Project Title: Study of proton induced gamma background un metallic backings
LNGS Access period: May 2002 – October 2002
Group Leader: Z. Fulop : ATOMKI Debrecen (Hungary)
Researchers:  Z. Fulop, G. Gyurky, E. Somorjai : ATOMKI Debrecen (Hungary)

Delivered access (filled by TARI administration): 56 man-days

Final scientific report (filled by group leader):
The 400 kV LUNA2 accelerator facility installed at the Laboratori Nazionali del Gran Sasso provides a unique possibility to study nuclear reactions at very low energies. Due to the extremely low cosmic background, the high energy γ-rays emerging from the astrophysically important 14N(p,γ)15O reaction can be measured here even at very low intensities. However, the presence of light element impurities in the targets can cause severe problems since the proton beam can induce high energy γ -radiation on these impurities. We intended  to study these impurities and to choose the way of target preparation where the beam induced background is minimized. Moreover, the low cross sections necessitate very long irradiations with high beam current. Hence the study of target density profile stability was also desirable.
Solid state N targets have been produced with three different procedures: implantation, evaporation and sputtering. The implanted ones were produced at the accelerator of the Universidade de Lisboa, Portugal, bombarding Ti, Cu and Ta backings with an isotopically pure 14N low energy beam. Evaporated targets were prepared in the ATOMKI in Debrecen, Hungary evaporating a thin layer of Ti on Ta backings and exposing the heated Ti layer to N gas with pressure of 50 torr. Sputtered (deposited) targets were obtained by the RF magnetron sputtering technique at the Laboratori Nazionali di Legnaro.
In the investigated range of proton energies between 140keV and 400keV the most relevant reactions on possible contaminants are 11B(p, γ)12C, 19F(p,αγ)16O and 18O(p, γ)19F. All these reactions emit gamma-rays of more than 4 MeV and show resonance structures in the relevant range of proton energies.
We concluded that the sputtered and the evaporated TiN targets on Ta backings have the most uniform density profile and withstand many days of beam bombardment with several hundreds of  uA without any significant deterioation. On the other hand, the sputtered targets had the lowest 11B contamination.
On the base of the work presented in this project it has been possible to develop reliable targets which allow to measure the reaction 14N(p,γ)15O at proton energies as low as 140 keV. Future experiments at LUNA2 will also largely benefit from our achievements.  


Publications:
“Target Stability and beam-induced background studies at the LUNA underground facility”, Nucl. Phys. A718(2003) 135

Evaluation by USP (March 2003)
The aim of this study was to define and test the optimal Nitrogen target for studying the 14N(p, g)15O reaction at astrophysically relevant low energies. All goals proposed have been properly achieved. Publication submitted (NP-A).