Detectors for the measurement of ionizing radiation
For the measurement of radiation, the following reactions during the irradiation of matter are predominantly utilized:
Ionization in gases (Ionization chamber, proportional flow counter, release counter)
Scintillation in solids and liquids (- and - scintillation counters)
Ionization in solids (semiconductor-detectors)
1 Detectors for the measurement of ionizing radiation
Ionization of gases (gas-filled detectors)
Ionization chamber: 50 – 300 V, air, no secondary ionization
2 Detectors for the measurement of ionizing radiation
Geiger-Müller Counter
GM counter: ≥ 800 V, Argon, electron cascade is generated (1010 electron pairs)
Quench gas is needed (Cl2) Only count information can be recorded, no energy Dead time: time interval after a pulse during which the counter is insensitive to further ionizing events Higher count rates mean more counts will be missed Geiger-Müller counters are most suitable for measuring
high-energy radiation (Emax >1MeV)
3 Detectors for the measurement of ionizing radiation
Proportional Flow Counter
Count rate and energy information on the incident radiation can be obtained Proportional counter: 300 – 800 V, argon or xenon, electron cascade is Discerning of alpha from beta generated (106 electron pairs) radiation
Total charge is proportional to the Especially suited for measuring energy deposited - and -emitters 4 Detectors for the measurement of ionizing radiation
Scintillation
Conduction Band
Band Scintillation gap photon
Valence Band
Scintillation is the property of Inorganic scintillators contain luminescence when exited by dense high Z materials ionizing radiation They are very efficient at detecting X- and -rays The energy of the original signal is preserved through the PMT, but precision is lost poor energy resolution 5 Detectors for the measurement of ionizing radiation
Solid Scintillation Detectors
In order to absorb the largest possible amount of the -radiation, thick crystals with large densities are used; e.g. sodium iodide crystals doped with thallium (ρ =3,67g·cm-3).
By using organic crystals like anthracene, trans-stilbene or p-terphenyl, radiation can be detected.
6 Detectors for the measurement of ionizing radiation
Scintillation / -scintillation counter (COBRA 5002)
Analytical Method: Quantitative
Detector: Thallium-activated sodium iodide crystal (through-hole design)
Manual Region: 15 – 2000 keV (e.g. Tc-99m 140 keV)
Efficiency: >72% for I-125 (others have to be distinguished)
7 Detectors for the measurement of ionizing radiation
Liquid Scintillation Detectors Primary Secondary Scintillators: Scintillators: 320 – 360 nm 410 – 470 nm
O N N PM Tube
Counter
O
N
Aromatic solvent in the scintillation cocktail: Absorbs the kinetic energy from a charged particle and transfers the energy to the primary scintillator molecules. 8 Detectors for the measurement of ionizing radiation
Liquid Scintillation Detectors
Quenching is the loss of counts due to sample or cocktail characteristics
Chemical Quenching Color Quenching Chemical quenchers absorb Color quenchers absorb light in radioactive energy before it is the range of the wavelength converted to light. emitted by the scintillator. Chemical quenchers reduce The number of photons emitted is the number of photons not changed, but the number generated by each β-particle. reaching the photomultiplier tube is reduced.
9 Detectors for the measurement of ionizing radiation
Liquid Scintillation Detectors
Analytical Method: Quantitative / “Qualitative”
Scintillation Cocktail: ULTIMA Gold XR Compatible with alkaline samples High holding capacity (up to 50%) High quench resistance High counting efficiency (up to 50% for H-3) -Spectra are recorded
10 Detectors for the measurement of ionizing radiation
Semiconductor Detector
Ionizing radiation produces electron-hole pairs as it passes through a semiconductor detector
The number of electron-hole pairs is proportional to the energy transmitted by the radiation to the semiconductor http://nsspi.tamu.edu/NSEP
Measuring the number of electron-hole pairs (pulse height) allows the energy of the incident radiation to be found
Excellent energy resolution
11 Detectors for the measurement of ionizing radiation
Semiconductor Detector
Measurement of natural probes (Elemental Analysis)
Measurement of probes after neutron activation
12 Detectors for the measurement of ionizing radiation
Semiconductor Detector
Measurement of natural probes (Elemental Analysis)
Measurement of probes after neutron activation
Aeroradiometrics Whole-body counter @ PSI
13 Detectors for the measurement of ionizing radiation
Relationship between activity and counting rate?
The net counting rate (RN) is proportional to the activity (A) of the sample and the average number of the emitted quanta per decay ()
RN = f · A ·
f = fG · fA · fS · fR · fi
fG: Geometric factor
fA: Absorption factor
fS: Self absorption factor
fR: Backscattering factor
fi: Response probability 14 Nuclear Forensic Science
„Analysis of intercepted illicit nuclear or radioactive material and any associated material to provide evidence for nuclear attribution.“ Nuclear Forensics Support, 2006. IAEA Nuclear Security Series No. 2. http://www-pub.iaea.org/MTCD/publications/PDF/Pub1241_web.pdf
“Scientific analysis of nuclear or other radioactive material, or of other evidence that is contaminated with radioactive material in the context of legal proceedings, including administrative, civil, criminal or international Law.” Nuclear Forensics in Support of Investigations, IAEA Nuclear Security Series No.2
“Analysis of nuclear material of unknown origin.”
K. Mayer, M. Wallenius, and Z. Varga, Chem. Rev. 2013, 113, 884−900
15 Nuclear Forensic Science
How to provide evidence for nuclear attribution?
What can be analyzed?
Isotopic Signatures of Plutonium and Uranium
Age Dating
Chemical Impurities
Morphology of Nuclear Material Powders
16 Nuclear Forensic Science
Isotopic Signatures Uranium and plutonium are the materials of primary concern
- - 238U (n, ) 239U 239Np 239Pu (n, )(n,240Pu ) 241Pu (n, ) 242Pu
-
(n,2n) fission 241Am
- 237U 237Np (n, ) 238Np 238Pu
(n, )
(n, ) 235U 236U The probability of the different neutron reactions (capture and fission) is a function of the neutron energy Different types of reactor show different neutron energy distributions The isotopic profile of plutonium can serve as signature of the type of reactor it was produced from 17 Nuclear Forensic Science
Isotopic Signatures Uranium and plutonium are the materials of primary concern
- - 238U (n, ) 239U 239Np 239Pu (n, )(n,240Pu ) 241Pu (n, ) 242Pu
-
(n,2n) fission 241Am
- 237U 237Np (n, ) 238Np 238Pu
(n, )
(n, ) 235U 236U Determination of the reactor class (242Pu compared to 240Pu)
Date of discharge (241Pu relationship to 240Pu and 242Pu)
Time since the last chemical processing (241Am compared to 241Pu) 18 Nuclear Forensic Science
Production date or age
Time elapsed since the last chemical processing of the material
Can be distinguished by daughter/ parent ratio measurements (s. radio chemical equilibrium)
sample type chronometer highly enriched 214Bi/234U uranium 230Th/234U 231Pa/235U uranium oxides 230Th/234U uranium ore 228Th/232Th concentrates
19 Synthesis of Elements
Heaviest stable element is Bismuth Holes in the periodic Table: Technetium, Promethium 20 Synthesis of Elements
Artificial elements
96 2 97 1 42Mo 1H 43Tc0 n Molybdenum Technetium
209 4 211 1 83Bi 2 He 85 At 20 n Bismuth Astatinium
230 1 223 4 Thorium Francium 90Th1H 87 Fr 22 He
21 Synthesis of Elements
Synthesis of Trans-Uranium Elements
n, - 238 239 239 McMillan 1940 U U Np (fission product)
n,2n - 238U 237U 237Np - 235U n, n, 237U 237Np
d,2n - 238U 238Np 238Pu Seaborg 1940
- 239Pu n, n, 241Pu 241Am Seaborg 1944
n, - 241Am 242Am 242Cm Seaborg 1944
n 242Cm 245Cf Thompson 1950
22 Synthesis of Elements
Synthesis of Trans-Uranium Elements
26Mg 248Cm 274Hs 270Hs
1·1017 1·1016 5·106 1 projectiles on target compound nuclei atom
23 Synthesis of Elements
Synthesis of Trans-Uranium Elements
24 Synthesis of Elements
Synthesis of Trans-Uranium Elements
atomic no. element name symbol
101 mendelevium Md 102 nobelium No
103 lawrencium Lr 104 rutherfordium Rf
105 dubnium Db
106 seaborgium Sg
107 bohrium Bh
108 hassium Hs 109 meitnerium Mt Current Periodic Table of the Elements with IUPAC approved 110 darmstadtium Ds numbering of groups and element symbols. The names for 111 roentgenium Rg elements 114 (Flerovium, Fl) and 116 (Livermorium, Lv) suggested by the team of discoverers have recently been 112 copernicium Cn officially accepted by IUPAC. 113 ununtrium Uut 114 flerovium Fl 115 ununpentium Uup 116 livermorium Lv 117 ununseptium Uus 118 ununoctium Uuo
Andreas Türler; Valeria Pershina; Chem. Rev. 2013, 113, 1237-1312. 25