A. Zyuzin

The fabrication of metallic 7Be targets with a small diameter for 7Be(p,γ)8B measurements

Abstract The fabrication process for a metallic 7 Be target of small diameter is described. Targets fabricated in this manner have been subjected to systematic tests and one of them has been used in a 7 Be(p,γ) 8 B measurement at the University of Washington. Target properties have been determined including the total amount of 7 Be, the 7 Be distribution over the target area derived via a decay γ-scan and the 7 Be depth profile. The latter has been measured with the E α =1376 keV resonance in the 7 Be ( α , γ ) 11 C reaction.

A new measurement of 7Be(p,γ)8B cross section and its astrophysical meaning

Abstract We measured the 7Be(p,γ)8B cross section from Ep = 221 keV to 1376 keV. A uniformly distributed beam that illuminated the whole area of a small diameter target was used to eliminate systematic error from 7Be target non-uniformity. The energy loss profile of the target to the incident beam was measured using the 7Be(α,γ)11C resonance at Eα = 1376 keV. The (α,γ) measurement also demonstrated that the target had a high 7Be atomic purity. The measured yield of the detected 8B was normalized to the activity of the target and the solid angle of the counting detector. Corrections for 8B decay during bombardment and arm rotation were applied. For the first time, the correction due to lost 8B from backscattering was determined experimentally. A new experiment is presently underway, extending to lower proton energy. Due to a problem in the determination of the α-detector solid angle in the first measurement, the solid angle in the new measurement will be determined by a different technique using a 148Gd α source and a silicon detector whose distance to the source can be precisely adjusted.

Development of an intense O-15 radioactive ion beam using low energy protons

Abstract The production of copious quantities of 15O, (half-life = 122.2 s) for astrophysical applications has been a source of concern at TRIUMF and ISAC for some time. An 15O beam is needed for two experiments (15O(α,γ)19 Ne and 15O(6Li,d)19Ne) at ISAC. The beam flux required for these experiments is extremely high, (between 109 and 1011 15O/s) and thus high efficiencies at all steps in the process will be required. Difficulties arise due to the fact that oxygen is very reactive chemically and thus is difficult to extract from a thick spallation target. The possibility of using one of the small cyclotrons on site (TR13, CP42 or TR30) for the production of this isotope (15O) has been discussed. This production approach will involve the use of low energy protons to interact with a nitrogen gas target via the 15N(p,n)15O reaction, which is accessible with attainable particle energies using these cyclotrons. Preliminary results using the 14N(d,n)15O reaction as a model for the 15N(p,n)15O reaction have been obtained and is presented describing the appropriate on-line chemistry to separate, trap, purify and transfer the 15O. The 15O will be converted to the preferred chemical form of C15O which will be available for introduction into an ECR ion source for the production of the high intensity 15O ion beam at ISAC.

A new determination of the astrophysical S-factor for the 7Be(p,γ)8B reaction from direct cross section measurements

We measured the 7Be(p,γ)8B cross section from Ēcm=186 to 1200 keV, with a statistical-plus-systematic precision per point of better than ±5%. All important systematic errors were measured including 8B backscattering losses. We obtain S17(0)=22.3±0.7(expt)±0.5(theor) eV-b from our data at Ēcm⩽300 keV and the theory of Descouvemont and Baye.