Bomko, V.A.

Kobets, A.P.

Mazalov, Yu.P.

Meleschkova, Yu.V.

Rudjak, B.I.

Sanin, V.M.

Zaitsev, B.V.

Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)

ION LINEAR ACCELERATOR AS A SOURCE OF NARROW-BEAMED NEUTRONSV.M.Sanin, V.A.Bomko, B.V.Zaitsev, A.P.Kobets, Yu.P.Mazalov, Yu.V.Meleschkova, B.I.RudjakNSC KIPT, Kharkov, UkraineFor  creation  of  intensive  fast  neutron  sources based on  accelerators of  charged particles one usually applied the beams of accelerated protons or deuterons which bombard the targets consisting of the elements of comparatively low atom masses (2H,  3H,  7Li,  9Be,  11B, 12C).  Asymmetry  of  angular  distribution  of  these neutrons  is  small.  For  many  researches  and  applied problems  the  directed  neutron  beams  are  necessary which can be obtained by collimating the neutron flux. Unfortunately,  this  procedure  leads  to  significant decrease of neutron flux efficiency and to necessity to create accelerators with a beam power of tens and even hundreds kW.The distinctive features of angular distributions of  neutrons  in  the  laboratory  system  are  determined mainly  by  kinematics  of  nuclear  reactions  used  for neutron generation. Increasing the energy of accelerated particles leads to increased asymmetry, and the neutron beam becomes  more  extended in  the  direction of  the momentum of initial accelerated particles. It occurs due to  increasing  the  mass  center  velocity  of  nuclear reactions.Directionality  of  the  neutron  beam  can  also  be obtained  at  the  energies  of  accelerated  protons  or deuterons near the threshold of nuclear reactions at the target-nuclei  being  heavier  than  deuterium.  It  follows from the fact that in this energy region there is an angle of  neutron  in  the  laboratory  system, which  is  limited kinematically  and  as  a  result  the  output  neutrons  are directed forwards. However, under these conditions the cross-sections  of  the  reactions  are  small,  and  for obtaining the intense neutron beams very high currents of accelerated particles are necessary.We suggest another way for obtaining the directed neutron beams which does not require operation at the near-threshold region with small cross-sections of reaction. In the suggested scheme the above mentioned reactions can be used but kinematically inverted in the laboratory system (in the system of center-of-mass they are the same reactions). In this case the nuclei of the target and a bombarding particle interchange their positions. The center-of-mass velocity in this version is higher than that in the former version (with the identical energies of the particles in the system of center-of-mass in both schemes). In this case there is a boundary angle of the neutrons in the laboratory system even for energies considerably higher than the threshold energy, and a possibility occurs to obtain high intense directed neutron beams with suitable currents of accelerated particles.We propose to create a lithium ion accelerator for producing of a directed neutron beam on the base of the existing  linear  accelerator  of  multicharged  ions (MILAC). The 1H(7Li,n) 7Be reaction above threshold in a  hydrogen  containing  target  can  be  useful  for  this purpose.  At  bombarding  energies  of  lithium  ions  of 17 MeV a resonance cross section region is captured.The boundary neutron angle in the 1H(7Li,n) 7Be reaction  as  a  function  of  the  lithium  ion  energy  is represented in the figure.12 14 16 18 200510152025303540Lithium ion energy,MeVBoundary angle,degFig. Neutron boundary angle versus lithium ion energyThis dependence shows that the boundary angle of  a  neutron  corresponding  to  maximum  energy  of lithium ions of 17MeV does not exceed 30o. The lithium ions will decelerate as they penetrate through the thick target,  and  they  will  have  energies  from  zero  to maximum,  but  only  energies  more  than  threshold (12.95MeV) will give a yield of neutrons from 1H(7Li,n) 7Be reaction. The neutrons will be radiated in the cone with  a  half-angle  29o.  We  note  that  in  the  proton accelerator  version  the  neutron  flux  have  no directionality [1,2]. It is a main advantage of the lithium accelerator version that allows one to rise an efficiency of the neutron beam use. Neutron energies are expanded to 4MeV.It  is  supposed  to  create  a  new  accelerating structure for energy of lithium ions of 17 MeV with the alternating phase focusing (APF) and the moving bunch center that provides considerable capture both in radial and in longitudinal motions. The accelerator is based on the  effective  interdigital  H-structure,  and  will  have  a smooth energy control.At  the  first  stage  it  is  assumed  to  create  an accelerator with the lithium current of 0.5 mA. Further, it will be increased to 1.5 mA. For creation of such an accelerator most of the existing equipment of MILAC accelerator  could  be  used:  RF  equipment,  vacuum system,  a  main  part  of  the  injector,  control  system, working  areas.  The  choice  of  such  scheme  of  the accelerator is stipulated by the large rate of acceleration, availability  of  the  ready  equipment,  experience  in development and creation of such systems, simplicity of manufacturing and also existing industrial basis.ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. №3.Серия: Ядерно-физические исследования. (34), с. 99-100.99The proposed neutron source could be constructed in the short time with the minimal financial contribution, and to provide investigations in this field. The evaluations show that it can be created in about two years, and the financial contribution of $100,000 is necessary for this purpose.The  neutron  beam  with  above-mentioned parameters  may  be  used  for  many  applications.  For example in nuclear medicine: radioisotope production, boron neutron capture therapy (BNCT) of the malignant tumors  and so  on.  At  the  present  time the  Ukrainian medicine has not enough radioisotopes for diagnostics of various diseases and treatment of malignant diseases. Ukrainian  medical  researchers  are  taking  an  active interest in the BNCT method which was accepted as a most  promising  in  treatment  of  malignant  diseases, especially some brain tumors which are incurable at the present  time.  There  is  a  number  of  large  medical institutions  interested  in  development  of  this  method, and are ready for cooperation in this area.Creation  of  the  neutron  source  needs  some upgrading  of  existing  systems,  creation  of  a  new accelerating  section  and  creation  of  the  radiation protection.  A special  hydrogen  containing  target  with the cooling system is necessary for removal of the heat power  of  10kW.  For  the  purpose  of  BNCT  it  is necessary to  create  the  output system which provides moderation, reflection and filtering of the neutron beam like those of the reactor based sources [3].The parameters of a designed lithium accelerator are shown in the Table.Main parameters of linear lithium ion acceleratorThe name of a parameter and unit1 Input energy of ions,                         keV 18.752 Output energy of ions,                      keV 25003 Mass-to-charge ratio, A/q 74 Operating frequency                        MHz 47.255 Electric field in gaps,                    MV/m 96 Aperture of drift tubes, mm 16-287 Length of accelerating structure,          m 4.78 Number of drift tubes 579 Number of focusing regions 810 Number of bunching regions 911 Radial acceptance                 pi mm mrad 1.212 Longitudinal capture,                       deg. 12013 Energy spread (for ∆Win.=1%)            % 1.514 Longitudinal of output bunch            deg 2015 Pulse RF power                                 kW 40016 Duty factor                                           % 2.517 Average beam current                       mA 0.5Mathematical  simulation  shows  that  the  total neutron  yield  from  a  water  target  will  be  about  5⋅1011 n/mQ,  and  about  2⋅1011  n/mQ from a  TiH target with a surface density about 1⋅1011·n/cm2·mA·s and 4⋅1010·n/cm2·mA·s, respectively  at,  the  distance  of  5cm from the target.REFERENCES1.  V.N.  Kononov  et  al.,  "Accelerator  based  Neutron Sources Application for Neutron Capture Therapy",  Proc. 2nd All-Union Symp. on the Use of Charge Particle  Accelerators  in  the  National  Economy, Leningrad,  SU,  October  1-3,  1975,  Leningrad, Efremov  Inst.  of  Electrophysical  Apparatus,  v.2, pp.60-68(1976) (in Russian).2. R.J. Kudchadker, F. Harmon, et al. "An Accelerator based Epithermal Neutron Source for BNCT", 6th Int. Conference on Nuclear Engineering, ICONE - 6451, May 10-15, 1998.H.B. Liu, D.D. Greenberg, J. Capala, F.J. Wheeler, «An Improved Neutron Collimator for Brain Tumor Irradiations in Clinical Boron Neutron Capture Therapy», Med. Phys. 23:2051-2060; 1996.100

Ion linear accelerator as a sourse of narrow-beamed neutrons

http://dspace.nbuv.gov.ua/bitstream/handle/123456789/81351/40-Sanin.pdf?sequence=1

Ion linear accelerator as a sourse of narrow-beamed neutrons

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Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)