First steps in in-trap conversion electron spectroscopy L

First steps in in-trap conversion electron spectroscopy L. Weissman Soreq NRC, Yavne 81800, Israel

ISOLDE 2000 -2002 1 -1. 4 Ge. V 3 1013 p/pulse average current 1 -2 A

Internal electron conversion Deexcitation of nuclear level may proceed via emission of a gamma ray or injection of an atomic electron (internal conversion process) An ideal gamma-spectrum E=E 0 An ideal electron-spectrum E 0 -EK E 0 -EL g E 0 -EM e E=0 E 0 carries more experimental information Conversion electron spectroscopy was flourishing in 1960 -70 s In old nuclear journals Nepublications ~ Ngpublications 1981 Kai Siegbahn, Noble prize for development of electron spectroscopy At present Nepublications << Ngpublications This is due to : 1. Impressive development of gamma detector technology 2. Fundamental problem of electron spectroscopy

In-trap conversion electron spectroscopy Fundamental problem of electron spectroscopy B detector E In-trap spectroscopy as an alternative B detector V E

Possible applications of in-trap electron spectroscopy Nuclear structure studies Atomic binding energies of radioactive isotopes Improvement of nuclear calibration standards Chemical effects in internal conversion Atomic consequences of nuclear decay Biological effects of low-energy electrons Fundamental interaction experiments

REX-ISOLDE post-accelerator ISOLDE – low-energy beams (only decay studies) REX-ISOLDE post-accelerator expands range of physics (reactions exotic nuclei)

The REX-TRAP beam from ISOLDE REXTRAP data Buffer gas = Argon Gas pressure < 10 -3 mbar B= 3 T confinement < 20 ms The REX-trap bunches and cools ISOLDE beams preparing it for the REX-ISOLDE post accelerator Trap capacity > 106 ions Trap length = 0. 9 m Longitudinal emittance = 5 s·e. V Efficiency > 20 %

Idea of test trap center, position of ion cloud electron trajectory ejection diaphragm detector

Detector Canberra RD ED 10 GC-500 P active area 10 mm 2 thickness 500 mm window 250 A 350 241 Am source Counts 300 250 200 150 100 x 10 50 0 0 10 20 30 40 E(ke. V) 50 60

Measurement of detection efficiency implanted 131 Ba source 8000 Counts in the test chamber 6000 131, 133 Ba 4000 and 207 Bi electron sources Intrinsic efficiency measured in a test chamber 2000 0 . b 0 20 40 60 80 120 140 160 180 200 E(ke. V) Total efficiency measured in the trap 131 50000 implanted Ba source in total Calculatedthe trap 40000 Counts 100 efficiency in the trap 30000 20000 10000 0 0 . c 20 40 60 80 100 E(ke. V) 120 140 160 180 200

ISOLDE layout First test with radioactive (2001) trapping radioactive ions Parasitic test: real experiment spectroscopy of heavy Indium isotopes Ge. V 3 1013 p/pulse 1 -1. 4 average current 1 -2 A laser ion source trapping 116 m 2 In and 118 m 2 In isomers (simple, stable daughters) Before the measurement: trap is optimized with stable isotopes (138 Ba) using an MCP after optimization Si detector is inserted ( no trap control) Parasitic test PC based data acquisition at 60 k. V Real experiment PBS booster cycle: 1 proton pulse in 16. 8 s Trap pulse : 30 ms collection, 100 ms cooling, synchronized with protons Data collection all the time

Stray electrons problem E (ke. V)

K stray electrons 116 m 2 In Trapped isomers trapped ions L M ~107 116 m 2 In per m. C of protons ~108 116 In per m. C of protons 4 ke. V energy resolution 118 m 2 In K L trapped ions M ~4 x 107 116 m 2 In per m. C of protons ~4 x 108 116 In per m. C of protons 6 ke. V energy resolution

Second trapping radioactive ions (early 2002) Off-line test (ISOLDE shutdown): the last experiment UC target& surface ionization source A lot of 225 Ac (T 1/2=10 d) in the target 221 Fr daughter (T 1/2=4. 9 min) is extracted and ionized Before the measurement: trap is optimized with more intense (223 Ra) using an MCP after optimization Si detector is inserted ( no trap control) PC based data acquisition at 60 k. V Simultaneous collection, cooling and measurement

Trapped a-decaying ions long collection short collection K L M/N K: L: M 1: 1. 17(3): 0. 39(3) 1: 1. 23 : 0. 43 theory 5 x 106 atoms/s from separator (x 80% transport efficiency, x 40% trapping efficiency) Observe correct electron lines intensities, energy resolution 2 ke. V Observe new feature : low energy background. 217 At daughter recoil average charge 9 -13 After “cleaning” the trap see background 213 Bi, granddaughter of 217 At transported to detector Resolution deteriorates with increasing trap saturation

1000 Diagnostic opportunites with electrons low-energy background f Trapping efficiency and number of calculated trapped ions 800 (from known detection efficiency and electron line branching ratio; 2. 5 % and 106 for continuous accumulation) M-line Counts Ion survival time (decay of electron signal after stopping ion collection; ~ 1 s) 600 Optimization of dumping RF frequency 400 Measurement of the ion cloud size (electron signal as a function of cloud position; 3. 5 mm) 200 Dependence of electron signal as a funcion of buffer gas pressure 0 4. 0 E-05 6. 0 E-05 8. 0 E-05 1. 0 E-04 Pressure in the trap center (mbar) 1. 2 E-04

Continuation of the program Thesis of Juho Rissanen , Univercity Of Jyvaskyla The JYFLTRAP The same detection system High resolution spectroscopic data from 10 fission isomers Energy resolution 2 -2. 5 ke. V The shortest isomer 117 m. Pd (T 1/2=19. 1 ms) The lowest electron energy 9. 9 ke. V

Summary Feasibility of in-trap electron spectroscopy was demonstrated The observed problems ( background from stray electrons, continuos background from beta, summing with low-energy electrons) could be solved by improving detection setup Electron signal from trapped ions can be used for diagnostics of the trapped ion cloud In-trap electron spectroscopy may open many interesting opportunities in different fields

People involved

Chemical effects in internal conversion The in-trap measurements will provide unique opportunity to compare IC electron spectra from isolated atomic and molecular ions

Difficulties in accurate measurements of IC electron branching ratios Even for the calibration sources intensities of electron lines measured in different experiments vary significantly. Example: Intensity of K-line corresponding to 160. 6 ke. V g-ray in 133 Ba J. E. Thun 1966 H. J. Hennecke 1967 S. Tornkvist 1970 H. E. Bosch 1968 Main problem : Integration of electron line Chemical effects This problems will be solved in in-trap measurements. In future new calibration standards will appear from in-trap measurements

Atomic consequences of nuclear decay Adjustment of atomic electron cloud after nuclear-decay, This “adjustment” is a violent and spectacular cascade of atomic electrons (Auger, shake off, shake up ) which lead to multiple ionization of residual nuclear. A. H. Snell and F. Pleasonton, Phys. Rev 107 (1957) 740 High-resolution in-trap spectroscopy will allow one to study these processes

Toxicity and therapeutic effects of low-energy electrons A. Kassis, NIM B 87 (1994) 279 -284 D. E. Charlton and J. Booz, Rad. Res. 87 (1981) 10

Experiments for studying fundamental interactions Example: Doppler shifted conversion electrons ( 33 Ar -like experiment, E. Adelberger et al ) e recoil b b e n det 2 det 1 b b det 3 From analysis of the electron lineshapes one can extract information on the nuclear recoil velocity and, hence, on b-n correlations