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
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)
Prompt Gamma Activation Analysis excitation: with neutron beams detected characteristic radiation gamma radiation DEEP PENETRATION no sample preparation average composition
Typical reactions Neutrons Thermal capture: 0.0001 100 000 barn Epithermal capture: some strong resonances (n,n ) in the barn region (n,p) and other threshold reactions barns Fission 1 1000 barn Gammas A few decay γ: ~100 2500 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: ~50 5000 kev, Σ = 15 MeV
Present activity PGAA in thermal and cold neutron beams
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
Budapest PGAA facility
Research Reactor 20 MW water cooled water moderated thermal flux 10 14 cm -2 s -1
Cold neutron source at Budapest 400 cm 3 20 K liquid H 2
Neutron guides Ni or supermirror guides relatively small losses low background
PGAA facility in Budapest collimated detector collimated cold neutron beam
The sample chamber is also a container... bkg = 4 cps in vacuum γ Pb 6 Li-poly n 6 Li-poly Al
The methods of looking inside the container invisible container method gases in cylinders average composition U in lead container
The container is invisible
When the container is always visible...
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
1. Binding energy of neutron (S n ) 12000 Neutron kötési energia (kev) 10000 8000 6000 4000 2000 0 0 20 40 60 80 100 Rendszám
1. Nuclides with the highest S n N 10831 kev 11 mb Mg 11091 kev,... <0.1 mb Si 10607 kev 0.4 mb S 11415 kev <0.1 mb Ti 10641 kev 2 mb cross-sections are too low...
1. 1 % N (77 mb) in Ni (4.5 b) 10000 Ni N Beütésszám 1000 100 10 1 0 2000 4000 6000 8000 10000 12000 Energia (kev)
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 ~ 2 -- 10 barn Pb 1230 mm x 1/2 ~ 5 -- 20 mm
2. Gamma-transmission through 1cm of absorber Transzmisszió 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 2000 4000 6000 8000 10000 Energia (kev) Al üveg Fe Pb
2. Counting efficiency for samples in lead containers ( 152 Eu, 226 Ra, Cl) 0.01 0.001 Efficiency Pb 0,5 cm Pb 1,5 cm 0.0001 0.00001 100 1000 10000
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 0.01 0 2000 4000 6000 8000 10000 Energia (kev)
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+00 0 1000 2000 3000 4000 5000 6000 7000 8000 Energia (kev)
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
2.Masking with radioactive source (count rates/cps) materia decay decay in Pb prompt prompt in Pb 152 Eu 105 17 nat. U 6,2 1,1 4000 880 235 U 12 1,1 6600 4900
2. Masking of U with 152 Eu in Pb 1 0.1 Eu-152 U Számlálási sebesség (cps) 0.01 0.001 0.0001 0.00001 0 500 1000 1500 2000 Energia (kev)
3. Beam chopper Beam periodically shielded by Gd, 6 Li Variable opening: 0.2 50% variable frequency: 3 100 Hz
3. Measurement in chopped beam detector chopper gamma radiation n
3. Prompt and decay spectrum of Tc-99 1E+2 172 Tc-100 p 1E+1 Tc-100 decay Tc-99 capture 511 Annih. 690 1026 1131 1201 1364 1326 1848 1811 Mn 2114 Mn 90 Tc-99 847 Mn 823 1513 1779 Al 538 590 1E+0 1E-1 1E-2 Count rate [cps] 1E-3 1E-4 1E-5 0 500 1000 1500 2000 2500 Eγ [kev]
Uranium spectra 1000000 100000 10000 counts 1000 100 10 1 BEAM DECAY 0 2000 4000 6000 8000 10000 Energy (kev)
3. Spectra in prompt and decay phases of 95% enriched U in 1cm thick Fe container
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 0.5 1.5-cm-thick Pb (1 2 kg), its enrichment can be determined other tricks for visible container chopper high-energy peaks
Plans PGAA (NAA) with epithermal and fast neutrons With the helps of Tamás Belgya Hungary, Fernando Sanchez, Argentina
Neutron generators D-D generator 2.4 MeV relatively low intensity D-T generator 14 MeV much higher intensity
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
Analytical application of 2.4 MeV neutrons Not used until now, D-D generators were too week Only after thermalization
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
Continuous Neutron Analyzer (CNA)
CNA
Berkeley neutron generator D+D or D+T reaction 10 9-11 fast n/s E = 2.4 or 14 MeV desktop instrument pulsed beam...
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
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)
First analytical application of 2.4 4 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
Steps needed shielding of the NG W + Li-6??? measuring the whole Periodic Table spectrum atlas standardization analytical problems matrix effects thermalization... detector demage
Schematic facility of the NG shielding sample beam stop HPGe detector W
W shielding of 2.4 MeV NG 3.0E-05 Transmission 2.5E-05 2.0E-05 1.5E-05 1.0E-05 5.0E-06 5 cm W 10 cm W 0.0E+00 0.0 0.5 1.0 1.5 2.0 2.5 Energy (MeV)
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)
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
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
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
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