Method for joint measuring argon-argon age and cosmic ray exposure age of extraterrestrial samples

A method for joint measuring argon-argon (Ar—Ar) age and cosmic ray exposure age of an extraterrestrial sample, comprising:

• step A, sample packaging:
• packaging a sample to be determined into cylindrical shapes with a diameter of 5 millimeters (mm) with aluminum foils to obtain packaged samples, placing the packaged samples and a chronology standard sample at intervals in a vertical direction, and then putting the packaged samples and the chronology standard sample into a glass tube;
• step B, placing the packaged samples in the glass tube into a neutron reactor for irradiation:
• packaging a potassium salt and a calcium salt individually into cylindrical shapes with a diameter of 5 mm, and then performing a neutron irradiation on the potassium salt and the calcium salt together with the glass tube containing the packaged samples, wherein 1-2 cylindrical shapes of potassium salt and 1-2 cylindrical shapes of calcium salt are used during each time of the neutron irradiation;
• and
• step C, determining Ar isotopes of the packaged samples after being performed with the neutron irradiation and thereby calculating argon-argon age and cosmic ray exposure age:
• releasing gas components of the packaged samples after being performed with the neutron irradiation by means of laser heating and melting or high temperature furnace heating and melting, removing active gas from the gas components to obtain remaining gas, and subsequently delivering the remaining gas to a rare gas mass spectrometer to determine the Ar isotopes;
• wherein formulas for calculating the argon-argon age are:
• t
• =
• 1
• λ
• ⁢
• ln
• ⁡
• (
• 1
• +
• J
• ⁢
• 40
• Ar
• *
• 39
• Ar
• K
• )
• ,
• J
• =
• 39
• K
• 40
• K
• ⁢
• λ
• λ
• e
• +
• λ
• e
• ′
• ⁢
• Δ
• ⁢
• ∫
• ∅
• ⁡
• (
• E
• )
• ⁢
• σ
• ⁡
• (
• E
• )
• ⁢
• dE
• ;
• wherein a formula for calculating the cosmic ray exposure age is:
• Exposure
• ⁢
• age
• =
• (
• 38
• Ar
• c
• ⁢
• o
• ⁢
• s
• 37
• Ar
• ca
• )
• ⁢
• (
• γ
• P
• 3
• ⁢
• 8
• ❘
• "\[LeftBracketingBar]"
• C
• a
• ❘
• "\[RightBracketingBar]"
• )
• ;
• where t is the argon-argon age, λ is a decay constant, λe and λ′e are decay constants of two branches decaying from 40K to 40Ar respectively, 40Ar* is a radiogenic factor, 39ArK is 39Ar produced by the neutron irradiation at 39K, 39K and 40K are potassium isotopes respectively, A is an irradiation time, Ø(E) is a neutron flux with energy E, σ(E) is a neutron reaction cross section with energy E, Exposure age is the cosmic ray exposure age, 38Arcos is cosmogenic radionuclide 38Ar, 37ArCa is37Ar produced by Ca during the neutron irradiation in the neutron reactor,
• P
• 3
• ⁢
• 8
• ❘
• "\[LeftBracketingBar]"
• C
• a
• ❘
• "\[RightBracketingBar]"
• is a yield of 38Arcos relative to Ca concentration, and γ is an irradiation parameter related to 37ArCa and Ca content.