UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Bergen June 2008
Brit SalbuIsotope Laboratory
Norwegian University of Life SciencesUMB
Risø NKS November 16, 2009
Speciation of radionuclides
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
• Radionuclides can be present in different physico-chemical forms influencing transport/mobility and bioavailability
Take home message
• Radionuclide species depend on sources and release conditions and transformation processesoccurring in the environment.
• Speciation/fractionation techniques are needed to distinguish between radionuclides species.
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Semipalatinsk
KuwaitKosovo
Thule, GreenlandPalomares, Spain
KurdayKadji-sayTabusharDigmai
Chernobyl, UkraineWindscale/Sellafield, UKDounray, UKLa Hague, FranceMayak, Krashnoyarsk, RussiaSavannah River Site, USAOscarshamn, Forsmark, Sweden
NovayaZemlyaKara SeaNW Russia
Nuclear weapon tests -filtersUMB archive
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
• Definitions
Outline
• Speciation/fractionation techniques applied
• In water• In soils/sediments• In biological materials
• Relevance in radioecology
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Definition: radionuclide species
Radionuclide species are defined according to their physico-chemical properties;
Molecular massCharge propertiesOxidation state – valenceStructureComplexing abilityetc.
e.g. ions, molecules, complexes, colloids, particles
Modified after IUPAC (excluded isotopic composition)(Salbu, JER, 2009)
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Definition: Speciation of radionuclides
Speciation of radionuclides is defined as the distribution of radionuclide species in a system
In accordance with IUPAC 2000
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Definition: Speciation analysis
IUPAC 2000: “The analytical activities of identifying and/or measuring the quantities of one or more individual chemical species in a sample”
Revised: Application of analytical techniques to identify and quantify one or more individual radionuclidespecies in a sample ( i.e. application of in situ, at site, on line, at lab. fractionation techniques prior to measurements).
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
• Radioactive particles in the environment are defined as localised aggregates of radioactive atoms that give rise to inhomogeneous distribution of radionuclides significantly different from that of the matrix background
Definition: Radioactive particles (IAEA, 2001 and 2009)
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
• Fragments – larger than 2 mm
Definition: Particles (IAEA, 2001 and 2009)
In water/sediment/soil/biota
• Particle size range: 0.45 µm – 2mm (includes sand+silt fraction)
• Colloidal (nanoparticle) size range: 1 nm - 0.45 µm
• Low molecular mass species: less than 1 nm
In air:
• Particles (submicrons in aerosols to fragments) are classified according to their aerodynamic diameters.
• Particles less than 10 μm are considered respiratory.
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø,2009
Speciation of radionuclides
Diameter 1 nm 10 nm 0.1 µm 0.45 µm 1 µm 10 µm
Molecular mass
x 102 x 104 x 106 x 108
Category simple compounds hydrolyzates/colloids polymers / pseudocolloids suspended particles
Cases inorganic, organic ions,complexes, molecules etc.
nanoparticlespolyhydroxo complexespolysilicatesfulvic acidsfatty acids
metal hydroxides clay mineralshumic acidsproteins
inorganic mineral particlesorganic particlesmicroorganisms
Determination of total activity concentration of radionuclides in acidified samples.
Dissolved radionuclides, determination of total in 0.45 µm filtered sampled and acidified
Methods,
Size fractionation techniques
Diffusionrate measurement
Ultrafiltrationultracentrifug.dialysis
FiltrationSedimen-tation
Charge fractionation techniques
Ion chromatography – undefined fractions Complexation – undefined fractions
LMM species
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Fractionation/speciation techniques
Size fractionation Charge fractionation Solid state speciation
Filtration
Tangential flow/hollow-fibre ultra filtration
Continous flow centrifugation
In situ dialysis (small volumes)
Ultracentrifugation
Density centrifugation
Dialysis
Gel chromatography
Exchange chromatography (cation, anion, adsorption)
Liquid-liquid extraction
Sequential extractions
Electrochemical methods
Crown ether chromatography
Electronmicroscopytechniques (SEM, TEM)
X-ray induced spectroscopy (μ-XRD, μ-XAS, μ-XANES, EXAFS)
Laser-induced spectroscopy (LIPAS, LITLS, LAMMA)
Electron energy loss spectroscopy
Raman spectroscopy
Nuclear magnetic resonance spectroscopy
Low activity concentrations – no direct specie-specific techniques are available
Techniques must be combined to provide specie characteristics
Advanced techniques within other disciplines increasingly needed
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Diameter
Size and charge distribution pattern
1 nm
Total activity concentration
0.1 µm 1 µm10 nm
Species Low molecular mass species
ParticlesColloids
Mobile and bioavailable species
Inert species
LMM positively/ negatively charge or neutral species
Recommended1. Fractionation according to size
i.e. particles and colloids2. Fractionation according to charge
i.e. charged LMM species
To avoid analytical problems
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
For identification of radionuclide species in the environment – during events - we need in situfractionation techniques – avoid storage effects
Fractionation of radionuclides in rivers under high flow conditions
Fractionation in the field
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Size and chargedinterfaced system
FiltersFilters
CationCationresinsresins
cation
peristaltic pump
exchange resins (Amberlite)
Charge fractionation
Size fractionation
wasteultrafiltrate
peristaltic pump
in situ sampling
membrane filter0.45μm
Hollow-fibre 10 kDa
HollowHollow fibresfibres
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Colloids in effluents from reprocessing plants – Transmission Electron microscopy (TEM) reflect the presence of colloids. Effluents contain: ions, colloids, particles
200nm
SE A TA N K
SIX EP
La Hague
Sellafield
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Case: size fractionation of effluent from La Hague
La Hague effluentUltrasentrifugation
0 %
10 %
20 %
30 %
40 %
50 %
60 %
70 %
80 %
90 %
100 %
Mn-54 Co-60 Sb-125 Cs-134 Cs-137
LMW < 1E+3 DaColloidal 1E+3-1E+4 DaColloidal 1E+4Da-0,45umParticles >0,45 um
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
ISOTOPE LABORATORY DEPARTMENT PLANT AND ENVIRONMENTAL SCIENCES
Fractionation water+ AMS: Trace of weapon grade Pu in colloidal phase in Jenisey, all the way into Kara SeaTotal sample = fallout
Lind, OC., Lind, OC., OughtonOughton, DH., , DH., SalbuSalbu, , B., B., SkipperudSkipperud, L., et. al., (2006) , L., et. al., (2006) Earth and Planetary Science Earth and Planetary Science LettersLetters
Pycnocline28 psu
Surface23,8 psu
Near bottom0 psu
Surface0,1 psu
Particulate (>0,45 um )
Colloidal (8kDa-0,45um )
LM M (<8kDa)
82
7019
8Ob Ye
nise
y52 29
19
44525
30
48
1636
68
Pycnocline24,3 psu
73
621Near bottom32,9 psu
72
Surface0 psu
33
3631
333631
Pycnocline28 psu
4161
7
32
732
615141
8
13
78
911
19 29
52
19 2952
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Speciation of radionuclides
Diameter 1 nm 10 nm 0.1 µm 0.45 µm 1 µm 10 µm
Molecular mass
x 102 x 104 x 106 x 108
Category simple compounds hydrolyzates/colloids polymers / pseudocolloids suspended particles
Cases inorganic, organic ions,complexes, molecules etc.
nanoparticlespolyhydroxo complexespolysilicatesfulvic acidsfatty acids
metal hydroxides clay mineralshumic acidsproteins
inorganic mineral particlesorganic particlesmicroorganisms
Proccesses Mobilization mechanisms:Mobilization mechanisms:••desorptiondesorption••dissolutiondissolution••dispersiondispersion
Molecular massMolecular massgrowth mechanisms:growth mechanisms:
••hydrolysishydrolysis••complexationcomplexation••polymerisationpolymerisation••colloid formationcolloid formation••aggregationaggregation
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Case: Autoradiography using P imaging –soils contaminated with Chernobyl fallout
Chernobyl soil (Western trace)
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Sorption mechanisms – importantfor mobility
Physical sorption
Electrochemicalsorption
Chemisorption
Strategy: sequential extractions
Increased dissolution power of agent
Consecutive layersreversible
Monolayerreversible
Monolayerirreversible
Inertelectrolyte
IonexchangepH
red/ox
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Sequential extraction– processes, models, agents and reagents
Processes Model Agents Reagents
Physical sorption Consecutive layers, reversible reaction
Indifferent (inert) electrolyte
H2O
NH4OAc, soil/ sediment pH
Electrostatic sorption
Monolayer, Reversible reactions
Ion-exchangeblespecies, increased acidity (pH)
pH<soil/sediment
NH4OAc, pH5
Chemisorption Monolayer, Irreversible reaction
Red/ox agents, increase in temperature
Weak reducing: NH2OH•HCl
Weak oxidizing: H2O2, pH 2
Strong oxidizing: 7 M HNO3, 80°C
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Sequential Extraction of Radionuclides and Stable Analogues from Chernobyl contaminatedSoil - Caesium
Oughton et al., Analyst 1992
Weathering – predict decreasedmobility and decreased doses
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Oughton et al., Analyst 1992
Sequential Extraction of Radionuclides and Stable Analogues from Chernobyl contaminated Soil - Strontium
Weathering – predict increasedmobility and increased doses
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Case: Chernobyl fallout. Repeated extractions withwater, NH4Ac (soil pH), and NH4Ac (pH 5).Differentiate between reversible and irreversible
sorption processes
Sr-90Cs-137
Reversible: 1 extraction gives 50 %
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Lower pH
Pu(III)Pu3+
Reducing OxidizingLower pHHigher pH Higher pH
Precipitation
Pu(IV)Pu4+
Pu(V)PuO2
+Pu(VI)PuO2
2+
PuO2 xH2O
Redox-reactions
HydrolysisComplexation
Sorption
HydrolysisComplexation
Sorption
Pu in the environment – model experiments
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Tracer experiments: Pu-species in soil/sediment – water systemsTracer experiments: Pu-species in soil/sediment – water systems
k2
Soil solution
Easilyexchangeable(NH4Ac)”Mobile fraction”
Redox sensitive/Amorphous”Bound fraction”
Irreversibly bound “Fixed fraction”
k1
k4k3
0,00 10,00 20,00 30,00 40,00 50,00 60,00 70,00 80,00
H2O
NH4Ac pH Soil
NH4Ac pH=5
NH2OHHCl
H2O2
HNO3
Frac
tions
1h24h168h720h2160h
BoundFixedMobile
0 500 1000 1500 2000 2500Time (hour)
0
20
40
60
80
100Mobile (%)
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Kd for Pu species as f(t) in a soil-water systemsKKdd for for PuPu speciesspecies as as f(tf(t)) in a soilin a soil--water systemswater systems
Skipperud, L., Oughton, D. H. and Salbu, B., (2000) "The impact of Pu speciation on the distribution coefficients in Mayak soil" Science of the Total Environment
1,00
10,00
100,00
1000,00
10000,00
100000,00
0 500 1000 1500 2000 2500Contact time (hours)
KD
(mg/
ml)
Pu-V,VIPu-III,IVPu-III ,IV+ EDTAPu-III,IV + Citrat
4oC Soil : Water
1: 10
Pu-species T1/2 (d)
Associated
T1/2 (d)
Fixation
PuIII,IV 0.4 ± 1 % 34 ± 7 %
PuV,VI 0.8 ± 10 % 40 ± 5 %
PuIII,IV-organic 0.8 ± 1 % 39 ± 6 %
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Modelling Doses to humansDose from 1 GBq release
Skipperud, L., Oughton, D. H., and Salbu, B., (2000) Health Physics
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Radioactive particles are present in most contaminated areas. Identifying single U particles: autoradiography – SEM/BEI mode
BEI
P-imaging
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
SEM and XRMA
SEI-mode •characterization of particle surface structure.
BEI-mode •localization of particles containing heavy elements
X-ray mapping•localization of particles containing radionuclides.
XRMA•element analysis
SEM - XRMALocalization, Isolation and Characterization of U containing particles (UMB)
0 5 10 15 20Energy (keV)
0
50
100
150
200
Counts
U
U
U
UU
U
U
UU
SEI
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
X-ray Absorption Spectroscopy - ESRF
• Photons -> • exitation -> • deexitation
K, L, M electrons• Emittance
• X-ray fluorescence (XRF)
• Auger electrons• Transmission of the
beam – absorption
•µ-XRF- element•µ-XANES-ox state•µ-XRD-structure•EXAFS – fine structure
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Particle characterization methods
1. Digital autoradiography to identify heterogeneities and sample splitting/gamma measurements
2. ESEM/TEM with XRMASurface structure and elemental composition
3. SR-based 2D and 3 D µ-XRF (micro X-ray fluorescens)Subsurface/volume elemental composition
4. SR-based 2D µ-XANES (micro X-ray absorption near edge structure spectrometry)
Oxidation state determination, and confirmed by5. SR-based µ-XRD (micro X-ray diffraction)
Crystallographic forms6. µ-XAS tomography
Spatial distribution7. Source identification of isotope ratios by MS techniques
8. Leaching experiments to identify mobilisation potential
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Complex 3D aggregates of different phases
• Absorption X-ray microtomography: 3D density distributionexcellent tool for overall 3D sample exploration> 0.5 μm resolution
• Confocal μ-XRF: 3D elemental distributionelemental tomograms in selected planes within the sampleROI imaging possiblemajor elements to trace constituentscombination with confocal μ-XANES> ~ 5-10 μm resolution (secondary polycapillaryoptics)
• Tomographic μ-XRD: 3D structure distribution phase-tomograms in selected planes within the sampleminimization of self-absorption> ~ 10 μm resolutionbetter resolution possible via KB, CRL, optics
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Synchrotron radiation 2D μ-XRF mapping at HASYLAB, Germany
Ar K Ca Ti
Cr Mn Fe Zn
Sr Zr Mo Ru
Sn Ba Pb U
Chernobyl particles contain while inclusion Ru+MoCorresponding distribution: U, Zr, Sr
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Synchrotron radiation μ-XANES for determination of oxidation states of U in a Chernobyl U particle (ESRF) – should be combined with μ-XRD.
oxidation state+4 ±0.5
oxidation state +5±0.5
W
N
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Explosion: inert U fuel particle, low weathering rate, low soil-plant transfer. Fire: Oxidized U fuel, high weathering rate, high soil-plant transfer.
Oxidation state +4 ±0.5 – UO2
0
10
20
30
40
50
60
70
80
90
100
1986
1990
1994
1998
2002
2006
2010
2014
2018
2022
2026
2030
2034
2038
2042
2046
2050
% R
esid
ual F
P
Weathering of particles at pH6
West
North
Year
West: Initial release (explosion)
North:Subsequent release (fire)
Oxidation state +5 ± 0.5U3O8
Oxidation state +2.5 ± 0.5U-O-Zr, U-Carbide
•Same source – UO2•Two different release scenarios•Different particle characteristics•Different ecosystem behaviour
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Bergen June 2008
Radioactive particles released during ”all” types of severe nuclear events. The source determines the composition, the release scenarios dictate particle propertiesNuclear testSemipalatinsk
Thule
XRMA
Sellafield
Aggregate from theChernobyl explosion
Corrosion productWaste in Kara Sea Krasnoyarsk U particle
Dounrey
Kuwait
Particle deposition?
•Hot spots – problems with representative sampling•Partial leaching – analytical errors - transuranics•May underestimate the inventories
Adds significantly to the overall uncertainties
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Biological relevance of particles• Transfer of nano-particles through skin of earthworms.
Accumulation of Co-60 labelled nanoparticles in spermatogonetic cells and cocoons (Oughton et al)
• Retention of micrometer particles in GI tract (Salbu et al)Effects from particle exposure – IAEA 2008
Smeer of spermatogenic cells
Cocoons
Male reproductive organs
Clitellum
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
U-Ti alloyImpactInitially very high, subsequently moderate temp.
FireHigh temp.
CorrosionLow temp.
Release scenario
Source Weatheringconditions
Dissolution behaviour
Solid state speciation
MountainousHumid
DesertArid
DesertArid
XANES: +4 - +5.3XRD: UO2, UO2.34, UC, metallic U
XANES: +6XRD: UO3·x H2O
XANES:+4.6 - +6XRD: n.a.
25% in 2 hrs, 87% in 1 week
83% in 2 hrs, 96% in 1 week
24% in 2 hrs, 73% in 1 week
Linking source and release scenarios to particle characteristics and remobilization potential (0.1 M HCl extractions)
Case: DU particles from Kosovo and Kuwait
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Radionuclide species in biological material
DigestedMilk
Digestion STEP 1
37 °C 30 min.
Juice from human stomach
Juice from human duodenum
pH adjustedto 2,5
pH adjusted to 7,5
Heat treatmentDigestion STEP 2
37 °C 30 min.
Milk from Norwegiangoat
Milk from Norwegiancow
pH is measured everyminute during this step
Human gastric juice (HGJ) and Human duodenal juice (HDJ)
•Extraction with agents – poor analytical control•Separations – size exclusion techniques –proteins etc•Low level detection•On line systems – corresponding signals from radionuclides and proteins
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
In vitro extraction with Human gastric juice (HGJ) and Human duodenal juice (HDJ)Mimicking the degradation of food samples in GI tractOne MBq particle: 2 % released in HGJ, 5 % in HDJ
G. E. Vegarud, UMB
2 D electrophoresis of milk from different animalsChallenges – sufficient activity to be registered by autoradiography. Still restricted to tracer experiments.
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
trypticdigestion
Time, min0
2
4
6
16 18 20 22 24 26 28
Inte
nsit
y, c
ount
s(77
Se)
AB C
x104
SeM
et
0.5
1.0
1.5
2.0
2.5
3.0
10 15 20 25 30 35Time, min
Inte
nsit
y, c
ount
s80
Se
1 2 3 4 5 680Se
x103
Identification
SEC purification of biomolecule fraction
Extraction of proteinsfrom a biological sample
SEC purification (2D gel electrophoresis) of biomolecules
Challenges Need relative high activityconcentrations to obtainsignals above detection limits
After Szpunar et al
Low level detection
Fractionation/speciation of biomolecules in the future
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Challenges in radioecology: Linking radionuclide species in sources to impact and risk assessment
Transport in different ecosystems
Processes in soil / water / sediments
Bioavailability
Exposure
Biological membrane
Uptake/effect
Impact/risks
Climate
conditions
Sources Sources Sources
Pathogens/virus
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
• Radionuclides can be present in different physico-chemical forms influencing transport/mobility and bioavailability
Conclusions: Take home message
• Radionuclide species depend on sources and release conditions and transformation processesoccurring in the environment.
• Speciation/fractionation techniques are needed to distinguish between radionuclides species.
UN
IVERSITETET FO
R M
ILJØ-
OG
BIOVITEN
SKAP
Brit Salbu, UM
B, Risø, 2009
Foto: UMBs fotoarkiv
Thank youAcknowledgement to a series of collaborators
