Application of prompt gamma activation analysis with neutron beams for the detection and analysis of nuclear materials in containers

Transcription

1 Application of prompt gamma activation analysis with neutron beams for the detection and analysis of nuclear materials in containers Zsolt Révay Institute of Isotopes, Budapest, Hungary

2 Dept. of Nuclear Research, Institute of Isotopes nuclear physics & chemistry with (n,γ), (n,n γ) PGAA with neutron beams at reactors Atlas and data library for every element Fissile and other nuclear material Spectroscopic problems Sample problems γ-γ-coincidence Cooperation with LBNL PGAA with compact neutron generator Cooperation with University of Kentucky (n,n ) Cooperation with the IAEA (PGAA, nuclear data)

3 Prompt Gamma Activation Analysis excitation: with neutron beams detected characteristic radiation gamma radiation DEEP PENETRATION no sample preparation average composition

4 Typical reactions Neutrons Thermal capture: barn Epithermal capture: some strong resonances (n,n ) in the barn region (n,p) and other threshold reactions barns Fission barn Gammas A few decay γ: ~ kev, Σ = 1 2 MeV Several hundreds of prompt γ : ~100 kev 11 MeV, Σ = 6 10 MeV 1 or 2 γ from (n,n ): a bit higher than decay Several thousand γ from fission: ~ kev, Σ = 15 MeV

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7 Present activity PGAA in thermal and cold neutron beams

8 Sample in container is the particular case of inhomogeneous sample containers: glass (almost transparent) borosilicate-glass (B neutron absorber) lead (absorbs low-e gammas) other high-z element

9 Budapest PGAA facility

10 Research Reactor 20 MW water cooled water moderated thermal flux cm -2 s -1

11 Cold neutron source at Budapest 400 cm 3 20 K liquid H 2

12 Neutron guides Ni or supermirror guides relatively small losses low background

13 PGAA facility in Budapest collimated detector collimated cold neutron beam

14 The sample chamber is also a container... bkg = 4 cps in vacuum γ Pb 6 Li-poly n 6 Li-poly Al

15 The methods of looking inside the container invisible container method gases in cylinders average composition U in lead container

16 The container is invisible

17 When the container is always visible...

18 Visible sample in visible container 1. if E max,sample > E max,container the end of the spectrum comes from the sample 2. if σ sample > σ container (Sn, Zr, Pb containers) signal from the sample is stronger 3. if the sample activates, while the cont. no measurement in chopped beam, counting the sample in the decay (closed) phase

19 1. Binding energy of neutron (S n ) Neutron kötési energia (kev) Rendszám

20 1. Nuclides with the highest S n N kev 11 mb Mg kev,... <0.1 mb Si kev 0.4 mb S kev <0.1 mb Ti kev 2 mb cross-sections are too low...

21 1. 1 % N (77 mb) in Ni (4.5 b) Ni N Beütésszám Energia (kev)

22 2. mean free path (absorption) for thermal neutrons Al 500 mm glass 2700 mm Fe 31 mm B-glass (5% B) Co 2 mm 2,8 mm Zr 870 mm concrete 330 mm Cd 0,06 mm W 6 mm σ scat ~ barn Pb 1230 mm x 1/2 ~ mm

23 2. Gamma-transmission through 1cm of absorber Transzmisszió Energia (kev) Al üveg Fe Pb

24 2. Counting efficiency for samples in lead containers ( 152 Eu, 226 Ra, Cl) Efficiency Pb 0,5 cm Pb 1,5 cm

25 2. Rel. intensities for Cl peaks (NaCl sample in Pb container) 1 "Transzmisszio" 0.1 elm 5mm elm 15 mm Pb 0.5cm Pb 1.5 cm scattering, positioning Energia (kev)

26 2. PGAA spectrum of U+Pb cont. Beütészám Beütészám (cps) (cps) 1.E+06 1.E+06 1.E+05 1.E+05 1.E+04 1.E+03 1.E+02 1.E+02 Pb U Pb tokban U/10 U/10 Pb 1.E+01 1.E Energia (kev)

27 2. Intensities of U peaks with and without container (meas. 10 h) Sample Energy (kev) Count rate (cps) Count rate (cps) in 0.5 cm Pb 2223 (H) 32,0(3) 0,70(4) UO 2 (CH 3 COO) 2 2H 2 O 4060 ( 238 U) 0,99(3) 0,038(4) 6395 ( 235 U) 0,0111(3) 0,004(2) U 3 O 8 (~95% 235 U) 4135 ( 90 Rb) 0,200(10) 0,140(10) 6395( 235 U) 0,0362(10) 0,022(3) peak ratios are the same enrichment, composition smaller local flux

28 2.Masking with radioactive source (count rates/cps) materia decay decay in Pb prompt prompt in Pb 152 Eu nat. U 6,2 1, U 12 1,

29 2. Masking of U with 152 Eu in Pb Eu-152 U Számlálási sebesség (cps) Energia (kev)

30 3. Beam chopper Beam periodically shielded by Gd, 6 Li Variable opening: % variable frequency: Hz

31 3. Measurement in chopped beam detector chopper gamma radiation n

32 3. Prompt and decay spectrum of Tc-99 1E Tc-100 p 1E+1 Tc-100 decay Tc-99 capture 511 Annih Mn 2114 Mn 90 Tc Mn Al E+0 1E-1 1E-2 Count rate [cps] 1E-3 1E-4 1E Eγ [kev]

33 Uranium spectra counts BEAM DECAY Energy (kev)

34 3. Spectra in prompt and decay phases of 95% enriched U in 1cm thick Fe container

35 Conclusions samples in containers can be measured with thermal beam PGAA invisible container geometry 1 g of nat. U, or 0.1 g of 235 U can easily be detected in cm-thick Pb (1 2 kg), its enrichment can be determined other tricks for visible container chopper high-energy peaks

36 Plans PGAA (NAA) with epithermal and fast neutrons With the helps of Tamás Belgya Hungary, Fernando Sanchez, Argentina

37 Neutron generators D-D generator 2.4 MeV relatively low intensity D-T generator 14 MeV much higher intensity

38 Analytical use of 14 MeV neutrons Threshold reactions 16 O(n,p), 14 N(n,2n) F, Mg, Al, Si, Cu, Fe, P and Zn Problems with interfering reactions major and minor components

39 Analytical application of 2.4 MeV neutrons Not used until now, D-D generators were too week Only after thermalization

40 A practical use of D-D neutron generators on-line analyzer partly moderated beam extremely large sample used for light elements (minerals, cement) major components activated by epithermal neutrons similarly

41 Continuous Neutron Analyzer (CNA)

42 CNA

43 Berkeley neutron generator D+D or D+T reaction fast n/s E = 2.4 or 14 MeV desktop instrument pulsed beam...

44 Neutron generator facility at Berkeley 10 9 fast n/s E = 2.4 MeV rabbit system future facilities: thermal NAA fast NAA thermal PGAA fastpgaa

45 Analytical use of 2.4 MeV monochromatic neutrons typical reaction: (n,n γ) cross-sections are around 1 b almost every element (nuclide) can be analyzed with similar sensitivity (not the light elements) minor and major components (no trace analysis) deep penetration of neutrons gammas of mid energy range (several hundreds of kevs)

46 First analytical application of MeV monochromatic neutrons University of Kentucky, S.W. Yates, 1978 Van der Graaff accelerator, D-s up to 6 MeV D-D reaction Neutron energy can be tuned to include/exclude certain excitations

47 Steps needed shielding of the NG W + Li-6??? measuring the whole Periodic Table spectrum atlas standardization analytical problems matrix effects thermalization... detector demage

48 Schematic facility of the NG shielding sample beam stop HPGe detector W

49 W shielding of 2.4 MeV NG 3.0E-05 Transmission 2.5E E E E E-06 5 cm W 10 cm W 0.0E Energy (MeV)

50 Charged particle reactions (shielding) Cross-section (barn) 1.E+03 1.E+02 1.E+01 1.E+00 1.E-01 1.E-02 6Li (n,t) 10B (n,a) 14N (n,p) 32S (n,a) 1.E-03 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 Energy (ev)

51 PGAA library 1 H O 1 D O 2 He 3 Li CO 3,C-F 11 Na * CO3,C-H-O 19 K 4 Be * O 12 Mg * 20 Ca * O HCO 3 CO3 37 Rb 38 Sr O CO3 CO3 55 Cs 56 Ba O OH,CO 3 87 (Fr) 88 (Ra) 89 (Ac) 5 B C, H-O H 6 C ** 13 Al 14 Si ** O * O N 7 N 8 O 9 F C-D-O, NO 3 H, Be C 15 P 16 S 17 Cl * O ** 21 Sc 22 Ti 23 V 24 Cr 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn 31 Ga 32 Ge 33 As 34 Se 35 Br O ** O O * O-H * O ** * ** * O * O ** * O O * O-H * 39 Y 40 Zr 41 Nb 42 Mo 43 (Tc) 44 Ru 45 Rh O O O ** ** * 57 La 72 Hf 73 Ta 74 W 75 Re 76 Os O * O * O O * * O C-H C-H 46 Pd * 47 Ag ** 48 Cd ** 49 In * 50 Sn ** C,C-H C-H 10 Ne 18 Ar * 36 Kr * 51 Sb 52 Te 53 I 54 Xe O ** * C-H F 77 Ir 78 Pt 79 Au 80 Hg 81 Tl 82 Pb 83 Bi 84 (Po) 85 (At) 86 (Rn) * O * * ** O * ** ** 58 Ce O C-H-O 90 Th NO3 59 Pr 60 Nd 61 (Pm) 62 Sm 63 Eu 64 Gd 65 Tb 66 Dy 67 Ho 68 Er 69 Tm 70 Yb 71 Lu O O O O O O * O O O O O 91 (Pa) 92 U O C-H-O

52 Detection of U 238 U is also fissile cross-section in the barn region, ~ 15 MeV/fission emitted in gammas high compared to gammas following (n,n ) characteristic peaks other than those for 235 U similar spectrum shape to that for 235 U

53 Conclusion Elemental analysis can already be performed with the present D-D reactors (LBNL) Characteristic reaction (n,n γ), no interference from other reactions Similar sensitivities for every nuclide Problems of shielding and detector damage must be solved Will be applicable for the detection of nuclear materials in containers

54 Method proposed for identifying illicit fissile material Passive counting with HPGe If radioatcive than further check Active interrogation with portable NG If fissile, than further check Irradiation in a beam at a reactor Detailed analysis, what container, what fissile material, what enrichment