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Collinear photodetachment spectroscopy I - + h I + e - Energy I - I Wigner law: = k (E-E 0 ) l+1/2 D.Hanstorp and M. Gustafsson JPB 25 (1992) 1773
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Dag Hanstorp
Determination of the electron affinity of astatine and polonium by laser photodetachment
S. Rothe, J. Champion, K. Chrysalidis, T. Day Goodacre, V. Fedosseev, N. Galland, D. Hanstorp, R. Heinke, U. Kster, T. Kron, Y .Liu, B. Marsh, G. Montavon, E. Renault, A. Ringwall-Moberg, R. Rossel, C. Seiffert, J. Sundberg, J. Welander and K. Wendt
INTC meeting 3-4 February 2016
Follow up of Letter of Intent (LOI) INTC-I-148
Collinear photodetachment spectroscopy
I- + hn I + e-
Energy
I- I
Wigner law:
s= k (E-E0) l+1/2
D.Hanstorp and M. Gustafsson JPB 25 (1992) 1773
Neutral particle detection in collinear laser spectroscopy
D. Hanstorp, Meas. Sci. Technal. 3 (1992) 523-527.
For each laser pulse:
Signal:
0.01 atom
Background:
1014 photons
Glass plate coated with ITO (In2O3:Sn)
Targeted Alpha Therapy (TAT)
Immunology
Structural biology
Coordination chemistry
Nuclear physics and radiochemistry
a - range
cancer cells
211At particularly suitable isotope
7 h lifetime
No long lived daughters
Non-toxic daughters
Suitable a energy
Target
Radioactive
payload
Linker
Antibody
Receptor
Carrier
*
Astatine
Least abundant element on earth
70 mg in the crust of the earth (1 atom per 100 kg mass)
Small knowledge about chemical and physical properties
Halogen or metal?
ISOLDE Workshop and Users Meeting 20152-4 Dec 2015
*
Sebastian RotheCERN, Engineering Department
Spectroscopy of Rydberg levels
7
9
5
n
m
0 cm-1
46234 cm-1
58805 cm-1
75151 cm-1
IP
216 nm
610 630 m
IPThreshold allowed choice of laser dyeHigh resolution laser scan across the IP205At measured on Faraday cup50 Rydberg levels found
205At
Rydberg-Ritz formula
Conventional Rydberg-Ritz analysis
Fit each resonance, plot centroids versus nFit the Rydberg formula (2 parameters)In reality: 120 resonances, 7series
IPRydberg(At) = 75150.8(7) cm-1
http://www.nature.com/ncomms/journal/v4/n5/full/ncomms2819.html
Motivation for EA measurement of At and Po
Astatine
EA equally important as the IP
determine electronegativity
nature of chemical bonds
Important for computer simulations
for binding of At to receptor
No experimental value for EA(At) yet
Scattering of theoretical predictions ~1 eV
Polonium
Po is considered important component of the natural radiation affecting humans
Physico-chemical properties need to be understood to develop decorporation treatments
PHYSICAL REVIEW A 91, 020501(R) (2015)
145.unknown
GANDALPH
Gothenburg ANion Detector for Affinity measurements by Laser PHotodetachment
Built in spring 2015 in Gothenburg
Moved to ISOLDE, June 2015
Installed and put into operation at GLM
full control of system
Laser transport from RILIS
Photodetachment of I-, July 2015
GANDALPH
Drawing:
Annie
Ringvall
-Moberg
I-
FC
ITO covered glass
e-
a
I
I-
Test of GANDALH: Photodetachment of stable I-
Low 10-8 mbar vacuum
~ 8% transmission to the neutral detector
Photodetachment signal of I-
Threshold still measurable at very low ion rates (
Improvements prior to next run:
Improve transmission additional Einzel-lenses
Low 10-8 mbar to high 10-10 mbar new ion pump + baking
Moveable a-detector detection of selected At isotopes
BEAM TIME REQUEST
~We can select the most suitable isotope
(Any isotope could be used to determine EA)
Experiment possible with 3 105 ions ( but with lower resolution)
Requested 3 107 ions but experiment possible also with 3 105
The background signal resulting from collisions will be reduced proportional to the reduced ion beam intensity.
The pressure of GANDALPH will be reduced by a factor 20 through baking and the addition of ion pumps, giving the corresponding additional reduction of the background.
The reduced ion beam intensity will reduce the statistics for a given recording time. In order to stay within the requested shifts and maintain the statistics per laser wavelength step, we can increase the step-size of the scanning laser.
As photodetachment is a threshold process we can extract the EA even from a low resolution laser scan. With a reduced ion beam intensity, we will not reach the precision of the bandwidth of the laser of six significant figures (s.f.) as aimed for initially, but the EA today is not even known to within one significant figure. Even a resolution of two s.f. would be of great interest.
The background (collisions) proportional to ion beam intensity
Lower current compensated with increased acquisition time
Pressure down x20 x20 reduction in background
Photodetachment is a threshold process:
Lower current compensated with larger steps in photon energy
threshold measurement but with lower resolution
Goal: Determine EA with resolution of 40 meV
but: today is today completely unknown!
Even resolution 10 meV is very important result
3,06092(10)
Thank you for your attention!
20
40
60
80
100
120
1
2
3
PHYSICAL REVIEW A 91, 020501(R) (2015)
expt.
4c+CCSD(T)+breit+QED
MCDF+empirical
DK6+DFT
electron Affinity (eV)
Atomic number
F
Cl
Br
I
At
117
O
S
Se
Te
Po
Lv