Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe $^{6}$H states studied in the $d(^8text{He},alpha)$ reaction and evidence of extremely correlated character of the $^{5}$H ground state
116
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The extremely neutron-rich system $^{6}$H was studied in the direct $^2text{H}(^8text{He},{^4text{He}})^{6}$H transfer reaction with a 26 $A$ MeV secondary $^{8}$He beam. The measured missing mass spectrum shows a broad bump at $sim 4-8$ MeV energy relative to the $^3$H+$3n$ decay threshold. This bump can be interpreted as a broad resonant state in $^{6}$H at $6.8(5)$ MeV. The population cross section of such a presumably $p$-wave state (or may be few overlapping states) in the energy range from 4 to 8 MeV is $dsigma/dOmega_{text{c.m.}} simeq 190(40)$ $mu$b/sr in the angular range $5^{circ}<theta_{text{c.m.}}<16^{circ}$. The obtained missing mass spectrum is practically free of the $^{6}$H events below 3.5 MeV ($dsigma/dOmega_{text{c.m.}} lesssim 5$ $mu$b/sr in the same angular range). The steep rise of the $^{6}$H missing mass spectrum at $sim 3$ MeV allows to derive the lower limit for the possible resonant state energy in $^{6}$H of $4.5(3)$ MeV. According to the paring energy estimates, such a $4.5(3)$ MeV resonance is a realistic candidate for the $^{6}$H ground state (g.s.). The obtained results confirm that the decay mechanism of the $^{7}$H g.s. (located at 2.2 MeV above the $^{3}$H+$4n$ threshold) is the true (or simultaneous) $4n$ emission. The resonance energy profiles and the momentum distributions of fragments of the sequential $^{6}$H$ ,rightarrow , ^5$H(g.s.)+$n, rightarrow , ^3$H+$3n$ decay were analyzed by the theoretically-updated direct four-body-decay and sequential-emission mechanisms. The measured momentum distributions of the $^{3}$H fragments in the $^{6}$H rest frame indicate very strong dineutron-type correlations in the $^{5}$H ground state decay.
rate research
Read More
Evidence for the neutron-rich hypernucleus 6{Lambda}H is presented from the FINUDA experiment at DA{Phi}NE, Frascati, studying ({pi}+, {pi}-) pairs in coincidence from the K- +6Li rightarrow 6 H+{pi}+ production reaction followed by 6{Lambda}H rightarrow 6He + {pi}- weak decay. The production rate of 6{Lambda}H undergoing this two-body {pi}- decay is determined to be (2.9pm2.0)cdot10-6/K-. Its binding energy, evaluated jointly from production and decay, is B{Lambda}(6{Lambda}H) = (4.0pm1.1) MeV with respect to 5H+{Lambda}. A systematic difference of (0.98 pm 0.74) MeV between B{Lambda} values derived separately from decay and from production is tentatively assigned to the 6{Lambda}H 0+g.s. rightarrow 1+ excitation.
The extremely neutron-rich system $^{7}$H was studied in the direct $^2$H($^8$He,$^3$He)$^7$H transfer reaction with a 26 AMeV secondary $^{8}$He beam [Bezbakh et al., Phys. Rev. Lett. 124 (2020) 022502]. The missing mass spectrum and center-of-mass (c.m.) angular distributions of $^{7}$H, as well as the momentum distribution of the $^{3}$H fragment in the $^{7}$H frame, were constructed. In addition to the investigation reported in Ref. [Bezbakh et al., Phys. Rev. Lett. 124 (2020) 022502], we carried out another experiment with the same beam but a modified setup, which was cross-checked by the study of the $^2$H($^{10}$Be,$^3$He$)^{9}$Li reaction. A solid experimental evidence is provided that two resonant states of $^{7}$H are located in its spectrum at 2.2(5) and 5.5(3) MeV relative to the $^3$H+4$n$ decay threshold. Also, there are indications that the resonant states at 7.5(3) and 11.0(3) MeV are present in the measured $^{7}$H spectrum. Based on the energy and angular distributions, obtained for the studied $^2$H($^8$He,$^3$He)$^7$H reaction, the weakly populated 2.2(5) MeV peak is ascribed to the $^7$H ground state. It is highly plausible that the firmly ascertained 5.5(3) MeV state is the $5/2^+$ member of the $^7$H excitation $5/2^+$-$3/2^+$ doublet, built on the $2^+$ configuration of valence neutrons. The supposed 7.5 MeV state can be another member of this doublet, which could not be resolved in Ref. [Bezbakh et al., Phys. Rev. Lett. 124 (2020) 022502]. Consequently, the two doublet members appeared in the spectrum of $^{7}$H in [Bezbakh et al., Phys. Rev. Lett. 124 (2020) 022502] as a single broad 6.5 MeV peak.
Measurements of the t-t and p-t coincidence events in the $^3$H ($alpha$, ttp) reaction have been obtained at $E_alpha$ incident energy of 67.2 MeV. Various appropriate angular configurations of detectors were chosen in order to observe the population of the $^6$He$^*$ state at around 18 MeV. Its contribution appears at the $E_{rm tt}$ relative energy of 6.0 MeV by the analysis of bidimensional spectra. We found the formation of the $^6$He excited state at $E^* = 18.3 pm 0.2$ MeV (with a $Gamma$ width of 1.1 $pm$ 0.3 MeV) by the decay into the t+t binary channel, since the threshold energy of the t+t channel is 12.31 MeV. In each analyzed bidimensional energy spectrum of ($E_{rm t}$, $E_{rm t}$) and ($E_{rm p}$, $E_{rm t}$) coincidence events resonance structures are present due to the formation of both $^6$He$^*$ and $^4$He$^*$ excited states. Our results on the $E^*$ and $Gamma$ values regarding the $^6$He$^*$ level of about 18 MeV are compared with the results obtained by other reactions. Moreover, we also found new $Gamma$ width values of 0.7 $pm$ 0.3 and 0.8 $pm$ 0.4 MeV for the 14.0 $pm$ 0.4 and 16.1 $pm$ 0.4 MeV $^6$He levels, respectively.
Two new low-lying $^6$He levels at excitation energies of about 2.4 and 2.9 MeV were observed in the experimental investigation of the p-$alpha$ coincidence spectra obtained by the $^3$H($^4$He,p$alpha$)2n four-body reaction at $E_{rm ,^4He}$ beam energy of 27.2 MeV. The relevant $E^*$ peak energy and $Gamma$ energy width spectroscopic parameters for such $^6$He$^*$ excited states decaying into the $alpha$+n+n channel were obtained by analyzing the bidimensional ($E_{rm p}$, $E_{rm alpha}$) energy spectra. The present new result of two low-lying $^6$He$^*$ excited states above the $^4$He+2n threshold energy of 0.974 MeV is important for the investigation of the nuclear structure of neutron rich light nuclei and also as a basic test for theoretical models in the study of the three-cluster resonance feature of $^6$He.
In a measurement of the 9Be(7Li,alpha 7Li)n alpha reaction at E = 52 MeV it is unambigously established for the first time that the 9Be excited states around 6.5 and 11.3 MeV decay into the alpha + 5He channel. This fact may support previous claims that the 11.3 MeV state is also a member of the ground state rotational band.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
