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An improved technique for the preparation of O17 targets
NUCLEAR
INSTRUMENTS
AN IMPROVED
AND
METHODS
TECHNIQUE
27
(I964)
357;
©
NORTH-HOLLAND
FOR THE PREPARATION
PUBLISHING
CO.
O F 017 T A R G E T S
A. H. F. MUGGLETON and C. T. PARSONS A W R E Aldermaston, Berks., UK
Received 23 April 1964 This note describes an improved technique for producing thin films containing O ~7, suitable for nuclear spectroscopy. Tungsten oxide is obtained from the chemical reaction between a heated tungsten filament and enriched oxygen gas. The oxide is then evaporated on to thin carbon backings. b 1. Introduction
In a previous report 1) a technique is described for preparing tungsten oxide, enriched in the 018 isotope, from D2 Ors. The resulting targets contained a high percentage of O ~6 due to trapping of residual atmospheric oxygen in the frozen D2018 during initial evacuation of the vacuum chamber. As small quantities of highly enriched oxygen gas became more readily available it was decided to modify the previous technique and make the process more efficient.
II
Fig. 1. View of the apparatus used in the preparation of enriched tungsten oxide.
The apparatus, used for preparing the enriched oxide, is depicted in fig. 1. It is constructed of borosilicate glass and consists of the main chamber (a) to which is sealed a bottle (b) containing 20 atmospheric millilitres of 017 enriched gas*. Two cleaned tungsten filaments (c) 0.5 mm diameter x 5 cm long are spot welded to a standard glass valve base which is sealed into the main chamber. The assembled apparatus is sealed to a glass high vacuum pumping system, care being taken to ensure the small plug (d) does not fracture the break-off seal isolating the O ~7 gas from tile main chamber. The system is now evacuated to a pressure of 1 × 10 - 6 torr and baked at 350°C for approximately 4 hours. After allowing to cool, the
apparatus is sealed from the pumping system and O ~7 gas admitted to the main chamber by fracturing the break-off seal with plug (d). Both tungsten filaments are heated in turn to approximately 2500°C and the tungsten oxide formed is deposited on the chamber walls. When no further oxide is seen to form, the apparatus is allowed to cool and carefully broken open. The deposited tungsten oxide is then removed and stored for future use. Theoretically the maximum amount of WOX73 obtainable from 20 atmospheric milli-litres of O172 is 140 mg. This technique produced 118 mg; a yield efficiency of 84 ~ . The collected WOt 7 3 is evaporated from a collimated platinum boat onto thin self supporting carbon1), giving targets with an 017 enrichment greater than 4 0 ~ from 51 ~ enriched O172.
* Obtained from the Weizmann Institute, Rehovoth, Israel.
1) A. H. F. Muggleton and F. A. Howe, Nucl. Instr. and Meth.
2. Preparation of O x7 enriched tungsten oxide
Enrichments of > 50°/are available.
12 (1961) 192.
357
INSTRUMENTS
AN IMPROVED
AND
METHODS
TECHNIQUE
27
(I964)
357;
©
NORTH-HOLLAND
FOR THE PREPARATION
PUBLISHING
CO.
O F 017 T A R G E T S
A. H. F. MUGGLETON and C. T. PARSONS A W R E Aldermaston, Berks., UK
Received 23 April 1964 This note describes an improved technique for producing thin films containing O ~7, suitable for nuclear spectroscopy. Tungsten oxide is obtained from the chemical reaction between a heated tungsten filament and enriched oxygen gas. The oxide is then evaporated on to thin carbon backings. b 1. Introduction
In a previous report 1) a technique is described for preparing tungsten oxide, enriched in the 018 isotope, from D2 Ors. The resulting targets contained a high percentage of O ~6 due to trapping of residual atmospheric oxygen in the frozen D2018 during initial evacuation of the vacuum chamber. As small quantities of highly enriched oxygen gas became more readily available it was decided to modify the previous technique and make the process more efficient.
II
Fig. 1. View of the apparatus used in the preparation of enriched tungsten oxide.
The apparatus, used for preparing the enriched oxide, is depicted in fig. 1. It is constructed of borosilicate glass and consists of the main chamber (a) to which is sealed a bottle (b) containing 20 atmospheric millilitres of 017 enriched gas*. Two cleaned tungsten filaments (c) 0.5 mm diameter x 5 cm long are spot welded to a standard glass valve base which is sealed into the main chamber. The assembled apparatus is sealed to a glass high vacuum pumping system, care being taken to ensure the small plug (d) does not fracture the break-off seal isolating the O ~7 gas from tile main chamber. The system is now evacuated to a pressure of 1 × 10 - 6 torr and baked at 350°C for approximately 4 hours. After allowing to cool, the
apparatus is sealed from the pumping system and O ~7 gas admitted to the main chamber by fracturing the break-off seal with plug (d). Both tungsten filaments are heated in turn to approximately 2500°C and the tungsten oxide formed is deposited on the chamber walls. When no further oxide is seen to form, the apparatus is allowed to cool and carefully broken open. The deposited tungsten oxide is then removed and stored for future use. Theoretically the maximum amount of WOX73 obtainable from 20 atmospheric milli-litres of O172 is 140 mg. This technique produced 118 mg; a yield efficiency of 84 ~ . The collected WOt 7 3 is evaporated from a collimated platinum boat onto thin self supporting carbon1), giving targets with an 017 enrichment greater than 4 0 ~ from 51 ~ enriched O172.
* Obtained from the Weizmann Institute, Rehovoth, Israel.
1) A. H. F. Muggleton and F. A. Howe, Nucl. Instr. and Meth.
2. Preparation of O x7 enriched tungsten oxide
Enrichments of > 50°/are available.
12 (1961) 192.
357