RIB Target Systems

In general, many radioactive nuclei of interest to the research programs at the HRIBF have short lifetimes, are only produced in small quantities and undergo substantial losses during release, transport and ionization in the target/ ion source. Production of usable intensities of RIBs, therefore, is usually preceded by the development of a target/ ion source technique which optimizes release of the radioactive species from the target material, transport to ionization region and efficient ionization of the specific chemical species. This page presents a few highlights of some new target techniques which have been or shortly will be employed on the RIB injector.

 

 New Oxide Target Materials and Techniques

Early investigations into 17 F production through the 16 O(d,n)17F reaction were conducted with fibrous targets of Al2O3 and the maximum 17 F - yield measured leaving the RIB platform was 5x104 ions/s, an insufficient intensity for RIB experiments. To solve this problem we have designed several new target systems which are based on a technique of forcing a reactive, electropositive transport vapor through a fibrous metal oxide network which is considerably more refractory than Al2O3. The table below shows several oxides which are commercially available in fiber form (4-6 um dia.) and packed to densities of 3-10% of the pure material generally in the form of a weave or felt.  See for example, Zircar Products Inc.

 

Material

Temperature at which the 

vapor pressure reaches 10-4 Torr

HfO2
2500 C
ZrO2
2200 C
Y2O3
2000 C
CeO2
2310 C
ZrO2/Y2O3
1900 C
Al2O3
1550 C

The maximum operating temperature of the target material is set by the characteristic vapor pressure curve for that material since the closely coupled ion source cannot tolerate a vapor loads greater than 10-4 Torr.  Since, the major RIB loss processes; diffusion, desorption and effusion generally depend exponentially on temperature, we expected the gains made by increased operating temperature and increased production (more production beam on target) to far out weight the effect of shorter production ranges due to increased stopping power of the higher Z, more refractory materials: Hf, Zr, Y, Ce versus Al.  HfO2 is the most refractory of these materials and the microstructure of HfO2 target is shown here.  The following target system designs are based on this material and have been used or are being developed for use at the HRIBF.

New Liquid Target Techniques

A simple non re-circulating liquid Ge target system was employed for 69 As and 67Ga produced through the 70Ge(p,2n)69As and 70Ge(p,a)67Ga reactions.  Approximately 1x106 ions/s of 69As and 1x105 ion/s of 67Ga ions/s were delivered to an experimental target. In the near future, several experiments are planned which require roughly an order of magnitude more intensity. To achieve these goals several new liquid target systems have been designed and are currently being tested:


 
 

Actinide Target Materials


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HRIBF

This page was last updated on February 11, 1999

Send questions and comments to Robert Welton