z. Mrázová (CTU), O.Šimek (CTU), J. Sieracki (UZG)



Scheme of pulse reactor IBR-2



The mechanism of delayed neutron generation



Motivations of the measurements of the yields of the delayed neutrons for transuranium elements

• Well known the fundamental role of delayed neutrons in the safety operation and time-dependant behavior of nuclear reactors.

• The delayed neutron data such as the absolute yield of DN, relative abundances of DN, half-lives of their precursors, and energy spectra of DN are important for kinetics and safety operations of nuclear reactors.

• In spite of great efforts in investigation of delayed neutron physics the fundamental delayed neutron characteristics for most common fissionable reactor isotopes are little-studied.



The experimental installation “Isomer-M”

Fig. 1. The scheme of the “Isomer-M” installation: 1 – IBR-2 reactor core and the moderator of neutrons, 2, 3 – collimators, 4 – bent mirror guide , 5 – Cd-Ping-Pong, 6 – chopper, 7 – neutron

detector assembly and combined shield , 8 – 3He-counters, 9 – Cd-shield, 10 – sample.



The method of experiment and measurement

dEnEN ff

ppfp NN

ddfd NN

The number of fission events, which happened in a sample for all time of measurement

The number of prompt neutrons registered by the detector

The number of delayed neutrons registered by the detector

dd

pp

d

p

N

N

pdd p

p d

N

N



Calibration measurement of 235U sample

Fig. 2 . The time-of-flight spectrum of 235U measured at the “Isomer-M” installation: а – effect + background (235U), b – background (235U+Cd-shield).

500 1000 1500 2000 2500 3000 3500 4000

1E-4

1E-3

0,01

0,1C

ou

nts

pe

r ch

an

ne

l

Channel number

a - 235U

b - 235U + Cd

a

b

500 1000 1500 2000 2500 3000 3500 4000

1E-4

1E-3

0,01

0,1

Счё

т на

ка

на

л

Номер канала

a

b

a - 237Np

b - 237Np+Cd

Fig. 3 . The time-of-flight spectrum of 237Np measured at the “Isomer-M” installation: а – effect + background (237Np), b – background (237Np+Cd-shield).


Calibration measurement of 237Np sample




DetectorCount

components

Count numbers

without Cd filter with Cd filter

Thermal peak region(210 - 730 channels)

Ns + Nbgr

Nα n

Nf n

Npexp

0.965 ± 0.0010.0410 ± 0.00010.0058 ± 0.00054.67 ± 0.003

0.0542 ± 0.00020.410 ± 0.00010.0058 ± 0.00050.1010 ± 0.0005

Delayed-neutron region(1200 - 4096 channels)

Nsc + Nbgr

Nα n

Nf n

Ndexp

0.2220 ± 0.00040.2960 ± 0.00060.028 ± 0.0020.556 ± 0.001

0.2183 ± 0.00040.2960 ± 0.00060.028 ± 0.0020.542 ± 0.001



From calibration measurements with 237Np, mean value of isp

d

pdd p

p d

N

N

The final result is

νd = 0.0110 ± 0.0009

02.076.0 d

p

14.047.2237 Npp

Known constant νp is

And so, from

Special thanks for our supervisors, whose patiently answered for all kinds of our questions.

For Mr. Zawodny and Mr. Chmielowski for help to survive in this beautiful country.

And, of course, for direction of all JINR sections for possibility to seeone of the biggest laboratories in the world.



Thank You for attention

Grzegorz Parzych, Jaroslaw Sieracki, Pawel Sibczynski

measurement of delayed-neutron yield from 237 np fission induced by thermal neutrons frank...

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