Time of flight (TOF) spectrometer for accurate measurement of mass and angular distribution of fission fragments in heavy ion induced fission reactions

Ghosh, T. K.; Pal, Santanu; Sinha, T. P.; Chattopadhyay, S.; Golda, K. S.; Bhattacharya, Purba

doi:10.1016/j.nima.2004.11.029

Cited by 29 publications

(8 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The masses of the fission fragments were determined event by event from precise measurements of flight paths and flight time differences of the complimentary fission fragments [13,20]. The extracted FFMD at different excitation energies of the compound nucleus are shown in Fig.…”

mentioning

confidence: 99%

“…The target was a self-supporting 232 Th of thickness 1.1 mg/cm 2 . For the detection of fission fragments, two large-area (20 cm × 6 cm) positionsensitive multiwire proportional counters (MWPCs) [13] were placed at the folding angle, covering 67• and 83• , respectively, on either side of the beam axis. For each fission event, the time difference of the fast anode pulses…”

mentioning

confidence: 99%

See 1 more Smart Citation

Direct evidence of “washing out” of nuclear shell effects

et al. 2015

Self Cite

View full text Add to dashboard Cite

Constraining excitation energy at which nuclear shell effect washes out has important implications on the production of super heavy elements and many other fields of nuclear physics research. We report the fission fragment mass distribution in alpha induced reaction on an actinide target for wide excitation range in close energy interval and show direct evidence that nuclear shell effect washes out at excitation energy ∼ 40 MeV. Calculation shows that second peak of the fission barrier also vanishes around similar excitation energy. One of the major areas that have generated unprecedented interest among contemporary nuclear physicists and chemists is the synthesis of super heavy elements (SHE). It is known from the Liquid Drop Model (LDM) of the nucleus [1] that if the two fundamental nuclear parameters, the attractive nuclear surface potential and the repulsive coulomb forces are taken into account, then our nuclear chart may end at around element number 104. This is simply because, nuclei with Z ≥ 104 immediately fission as there is no barrier to prevent their decay. However, elements have been synthesized beyond that atomic number [2].The observed stability of these heavy elements is believed to originate from the microscopic shell effects in nuclei. While LDM predicts the bulk properties of nuclei and explains their collective behavior, nuclear Shell Model [3] explains these shell gaps and the single-particle nature of nuclear states. Both the bulk properties and the shell properties of nuclei can be incorporated by adding a shell-correction term to the liquid-drop model energy. Strutinsky [4,5] considered the shell effect as a deviation from uniform liquid drop model prediction and used the shell averaged single particle energy as a correction term to the liquid drop model energy. The liquid drop barrier height diminishes smoothly with the increase in atomic number as the nuclear fissility increases. However, as the shell correction term retains the fluctuations in the shell model energy, it is found that the incorporation of this shell correction alters the fission barrier and in fact, causes to develop large barrier to decay that can increase alpha or fission half-lives by several orders of magnitude for the heavy elements. Thus shell effects play a central role in determining the stability of the super heavy elements. Many important nuclear phenomena such as the fission isomers [6], super deformed nuclei [7] and new magic numbers in the exotic nuclei [8] are the consequences of the shell effect. * tilak@vecc.gov.in It is generally believed that shell effects are washed out at higher excitation energy [9]. For the production of the super heavy elements by heavy ion bombardment on actinides targets, the compound nuclei are always formed with an excitation energy exceeding a few tens of MeV. Judicious choice of the excitation energy is critical as the production cross section of the SHE may be increased by a few orders of magnitude if the beam energy is increased by few MeV. Therefore, constraining the exci...

show abstract

mentioning

confidence: 99%

mentioning

confidence: 99%

Direct evidence of “washing out” of nuclear shell effects

et al. 2015

Self Cite

View full text Add to dashboard Cite

show abstract

“…• Flerov Laboratory for Nuclear Reactions (FLNR) in Dubna, Russia, using the CORSET setup [135,136,137,138,139,140,141,142,143,144,145,146,35], • 15UD Pelletron at the Inter University Accelerator Centre (IUAC) in New Delhi, India [147,148,149,150,151,152,153,154,155,156,157,158,159] • Pelletron LINAC facility in collaboration between BARC (Bhabha Atomic Research Centre) and Tata Institute of Fundamental Research (TIFR) in Mumbai, India [160] In the following, selected examples of applied techniques are presented in some details.…”

Section: Page 10 Of 77 Author Submitted Manuscript -Ropp-100800r2mentioning

confidence: 99%

Nuclear fission: a review of experimental advances and phenomenology

2017

View full text Add to dashboard Cite

In the last two decades, through technological, experimental and theoretical advances, the situation in experimental fission studies has changed dramatically. With the use of advanced production and detection techniques both much more detailed and precise information can now be obtained for the traditional regions of fission research and, crucially, new regions of nuclei have become routinely accessible for fission studies. This work first of all reviews the recent developments in experimental fission techniques, in particular the resurgence of transfer-induced fission reactions with light and heavy ions, the emerging use of inverse-kinematic approaches, both at Coulomb and relativistic energies, and of fission studies with radioactive beams. The emphasis on the fission-fragment mass and charge distributions will be made in this work, though some of the other fission observables, such as prompt neutron and γ-ray emission will also be reviewed. A particular attention will be given to the low-energy fission in the so far scarcely explored nuclei in the very neutron-deficient lead region. They recently became the focus for several complementary experimental studies, such as β-delayed fission with radioactive beams at ISOLDE(CERN), Coulex-induced fission of relativistic secondary beams at FRS(GSI), and several prompt fusion-fission studies. The synergy of these approaches allows a unique insight in the new region of asymmetric fission around [Formula: see text]Hg, recently discovered at ISOLDE. Recent extensive theoretical efforts in this region will also be outlined. The unprecedented high-quality data for fission fragments, completely identified in Z and A, by means of reactions in inverse kinematics at FRS(GSI) and VAMOS(GANIL) will be also reviewed. These experiments explored an extended range of mercury-to-californium elements, spanning from the neutron-deficient to neutron-rich nuclides, and covering both asymmetric, symmetric and transitional fission regions. Some aspects of heavy-ion induced fusion-fission and quasifission reactions will be also discussed, which reveal their dynamical features, such as the fission time scale. The crucial role of the multi-chance fission, probed by means of multinucleon-transfer induced fission reactions, will be highlighted. The review will conclude with the discussion of the new experimental fission facilities which are presently being brought into operation, along with promising 'next-generation' fission approaches, which might become available within the next decade.

show abstract

“…The masses of the fission fragments were calculated using the time of flight difference between the correlated fragments, the azimuthal and polar angles, the recoil velocities and the momenta of the fission fragments. This prescription for calculation for masses is described in [14]. In order to correct for the energy loss of the fragment in the backing (for the 206 Pb target) and half the target thickness, the gold deconvolution [15] process was implemented to find the correct width of the mass distributions.…”

Section: Analysis Of Datamentioning

confidence: 99%

Fission fragment mass distributions from Po210 and At213

et al. 2017

Self Cite

View full text Add to dashboard Cite

Background: The influence of shell effect on the dynamics of the fusion fission process and it's evolution with excitation energy in the pre-actinide Hg-Pb region in general is a matter of intense research in recent years. In particular, a strong ambiguity remains for the neutron shell closed 210 Po nucleus regarding the role of shell effect in fission around ≈ 30 -40 MeV of excitation energy.Purpose: We have measured the fission fragment mass distribution of 210 Po populated using fusion of 4 He + 206 Pb at different excitation energies and compare the result with recent theoretical predictions as well as with our previous measurement for the same nucleus populated through a different entrance channel. Mass distribution in the fission of the neighbouring nuclei 213 At is also studied for comparison.Methods: Two large area Multi-wire Proportional Counters (MWPC) were used for complete kinematical measurement of the coincident fission fragments. The time of flight differences of the coincident fission fragments were used to directly extract the fission fragment mass distributions.Results: The measured fragment mass distribution for the reactions 4 He + 206 Pb and 4 He + 209 Bi were symmetric and the width of the mass distributions were found to increase monotonically with excitation energy above 36.7 MeV and 32.9 MeV, respectively, indicating the absence of shell effects at the saddle. However, in the fission of 210 Po, we find minor deviation from symmetric mass distributions at the lowest excitation energy (30.8 MeV).Conclusion: Persistence of shell effect in fission fragment mass distribution of 210 Po was observed at the excitation energy ≈ 31 MeV as predicted by the theory; at higher excitation energy, however, the present study reaffirms the absence of any shell correction in the fission of 210 Po.

show abstract

Time of flight (TOF) spectrometer for accurate measurement of mass and angular distribution of fission fragments in heavy ion induced fission reactions

Cited by 29 publications

References 25 publications

Direct evidence of “washing out” of nuclear shell effects

Direct evidence of “washing out” of nuclear shell effects

Nuclear fission: a review of experimental advances and phenomenology

Fission fragment mass distributions from Po210 and At213

Contact Info

Product

Resources

About