Table 1 The most promising inverse beta decay (IBD) target isotopes and expected geoneutrino signals

From: Probing Earth’s missing potassium using the antimatter signature of geoneutrinos

Target process

IA [%]

Eth [MeV]

Log(ft)

Refs.

S(U) [TNU]

S(Th) [TNU]

S(K) [TNU]

1H → 1n

99.99

1.806

3.0170

64

31.5 [24.0, 47.0]

9.0 [6.4, 14.1]

/

63Cu → 63Ni

69.15

1.089

6.7

59

0.85 [0.64, 1.26]

0.49 [0.35, 0.77]

0.10 [0.07, 0.13]

63Cu → 63Ni*

 

1.176

5

22

   

35Cl → 35S

75.76

1.189

5.0088

65

0.73 [0.56, 1.09]

0.43 [0.30, 0.67]

0.10 [0.07, 0.13]

106Cd → 106Ag

1.25

1.212

4.1

66

(1.7 [1.3, 2.6]) × 10−1

(9.7 [6.9, 15.2]) × 10−2

(5.1 [3.7, 6.6]) × 10−3

  1. The 1st column lists the target and product isotopes involved in the IBD reaction, the 2nd column the IBD target Isotopic Abundance (IA) in percentage, the 3rd column the IBD reaction energy threshold (Eth) in MeV, the 4th column the Log(ft) value for the corresponding β decay of the final state, which is a measure of the reaction cross section. The IA, Eth and Log(ft) values are taken from the ENSDF database59, whose specific references are found in the 5th column. The 6th, 7th and 8th columns report, as central values, the expected geoneutrino signal in the [Eth, 3.272] MeV energy range respectively from uranium, thorium and potassium distributed in the Earth’s lithosphere and mantle. The hypothetical location of the Laboratori Nazionali del Gran Sasso has been chosen as example site. The range in square brackets provides the variability of the expected predicted signal, thus defining the ‘minimal’ and ‘maximal’ scenarios for the masses and distributions of heat-producing elements in the Earth determined with different Bulk Silicate Earth compositional models. See ‘Methods’ for further details. The expected geoneutrino signals are given in Terrestrial Neutrino Units (TNUs), corresponding to a 1-year acquisition time and 1032 atoms for each chemical species (i.e. a number of IBD target atoms corresponding to 1032 scaled by the isotopic abundance) and assuming 100% efficiency. Chlorine (35Cl) and copper (63Cu) represent the most promising targets for 40K geoneutrinos detection, while hydrogen (1H), and cadmium (106Cd) are here reported for comparison. A full list of the suitable target isotopes for 40K geoneutrinos detection can be found in the ‘Methods’ section.
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