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Release of Light Alkalis (Li, Na, K) From ISOLDE Targets

Strahinja Lukić, 18.10.2005

18-10-2005 Release of the Light Alkalis From ISOLDE Targets

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Outline

Release of nuclides from ISOLDE targets

Release measurement technique

Results

18-10-2005 Release of the Light Alkalis From ISOLDE Targets

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Release of Nuclides from ISOLDE Targets

Nuclide production

Thermal diffusion

Effusion

Ionization

Extraction by 60 kV field

Losses to chemical reactions, leaks, radioactive decay...

Proton beam

18-10-2005 Release of the Light Alkalis From ISOLDE Targets

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Typical ISOLDE Target

20 cm

18-10-2005 Release of the Light Alkalis From ISOLDE Targets

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Ion-Sources Surface

Hot transfer line made of a metal with high work function (W, Ta)

Plasma Electron beam ionizing a gas

mixture (Ar+Xe)

Hot or cold transfer line

Laser excitation and ionization using

characteristic wavelengths in 2-3 steps

Chemical selectivity

Surface Ion-Source

EXTRACTION ELECTRODE

http://isolde.web.cern.ch/ISOLDE/

18-10-2005 Release of the Light Alkalis From ISOLDE Targets

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ISOLDE Facility LayoutTransmission Losses

http://isolde.web.cern.ch/ISOLDE/

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Release Measurement Using the Tape Station

Proton beam pulses are spaced by 14 - 20 s

Ion beam implanted on a tape at a certain time after the p+ bunch Timing and duration controlled by a

deflector magnet

Tape carries the ions to the detector (1s)

Detection of β, α, γ or n during a specified time

Detector

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The Release Curve

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Yield and In-Target Rates

The release curve is established for a long lived isotope and applied to the shorter lived isotopes of the same element

The decay losses can be deduced and in-target production rates calculated

But, losses to leaks and chemical reactions impossible to estimate → yields are not always reproducible

18-10-2005 Release of the Light Alkalis From ISOLDE Targets

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Cross-sections

Production cross-sections can be estimated assuming that: All the nuclides are produced in primary reactions

(approximately correct for Li, Na and K)

Production cross-sections are constant along the target despite the proton energy loss (approximately correct for 1 GeV protons ? Energy loss ~50 MeV, xs variation ~20-30% ?)

mol

atottg

M

Nd

tot

i eCP

110242.6]/1[ 12

18-10-2005 Release of the Light Alkalis From ISOLDE Targets

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Some Results

Order of magnitude good except data from specific targets

Shape of the distribution approximately good (steeper than in ABRABLA results)

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Some Results

Very few data, incompletely documented

Order of magnitude good

Shape of the distribution approximately good

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Other Results - K

Too few data for potassium in the segment that was treated

Order of magnitude good except in the same specific targets as for sodium

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Other Results - Li

Very difficult element for ISOL Small atom - leaks through solid materials

Fast diffusion – faster than the measurement system?

No sufficiently long-lived isotope – difficult to establish the release curve.

Extrapolate the release curve parameters from K and Na?

18-10-2005 Release of the Light Alkalis From ISOLDE Targets

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Other Results - Li

Estimated release curves extremely long (not logical for Li) → apparently high decay losses → high xs

Using parameters extrapolated from sodium doesn't seem to work

Possible errors because of the time-dependent background (He)

8Li produced in U-Carbide

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Other Results - Li

No experimental data to compare to.

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Conclusions

The method seems to work although it would be difficult to use it for independent cross-section measurements.

The main problem - unpredictable losses

Yield data are scarce, at least in the period that was treated (1993 – 2002)

Systematic measurement of the time-dependent background could help, particularly for lithium