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