In-situ K-Ar dating using LIBS in the VUV range

Shingo Kameda1, Yuichiro Cho2, Yasuhito Sekine2, Seiji Sugita2

1 Rikkyo University, 2 The University of Tokyo

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K–Ar dating

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40K

40Ca

40Ar

β ~90%

EC ~10%

Half-life~1.8 By• Rock:

– Ar degassing occurs before solidifiedThe dominant source of 40Ar is 40K decay.– Ca is abundant Difficulty to estimate the amount

of 40K originated Ca.

Ca Ca40K/K ~10-4

K–Ar dating

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• Ice:– K has a high solubility in water– Ar degassing also occurs before frozen. The dominant source of 40Ar in ice should be also 40K decay.

・ Possibility of K-Ar dating on Europa [Swindle et al., 2005]

Europa’s surface: tens of My. Ganymede’s surface: hundreds of My.

LIBS: Laser Induced Breakdown Spectroscopy

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• Optical elemental analysis technique– Ablation: a high intensity pulse laser

Pulse laser Ablation

LIBS: Laser Induced Breakdown Spectroscopy

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• Optical elemental analysis technique– Ablation: a high intensity pulse laser– Plasma emission spectroscopy:

spectrometer

SpectrometerPlasma emission

K-Ar dating using LIBS (MSL/ChemCam)

6MSL/Chemcam NASA

K• LIBS in UV-Vis-IR range• K emission lines: 767nm, 770nm

K-Ar dating using LIBS (MSL)

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K• LIBS in UV-Vis-IR range• K emission lines: 767nm, 770nm

Ar ・ Vacuum chamber and mass spectrometerMeasuring the mass of the sample and the amount of outgassing Ar with heating.

Pulse Laser

Spectrometer

target

K-Ar dating using LIBS (MSL)

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K• LIBS in UV-Vis-IR range• K emission lines: 767nm, 770nm

Ar• Vacuum chamber, mass spectrometer,…Measuring the mass of the sample and the amount of outgassing Ar with heating.

VacuumChamberPulse Laser

Spectrometer

Q Mass

armrobotic

target

Determination of quantity of Ar using LIBS

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New idea to observe Ar emission line.Ar emission lines: 104.8nm and 106.7nm・ Vacuum chamber is not necessary on the airless body. Less mass

•

Pulse Laser

Spectrometer VacuumChamber Q Mass

armrobotic

Determination of quantity of Ar using LIBS

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New idea to observe Ar emission line.Ar emission lines: 104.8nm and 106.7nm・ Vacuum chamber is not necessary on the airless body. Less mass・ Remote Sensing (1m TBC)

No experiment for Ar in rocks yet. (LIBS experiment for Ar atmosphere was performed.)

Pulse Laser

Spectrometer

target

Determination of quantity of Ar using LIBS

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Nd:YAG Sample

Grating

MCP with Phosphor

• K-feldspar(Age and composition are unknown..)

Ar Lamp

Rikkyo Univ.

Preliminary result

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• K-feldspar

• Still in preparation.←Spectrum of Ar Lamp • FWHM is 0.3 nm.• Preliminary result

102 104 106 108 1100

1000

2000

3000

4000

5000

Inte

nsity

, AD

U

Wavelength, nm

0.31nm

Toroidal grating4800gr/mm

Banpass filter for K~767nm

Detector

MCP+multi anordOr

MCP+Phosphor+CCD

100mm

25mm

62.5mm

Blue: Ar 106.7 nm 　 Pink: He 58.4 nmRed: 0-order25mm x 25mm x 62.5mm 　 < 105 g w/o Pulse Laser

Optical Design

Ganymede Lander & Orbiter (JUICE)

Lander: In-situ K-Ar Absolute ageOne point

JUICE: Crater-countGlobal MapRelative age

ComplementaryNASA

Another activity on LIBSSELENE-2 (Lunar Rover, ‘Pre’-Project)

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• ChemCam-like LIBS is too big (9-11kg) to install on the gimbal on the mast unit of the SELENE-2 rover.Install LIB-S2 on the body to reduce the total mass. (Fiber becomes unnecessary.)3.5 kg

• Closer to the ground Distance range can be reduced.

Optical design of Telescope

16• FOV: φ10mm Spectral range: 360-1064nm

Interface point (Optics)SpainDr. F. Rull

Movement

FranceDr. O. GanaultDr. S. Maurice

Install Visible LD in Japan on the base plate.Align Laser & Spectrograph with Vis. LD in France & Spain.Fix them on the B/P. 17

• Movable telescope• Automatic focus adjustment

Specification• Distance: 1.0 – 1.5 m• Spectral range: 360 – 1064 nm• Laser intensity: ~10 mJ/pulse

(Nd:KGW, almost the same as ChemCam)• Laser spot diameter: < 300 um• FOV: φ10mm at the target plane• Spatial resolution of

the imager: 30um/pix• Scanning gap: ~300um• Mass: 3.52kg• Power: 7W(max)• 3 movement systems:#1 wide-range vertical movement,#2 short-range horizontal scanning,#3 focus adjustment 18