Nuclear structure studies of 125Te with (n,γ), (d,p) and (3He,α) reactions

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<ul><li><p>ELSEVIER Nuclear Physics A 645 (1999) 331-375 </p><p>NUCLEAR PHYS ICS A </p><p>Nuclear structure studies of 125Te with (n,y), (d,p) and (3He,ce) reactions </p><p>J. Honzfitko a, I. Tomandl a,l, W. Bondarenko b'e'2, D. Bucurescu c, T. von Egidy b, j. Ott d, W. Schauer b, H.-E Wirth b, C. Doll h, A. Gollwitzer d, G. Graw d, R. Hertenberger d, B. D. Valnion o </p><p>a Nuclear Physics Institute, 250 68 l~e~, Czech Republic b Physik-Department, Technische Universittit Miinchen, D-85748 Garching, Germany </p><p>c Institute of Atomic Physics, Bucharest, Romania d Sektion Physik, Universitd't Miinchen, D-85748 Garching, Germany </p><p>e Nuclear Research Center, Latvian Academy of Sciences, LV 2169 Salaspils, Latvia </p><p>Received 23 July 1998; revised 14 October 1998; accepted 26 October 1998 </p><p>Abstract </p><p>Levels in ~25Te were investigated in the range up to 3.3 MeV excitation energy by the (n,y), (d,p) and (3He,a) reactions. Over 160 levels and about 360 y-transitions were established, most for the first time. The states below 2.3 MeV with the most complete spectroscopic information were interpreted in terms of the interacting boson-fermion model (IBFM). Unitary treatment of both positive- and negative-parity states is achieved with the same model parameter close to the intermediate case between 0(6) and U(5) limits. Excitation energies, electromagnetic transition rates, y-branchings and spectroscopic factors are discussed in connection with the possible structures. A family of low-spin negative-parity states has been identified and understood by the IBFM proving their antialigned origin. (~ 1999 Elsevier Science B.V. </p><p>PACS: 21.10.-k; 23.20.Lv; 27.60.+j Keywords: Nuclear reactions: 124Te(n,y), E = thermal, measured E~, I v, ),),-coin.; Binding energy; :24Te(d,p), E = 17 MeV; 126Te(3He,a), E = 32 MeV; Measured particle spectra; Enricbed targets; Ge detectors; Magnetic spectrograph; 125Te deduced levels; J, ~', ),-Branching ratios; Spectroscopic factors; Interacting boson-fermion model calculation and comparison </p><p>t Corresponding author. E-mail: tomandl@ujf.cas.cz 2 Permanent address: Nuclear Research Center, LV 2169 Salaspils, Latvia. </p><p>0375-9474/99/$- see front matter (~) 1999 Elsevier Science B.V. All rights reserved. PII S0375-9474(98) 00588-0 </p></li><li><p>332 J. Honz6tko et al./Nuclear Physics A 645 (1999) 331-375 </p><p>I. Introduction </p><p>Te nuclei with only two protons beyond the closed shell Z = 50 span the wide neutron number region N = 50-82 (A = 112-134) allowing the investigation of the evolution of the main nuclear structures when the number of valence neutrons is gradually changed. </p><p>In general, the level schemes of odd-mass tellurium nuclei are expected to result from the lg7/2, 2d5/2, 2d3/2, 3sl/2 and unique-parity lh11/2 neutron orbits coupled to the even-even core states [ 1-3]. This type of coupling accounts for the low-lying positive- parity states in 125Te [4] as well as many high-spin states [5]. At higher excitation energies the single neutron states are strongly fragmented in a wide energy region. The systematics of their population in nucleon transfer reactions were studied in detail in Refs. [ 6-9]. One puzzling result from these experiments is the anomalous asymmetrical population of the lh1~/2 neutron orbit observed in the stripping and pick-up process. </p><p>The negative-parity states are of particular interest. The systematic appearance of low-lying intruder states j - 1, j - 2, etc. arising from the hn~/2 orbit was previously explained by Kuriyama et al. [ 10] using so-called dressed three- and more-quasiparticle modes. On the other hand, in accordance with the systematic finding in a wide region Z = 44-57, the aligned coupling scheme of the hi 1/2 orbit is one of the most fundamental excitation modes in nuclei across the Z = 50 shell closure. In going from Sn (Z = 50) to Ba (Z = 56) nuclei the general character of negative-parity yrast states is changed from AJ = 2 to AJ = 1 structures due to different aspects such as position of chemical potentials, sign of the product qQ, blocking effect, shape dynamical polarization, etc. Experience [ 11 ] shows that the sequence of favored high-spin states is not particularly sensitive to model assumptions. In this respect the position of the low-spin negative- parity states could be more sensitive to details of particle core coupling. In a simple picture suggested in Refs. [ 12,13] the appearance of low-spin states of the same lhll/2 family occurs under small quadrupole deformation. In the context of the model these states could be interpreted as antialigned members (with antiparallel angular momenta of the odd particle and the core). Experimentally, such states have been identified in Pd nuclei [12,14], 113Cd [15] and 135Ba [16]. The alternative description of these structures by the interacting boson-fermion model [ 17], the pairing-plus-recoil rotor model [ 18], and the triaxial rotor model [ 19] is as good as or even better than by the simple models of Refs. [ 12,13]. </p><p>Deeper understanding of the various aspects mentioned above needs extensive and complete experimental information. As a continuation of our systematic studies of Te isotopes [20-23] we present here experimental data obtained with the different and complementary reactions (n,y), (d,p) and (3He,or). In the present work the interact- ing boson-fermion model (IBFM) has been applied extensively for the description of both negative- and positive-parity states. Some results of this complex work have been reported separately [24-26]. </p></li><li><p>J. Honz6tko et al./Nuclear Physics A 645 (1999) 331-375 </p><p>2. Experimental procedures </p><p>333 </p><p>2.1. Thermal neutron capture studies </p><p>2.1.1. Single y-ray measurements </p><p>Single y-ray spectra and yy-coincidences following thermal neutron capture in 124Te were measured with semiconductor detectors at the light-water reactor LWR-15 at l~e~. The target consisted of 1.2 g of metallic Te enriched in 124Te to 92.4%. It was irradiated by thermal neutrons from a neutron guide [27]. Single y-ray spectra were recorded with a 22% HPGe detector with a resolution of 2.0 keV at the 1332 keV 6Co line and 4.8 keV at 6533 keV. For calibration purposes an auxiliary measurement was performed with a mixed Te-CI target. The energy calibration was carried out with the well-known low-energy transitions in 125Te [41], y-rays from the 35Cl(n,y) reaction [28] and prominent background lines of 2H and 6Co. The intensities of y transitions in 125Te were normalized using the absolute intensity of 7.8% of the 6620 keV line in 36C1 [28]. The systematic error of 20% in the determination of absolute intensities in 125Te is associated with the uncertainty of the capture cross section of 12aTe [29]. In order to identify the y-rays belonging to the 123Te(n,y) reaction a separate run was performed with a natural tellurium target. All y-rays assigned to 125Te with a possible placement in the level scheme are listed in Table ! of Ref. [40]. </p><p>2.1.2. yy-coincidence measurements The yy-coincidence measurements were undertaken with a 22% HPGe and a 12% </p><p>Ge(Li) detector. The present measurements were performed with higher statistics and number of coincidence gates than in our previous study [24]. For a period of 21 days, altogether 4 108 coincidences were accumulated and stored in an event-by-event format. Coincidence spectra were obtained off-line by setting gates on 29 primary transitions and 34 secondary transitions. An example of such a spectrum is given in Fig. 1. Further details of the experimental setup and acquisition system are given elsewhere [27]. The results of the yy-coincidence measurements are given in Table 1. </p><p>2.2. Light ion induced reactions </p><p>The nucleon transfer reactions with light ions are an important complementary tool to the (n,y) reaction for studying the properties of nuclear states. The experiments were performed at the Tandem Accelerator of the University and Technical University of Munich. The reaction products were analyzed in the Q3D spectrograph [30] equipped with a position sensitive cathode strip detector with a single strip readout [31,32] and a long focal plane detector with trace reconstruction [ 33]. The type of incident particle in a gas-filled detector chamber can be identified by sorting the energy loss signal from the anode wires versus the energy rest signal produced by the plastic scintillator. </p></li><li><p>334 J. Honzdtko et al./Nuclear Physics A 645 (1999) 331-375 </p><p>Table 1 Results from ),y-coincidence measurements </p><p>Gated y-ray y-Rays observed in coincidence (keV) (keY) </p><p>176 a </p><p>204 a 380 </p><p>408 </p><p>428 </p><p>444 </p><p>463 b </p><p>502 </p><p>529 538 </p><p>547 </p><p>574 590 </p><p>204,248, 285, 321,466, 518, 533, 536, 547, 557, 628, 702, 751, 786, 794, 797, 889, 913, (924), 938, 1001, 1037, (1132), 1306, (1579), (2053), 2070, (3361), 3427, (3919), 3964, 4020,4461, 4561, (4612), 5250 176,248, 547, 628, 684, (786), 794, 797, (922), 938, 1037, (1132), (1307), 1578, 5250 247, 261,377, 380, 547, 581,591,628,636,685, (701), 786, 794, 797, 840, 885,910, 923, 938, 976, 1005, 1030, 1037, 1127, 1132, 1175, 1241, 1244, 1307, 1338, 1386, 1470, 1478, 1535, 1578, 1622, 1699, (1714), 1844, 1864, 1911, 1994, 2067, 2071, (2103), (2124), (2150), (3361), 3394, 3427, (3798), 3919, 4018,4461, (4493), 4560, (4612), 5250 286, 574, 611,623, (688), (799), 822, 876, (903), 993, 1087, 1144, (1208), 1227, (1256), 1270, 1323, 1328, 1422, (1428), (1452), 1456, 1461, 1475, 1513, (1534), (1547), (1565), 1606, 1617, 1665, 1687, (1733), 1738, 1759, 1783, 1789, 1808, 1869, (1897), 1908, 1938, 2023, 2051, 2061, (2076), 2107, 2124, 2142, (2152), (2332), (2371), (2422), 2609, 2663, (2676), (2730), (2955), 3038, 3089, 3462, 4344, (4439), (4460), 4508, 4612, 6125 555, 567, (576), 591,603, 780, 783, 800, 856, 972, 1058, 1066, 1296, 1308, 1350, 1435, 1448, 1493, 1586, (1597), 1669, 1675, 1682, 1687, 1725, 1763, 1847, 1852, 1887, (1910), (1916), 1921, 1948, 2003, 2029, 2033, 2041, (2086), 2104, (2122), (2127), 2186, (2307), (2322), (2337), (2357), 2435, 2511, 2527, 2539, 2558, (2626), 2643, (2674), 2746, (2771), 2963, 3013, 3092, 3360, 3462, 3548, 3566, (3594), 3919, 3984, (4001), (4256), 4344, (4560), (5041), 4612, 5249, 6105 286, 574,611, 623, 628, (800), 822, 876, (903), (993), 1086, (1136), 1144, 1227, (1256), 1270, 1323, 1328, (1386), 1411, 1422, (1429), 1456, 1462, 1475, 1513, (1535), (1538), (1547), 1578, 1606, 1617, (1624), 1645, 1686, (1689), 1731, 1738, 1782, 1789, (1803), 1808, 1869, 1907, (1929), 1936, 1940, (1950), 2023, (2107), 2125, 2142, (2152), (2205), 2332, (2521), 2526, 2546, (2579), (2610), 2663, (2698), 2730, (2763), (2916), 2955, 3036, 3088, 3095, 3361, 3463, 4001, (4019), 4102, 4344,4440,4461, (4493), 4508, 4612, (4664), (4671), (4703), 5040, 5839, 6125 176, (207), 285, 533, 536, 555, 567, (575), 591, 604, 628, 636, 671,783, 856, 867, 913, 974, 980, (1058), 1066, 1170, 1297, 1308, 1349, (1449), 1493, (1597), (1681), (1762), 1852, (1889), (1910), (1922), (2104), 2186, 2558, (3092), (3361), (3461), 3548, 3566, 3919, (4253), (4561), 4612, (5040), 5250 516, 529, 595, 705,782, 1133, 1237, (1327), 1367, 1419, 1441, 1549, 1592, 1644, 1713, 1733, (1778), 1835, 1842, (1855), 1929, (2013), (2029), 2047, (2216), (2693), (3337), (3548), (4508), 4590, 4613, 5249,6031 502, 538, (798), (833), (841), 1160, (1285) 176, 191,466, 529, 596,642, 652, 705, 782, 786, (1115), 1132, 1237, (1276), (1285), 1328, 1367, 1381, 1419, 1441, (1523), 1549, 1592, 1644, 1713, 1733, 1778, (1835), 1841, 1856, (1900), 1929, (2014), 2048, (2069), 2192, 2216, (2233), (2609), 2694, (3125), 3336, 3549, (4190), (4509), 4590, 4612, 5249, 6031 176, 193, 204, 247, 380, 580, 628, 840, 885, 923, 932, 938, 975, 1005, 1037, 1078, 1132, 1175, 1244, 1338, (1422), 1478, 1535, 1578, 1699, 1713, 1871, (1878), (1949), 2071, (2103), (2493), 2941, 3394, 3549, 3426, 3798, 3919, 3961, (4019),4461,4492, 4560, 4612, 5250 408,444, (882), (898), (1136), (1233), (1264), (1957), (2254), (2260), (3459) 428, 463, 636, (671), 694, 729, (784), 903, (1298), (1307), (2039), (4216), 5249 </p></li><li><p>J. Honzdtko et al./Nuclear Physics A 645 (1999) 331-375 335 </p><p>Table 1 - - continued </p><p>Gated y-ray y-Rays observed in coincidence (keY) (keV) </p><p>601 </p><p>607 </p><p>610 623 628 636 </p><p>642 671 694 </p><p>729 751 7820 794 c </p><p>888 r </p><p>937 1098 </p><p>1207 1419 1493 1578 2009 3361 3394 3463 3798 3919 </p><p>3962 3983 4001 4019 4101 </p><p>4189 4217 4256 </p><p>428, 497, 518, (610), (678), 894, (1034), 1123, 1126, 1264, 1269, 1296, 1385, 1414, 1425, (1496), 1583, (1590), 1657, (1829), (1933) 408, 412, 425,444,449, 491, 715, 888, 1010, (1090), 1118, 1259, 1327, 1378, 1576, (1949), 2105, (5039) 408,444, 601, (706), 718, 889, 903, 1261, (1298), 1412, (1514), 1960, (4612) 408,444, (586) (286), 377, 380, 465, 546, 601,694, 751, (1252), (1752) (346), 382, 462, 571, (574), 594, (643),649, 687, (695), 765, 981,998, (1029), 1042, 1088, 1161, 1229, 1233, (1247), 1261, 1285, 1338, 1349, 1378, 1389, 1397, (1461), 1474, (1504), 1510, 1548, 1555, (1580), 1600, 1672, 1680, 1708, 1713, 1720, 1743, (1768), 1795, (1850), 1857, (1897), (2018), (2149), 2303, (2319), 2332, 2401, (2423), 2434, 2474, (2504), (2791), (3462), (3577), 4218, 4343, (4350), 4560, 4613 285, 533, 536, 651, (866), 913, (1036), (1169), (2728), 5250 382, 462, 572, (594), (1338), 1555, (1851), (1856), 4343 404, 590, (593), 801,858, 923, 941, 985, 1030, 1170, 1176, 1189, (1227), 1262, 1280, 1320, (1331), (1453), 1497, 1504, 1508, 1522, 1525, 1533, 1542, (1582), (1585), 1622, 1650, 1686, 1710, 1799, 1831, 1839, 1877, 1921, 1947, (2244), (2261), (2274), (2292), (2608), (2863), 3166, 3567, (3578), 4189, 4345, 4855, 5250, 5839 548, 591, (801), 923, 941,985, (1030), (1263), (1498), (1947), (2547), 5249, 5839 176, 248, 628, 938, 1037, (2071), 2900, (3425), (4460), (4560), (4613), 5250 428, 440, 464, 502, 538, 797, 889, (1331), 2196,4460, 5249 176, 204, 220, 361, 370, 375, 380, (637), 687, 694, 786, 882, 889, 1088, 1097, 1330, (1453), (1699), (3920),4459, (4560), 5250 176, 321, 367, 375, 380, 547, 557,607, 623, 702, 785, 794, (852), (1140), (1230), (1320), 3251, 3578, 4612, (5040) 285, 380, (465),547, 751, 1098, 4560, 4612 626, (638), 772, (800), 1139, 1183, (1219), 1435, (1516), 1596, 2480, 2955, (3461), (4002), (4253) 767, 1050, 1830, 502, 538, 4612 428, 463, 4612 380, 547, 602, (751), 3126, 3919 (538), (543), (629), (642), (2447), (2624), 4560 380, (408), 428,444, (464), (794), 1888, (2744), (2764), 3173, 3208 380, 547, (635), 2103, 3139 408, 428,444, (464), (502), (538), (1116), (1207), 2434, 2568, (2643), 2662, 3106 (380),444, 538, 547, (751), 1699, (2233), 2735, 2771 380, 428,444, 464, (537), 547, (1331), (1516), 1578, 1584, (1595), 1920, 2186, (2206), 2614, 2650 380, (408), (428), 547, (795), (1288), 1535, (2571), 2607 (408), (428),444, (538), (1005), 2041, 2047, 2077, (2121), 2142, 2551, (2585) 408, 428,444, 1617, (1839), (1897), 2104, 2124, 2533, 2568 380, (428),444, (502), (537), (592), 888, 1066, 1231, 2013, 2106, 2515, 2550 380, 408, 427, 464, 502,538, 546, 636, 885, 1285, 1419, 1493, 1513, 1795, 1920, 1929, 1956, 2003, 2023, 2430, 2467 408,444, (538), (636), 694, 1650, 1842, (1937), 2380 (408)...</p></li></ul>