A 3He neutron detector for the measurement of reactions

Falahat, S.; Best, A.; Couder, M.; Görres, J.; Kratz, Karl; Ott, U.; Stech, E.; Wiescher, M.

doi:10.1016/j.nima.2012.10.036

Cited by 30 publications

(28 citation statements)

References 27 publications

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“…This resonance was also observed in earlier measurements of the proton and alpha channels [22,[24][25][26][27]. Our measurement includes a 15% systematic uncertainty which primarily results from the uncertainties in the beam current (10%), beam energy (2%), detector efficiency (6%) [20], angular distribution (5%), and stopping power (7%) [21,28]. The Dayras results also have an additional systematic uncertainty of 16% [10] not shown in Fig.…”

supporting

confidence: 74%

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First Direct Measurement ofC12(C12
Bucher¹,
Tang²,
Fang³
et al. 2015
Phys. Rev. Lett.
35
3
55
0
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Neutrons produced by the carbon fusion reaction 12 C( 12 C,n) 23 Mg play an important role in stellar nucleosynthesis. However, past studies have shown large discrepancies between experimental data and theory, leading to an uncertain cross section extrapolation at astrophysical energies. We present the first direct measurement that extends deep into the astrophysical energy range along with a new and improved extrapolation technique based on experimental data from the mirror reaction 12 C( 12 C,p) 23 Na. The new reaction rate has been determined with a well-defined uncertainty that exceeds the precision required by astrophysics models. Using our constrained rate, we find that 12 C( 12 C,n) 23 Mg is crucial to the production of Na and Al in Pop-III Pair Instability Supernovae. It also plays a non-negligible role in the production of weak s-process elements as well as in the production of the important galactic γ-emitter 60 Fe. The first stars in the early Universe formed about 400 million years after the big bang. Verification of the existence of these stars is important for our understanding of the evolution of the Universe [1]. It has been predicted that for Population-III (metal-free stars [2]) stellar production yields, the abundances of odd-Z elements are remarkably deficient compared to their adjacent even-Z elements [3]. Astronomers are searching for long-lived, low mass stars with the unique nucleosynthetic pattern matching the predicted yields [4]. The relevance of 12 C( 12 C,n) 23 Mg in the first stars has been discussed by Woosley, Heger, and Weaver [5]. By the end of helium burning in Pop-III stars, the neutron to proton ratio in the ash is almost exactly 1. However, in the subsequent carbon burning phase, frequent β + decay of produced 23 Mg converts protons into neutrons, thus increasing the neutron to proton ratio. A slight excess of neutrons would significantly affect the abundances of the odd-Z isotopes with neutron to proton ratios higher than 1, e.g.23 Na and 27 Al.12 C( 12 C,n) 23 Mg is also a potentially important neutron source for the so-called weak s-process occurring in massive ) and ) stars. The weak s-process takes place during the core helium and shell carbon burning phases and is largely responsible for the s-process abundances up to A≈90 [6]. Pignatari et al. recently performed a study of the weak s-process during carbon shell burning for a 25 M stellar model using different 12 C( 12 C,n) 23 Mg rates [7]. They found that a factor of 2 precision or better would be desirable to limit its impact on the s-process predictions to within 10%.Stellar carbon burning has three main reaction channels:12 C + 12 C → 23 Mg + n − 2.60 MeV → 23 Na + p + 2.24 MeVWith Q < 0, the probability of decay through the neutron channel is weakest among the three at the low energies relevant for astrophysics. For a typical carbon shell burning temperature T 9 = 1.1, the important energy range for this channel is 2.7 < E cm < 3.6 MeV. The reaction was first studied in 1969 by Patterson et al. [8] who measured t...

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supporting

confidence: 74%

“…The detector efficiency has been simulated using Geant4 and MCNP in the range 0 to 3 MeV and experimentally validated with monoenergetic neutrons between 50 and 650 keV [20]. For this experiment, the Geant4 code was modified to include the strong angular dependence of the neutron energy from the 12 C( 12 C,n) 23 Mg kinematics.…”

mentioning

confidence: 99%

First Direct Measurement ofC12(C12
Bucher¹,
Tang²,
Fang³
et al. 2015
Phys. Rev. Lett.
35
3
55
0
View full text Add to dashboard Cite

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“…A more detailed description of the detector and the efficiency determination can be found in Ref. [40]. The simulations assumed an isotropic angular distribution of the emitted neutrons.…”

Section: Bmentioning

confidence: 99%

Measurement of the reaction17O(α,n)20Ne and its impact on thes
Best
¹
,
Beard
²
,
Couder
³

et al. 2013
Phys. Rev. C
42
3
61
2
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Background:The ratio between the rates of the reactions 17 O(α, n) 20 Ne and 17 O(α, γ) 21 Ne determines whether 16 O is an efficient neutron poison for the s process in massive stars, or if most of the neutrons captured by 16 O(n, γ) are recycled into the stellar environment. This ratio is of particular relevance to constrain the s process yields of fast rotating massive stars at low metallicity.Purpose: Recent results on the (α, γ) channel have made it necessary to measure the (α, n) reaction more precisely and investigate the effect of the new data on s process nucleosynthesis in massive stars. Method:The 17 O(α, n (0+1) ) reaction has been measured with a moderating neutron detector. In addition, the (α, n1) channel has been measured independently by observation of the characteristic 1633 keV γ-transition in 20 Ne. The reaction cross section was determined with a simultaneous R-matrix fit to both channels. (α, n) and (α, γ) resonance strengths of states lying below the covered energy range were estimated using their known properties from the literature. Results: The reaction channels17 O(α, n0) 20 Ne and 17 O(α, n1γ) 20 Ne were measured in the energy range Eα = 800 keV to 2300 keV. A new 17 O(α, n) reaction rate was deduced for the temperature range 0.1 GK to 10 GK. At typical He burning temperatures, the combination of the new (α, n) rate with a previously measured (α, γ) rate gives approximately the same ratio as current compilations. The influence on the nucleosynthesis of the s process in massive stars at low metallicity is discussed.Conclusions: It was found that in He burning conditions the (α, γ) channel is strong enough to compete with the neutron channel. This leads to a less efficient neutron recycling compared to a previous suggestion of a very weak (α, γ) channel. S process calculations using our rates confirm that massive rotating stars do play a significant role in the production of elements up to Sr, but they strongly reduce the s process contribution to heavier elements.

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“…The 3 He counters were arranged in two concentric rings with 8 in the inner ring and 12 in the outer ring. The neutron detection efficiency was obtained from a Geant4 simulation package which was calibrated by experimental efficiency data [27] but modified for neutron kinematics characteristic of 12 C+ 12 C [20].…”

Section: Methodsmentioning

confidence: 99%

Constraining the¹²C+¹²C fusion cross section for astrophysics

Bucher

Fang

Tang

et al. 2015

EPJ Web of Conferences

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Abstract. The 12 C+ 12 C reaction is one of the single most important nuclear reactions in astrophysics. It strongly influences late evolution of massive stars as well as the dynamics of type Ia supernovae and x-ray superbursts. An accurate estimation of the cross section at relevant astrophysical energies is extremely important for modeling these systems. However, the situation is complicated by the unpredictable resonance structure observed at higher energies. Two recent studies at Notre Dame have produced results which help reduce the uncertainty associated with this reaction. The first uses correlations with the isotope fusion systems, 12 C+ 13 C and 13 C+ 13 C, to establish an upper limit on the resonance strengths in 12 C+ 12 C. The other focuses on the specific channel 12 C+ 12 C→ 23 Mg+n and its low-energy measurement and extrapolation which is relevant to s-process nucleosynthesis. The results from each provide important constraints for astrophysical models.

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A 3He neutron detector for the measurement of reactions

Cited by 30 publications

References 27 publications

First Direct Measurement ofC12(C12
Bucher¹,
Tang²,
Fang³
et al. 2015
Phys. Rev. Lett.
35
3
55
0
View full text Add to dashboard Cite

First Direct Measurement ofC12(C12
Bucher¹,
Tang²,
Fang³
et al. 2015
Phys. Rev. Lett.
35
3
55
0
View full text Add to dashboard Cite

Measurement of the reaction17O(α,n)20Ne and its impact on thes
Best
¹
,
Beard
²
,
Couder
³

et al. 2013
Phys. Rev. C
42
3
61
2
View full text Add to dashboard Cite

Constraining the¹²C+¹²C fusion cross section for astrophysics

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A 3He neutron detector for the measurement of reactions

Cited by 30 publications

References 27 publications

First Direct Measurement ofC12(C12Bucher1, Tang2, Fang3 et al. 2015Phys. Rev. Lett.353550View full textAdd to dashboardCite

First Direct Measurement ofC12(C12Bucher1, Tang2, Fang3 et al. 2015Phys. Rev. Lett.353550View full textAdd to dashboardCite

Measurement of the reaction17O(α,n)20Ne and its impact on thesBest1, Beard2, Couder3 et al. 2013Phys. Rev. C423612View full textAdd to dashboardCite

Constraining the12C+12C fusion cross section for astrophysics

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About

First Direct Measurement ofC12(C12
Bucher¹,
Tang²,
Fang³
et al. 2015
Phys. Rev. Lett.
35
3
55
0
View full text Add to dashboard Cite

First Direct Measurement ofC12(C12
Bucher¹,
Tang²,
Fang³
et al. 2015
Phys. Rev. Lett.
35
3
55
0
View full text Add to dashboard Cite

Measurement of the reaction17O(α,n)20Ne and its impact on thes
Best
¹
,
Beard
²
,
Couder
³

et al. 2013
Phys. Rev. C
42
3
61
2
View full text Add to dashboard Cite

Constraining the¹²C+¹²C fusion cross section for astrophysics