Alfred O. Nier

A Mass Spectrometer for Isotope and Gas Analysis

A mass spectrometer suitable for routine isotope analyses of the lighter elements is described. Complete electronic circuits are given. An all metal mass spectrometer tube is employed. A null method of determining relative abundances of the elements carbon, nitrogen, and oxygen is used. Although designed primarily for analyzing elements for which separated isotopes are available as tracers, the instrument may be modified for use over the entire atomic table or for making gas analyses.

A Mass Spectrometer for Routine Isotope Abundance Measurements

A mass spectrometer suitable for routine isotope analyses of carbon, nitrogen, and other light elements which may be put in the gaseous or vapor form is described. Although a simple, relatively inexpensive magnet consuming little power is used, good resolution is obtained.

Search for organic and volatile inorganic compounds in two surface samples from the Chryse Planitia region of Mars

Two surface samples collected from the Chryse Planitia region of Mars were heated to temperatures up to 500�C, and the volatiles that they evolved were analyzed with a gas chromatograph-mass spectrometer. Only water and carbon dioxide were detected. This implies that organic compounds have not accumulated to the extent that individual components could be detected at levels of a few parts in 109 by weight in our samples. Proposed mechanisms for the accumulation and destruction of organic compounds are discussed in the light of this limit.

Isotopic Composition of Nitrogen: Implications for the Past History of Mars' Atmosphere

Models are presented for the past history of nitrogen on Mars based on Viking measurements showing that the atmosphere is enriched in 15N. The enrichment is attributed to selective escape, with fast atoms formed in the exosphere by electron impact dissociation of N2 and by dissociative recombination of N2+. The initial partial pressure of N2 should have been at least as large as several millibars and could have been as large as 30 millibars if surface processes were to represent an important sink for atmospheric HNO2 and HNO3.

Composition and Structure of the Martian Atmosphere: Preliminary Results from Viking 1

Results from the aeroshell-mounted neutral mass spectrometer on Viking I indicate that the upper atmosphere of Mars is composed mainly of CO2 with trace quantities of N2, Ar, O, O2, and CO. The mixing ratios by volume relative to CO2 for N2, Ar, and O2 are about 0.06, 0.015, and 0.003, respectively, at an altitude near 135 kilometers. Molecular oxygen (O2+) is a major component of the ionosphere according to results from the retarding potential analyzer. The atmosphere between 140 and 200 kilometers has an average temperature of about 180� � 20�K. Atmospheric pressure at the landing site for Viking 1 was 7.3 millibars at an air temperature of 241�K. The descent data are consistent with the view that CO2 should be the major constituent of the lower martian atmosphere.

Structure of the neutral upper atmosphere of Mars: results from viking 1 and viking 2.

Neutral mass spectrometers carried on the aeroshells of Viking 1 and Viking 2 indicate that carbon dioxide is the major constituent of the martian atmosphere over the height range 120 to 200 kilometers. The atmosphere contains detectable concentrations of nitrogen, argon, carbon monoxide, molecular oxygen, atomic oxygen, and nitric oxide. The upper atmosphere exhibits a complex and variable thermal structure and is well mixed to heights in excess of 120 kilometers.

Measurements concerning the vapour-liquid equilibrum of solutions of He3 in He4 below 2.19°K

Abstract From vapour pressure measurements of a known quantity condensed mixture of He3 and He4 (concentration of He3 5.10−4) in a vessel of 0.33 cm3 we calculated the concentrations of He3 in the liquid and vapour phase assuming: 1. a. perfect solubility of He3 in the “normal” helium fluid only 2. b. a perfect gas in the vapour phase, and 3. c. that the equilibrium between the two fluids of the helium II system is not altered by the He3. The two concentrations together with the measured amounts of vapour and liquid in the vessel made it possible to compute the total amount of He3 present in the vessel. Now, this value agreed under various circumstances with the known quantity of He3 which was condensed in the vessel. We conclude therefore that the above mentioned assumptions are confirmed and that the first one especially, which is very important in these calculations, is satisfied.

A Null Method for the Comparison of Two Ion Currents in a Mass Spectrometer

A method of determining the ratio of two small currents which vary intermittently or continuously, but always have the same relative magnitudes, is described. Although applied only to the case of making precise measurement of ratio of two ion currents in a mass spectrometer for the purpose of measuring the relative abundance of isotopes, the method would be useful in other applications as well.

An asteroidal breccia: The anatomy of a cluster IDP

Abstract We report results of a consortium study of a large interplanetary dust particle known as cluster L2008#5. This cluster is composed of fifty-three fragments (>5 pm in diameter) and several hundred fines ( Several methods were used to estimate the degree of heating that this cluster experienced. Variations in the inferred peak temperatures experienced by different fragments suggest that a thermal gradient was maintained. The cluster as a whole was not strongly heated; it is estimated to have a low earth-encounter velocity which is consistent with origin from an object in an asteroidal orbit rather than from a comet, which would most likely have a high entry velocity. Our conclusions show that cluster L2008#5 consists of a chemically and mineralogically diverse mixture of fragments. We believe that cluster L2008#5 represents a heterogeneous breccia and that it was most likely derived from an object in an asteroidal orbit. We also present an important cautionary note for attempts to interpret individual, small-sized 10–15 μm IDPs as representative of parent bodies. It is not unique that individual building blocks of IDPs, such as discrete olivine, pyroxene, sulfide grains, regions of carbonaceous material, and other noncrystalline material, are found in several fragments; however, it is unique that these building blocks are combined in various proportions in related IDPs from one large cluster particle.

Venus Thermosphere: In situ Composition Measurements, the Temperature Profile, and the Homopause Altitude

The neutral mass spectrometer on board the Pioneer Venus multiprobe bus measured composition and structral parameters of the dayside Venus upper atmosphere on 9 December 1978. Carbon dioxide and helium number densities were 6 x 106 and 5 x 106 per cubic centimeter, respectively, at an altitude of 150 kilometers. The mixing ratios of both argon-36 and argon-40 were approximately 80 parts per million at an altitude of 135 kilometers. The exospheric temperature from 160 to 170 kilometers was 285 � 10 K. The helium homopause was found at an altitude of about 137 kilometers.