中子屏蔽

DOI 10.1140/epjp/i2013-13077-1

Regular Article

Eur.Phys.J.Plus (2013)128:77T HE E UROPEAN

P HYSICAL J OURNAL P LUS

Concrete shielding of neutron radiations of plasma focus and dose examination by FLUKA

M.J.Nemati a ,R.Amrollahi,and M.Habibi

Nuclear Engineering and Physics Department,Amirkabir University of Technology,Tehran,Iran

Received:30January 2013/Revised:26May 2013

Published online:22July 2013–c Societ`a Italiana di Fisica /Springer-Verlag 2013

Abstract.Plasma Focus (PF)is among those devices which are used in plasma investigations,but this

device produces some dangerous radiations after each shot,which generate a hazardous area for the op-erators of this device;therefore,it is better for the operators to stay away as much as possible from the area,where plasma focus has been placed.In this paper FLUKA Monte Carlo simulation has been used to calculate radiations produced by a 4kJ Amirkabir plasma focus device through different concrete shielding concepts with various thicknesses (square,labyrinth and cave concepts).The neutron yield of Amirkabir plasma focus at varying deuterium pressure (3–9torr)and two charging voltages (11.5and 13.5kV)is (2.25±0.2)×108neutrons/shot and (2.88±0.29)×108neutrons/shot of 2.45MeV,respectively.The most influential shield for the plasma focus device among these geometries is the labyrinth concept on four sides and the top with 20cm concrete.

1Introduction

FLUKA is a general purpose tool for calculations of particle transport and interactions with matter,covering an extended range of applications spanning from proton and electron accelerator shielding to target design,calorimetry,activation,dosimetry,detector design,Accelerator Driven Systems,cosmic rays,neutrino physics,and radiotherapy [1].

The Plasma Focus (PF)is a coaxial discharge device that can generate short-lived (10–100ns)but high-temperature (0.1–2.0keV)and high-density (1018–1020particles/cm 3)plasma which gives fast neutron pulses (when using deuterium gas),soft as well as hard X-rays and highly energetic ion and relativistic electron beams [2].The PF first was discovered independently by Mather (in the USA)and Filippov (in the former Soviet Union)[3].The Mather and Filippov configurations are different in the electrode dimensions and the aspect ratio (diameter/length)of the inner electrode.The aspect ratio is lower and higher than one for the Mather-and the Filippov-type PFs,respectively [4].

A capacitor bank,a fast spark gap switch,coaxial electrodes,and a vacuum chamber are the fundamental elements of a PF device [5].Over the years,many plasma focus devices with store bank energy ranging from 1kJ to 1MJ have been built [6].Recently,some experiments have been carried out on the small PF devices in the range of tens to hundreds of joules of capacitor energy [7].When using deuterium gas,plasma focus devices produce fusion D–D reactions generating fast neutron pulses with energies around 2.45MeV.The neutron bursts usually last for about tens to hundreds of nanoseconds.Lee [8]proposed the scaling law which relates the stored energy to the physical sizes of the PF.He reported that by changing in the range of bank energy from 1kJ to 1MJ neutron emission spans the

interval from 107to 1012neutrons per pulse [9].Neutron scaling law of Y n =3.2×1011×I 4.5pinch

;Y n =1.8×1010×I 3.8

peak ;I peak (0.3to 5.7),I pinch (0.2to 2.4)in MA from numerical experiments was presented by S.Lee [10],where Y n is the neutron yield.

Although the neutron production mechanism of PFs has not been clearly determined yet,the thermonuclear fusion and beam target models are two widely accepted mechanisms to be in charge of neutron production [11].Antanasijevi´c et al.and Castillo et al.[12,13]have shown that,when the working gas is pure deuterium,the neutron angular distribution has a Gaussian function.Experimental results of A.Rossel and Choi proposed that,when a doping gas is added,there is a significant increase in the neutron anisotropy [14].According to Zakaullah

a

e-mail:arash nemati@aut.ac.ir