neutrons essentially interact only with the atomic nucleuscross-sections can vary dramatically and erratically based on complex interactions between all the nucleons in the nucleus and the incident neutronhuge effort and money has been spent to measure these cross-sections for many materials and a wide range of neutron energiesNeutron Interactions needed for shielding calculations and for many basic and applied type s of research:neutron scattering, crystal studies, DNAneutron activation analysisneutron radiography, paintingsweapons research, neutron bombsnuclear structureneutron depth profilingneutron dosimetryNeutron Interactions nuclear reactor most prolific sourceenergyspectrumfromthefissionof 2!"extends from several #e$ to more than %& 'e$most probable energy ( &)* 'e$average energy ( 2 'e$therearenonaturallyoccurringradioisotopes which emit neutrons +ources of Neutrons %) one can manufacture a radioactive neutron source by combining an alpha emitting radionuclide such as 2%&,o, 22-.a or 2/,u with a light metal such as 0e or 0the reactions that follow are:/0e1, n2%23%&01, n2%N%%01, n2%4Nthere is a continuous energy spectrum+ources of Neutrons SourceAvg Neutron Energy (MeV) Half-Life Ci /secn 210PoBe 210PoB 22!aBe 22!aB 2"#PuBe $%2 2%& "%# "%0 $%& 1"' ( 1"' ( 102 yr 102 yr 2$)$00 yr # 10& $ 10& 1%* 10* %' 10

1 10 +ources of Neutrons 15,n2 ),hotoneutron sources using 1,n2 reactionsby choosing radioisotopes with a single-ray then monoenergetic neutrons can be producedthesourcesareproducedinareactorusing conventional 1n,2 reactions except for 22-.a 6s then interact as follows:/0e1,n270e28e1,n2%8+ources of Neutrons +ources of Neutrons SourceAvg Neutron Energy (MeV) Half-Life

Ci /secn 2$NaBe 2$Na+2, 11$-nBe 12$S.Be 1$0LaBe 22!aBe 0%'" 0%22 0%"0 0%02$ 0%2 0%* (/a0) 1& 1r 1& 1r &$ /in 0 ( $0 1r 122 yr 1%"& 10& 2%* 10& '%2 10" 1%# 10& " 10" 1 10" 4)Accelerator Neutronsparticleacceleratorsareusedtogenerateneutrons by means of nuclear reactions such as:D-9, D-N, ,-N

81d,n248e - :-value ; %*)- 'e$ %4)%'e$ neutrons281d,n2

8e - :-value ; )2* 'e$*man distribution:1/2 kT / E3/2E e) kT (2= ) (E fwhere: 1?2 ; fraction of neutrons of energye@unit energy interval # ; 0olt>man constant %&-2 A@BC9 ; absolute temperature BC3lassification of Neutrons most probable energy is:?mp ; #9average energy at any given temperature is:kT23E for neutron2 at 2#" 34 /o2t 5ro.a.le energy i2 0%02& eV3lassification of Neutrons velocity:sec m/ 2200 = vkT =mv221

neutron half-life is %& minutescold neutrons are much slower3lassification of Neutrons neutrons are uncharged and can travel appreciable distances in matter without interactingneutrons interact mostly by inelastic scattering, elastic scattering and absorptionInteraction of Neutrons %) Inelastic scattering 1n,n2a part of the #inetic energy that is transferred to the target nucleus upon collisionthe nucleus becomes excited and a gamma photon@photons are emitted: %231n,n2%23this interaction is best described by the compound nucleus modelInteraction of Neutrons a threshold exists for such interactionsinfinity for hydrogen 1inelastic scattering can not occur2 - - 'e$ for oxygen and less than % 'e$ for uraniumcross-section for inelastic scattering is small, usually less than % barn for low energy fast neutrons but increases with increasing energy% barn ; %&-24 cm2 Interaction of Neutrons 2%Ela2tic 2cattering (n)n6)/o2tli7elyinteraction.et8eenfa2t neutron2 an( lo8 ato/ic nu/.er 9/o2ti/5ortant5roce22for2lo8ing(o8n neutron2interaction i2 a :.illiar( .all6 colli2ion 2catteringreaction2arere25on2i.lefor neutron slowing in reactor2 Interaction of Neutrons in general neutron2 e/itte( in ;22ion 1ave an average energy of 2 MeVt1e2e fa2t neutron2 lo2e 4%E% a2 a re2ult of 2cattering colli2ion2 8it1 nuclei 81ic1 act a2 /o(erator2 (eg - 8ater) gra51ite)n contra2t cro22-2ection2 for inela2tic 2cattering are 2/all for lo8 energy fa2t neutron2 .ut increa2e 8it1 increa2ing energycon2i(er a neutron 8it1 energy Eo) /a22 M an( velocity V 1itting a nucleu2 /