Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 49 (2016)

New Trojan Horse study of the 18 F(p, α)15 O reaction at astrophysicalenergies
S. Cherubini,∗1,∗2,∗3 G. D’Agata,∗1,∗2 M. Gulino,∗1,∗3,∗4 M. La Cognata,∗1 S. Palmerini,∗1 R.G. Pizzone,∗1S. Romano,∗1,∗2 R. Spartà,∗1 C. Spitaleri,∗1,∗2 H. Yamaguchi,∗5 K. Abe,∗5 O. Beliuskina,∗5 S. Hayakawa,∗5D.M. Kahl,∗5 Y. Sakaguchi,∗5 S. Kubono,∗3 D. Suzuki,∗3 N. Iwasa,∗6 K.Y. Chae,∗7 M. Kwag,∗7 H.S. Jung,∗8
D.N. Binh,∗9 V. Guimarães,∗10 and S. Bishop∗11deg.
One of the main problems encountered in the data
analysis of the previous work came from the existenceof various reaction channels with diﬀerent sets of threeparticles in the ﬁnal state. Though it was shown that
it is possible to disentangle the events coming fromthe reaction channel of interest from the others by applying various kinds of cuts in the phase space5) , thepossibility of having a direct identiﬁcation in Z of theoutgoing particles, at least for the heavier ones, wasone of the major improvements in this measurement.
To this end, a 20 µm thick silicon strip detector wasused as ∆E stage in front of each of the aforementioned
double sided multi strip detectors, such that the ∆E-E
telescopes cover angles from roughly 4 to 10 deg. This
will also result in a higher detection eﬃciency because
we expect that we will be able to recover regions of thephase space that had to be discarded in the previous
data analysis.
As already mentioned, the experiment was successfullyperformed in fall 2015 over a period of 18 days divided
into two runs. Given the much longer period of actual
data acquisition (15 days vs 2) and the higher detection eﬃciency, we also expect that we will be able tosigniﬁcantly increase the accumulated statistics withrespect to the previous experiment. The data analysisof the new set of data has started and we expect toobtain preliminary results within fall 2016.

The ﬁrst experiment on the application of the Trojan Horse Method1,2) was to measure the cross section of an astrophysically important reaction, namely
18F(p, α)15 O at nova energies3,4) via the 18 F(p, α15 O)nreaction with three bodies in the ﬁnal state, using aradioactive beam. This experiment has been recently
published in Ref. 5 and it is also presented in thisreport.6) Indeed, the whole idea of the Trojan Horse
Method is to study a suitably chosen reaction proceeding via a quasi-free mechanism with three body in theﬁnal state, in the present case 18 F(d, α15 O)n, in order
to infer pieces of information on the process of astrophysical interest, 18 F(p, α)15 O in this case.
In order to improve the statistics as well as the quality of data, a new measurement was performed atthe RIKEN Nishina Center using the CRIB apparatus from the University of Tokyo during OctoberNovember 2015. As in the previous work, the primarybeam of 18 O delivered by the AVF cyclotron was used
to produce a 18 F radioactive beam with intensity inthe range of 105 -106 pps. After the standard CRIB
apparatus, the radioactive beam of 18 F was tracked
by two PPACs and ﬁnally used to bombard thin (100200 µg/cm2 ) CD2 targets. The distance between thePPACs was optimized on the basis of the experienceacquired in the previous experiment. In addition, thedetection system based on the ASTRHO (A Silicon Array for Trojan HOrse) setup7) was upgraded. In particular eight double position sensitive silicon detectors(45 × 45 mm2 active area, 500 µm thick) mounted on asquare geometry were used to detect outgoing particles
with an exit angle of roughly 10 to 40 deg. Anotherset of two double sided multi strip silicon detectors (50× 50 mm2 , 500 µm thick) was used to detect particles
with exit angles ranging from approximately 4 to 10References1) R. E. Tribble et al., Rep. Prog. Phys. 77, 106901 (2014).
2) S. Cherubini et al., ApJ, 457, 855, (1996).
3) A. S. Adekola et al., Phys. Rev., C83 052801 (R) (2011).
4) A. M. Laird et al., Phys. Rev. Lett., 110, 032502 (2013).
5) S. Cherubini et al., Phys. Rev. C 92, 015805 (2015)6) S. Cherubini et al., in this report.
7) S. Cherubini et al., ASTRHO: an Array of Silicons for
TRojan HOrse studies with RIBs, in preparation.

∗1

INFN-LNS, Catania, Italy
Dipartimento di Fisica e Astronomia, Università di Catania,Catania, Italy∗3 Riken, Nishina Center, Wako, Saitama, Japan∗4 Università di Enna KORE, Enna, Italy∗5 Center for Nuclear Study, The University of Tokyo, Japan∗6 Department of Physics, Tohoku University, Sendai, Japan∗7 Department of Physics, Sungkyunkwan University, Suwon,Republic of Korea∗8 Department of Physics, Chung-Ang University, Seoul, Republic of Korea∗9 30 MeV Cyclotron Center, Tran Hung Dao Hospital, Hoan
Kiem District, Hanoi, Vietnam∗10 Universidade de São Paulo, Instituto de Fı́sica, Departamento de Fı́sica Nuclear, São Paulo, Brasil∗11 TUM, Garching, Germany∗2- 63 -