[Paper Review] Multifragmentation Studies in 84Kr Interactions with Nuclear Emulsion at around 1 A GeV

V. Singh, S. K. Tuli+3 more|ArXiv.org|Dec 22, 2004

Nuclear physics research studies3 citations

TL;DR

This study investigates multifragmentation in 84Kr interactions with nuclear emulsion at ~1 A GeV, using optical microscopy and track scanning to analyze projectile fragments. It finds strong projectile mass dependence in intermediate-mass fragment (IMF) production, with inverse power-law charge distributions consistent with liquid-gas phase transition behavior near critical point, indicating multifragmentation as a low-energy, heavy-ion phenomenon.

ABSTRACT

Projectile fragmentation of 84Kr in three different energy intervals has been studied. Many aspects of multifragmentation process have been examined in depth. It is observed that multifragmentation is a general low energy phenomenon associated with heavy beam. The number of Intermediate-Mass-Fragments (IMF's) shows strong projetile mass dependence.

Motivation & Objective

• To investigate the multifragmentation process in relativistic 84Kr interactions with nuclear emulsion at ~1 A GeV.
• To examine the dependence of intermediate-mass fragment (IMF) production on projectile mass and beam energy.
• To analyze the charge distribution of projectile fragments and test for power-law behavior indicative of critical phenomena.
• To compare results with heavier beams (139La, 197Au, 238U) at similar energies to assess system-size effects.

Proposed method

• Nuclear emulsion stacks (NIKFI BR2) were exposed to 84Kr beams at ~1 A GeV at SIS, GSI, Darmstadt.
• Beam tracks were scanned using an oil immersion objective (100X magnification) with digitized readout to ensure unbiased event selection.
• Fragment charge was estimated via blob/gap density (Z < 10), delta-ray density (Z ≤ 19), and range/width comparisons for heavier fragments, with ±1 unit accuracy.
• Events were divided into three energy intervals (A: 0.95–0.80 A GeV, B: 0.80–0.50 A GeV, C: <0.50 A GeV) for energy-dependent analysis.
• Alpha fragment multiplicity distributions were fitted with Gaussian functions, and cumulant moments (Cq) were calculated to probe correlation structure.
• Charge distributions were fitted to an inverse power law f(Z) ∝ Z^τ to assess critical behavior and compare with theoretical models.

Experimental results

Research questions

• RQ1 How does the multiplicity of intermediate-mass fragments (IMFs) in 84Kr interactions vary with beam energy and projectile mass?
• RQ2 What is the functional form of the charge distribution of projectile fragments, and does it follow a power law indicative of critical phenomena?
• RQ3 How does the multifragmentation behavior in 84Kr compare quantitatively with heavier beams (139La, 197Au, 238U) at similar energies?
• RQ4 Is there evidence of a liquid-gas phase transition in the multifragmentation process, as suggested by power-law scaling of fragment yields?
• RQ5 How does the exponent τ of the power-law distribution f(Z) ∝ Z^τ vary with beam energy and projectile mass?

Key findings

• The average multiplicity of Z ≥ 3 fragments (<Nf>) is 1.21 ± 0.04, and for alpha fragments (<Nα>) is 2.03 ± 0.06 across all 1100 events.
• Alpha fragment multiplicity shows a Gaussian distribution with a width of 8.76 and a tail extending to 11, indicating high multiplicity events.
• Cumulant moments Cq increase with q, showing stronger correlations at higher orders, though statistics limit definitive conclusions.
• The exponent τ for the power-law f(Z) ∝ Z^τ is -2.45 ± 0.16 (Z = 1 to Zb/2) and -1.49 ± 0.09 (Z = 3 to Zb/2) for 84Kr, consistent with critical phenomena.
• The exponent τ increases with beam energy (e.g., τ = -1.90 ± 0.21 at 0.50–0.70 A GeV vs. -2.05 ± 0.13 at 0.80–0.95 A GeV), indicating enhanced fragmentation at higher energies.
• Heavier beams (238U, 197Au, 139La) show systematically higher τ values than 84Kr at similar energies, indicating greater breakup tendency in heavier systems.