Gamma Ray Spectroscopic Measurements of Mars

A. E. Metzger; J. R. Arnold

doi:10.1364/AO.9.001289

Applied Optics
Vol. 9,
Issue 6,
pp. 1289-1303
(1970)
•https://doi.org/10.1364/AO.9.001289

Gamma Ray Spectroscopic Measurements of Mars

A. E. Metzger and J. R. Arnold

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A. E. Metzger and J. R. Arnold, "Gamma Ray Spectroscopic Measurements of Mars," Appl. Opt. 9, 1289-1303 (1970)

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Abstract

A gamma ray spectrometer placed in orbit around Mars is expected to yield significant compositional data which can be related to the evolution of that planet. Components of the observable gamma ray flux come from the Martian surface, galactic and intergalactic space, and the spacecraft itself. The flux can be detected by a scintillation crystal or solid state detector, either of which combines efficiency of detection with energy resolution, and returns information to the earth as a pulse height distribution in order to detect characteristic energy line structure. The data will be evaluated for evidence of elemental differentiation with reference to terrestrial, meteoritic, solar, and lunar abundances. A lengthy mission will allow the surface of Mars to be mapped in a search for possible correlations between composition and topography or albedo.

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Isotope	Half life	Decay mode	Energy (in MeV) and intensity (%) of principal gamma ray lines
K-40	1.2 × 10⁹ yr	β⁻; EC	1.46 (11)
Th-232	1.39 × 10¹⁰ yr	α	—
Ra-228	6.7 yr	β⁻	—
Ac-228	6.13 h	β⁻	0.34 (15); 0.908 (25); 0.96 (20)
Th-228	1.9 yr	α	—
Ra-224	3.64 days	α	—
Rn-220	54.5 sec	α	—
Po-216	0.158 sec	α	—
Pb-212	10.6 h	β⁻	0.239 (47)
Bi-212	60.5 min	α, β⁻	0.727 (7)
Po-212	3 × 10⁻⁷ sec	α	—
Tl-208	3.1 min	β⁻	0.511 (23); 0.583 (86); 0.860 (12); 2.614 (100)
U-238	4.49 × 10⁹ yr	α	—
Th-234	24.1 days	β⁻	—
Pa-234	1.18 min	β⁻	—
U-234	2.48 × 10⁵ yr	α	—
Th-230	8.0 × 10⁴ yr	α	—
Ra-226	1622 yr	α	—
Rn-222	3.825 days	α	—
Po-218	3.05 min	α	—
Pb-214	26.8 min	β⁻	0.295 (19); 0.352 (36)
Bi-214	19.7 min	β⁻	0.609 (47), 1.120 (17); 1.764 (17)
Po-214	1.6 × 10⁻⁴sec	α	—
Pb-210	22 yr	β⁻	—
Bi-210	5.0 days	β⁻	—
Po-210	138.4 days	α	—

Rock	K (%)	Th (ppm)	U (ppm)
Dunite	0.02	Low	Low
Chondrite	0.085	0.040	0.012
Basaltic achondrite	0.06	0.3	0.1
Oceanic basalt	0.4	1.5	0.3
Plateau basalt	1.2	5.5	0.9
granite	3.8	18.5	4.8

Mean altitude (km)	Geometric factor	Atmospheric transmission	Counting time (h)	C_min (%)
500	0.76	0.19	1	0.27
1000	0.58	0.21	1	0.30
2000	0.39	0.22	1	0.40
1000	0.58	0.21	10	0.096
1600	0.46	0.22	10	0.11
2000	0.39	0.22	10	0.13
2600	0.32	0.23	10	0.14
2000	0.39	0.22	100	0.400
2600	0.32	0.23	100	0.045

Δh (km)	$\sum_{1000}^{h} t$ t (h)	A, × 10⁸ (km)²	Cumulative number of frames $\sum_{1000}^{h} F$					Frame diameter, d_f (km)
Δh (km)	$\sum_{1000}^{h} t$ t (h)	A, × 10⁸ (km)²	C_K = 0.085%	C_K = 0.2%	C_K = 0.5%	C_K = 1.0%	C_K = 2.0%	C_K = 0.085%	C_K = 0.2%	C_K = 0.5%	C_K = 1.0%	C_K = 2.0%
1000–1150	45	1.91	3.2	17.6	110	441	1760	6307	2689	1076	537	269
1000–1600	120	1.00	7.5	41.6	260	1041	4164	4120	1749	700	350	175
1000–2300	185	1.10	10.1	55.7	348	1394	5574	3724	1586	634	317	158
1000–2800	245	1.17	11.9	65.8	411	1646	6582	3530	1501	601	300	150
1000–3500	299	1.20	13.2	73.1	456	1827	7308	3399	1445	578	289	144
1000–4500	383	1.26	14.4	80.0	499	1999	7997	3331	1416	566	283	141
1000–5500	461	1.29	15.2	84.1	525	2103	8412	3289	1397	560	280	104

Isotope	Half life	Decay mode	Energy (in MeV) and intensity (%) of principal gamma ray lines
K-40	1.2 × 10⁹ yr	β⁻; EC	1.46 (11)
Th-232	1.39 × 10¹⁰ yr	α	—
Ra-228	6.7 yr	β⁻	—
Ac-228	6.13 h	β⁻	0.34 (15); 0.908 (25); 0.96 (20)
Th-228	1.9 yr	α	—
Ra-224	3.64 days	α	—
Rn-220	54.5 sec	α	—
Po-216	0.158 sec	α	—
Pb-212	10.6 h	β⁻	0.239 (47)
Bi-212	60.5 min	α, β⁻	0.727 (7)
Po-212	3 × 10⁻⁷ sec	α	—
Tl-208	3.1 min	β⁻	0.511 (23); 0.583 (86); 0.860 (12); 2.614 (100)
U-238	4.49 × 10⁹ yr	α	—
Th-234	24.1 days	β⁻	—
Pa-234	1.18 min	β⁻	—
U-234	2.48 × 10⁵ yr	α	—
Th-230	8.0 × 10⁴ yr	α	—
Ra-226	1622 yr	α	—
Rn-222	3.825 days	α	—
Po-218	3.05 min	α	—
Pb-214	26.8 min	β⁻	0.295 (19); 0.352 (36)
Bi-214	19.7 min	β⁻	0.609 (47), 1.120 (17); 1.764 (17)
Po-214	1.6 × 10⁻⁴sec	α	—
Pb-210	22 yr	β⁻	—
Bi-210	5.0 days	β⁻	—
Po-210	138.4 days	α	—

Abstract

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Figures (14)

Tables (4)

Equations (10)

Applied Optics